Determination of Veterinary Residues in Food (Woodhead Publishing Series in Food Science, Technology and Nutrition)

DETERMINATION OF VETERINARY RESIDUES IN FOOD

DETERMINATION OF VETERINARY RESIDUES IN FOOD NEIL T.CROSBY

BSc, PhD, FIFST

Head of Fertilizer and Feeding Stuffs Laboratory of the Government Chemist, Teddington

WOODHEAD PUBLISHING LIMITED Cambridge England

Published by Woodhead Publishing Limited, Abington Hall, Granta Park, Great Abington, Cambridge CB21 6AH,England www.woodheadpublishing.com First published 1991 Ellis Horwood Limited Reprinted 1997. 2008 Woodhead Publishing Limited

0 1997, Woodhead Publishing Limited The authors have asserted their moral rights This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher cannot assume responsibility for the validity of all materials. Neither the authors nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from the publisher. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be ohtained in writing From Woodhead Publishing Limited for such copying. Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to intiinge. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library

ISBN 978- 85573-341-1 Printed in the United Kingdom by Lightning Source U K Ltd

Table of contents PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

ABBREVIATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11

UNITS FOR CONCENTRATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

13

I

CURRENT TRENDS IN AGRICULTURAL PRACTICE . . . . . . . . . . . . . 15 1 . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.2 World agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.2.1 World market for animal health products . . . . . . . . . . . . . . . 20 Agriculture in the EC. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.3 1.4 Importance of agriculture to the UK economy . . . . . . . . . . . . . . . . .23 I .4.1 Self sufficiency in food products in the UK . . . . . . . . . . . . . .25 25 I .5 Animal husbandry and feeding stuffs . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Types of animal feeding stuffs . . . . . . . . . . . . . . . . . . . . . . 27 1.5.2 Pet foods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 1.5.3 Main ingredients of compound feeding stuffs . . . . . . . . . . . . .29 I 21.4 Demand for compound feeds and feed ingredients . . . . . . . . .29 1.6 Additives in feeds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 I .6.1 Use of medicinal additives . . . . . . . . . . . . . . . . . . . . . . . . . 34 I .6.2 Types of medicinal additives . . . . . . . . . . . . . . . . . . . . . . . 35 1.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2 ANALYTICAL METHODOLOGY . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 . I The analytical problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 The analytical approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Classification of analytical methods for residue determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Performance characteristics of analytical methods . . . . . . . . .

37 37 39 40

.41

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Table of contents

2.2.3 Analytical procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.3 Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 2.3.1 Thin-layer chromatography . . . . . . . . . . . . . . . . . . . . . . . . 46 2.3.2 Gas-liquid chromatography . . . . . . . . . . . . . . . . . . . . . . . . 48 2.3.3 High-pressure liquid chromatography . . . . . . . . . . . . . . . . . 51 2.3.4 Column efficiency and interpretation of results . . . . . . . . . . . .54 2.4 Mass spectrometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.4.1 General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 2.4.2 Use of mass spectrometry in residue analysis . . . . . . . . . . . . .60 2.5 lmmunoassays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 2.5.1 Monoclonal antibodies . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 2.5.2 Principles of immunoassay . . . . . . . . . . . . . . . . . . . . . . . . . 62 2.5:3 Evaluation of antisera . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 2.5.4 Technique of immunoassay . . . . . . . . . . . . . . . . . . . . . . . . 62 2.5.5 Enzyme-linked immunosorbent assays . . . . . . . . . . . . . . . . .64 2.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 3

ANTHELMINTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Products on the market . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Analytical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. I Levamisole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Benzimidazoles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 lvermectin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Residues in tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Levamisole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Benzimidazole compounds . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Ivermectin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Maximum residue limits in food . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

66 67 74 74 74 76 77

77 77 77 77 78

4 ANTIBIOTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 4.1 Definition and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 4.2 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.2. I Chemical classification of antibiotics . . . . . . . . . . . . . . . . . .86 4.3 Problems with the use of antibiotics in feeds . . . . . . . . . . . . . . . . . 101 4.3.1 The Swann Report (1969) . . . . . . . . . . . . . . . . . . . . . . . . 103 3.4 Methods for the detection of antibiotics . . . . . . . . . . . . . . . . . . . . 103 3.4.1 Microbiological methods . . . . . . . . . . . . . . . . . . . . . . . . . 104 107 4.4.2 Electrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Thin-layer Chromatography . . . . . . . . . . . . . . . . . . . . . . . 108 4.4.4 Gas-liquid chromatography/mass spectrometry . . . . . . . . . . 109 4.4.5 High-pressure liquid chromatography . . . . . . . . . . . . . . . . 110 4.4.6 Card tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.5 Residues in tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Table of contents 5

7

COCCIDIOSTATS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.1 Coccidiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 5.2 Coccidiostats in use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.2.1 Named compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 5.3 Multi-detection methods for coccidiostats . . . . . . . . . . . . . . . . . . . 141 5.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

6 GROWTH PROMOTERS AND HORMONES . . . . . . . . . . . . . . . . . . . 148 6.1 Mechanisms of growth promotion . . . . . . . . . . . . . . . . . . . . . . . . 148 6.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 6.3 Antimicrobial agents as growth promoters . . . . . . . . . . . . . . . . . . 149 150 6.3.1 Rumen digestion modifiers . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Ionophores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 6.3.3 Chemical properties and methods of analysis . . . . . . . . . . . . 151 6.4 Hormones as growth promoters . . . . . . . . . . . . . . . . . . . . . . . . . 162 6.4.1 Mode of action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 6.4.2 Chemical properties of hormonal growth promoters . . . . . . . 165 6.4.3 Analytical methods for hormones . . . . . . . . . . . . . . . . . . . 169 6.1.4 Residues of hormones in tissues . . . . . . . . . . . . . . . . . . . . 170 6.5 Bovine somatotropin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171 6.6 P-agonists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 6.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 7

OTHER CONTAMINANTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 7.1 Pesticides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 180 7.1,l Pesticide residue surveys . . . . . . . . . . . . . . . . . . . . . . . . . 7.1.2 Analytical methods for the determination of pesticide residues 184 7.2 Trace elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 7.2.1 Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 7.2.2 Cadmium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 7.2.3 Copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 7.2.4 Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 7.2.5 Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 7.2.6 Selenium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191 7.2.7 Summary of data for essential nutrients in ruminants . . . . . . . 191 7.3 Mycotoxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 7.3,l Toxicity of mycotoxins . . . . . . . . . . . . . . . . . . . . . . . . . . 195 7.3.2 Aflatoxins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 7.3.3 Ochratoxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7.3.4 Trichothecenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7.4 Tranquillizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7.5 Probiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 7.6 Bovine spongiform encephalopathy . . . . . . . . . . . . . . . . . . . . . . . 202 7.7 Salmonella . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 7.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204

8

Table of contents

8 LEGISLATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 8.1 Development of food legislation in the U K . . . . . . . . . . . . . . . . . . 208 209 S.2 Current legislation in the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 The Food Safety Act 1990 . . . . . . . . . . . . . . . . . . . . . . . . 209 8.2.2 The Food and Environment Protection Act 1985 . . . . . . . . . 210 8.2.3 The Agriculture Acts 1970 and 1986 . . . . . . . . . . . . . . . . . 210 8.2.4 The Medicines Act 1968 . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.2.5 Standard withdrawal periods . . . . . . . . . . . . . . . . . . . . . . 214 8.3 EC legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 8.3.1 The Additives Directive (70/524/EEC) . . . . . . . . . . . . . . . . 216 8.3.2 The Undesirable Substances Directive (74/63/EEC) . . . . . . . 217 8.3.3 The Hormones Directive (81/60UEEC) . . . . . . . . . . . . . . . 217 8.3.4 Sampling and analysis of feeds . . . . . . . . . . . . . . . . . . . . . 219 8.3.5 Sampling and analysis of foods for veterinary residues . . . . . . 219 8.4 Legislation in the USA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 8.5 Codex Alimentarius Commission . . . . . . . . . . . . . . . . . . . . . . . . 222 8.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 8.6.1 Recent U K Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . 224 8.6.2 EC Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 8.6.3 USA Legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 9 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

226

SUGGESTIONS FOR FURTHER READING . . . . . . . . . . . . . . . . . . . 228

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

230

Preface Food ‘scares’ have become almost commonplace in recent years, fuelled by ‘media’ speculation. Thus expressions such as salmonella, ‘mad cow disease’ and listeriosis are becoming familiar to the general public as well as to specialists in microbiology and agricultural science. Despite the media ‘hype’. there is no doubt that food poisoning cases are rising and becoming a cause for concern. The blame for many of these problems has been laid, probably unjustifiably, at the door of the animal feed trade and the farming industry. Questions have been raised as to the ethicsof feeding processed animal protein to natural herbivores and to the use of antibiotics and other chemicals for prophylaxis and as growth promotants. Answers to such problems can only be obtained if reliable data are available to make a judgement. This book seeks to discuss current problems in the industry concerning the presence and use of chemicals in animal feeding stuffs, and their residues which may pass into the human food chain. The scope of UK, European and world agriculture is discussed in Chapter I , along with current practices in the feeding stuffs industry. The general analytical techniques available for the determination of chemical residues in foods and feeds are described in Chapter 2 . The remainder of the book deals with specific classes of chemicals such as anthelmintics. antibiotics, coccidiostats, growth promoters, hormones, pesticides, mycotoxins, trace elements and microbiological substances. A final chapter summarizes the legal system in the UK, the EC and the USA covering the use of medicinal additives in feeds and residues in foods. Information on t h e products on the market, their properties. chemical structures and methods for their determination in feeding stuffs and for the determination of residues in foods, is scattered widely throughout the commercial and scientific literature. This book attempts to bring together such information into one compact volume. With so extensive a literature it has been necessary to be selective. Preference has been given to readily available texts as opposed to those in obscure journals, symposia proceedings, etc. For those who wish to delve deeper into the subject some suggestions for further reading are provided at the end of the book. I would like to thank Dr Peter Baker (Laboratory of the Government Chemist) and Dr David Watson (MAFF) for kindly reading the manuscript and making many useful suggestions for improvement. May 1991

N . T. Crosby

Abbreviations ADI AFlD AMC

acceptable daily intake alkali flame ionization detector Analytical Methods Committee of the Royal Society of Chemistry

AOAC BHC b.p. BSE b.w.

Association of Official Analytical Chemists (USA) benzene hexachloride (=HCH) boiling point ("c) bovine spongiform encephalopathy body weight compound labelled with carbon-I4 isotope octadecyl derivative used as HPLC stationary phase chloramphenicol Central Statistical Office (UK) coefficient of variation dichloromethane dichlorodiphenyldichloroethane( r T D E ) dichlorobis(chlorophenyl)ethylene dichlorodipheny It richloroethane decomposes diethylstilboestrol dry matter dimethylformamide dimethylsulphoxide deoxyribonucleic acid electron-capture detector European Currency Unit European Community electron impact ionization enzyme-linked immunosorbent assay Food and Agriculture Organization ofthe United Nations (Rome) Food and Drug Administration (USA)

(UK)

'T cis

CAP

cso cv

DCM DDD DDE DDT dec. DES

DM DMF DMSO DNA ECD ECU EC El ELISA FA0 FDA

12 FI D FPD FPT GC/GLC GUMS ha HCB HCH HFB HMSO HPLC HPTLC IS0 Lambda (h) LDW Liq. MAFF MEK m.p. MRL MS MS/MS MW nm NPD PCB PML POM p.p.b. p.p.m. RIA

R RSD TLC I'

UKASTA

uv uv m , , , WHO

Abbreviations

flame ionization detector flame photometric detector Four-plate test, Frontier Post Test gas-liquid chromatography gas chromatography/mass spectrometry hectare hexachlorobenzene hexachlorocyclohexane (a, p. y-isomers) heptafluorobutyrate derivative Her Majesty's Stationery Office (UK) high-pressure (or high-performance) liquid chromatography high-performance thin-layer chromatography International Organization for Standardization (Geneva) wavelength in nanometres the dose of a chemical required to kill 50 per cent of a population of test animals liquid Ministry of Agriculture, Fisheries and Food (London) methyl ethyl ketone melting point maximum residue limit mass spectrometry tandem mass spectrometry molecular weight, or relative molecular mass nanometre (IO-"m) nitrogen phosphorus detector polychlorinated biphenyls Pharmaceutical Merchants' List prescription-only medicine parts per billion (lo-") parts per million (lo-") radioimmunoassay recovery (%) relative standard deviation thin-layer chromatography retention time United Kingdom Supply Trade Association ultraviolet wavelength of maximum absorption in the UV World Health Organization of the United Nations (Geneva)

Units for concentrations In scientific and technical journals, the system of units known as SI (Systeme International d'Unites) has now been adopted almost universally. S1 is an extension and refinement of the traditional metric system which is both logical and coherent and possesses many advantages for scientific work. However, trace amounts of additives and contaminants in feeding stuffs and in foods have been expressed in terms of parts per million (10") or parts per billion (10") for many years. These terms are still widely used and are more readily understood. They have been adopted throughout this book. The relationship between the various units is shown below: 1 p.p.m. = 1 mg/kg I p.p.b. = 1 pg/kg = 0.001 p.p.m.

To avoid confusion with toxicity experiments where chemicals are injected into an animal on the basis of its body weight, such doses are reported in units of mg/kg b.w., and not as p.p.m. I tonne = 1000 kg = 10000 m2 = 2.47 acres I nm = 1 x lo-'' m 1 ha

Current trends in agricultural practice

INTRODUCTION The basic needs of mankind for the maintenance and reproduction of the species include shelter, warmth, clothing, sex, food and water. Of these, food has a major part to play as it provides warmth, energy for mechanical activity, as well as the essential building materials for the repair and production of body tissues. Hence, agriculture has been an important human activity for many thousands of years, during which time man has obtained his food both by the growing and harvesting of crops and by hunting and rearing animals. These two activities are closely interrelated in that animals too require food and in this way are used to convert low-grade, often indigestible, poor nutritional value cellulosic materials (plants) and waste products into high-grade proteins such as meat, milk and eggs. Current practices in animal husbandry are designed to maximize this conversion at minimum cost. It has been estimated that livestock provides 17 per cent of food energy and 32 per cent of food protein for mankind (Boer, 1985). Agricultural practices are now so successful that, in the developed world at least, surpluses are beginning to be stockpiled to such an extent that they have become a political and financial embarrassment. In the European Community (EC), the excess of production over consumption during 1984 amounted to 15 per cent for cereals, 19 per cent for sugar, 27 per cent for dairy products and 27 per cent for wine (Tugendhat, 1986). I n 1988 overproduction of sugar had risen to 32 per cent. A recent estimate puts grain stocks in the EC at some 70 days’ supply (Anon., 1987). However, Community stocks of butter have fallen by 90 per cent since 1986 and cereal stockpiles by 60 per cent. Several countries have a surplus of wheat and coarse grains (Bixton and Shemlitt, 1983). the major exporters being USA (112). Canada (22), Argentina (16), Australia (14) and South Africa (5). Figures in parenthesis indicate their current surplus in million tonnes per annum. Whilst such surpluses are expensive to store and appear to be excessive, they do provide a buffer against poor harvests in future years. However, until relativeiy recent times, such problems of I .I

16

Current trends in agricultural practice

[Ch. 1

excess were unknown. The principal concern was to even out the food supply so that excesses obtained following a successful harvest could be preserved and made available in times of famine. Biblical accounts make reference to seven lean years and seven fat years (Genesis 41: 25-33). Methods of storage and preservation were therefore developed to smooth out such fluctuations in supply using treatments such as drying, smoking. brining and, more recently, canning, freezing and chemical preservation. Nevertheless, the global problem of providing sufficient food of good nutritional quality at the right place and the right time remains even today. The growth o f the world population is illustrated in Fig. 1.1. At the beginning of the 6

5

Year

FiS. I . 1 - World population incrcasc

Christian era the population was around 250million. It took over 16centuriesfor this total to double. In 1960, the total was almost double that for 1900 and it is estimated that the population will double again in as little as 40 years to around 6.2 billion by t h e year 2000. The 5 billion mark was reached in 1987. This growth rate corresponds to an increase of 80 million a year (or 150 a minute, or 200000a day) at the present time; almost three times the rate of increase of 100 years ago and, if sustained, will lead to an increase of 50 per cent in the world demand for food by the year 2000. Moreover. population increases are generally higher in the developing nations in Asia and South America than in t h e developed countries (Japan, Europe or North America). Some 90 per cent of the growth in world population is occurring in the developing countries. In 1974-76, a survey amongst 90developing countriesestimated that there

Sec. 1.2)

World agriculture

17

were 435 million seriously undernourished people consuming less than 1500 calories per day. i.e. less than half the normal intake of the population in the developed world. The number of calories consumed per head per day in different countries throughout the world is illustrated in Fig. 1.2. Protein deficiency is also a problem in the Near East ( l 4 g animal protein per person per day), Africa ( I I g) and Asia (Sg), compared to a recommended minimum of 20g. In contrast, the North Americandiet contains 66g of animal protein per person per day and that of Western Europe 33 g. There is no doubt that a large percentage of the world’s population still suffers from malnutrition even in today’s technological age, despite the fund-raising activities of ‘Live Aid’, Telethons etc.. various charitable groups and United Nations’ organizations such as FAO. which can provide only emergency short-term relief. Familyplanning coritrol programmes are now being undertaken in many of the developing countries with the highest rate of population increase. This should help to stabilize world population at a level of about 10000 million. In theory. agriculture can produce sufficient food for everyone. The total land area of the world is almost 15 000 million hectares ( ~ 3 7 0 0 0million acres) or 29 per cent of the total surface. Some 10 per cent of all land area is currently cultivated and it is theoretically possible to increase this proportion by a further 14 per cent. However, in Africa, whilst total food production has increased by 20 per cent over the last decade. production per capiru has. in fact, fallen by 1 1 per cent.

1.2

WORLD AGRICULTURE

Farming systems throughout the world are being optimized so that, whilst production of crops and animal products is maximized, inputs of human effort and industrial products (fertilizers, feeding stuffs and pesticides) are minimized. Agricultural policy in t h e developed world is designed to increase productivity through technical progress. thereby ensuring adequate food supplies for consumers at reasonable prices consistent with a fair standard of living for the agricultural community. Increasingly. these objectives are being constrained by environmental considerations. In the developing world, by contrast, the prime target is to produce as much food as possible at minimal cost to assuage hunger, often without the advantages of mechanization. irrigation. fertilizers and pesticides. Some feel for the sheer scale of world agriculture, particularly as it affects animal production, can be obtained from Table 1.1. Australia is equal in size to the USA but has to support only 6 per cent of the population of the USA. However, the USA not only has vast resources of land. water, minerals and power but has a workforce with the ingenuity in past years to develop the tractor and combine harvester. so enabling farmers to maximize output. Japan is a mountainous country suffering extremes of climate. A large proportion of cultivated land is double-cropped and relatively little meat and milk is produced owing to the lack of suitable land for grazing. Rice and fish feature more strongly in the diet than in other developed countries. Animal husbandry has increased in recent years. livestock being fed on concentrates. India is the second most populous country in the world but only seventh in land area. I t does support more cattle and buffalo than any other country (around one-quarter of the

18

Current trends in agricultural practice

Fig. 1.2 - World food consumprion

(Ch. 1

"

"

Kcnya. 'kiiizaiiia. Ugiiiid;i. A rgciii iiiii. Chilc . Urtigciay

Cattle (millions) Pigs (millions) Pou I t ry (ni i I I ions) Sheep and goats (millions)

Human population (in i I Iions) ' ' % I in irgriculturc Lilild area (million kin')

31.5 3. I 65 230

2.8 8

2(1

Australia and New Ze il Ia nd

27.2 0.6 68 31.6

18.4 I .7

58

East Africa"

99

78 I04

325

Europe (EC)

210 10 410 217

18.6 4. I

900

4.7 11.7 334 0.07

3.5 0.38

123

Japan

agriculturc 1988

India irnd Pilkistiln

Table 1.1 -World

64.7 5.4 68 65

4.8 3.7

47

S. America"

11.9 8.0 141 40.9

1 .o 0.24

57

UK

111.5 64.4 433 11.5

I .4 9.4

273

Canada

and

USA

98 58 790 140

10.7 22.4

287

USSR

(D

2 7

E

4.

D)

ii:

s 4

20

Current trends in agricultural practice

(Ch. 1

world bovine population) and produces one-fifth of the world rice crop. Rice is also the dominant crop in Pakistan. Some 70 per cent of the labour force are engaged in agriculture. U K and European agriculture are discussed in greater detail below. 1.2.1

World market for animal health products Animal husbandry on such a large scale has stimulated the development and need for health-care products. Increasing trends towards the husbandry of animals kept in close proximity to each other (poultry and pigs especially) has encouraged pharmaceutical manufacturers to develop products designed not only to cure disease but also for use as prophylactics to prevent the spread of disease. Thus a world market now exists worth around $8000 million distributed roughly according to Fig. 1.3. This also shows the structure of the market.

Structure of the market N. America W. Europe E. EuropeiUSSR Cent./S. America Japan Other

% 32 23 14.5 9.5 8.4

12.6

Sec. 1.31

Agriculture in the EC

21

In the USA in 1983.31.9 million pounds of antibiotics were produced, 58per cent being tetracyclines and penicillin. Over half of this quantity.was used in animal feeding stuffs. It has been estimated that 75 per cent of dairy calves, 60 per cent of beef cattle, 75 per cent of pigs and 80 per cent of poultry have received one or more drugs in their feed during their lifetime. Japan is the second largest consumer of animal health products behind the USA; 110 additives have been approved for use. Production has now reached 78 000 tonnes, worth 60000 million yen (f240 million).

1.3 AGRICULTURE IN THE EC Agricultural policy in Western Europe following the end of the Second World War was geared to increasing production, with the ultimate aim of achieving selfsufficiency in food products. This goal was achieved by financial support for the farming community through guaranteed commodity prices and loans/grants to utilize technological advances and increased mechanization. Farm productivity was also improved by the use of fertilizers, pesticides and the employment of new crop varieties. Similar advances were made in animal husbandry. The Treaty of Rome establishing the European Economic Community was signed on the 25 March 1957 by the six member states, namely Belgium, Germany, France, Italy, Luxembourg and The Netherlands. Article 39 of the Treaty relates to agriculture and specifies the following objectives:

- to increase agricultural productivity by promoting technical progress and by ensuring the national development of agricultural production and the optimum utilization of the factors of production. in particular labour;

- to ensure a fair standard of living for the agricultural community, in particular by increasing the individual earnings of persons engaged in agriculture;

- to stabilize markets; - to assure the availability of supplies;

- to ensure that supplies reach consumers at reasonable prices. The EC was enlarged in 1973 by the accession of Denmark, Ireland and the United Kingdom. Greece joined in 1981 and Spain and Portugal in 1986. Some statistical data relating to the current members of the Community are shown in Table 1.2. The importance of agriculture to the members of the Community is clearly shown. The Community's expenditure on agriculture was El9000 million in 1988. The original aims of Community policy have been achieved as indicated in Table 1.3. Success, however. brings its own problems and in some cases self-sufficiency has given way to food 'mountains' with attendant political problems. EC self-sufficiency in various commodities is shown in Table 1.4. Criticisms have been made regarding the large proportion of the EC budget devoted to agriculture. Problems of excess production have been tackled recently by quotas, reduction in price support guarantees and setaside schemes. Apart from milk production, such schemes have impinged mainly on cereals and have had limited effects on animal husbandry. As policy is changed to

Populiition (inillioiis)

”

Includcs Luxcinhourg.

15.5

I24

0.2

120 30

2.20 0.2

2.07

v;lluc C;ittlc (niillioiis)

Pigs (iiiillions) Sheep (ni iI Iionh) Poultry (inillioiis)

0.X 0.X“

2.6 28.7

2.0

I .4

31 220

10.4

12.0

1.2 10.8

21.2

0.8

15.8

I4.M

27.4

5.0

17.4

50

OS3X 8.1 31.0

France

22.0 I .5 77

2.0

7.2

3505 30.0 0.2

I0

0I IO(i33 S.(i 12. I

S

11020 8.5

I 0

XI20 3.0

Ariililc Iiiiid (million h;i) Agriculture a s ‘K of totiil cxlwrt

h;1)

‘%cinploycd in ;igriciilturc Agriciil1ur;il ;irc;i in use (inillion

G D P ( $ per capita)

Grcccc

Belgium I)ciim;irk Gcriii;iiiy

I I .o I20

-

X.74 7.4

0.5

0.4

57.5 0208 12.4 17.X

It;~ly

6.6

0.9X

0.6

27.X

I .o

3.5 5120 17.0 5.7

lrcl;ind

0.07 0.09

0.OX

0.21

-

0.06

0.13

4.3 27.2

5.1 2.1

X9

4.77 13.7 I .4

17.9 -

4.98 10.9

lS.6 14.3

-

0.8 10.3

39

Spilin

I4.X

0100

lands

Iiourg

0.4 8721 4.7

Ncthcr-

Luxcni-

Table 1.2 - General st;itistical data rclitting to member states in the EC. 1988

IX

s.2

1.39 2.X

2.9 8.2

10.3 0.5 4.5

Portug;ll

140

40.9

8.0

II.X7

0.8

0.9

1X.X

57 8072 2.2

UK

CD

E

D

2. e : s2.

5 -.3

3

1 CD

2 c

1 CD

1

E

Importance of agriculture to the UK economy

Sec. 1.41

23

Table 1.3 - EC stocks of commodities in 1990

Wheat, soft Wheat, durum Maize Barley Rye Butter Skim milk powder Beef

4.64 million tonnes 1.09 million tonnes 14 000 tonnes 2.37 million tonnes 966000 tonnes 66 000 tonnes 7000 tonnes 402 000 tonnes

Table 1.4 - EC self-sufficiency in selected Commodities

Product

Self-sufficiency in 1985-86

Total cereals Potatoes Fresh vegetables Sugar Whole-milk powder Butter Beef Lamb Poultry Pork

119 102 101 133 342 117 108

76 105 102

curb the production of commodities in surplus and to reduce the cost of agricultural support, environmental and consumer pressures have increased. Hence, limitations on the use of nitrogen fertilizers to reduce nitrate levels in drinking water have been suggested. Permitted levels of copper used as a growth promoter in pig feeds have been reduced and certain feed materials containing aflatoxins are strictly controlled in dairy feeds.

1.4

IMPORTANCE OF AGRICULTURE TO THE UK ECONOMY

Until the eighteenth century, the economy of the U K was principally dependent on agriculture, wool cloth being the only important manufacturing industry. Two industrial revolutions have since resulted in the growth and the development of many new industries. so that the relative importance of agriculture for employment has steadily declined. This trend has been enhanced by the enormous increase in

24

Current trends in agricultural practice

[Ch. 1

productivity resulting from improved farming practices. mechanization and the use of fertilizers -all these have increased yields and reduced the manpower working on the land. Nowadays, British agriculture employs about 2 per cent of the working population and there has been a steady loss of around 14000 ha (35000 acres) per annum of land devoted to agriculture. Nevertheless, three-quarters of the land area of the UK (24 million ha) is still used for agriculture, the rest being mountains, forest or reserved for urban use. 12 million ha (30 million acres) are under crops and grass, whilst 6 million ha (I5 million acres) are used for rough grazing. The output of farm crops is shown in Table 1.5. The enormous increases in output of wheat, potatoes, Table 1.5 - Estimated quantities and value of crops harvested from UK farms Crop

1975

1980

1985 1988

(Thousand tonnes) Wheat Barley Oats Potatoes Sugar-beet Rape (grown for oil-seed) Sprouts Cabbage and cauliflower Carrots Turnips and swedes Beetroot Onions and leeks Peas Lettuce Vegetables Fruit Total horticulture Total farm crops "

4490 8510 795 455 1 4864 61 162 1437 573 150 96 223 297 123

8 470 12 (150 11 640 10 325 9 740 8 690 600 615 557 7 109 6 895 6 899 7380 7715 8 5 0 0 895 300 228 154 170 1606 1312 1064 553 627 663 162 160 177 109 113 96 286 257 309 241 228 196 135 195 204

Value" ($ million)

1432

850 25 308 233 244

760 232 1240 3235

IOSS priccs.

sugar-beet and rape-seed over the last ten years is clearly seen, whilst horticultural crops have generally remained at or about the same level. The total value of farm and horticultural crops in 1987 was 4500 million. Table 1.6 shows the number of livestock on U K farms in the period 1975 to 1990, and the value of these animals at 1985 prices. Over the last few years there has been a slight fall in the numbers of cattle and poultry. with a small increase in sheep and lambs. An estimate of the value of such livestock is given and in total this amounts to $4300 million - almost equal to the value of farm and horticultural produce. Taken together, the value of crops and

Sec. 1.51

Animal husbandry and feeding stuffs

25

Table 1.6 - Livestock on UK farms ~~

~~

Thousands Value 1975

Cattle dairy beef Sheep and lambs Pigs Poultry

1980

1985

1990

14 717 3426 12 865 12 108 I3 242 3 228 3 150 3 042 1 899 1478 I 333 1 343 28 270 31 446 35 628 44 217 7 532 7 815 7 865 7 606 136 572 135 105 128 968 120 198

(.f million)

1919

-

590 978 813

livestock is about 1.5 per cent of gross domestic product (GDP). Gross agricultural output in 1985 totalled €1 1883 million. or 4 per cent of GDP. The figures reported here have been collated principally from Brituiri (1991) and the CSO Aiirtuul A hstructs of Stutistics ( 1990). 1.4.1 Self-sufficiency in food products in the U K In 1960. UK farms produced 50 per cent of the food requirements of the population, i.e. roughly two-thirds of those foods which it is possible to grow under UK climatic conditions. By 1985. this had increased to 67 per cent and three-quarters respectively. Figures for some individual food products are illustrated in Table 1.7. The UK now has virtual self-sufficiency in beef and veal. pork, poultry. cream and milk, eggs, wheat and potatoes, with significant shortfalls only in bacon and ham, mutton and lamb. butter. cheese and sugar. Correspondingly. food imports have fallen as a fraction of total imports from 25 per cent in 1960 to 10 per cent in 1985. Exports reached 6273 million in 1989 - an increase of 55 per cent in volume terms over the last ten years. This increase in self-sufficiency has been brought about largely through increases in productivity and output. Labour productivity rose by 69 per cent between 1975 and 1985 as a result of increased mechanization, and yields have increased as shown in Table 1.8, through improved agricultural practices such as plant and animal breeding and the use of fertilizers. The number of horses working on farms has fallen to almost negligible levels as tractors and combine harvesters have supplied the necessary mechanization. As a horse requires 1 ha of land for feeding, this change has released large areas of land for other uses. In arable farming. one person can now work 81 ha (200 acres) compared with an average of only 16 ha (39.5 acres) some 20 years ago. Similar trends have been seen in animal husbandry, with livestock now being kept in bigger and more intensive units (Royal Commission on Environmental Pollution, 1979).

1.5

ANIMAL HUSBANDRY AND FEEDING STUFFS

The feed must provide the basic needs of the animal. namely energy. and essential nutrients such as amino acids, fatty acids. trace elements and vitamins. The

26

[Ch. 1

Current trends in agricultural practice Table 1.7 - U K output of food products

output (thousand tonnes) I985

Food

Beef and veal Mutton and lamb Pork Bacon and ham Poultry meat Butter Cheese Cream Milk (million litres) Skimmed milk powder Eggs (million dozen) Sugar Wheat Pot a toes

Yo Self-sufficiency

1974-76

1985

1 040

295 764 213 787 24 1 243 73 15 260 354 1051 7 715 12 050 6 895

98 71 104 45 98 64 67 92 100 139 97 55 103 89

82 13 63 I 00

98 26 61 88

1988

93 96 65 100 98 58 113 90

Table 1.8 - Increased yields in UK agriculture

Commodity

Yield 1974-76

(Tanned hectare)

O/O

increase

1985 Wheat Barley Oats Potatoes Oil-seeds Sugar-beet Milk (gallons/dairy cow)

4.39 3.75 3.48 25.10 2.03 27.27 748

6.29 4.91 4.24 35.80 3.01 40.00 1044

43 31 22 42 50 47 40

nutritional requirements will vary with the type, sex and age of the animal and the manner in which it is reared. No single material (often called a ‘straight’) can provide all the nutritional requirements for a given animal, so different materials are usually mixed together to produce ‘balanced’ or ‘compounded’ feeds. A wide range of

Sec. 1.51

Animal husbandry and feeding stuffs

27

compound feeds is available to satisfy the differing needs of different categories of animals. In addition to compound feeds. many animals (especially ruminants) require large amounts of roughage in their diet. Suitable roughage materials include hay. straw and silage. all being high in fibre but low in digestible nutrients. Grass supplies 60-80 per cent of the feed required by cattle and sheep. Approximately twothirds of the surface area of the U K is covered by grass. yielding typically I5 000 kg of dry matter per hectarelyear. The growth of grass varies over the year. reaching a maximum of 120kg DM/ha per day in May and June. Excess grass is harvested and preserved either as hay or by silage making. A wide variety of vegetable and animal products is used to feed animals. The different types of feed and the major ingredients used will now be described. 1.5.1 Types of animal feeding stuffs Animals within the scope of UK legislation include bulls, cows. steers (young oxen). heifers. calves. sheep. goats. pigs. horses, farmed deer, rabbits, mink. partridges. pheasants, poultry, bees and farmed fish. Pet animals are now also included and are defined as those belonging to a species normally nourished and kept. but not consumed. by man except animals bred for fur. Food for dogs and cats forms the largest fraction of the pet-food market. For nutritional purposes. animals are often classified into two groups - ruminants and non-ruminants. Cattle, sheep and goats are examples of the former group, with pigs and poultry being examples of the latter group. The term 'ruminant' is used to describe cud-chewing animals with more than one stomach. in which the food is broken down into simpler molecules by a process of fermentation involving microflora present in the rumen. These simpler molecules can then be absorbed into the bloodstream and utilized as in non-ruminants, but a proportion will also be used as food for the microbes in the rumen. In non-ruminants. microbes have only a limited role, occurring predominantly in the large intestine, where they act on the residues from the initial acidic and enzymatic digestion processes taking place in the alimentary canal and stomach. Furthermore, nutritional requirements of animals vary widely not only between different species but also at different ages within the same species. The composition of animal feeding stuffs will vary similarly, not only depending on the type of animal and its stage of development. but also, in the case of poultry for example. depending on whether the animal is being reared as a broiler or for the laying of eggs. Equally. feeds for dairy cattle differ from those fed to animals being reared as beef cattle. In the UK. the Agricultural Development and Advisory Service (ADAS). the British Veterinary Association (BVA) and the Agricultural Supply Trade Association (UKASTA) have jointly agreed a preferred terminology to be used in the compound feed industry. Additionally, legal definitions are incorporated in the Feeding Stuffs Regulations 1988. An amalgamation of the two produces something along the following lines: C o m p o u d feedirig miff:

a mixture of ingredients of vegetable or animal origin, fresh or preserved. in their natural state or processed. for oral animal feeding in

28

Current trends in agricultural practice

[Ch. 1

such proportions as to provide a properly balanced diet at every stage of growth and development. The feeding stuff may also contain minerals, trace elements, vitamins and other additives mixed and blended in appropriate amounts. Complere feeding sluff: a compound feeding stuff which. by reason of its composition, is sufficient to ensure a daily ration. Complementury feeding stitff: a mixture of ingredients (some of which are in high concentration) which is sufficient for a daily ration only if used in combination with other feeding materials. Such feeds are often prepared for ruminants to supplement grass or other roughages and are frequently so named; e.g. for balancing straw, silage etc. Protein concenrrufes: contain protein-rich products such as fishmeal or soya and are designed for mixing with cereals or other farm products before feeding. 'Srraighrs': single feeding stuffs of animal or vegetable origin in the natural state or preserved, whether or not they contain an additive. Straightsseldom provide the complete nutritional requirements of livestock unless mixed with other materials. Pre-mixes: concentrated uniform mixtures of additives with another substance or substances used as a carrier or diluent, for use in the manufacture of feeding stuffs. Premixes are used to facilitate uniform dispersion of micro-nutrients in a larger mix. Supplemenfs: technical products for use at less than 5 per cent of the total ration and designed to incorporate known concentrations of vitamins, trace elements, non-nutrient additives and other special ingredients. The active material is usually first mixed with a diluent or carrier. 1.5.2 Pet foods Foods for companion animals are included within the scope of both E C and UK legislation for animal feeding stuffs, although both in terms of manufacturing methods and composition they are more akin to human foods. I n the UK alone, the dog and cat population is around 10 million and total pet-food sales in 1986 were f766 million. Tinned foods for dog and cats totalled just over f 3 0 0 million each, whilst an additional f 9 3 million was paid for dog biscuits and meal. Large pet-food markets also exist in Belgium, France, Japan and the USA, with pet foods accounting for nearly 10 per cent of total selling space in modern supermarkets. In the USA, there are over 56 million dogs and 52 million cats. Pet-food sales totalled 4.7 million tonnes for dogs and cats, worth $3.3 billion. I n Japan, the pet-food market is worth 16000 million yen (f64 million). Canned pet food is made from offal and by-products from abattoirs that are unacceptable for human consumption, including dried blood and bones. The material is comminuted and often mixed with cereal products. After filling in cans,

Sec. 1.51

Animal husbandry and feeding stuffs

29

the products are heat treated in a commercial sterilization process. Other pet foods include biscuits and meals which have been subjected to baking and possibly extrusion processes with or without addition of oils and fats. The composition and nutritional status of all these products is most carefully controlled. As most of the additives are used directly for human food and pet animals are not consumed by man. problems of residues in animal tissues resulting from the feeding stuff do not arise. Pet foods will not therefore be considered further. I S . 3 Main ingredients of compounded feeding stuffs A full list of ingrcdients permitted in the UK can be found in Schedule 2 of the Feeding Stuffs Regulations 1988. The major groups comprise:

Oilcukes rrrid meals: including palm kernel. groundnut, rape-seed, copra, coconut, soya bean, cotton seed. sunflower seed. linseed. wheat and maize germ and olive pulp meal. These are mainly by-products of edible oil manufacture and are the residues remaining after most of the oil has been pressed out or removed by solvent extraction. Some of these products (e.g. palm kernel and groundnut) may be subject to contamination by aflatoxins and cannot then be incorporated into dairy feed. The use of cotton seed products in feeds is often restricted by the presence of gossypol. which is toxic to certain species of animal (especially monogastrics). Soya bean meal has many advantages, including high protein content and digestibility, and hizh lysine content. which is important for pig and poultry feeds. Soya also has a low crude fibre content and good stability as most of the oil will have been extracted. Soya is low in toxic substances since antitrypsin factors occurring naturally are deactivated during processing. Cereuls utid oilier vegetable products:

mainly by-products of flour manufacture and milling after screening or grinding from wheat. rye. oats. barley or maize. Other products include peas, beans, potatoes. rice and various starch and sugary materials. yeast and by-products of the brewing and distilling industries.

obtained by artificially drying forage material to inactivate naturally occurring enzymes which otherwise would lead to deterioration. Materials used include grass, lucerne, clover. sugar-beet tops, manioc (cassava or tapioca) and sweet potatocs. These products are used mainly as substitutes.

Dried vegeiuble proditcis:

these range from dairy products such as skimmed milk powder, buttermilk and whey powders, blood-meal. meat and bone-meal, greaves (animal fat by-product), poultry waste, feather-meal. fish-meal and animal fats.

Atiimrrl proditcis:

Miticrul sirbsrutxes: including limestone, chalk. dolomite and natural phosphates. I .5.4 Demand for compound feeds and feed ingredients Demand for animal feeding stuffs is determined primarily by livestock numbers, which in turn reflect consumer demand for animal products. Most major countries

30

Current trends in agricultural practice

[Ch. 1

now adopt some scheme of agricultural support to smooth out fluctuations in t h e market. The decision of the EC through its Common Agricultural Policy to impose quota limitations on the dairy industry resulted in a slight fall in the numbers of dairy cattle in the U K (Table 1.6) and a corresponding fall in the output of cattle feed (Table 1.9). Other factors which have an influence on the demand for feeds are:

( I ) the weather. through its influence on the quality and quantity of grazing as well as on the availability of ’straights‘ used in compounding; (2) the performance of competing feeding systems and various economic factors such as cost. feed conversion efficiency and the price obtained at the market. Table 1.9 - UK compound feed production ~~~

~

~~

~

I983

1984 1986 million tonnes ~~

Cattle and calves Pig Poultry Others Total

3.5 2.3 3.5 0.4 12.1

~~~

~

4.8 2.1 3.3 0.5 10.7

1988

~~

4.9 2.2 3.5 0.6 11.2

4.1 2.2

3.7

0.8 10.8

Feed accounts for around 75-80 per cent of total production costs under intensive rearing systems - especially for pigs and poultry. The wide variety of ingredients available on the market enables manufacturers to use ‘straights’ interchangeably, within certain nutritional limits depending on market and economic pressures such as supply. quality and price. Modern feeds mills use computers to select suitable formulations based on minimum cost, so that they can be more flexible in adapting to market forces. The major proportion of feeds are pelletized in the form of small pencils. Poultry feeds are often marketed as meal or mash. Recent food scares (e.g. salmonella in eggs. bovine spongiform encephalopathy) have increased pressure from consumers for information as to the ingredients present in a feeding stuff in addition to the nutritional declaration of protein content, oil content. etc.

1.5.4.1 Demand in the UK Compound feed production in the UK is shown in Table 1.9. After reachinga peak in 1983, there has been a slight fall in recent years. In money terms this output represents around f2000 million. The principal ingredients used in UK compound feeds in 1983 are listed in Table 1.10 (Edwards. 1985). Cereals and their by-products make up over half the total production. Over the last ten years the major changes in use of raw materials has been an increase in the use of oil-seed products, especially rape. and diversifications into other materials. Less barley and maize are now

Sec. 1.51

31

Animal husbandry and feeding stuffs

Table 1.10 - Principal raw materials used in U K feeds (1988-89)

Commodity

~~

Amount used (million tonnes) ~~

~

Wheat Barley Oats Maize and flaked maize Wheat by-products Field beans and peas Rape-seed cake and meal High-protein material Low-protein material Maize gluten Sugar-beet pulp Animal substances Protein concentrates Oils and fats Molasses Minerals Other

Yo

3.01 0.63 0.05 0.2 0.97 0.36 0.49 1.3 0.29 0.3 0.14 0.46 0.09 0.25 0.45 0.29 1.54

27.8 5.8 0.5 1.8

9.0 3.3 4.5 12.0 2.7 2.8 1.3 4.3 0.7 2.3 4.4 2.7 14.1

incorporated into formulations. There are about 450 mills producing feeding stuffs situated close to the cereal-producing and livestock-raising regions and often within close reach of small to medium-sized harbour facilities. Some 40 per cent of feeds are produced by on-farm mixing. 1.5.4.2 Demand in the EC The EC is the second largest producer of animal feeds after the USA. Trends in the production of animal feeds in EC countries since 1976 are shown in Fig. 1.4. Italy. France, the Netherlands and Germany have steadily increased their output over the last ten years. whilst production in Ireland. Denmark, Belgium and the UK has remained relatively unchanged over the same period. Current political pressure to reform the Common Agricultural Policy and to reduce the subsidy to agriculture is likely to restrict any expansion in the medium term. In the period 1979-84 expenditure on agriculture rose by 76 per cent. by which time money spent on agriculture (19000 million ECUs) accounted for 70 per cent of the total Community budget. Approximately one-third of the agriculture budget is spend on export subsidies which are needed in order to dispose of surplus production o n world markets. Some general data illustrating the size of the EC and the relationships between the member states is shown in Table 1.2. The predominance of Germany. France, Italy and the

32

Current trends in agricultural practice 18

[Ch. 1

I-

I = Italy P = Portugal

S = Spain U = United Kingdom

I

I

I

I

I

1

1

1

1976

1978

1980

1982

1984

1986

1988

1990

Year Fif. I .-I- EC output 01 animal Iccds.

U K in terms of size is clearly demonstrated, along with the importance of agriculture to countries such as Greece and Ireland. Some information on the numbers of cattle

and pigs in each country is also included in the table. Numbers of cattle are slowly declining whilst numbers of pigs are on the increase. A breakdown of the raw materials used by EC countries in the production of animal feeding stuffs is presented in Table 1.1 I . A direct comparison with Table 1.10 -materials used in the UK -is not possible since the categories of commodities are not defined in exactly the same way. Until 1983 cattle feed production was rising rapidly. with smaller increases for pig and poultry. In future years there is likely to be a slight decline in cattle feed consumption following the imposition of dairy quotas but pig and poultry feeds should remain stable, and feed for sheep is likely t o increase marginally. I n summary, the demand for animal feeding stuffs in the EC is currently around 300 million tonnes, comprising 135 million tonnes of compounded feeds and 165

Sec. 1.61

Additives in feeds

33

Table 1 . 1 1 - EC consumption of raw materials in compound feeds Commodity

1983 (million tonnes)

Cereals Manioc By-products from food industry Oils and fats Vegetable protein Animal meals Dairy products Dried forage Minerals. etc. Others

29.3 5 .o 20.0

Total

83.5

1 .o 20.1 2.0

2.3 0.8 1.2 1.8

n /'

35 6 24 1 24 2 3 1 1

2

million tonnes of roughage material. Of the compounded feeds only two-thirds are produced internally, with about one-third being imported. The industry consists of about 3500 feeds mills. The EC is a major importer of feed ingredients such as soya beans, oilcake, manioc, corn gluten products, citrus waste and molasses, even though imports are limited by a system of levies and quotas designed to protect the internal cereal market. Almost half the imports were received from developing countries which have freer access to the EC market through the Lome convention. In recent years there have been moves to increase self-sufficiency in protein products by replacing soya meal with peas, beans and lupins. The use of cereals has been slowly declining, but they remain a major component of feeding stuffs. 1.5.4.3 World supply and demand World production of compound feeds in 1981 totalled 377 million tonnes, 90 per cent being produced by the developed countries. The USA is !he largest producer (I25 million tonnes) followed by the EC (83 million tonnes); 43 million tonnes were produced by the developing countries in 1981, mainly Latin America and Eastern Asia. Less than 2 million tonnes were produced in Africa. However, production growth rates were nearly four times higher in the developing than the developed countries. The USA has some 2000 manufacturers of prepared feeds as well as 300 pet-food manufacturers. About 12 per cent of this production is exported, mainly soya bean products and maize gluten onto the European market. Imports are negligible apart from cross-border trade with Canada. 1.6 ADDITIVES IN FEEDS

Additives are substances which are incorporated into animal feeds in order to influence the character of the feed or affect animal production. In the first category

34

Current trends in agricultural practice

[Ch. 1

one can list antioxidants, colorants, emulsifiers. stabilizers. thickeners, gelling agents. binders. anticaking agents, coagulants. aromatic or appetizing substances and preservatives. The main substances falling into the second category are vitamins, trace elements and medicinal compounds. Many of the above substances are used in human foods and, hence. their addition to animal feeds is unlikely to give rise to concern. The animal is, in effect, acting as a further safety buffer and few of the above chemicals produce residues in animal tissues. Medicinal additives. however. are not used in human foods and some do produce residues in animal tissues, although normally at very low concentrations - often below the limit of detection by all but the most recent methods of analysis. Concern has been expressed as to the possible effects of such residues in meat, milk and eggs on susceptible humans who subsequently consume such products. This volume examines the use of such additives, the different types currently on the market and methods of analysis available for their detection in feeds and foods.

1.6.1 Use of medicinal additives Modern farming practices. involving the intensive rearing of animals in restricted accommodation, inevitably increase the incidence and spread of disease. since the conditions could hardly be more favourable for the rapid multiplication of parasites. Fig. 5 . I (p. 124) shows a typical poultry house where large numbers of animals are confined in a restricted area, in contrast to the traditional system of free-range husbandry where the animals were allowed to wander around wide areas of the farm in the open air to forage for food. Hence there is a need to add medicinal compounds to animal feeds for three main purposes: ( 1 ) therapy: t h e curing of outbreaks of disease; (2) prophylaxis: the prevention of outbreaks of disease:

(3) growth promotion: the improvement of feed conversion efficiency and, hence growth rate. I t has been estimated that approximately one-third of all UK feeding stuffs contain medicinal compounds licensed for inclusion without a veterinary prescription, whilst only 5 per cent of feeds contain medicaments for therapeutic use (Anon., 1984). Medicated feeds produced are primarily for the pig and poultry industries, although feeds containing growth promoters are of importance for beef and dairy cattle too, where disease prevention is less of a problem. particularly during the summer mont hs. The therapeutic use of medicinal substances is obviously essential to cure outbreaks of disease whenever they occur. As such treatment iscarried out under the direction of a veterinary surgeon, no problems should arise for animals or humans, particularly as such treatments will be spasmodic rather than continuous. However, residues can occur in animal products when large doses are administered immediately prior to slaughter, or in the milk of animals undergoing treatment. Prophylaxis is again an important component in modern farm management and animal welfare where large numbers of animals are herded together in close

Sec. 1.61

Additives in feeds

35

confinement. Once the clinical signsof an outbreak are recognized, it may be too late to effect a cure. Hence, subtherapeutic levels of medicinal compounds are added to feeds as part of a continuous feeding programme to prevent such outbreaks and to control the spread of disease. Medicinal additives used in this way include antimicrobials, antibiotics, coccidiostats and anthelmintics. Other substances are added primarily for their growth-promoting action, e.g. hormones, or copper in pig feeds, or certain veterinary drugs in a wide range of products. Some substances possess a dual action. By controlling t h e microbial population inside the animal. they assist in increasing the feed conversion efficiency and, hence, the animal's daily live-weight gain. I t is this latter aspect which has given rise to the greatest public concern. I n addition to the possible problems created by residues of highly active chemicals such as hormones and antibiotics in human food, the need for such treatments in the light of over-production is also increasingly being questioned. The animal health and nutrition products' market was estimated to be worth over $9000 million in 1986, with feed additives and pharmaceuticals each contributing 45 per cent of the total. The USA had 28 per cent of the market and Western Europe 24.5 per cent. The UK had 3.1 per cent of the total, a small decline on previous years. A breakdown by animal usage showed that cattle comprised 32 per cent, with poultry 24 per cent, pigs 21 per cent. sheep 10 per cent and horses 4 per cent.

1.6.2 Types of medicinal additives Chemicals added to animal feeds for the treatment and prevention of disease in animals can be classified into the following groups:

( I ) anthelmintics; (2) antibacterials and antibiotics: 13) coccidiostats. Some chemicals have dual function and can properly be classified in more than one of the above groups. In addition. chemicals are added to feeds for growth promotion purposes. These may be classified as: (4) hormones; (5) feed conversion improvers. Again. considerable overlap occurs in all the groups one to five. Other preparations used in animal husbandry include pesticides to control external parasites, vaccines for disease prevention and tranquillizers. All of these groups of chemicals may produce residues of the parent compound or its metabolites in the animal's tissue. Where such tissues are subsequently consumed as food by man, concern has been expressed as to the possible dangers of such residues entering the human system. This volume is primarily concerned with current methods of analysis which have been developed for the determination of such residues in animal tissues. Recent work will be reviewed and t h e results of surveys

36

Current trends in agricultural practice

[Ch. 1

which have been undertaken will be summarized. As the dangers of the use of medicinal additives have been recognized for many years. a system of legal control has been established. The effectiveness of such control measures will be examined.

REFERENCES Anon. (1984) The feed Compounder. 4.8. Anon. (1987) Milling, 180,6. Bixton, G . & Shemlitt, L.W. (eds.) (1983), Chemistry and world food supplies: perspectives and recommendations. International Union of Pure and Applied Chemistry, Oxford. Boer, de F. (1985) feeding Vulue of by-products and their use by beef cattle. Report EUR 8918 EN. Commission of the European Communities. Luxembourg, p.7. Britain: An oflicial handbook. (1991) HMSO, London. CSO Annual Abstracts of Statistics (1990) No. 125. HMSO, London. Edwards, R. V. (1985) The feed Compounder, 5 ( I ) , 34. Royal Commission on Environmental Pollution, 7th Report (1979). HMSO, London, p. 20. Rutherford, B. (1985) The Feed Compounder, 5 (1 I ) , 39. The Feeding Stuffs Regulations 1988, Statutory Instrument No. 1396 as amended by S.I. 2014 (1989). HMSO, London. Tugendhat, C. (1986) In: Making sense of Europe. Viking Penguin, Harmondsworth. UK. 1.7

Analytical methodology

THE ANALYTICAL PROBLEM The job of an analytical chemist is to obtain information concerning the composition of materials using mainly chemical techniques, although nowadays other methods which are more physical or biological are increasingly being applied. Samples submitted to an agricultural laboratory may include fertilizers, animal feeding stuffs, foods for human consumption, as well asclinical samples such as blood, plasma, bile, urine, faeces and pathological specimens. Determinations of a wide range of drugs, trace elements, pesticides and other contaminants may be requested. This work is concerned primarily with the determination of veterinary products in foods and feeds for the regulatory control of animal health-care products in modern agricultural practice. Legislation exists (see Chapter 8) to control the use of medicinal additives in animal feeding stuffs and the presence of contaminants in human foods. Such regulations are of little use unless they can be enforced. Enforcement requires analytical methods that are specific and quantitative so that the results obtained are reliable and informative. Veterinary products are added to animal feeding stuffs usually at t h e part per million level, and so the analytical problem is to detect the compound(s) of interest in the presence of a large amount of other material which may well interfere in the analytical procedure. Residues of such compounds may find their way into foods for human consumption but normally only at concentrations at the parts per billion (lo-") level. This presents an even greater analytical problem, so that methods of extraction, removal of co-extractants, sensitivity and specificity of the detection system must be developed that are equal to thischallenge. Fortunately, there is seldom any restriction on the sample size available to the analyst. Methods for use with foods and feeds are generally similar in principle. The former are scaled down so that levels two to three orders of magnitude lower can be detected. Hence, both types of analysis will be discussed throughout this work, particularly as the control of drug residues in foods can only be achieved through the controlled use and monitoring of such products in feeds. 2.1

38

Analytical methodology

[Ch. 2

The large number of ingredients used in the manufacture of animal feeding stuffs has been referred to previously (p. 29). Foods for human consumption similarly are mixtures of fats, proteins, carbohydrates, water, minerals. vitamins and other additives. For example, the potato contains around 90 per cent of its weight as water and the rest is mainly starch. Even so, at least 150 separate chemical compounds have been identified as constituents of potatoes and there may well be others which have yet to be identified. Orange oil is known to contain at least 12 different alcohols, 9 aldehydes, 2 esters, 4 ketones and 14 hydrocarbons. Nursten and Williams (1969) have identified 98 volurile compounds in blackcurrants. including 23 hydrocarbons, 14 carbonyls. 30 alcohols, 8 acids, 22 esters and 1 ether. Furthermore, foods, being natural products. are subject to compositional variations depending on such factors as the weather. soil conditions, time of harvest, nutritional status (in the case of animal products), post-harvest treatment and processing. Processed foods may also contain a number of chemical additives such as colours, flavours, preservatives, antioxidants. emulsifiers or sweeteners which the manufacturers incorporate in order to enhance the flavour, acceptability, storage life or safety of the product. Although most individual foods contain only a very few such additives, several thousand chemicals are approved worldwide for use in this way. For example, the composition of an infant milk food is shown in Table 2.1. For such a product, a

Table 2.1 - Ingredients of an infant milk food

Skimmed milk powder Electrodialysed whey Lactose Oleo oil Coconut oil Soya bean oil Oleic (safflower) oil Soya bean lecithin CaC 1 2 NaHCOz Vitamin C Calcium citrate FeSO,

KOH KHCO3 ZnSO, Vitamin E Nicotinamide Vitamin A

cuso,

Calcium pantothenate Vitamins B I , Bz,B, p-Ca rotene

K1 Folic acid Vitamins D3, B I z

proximate analysis might show: fat 28%. carbohydrate 56%, ash 2.0%, protein 12% and water 2.0%. This gives little clue as to the true complexity of the food. The fatty matter present is itself a multi-component mixture of fatty acids and glycerol, and several different proteins are included under the generic headings whey and skimmed milk powder. Fortunately, the residue chemist is not normally asked to perform a full analysis and separation of all the components present in a sample. Nevertheless. it is important to recognize the true complexity of most foods and feeds

Sec. 2.21

The analytical approach

39

and to take precautions to ensure that no individual constituent can interfere with the analysis. Second only to the complexity of the matrix is the low levels at which a drug might be found in either feeds or foods. Drugs are normally added to feeds within the range 3-250 parts per million, or mg/kg. The analytical problem can be described by considering the difficulty of finding one particular particle in a 2 Ib bag of sugar, or identifying 50 named individuals in the whole population of the United Kingdom. Residues of drugs in foods will occur primarily at the part per billion level, or pg/kg. 1 part in a billion represents approximately 1 0 s in the time-span since the birth of Christ, or the detection of one grain of sugar in an Olympic-size swimming pool. These problems can only be overcome by prior treatment of the sample to remove as much of the matrix away from the drug residue as possible, followed by highly sensitive and selective detection systems that can discriminate between particular drug residues and matrix constituents. The principal methods of extraction, separation and detection of drug residues will be discussed in full in general terms and in detail for particular compounds in the following chapters. One further problem which must be considered by the residue chemist concerns the form of residue present in the food. This form may not be the form that was originally added to the feeding stuff. Some compounds are metabolized by the animal to products that can be either more or less active than the parent compound. Such metabolic changes cannot be ignored, particularly where the ‘daughter’ compound is more biologically active than its parent. Such changes can occur postmortem and even during storage in the feed owing to the influence of heat and/or light. The possibility of changes occurring in the food during freezing or cooking must also be investigated. On the other hand, many drugs bind with sulphuric or glucuronic acids and proteins and thus occur in the food or in body fluids as conjugates. Some analysts like to differentiate between the ‘free’ and ‘bound’ concentration of t h e drug. Total residue levels (free and bound) can often only be determined following an enzymatic pretreatment, for example with P-glucuronidase or arylsulphatase, to release the bound portion of the residue. Finally, all analysts and analytical laboratories are under great pressure to produce more and more results in less and less time, more cheaply with greater accuracy and precision than ever before with fewer, less well-trained and experienced staff.This may lead to corner cutting and a fall-off in the reliability of the data obtained. There is no place for short cuts in residue analysis.

2.2 THE ANALYTICAL APPROACH All the above difficulties emphasize the need to have a clear idea and purpose before starting work on the analytical programme. There is little point in accumulating large amounts of data at great cost unless t h e results are valid and will be used to take decisions of benefit to animal or human health. The stages in a modern analytical procedure are shown in Table 2.2. A clear understanding of the problem and, hence, reasons for the analysis must be worked out at the beginning. This assessment will

41

Analytical methodology

[Ch. 2

Table 2.2 - Stages in the analysis of foods for veterinary residues ~~

I . Definition of the problem 2. Sampling 3. Isolation (or separation) of the residue from the matrix 4. Removal of co-extractives (clean-up) 5. Concentration 6. Final determination.

include toxicological data, legislative aspects and use of the drug, alongside the occurrence of residues and their possible consumption by the public. Such considerations will enable a drug control and surveillance programme to be designed, including the number of samples to be taken, their nature and source, the analytes to be determined and the detection limit required. Methods of analysis will need t o be agreed as well as the desirability of subjecting those samples found to be positive to a separate confirmatory analysis. Where collaboratively, studied methods are available, they should be used. Otherwise, methods adapted or developed de novo will need to be validated and the scope of the validation required will have to be agreed. The different types of methods available for use in residue work will now be considered.

2.2. I Classification of analytical methods for residue determination 2.2. I . I Screening methods These tests can often be carried out in the field by staff using commercial kits without

the need for laboratory facilities. The tests are rapid, so that a result may be obtained within minutes. Hence, many samples can be examined at a relatively low cost. Modern tests are based on immunoassays which are highly specific. The results are qualitative only. or at best semi-quantitative. with a detection limit which should be below the maximum residue limit (MRL). Precautions should be taken to validate each batch when using commercial kits and some assessment of the possible occurrence of false positives and false negatives needs to be made. Screening tests can be applicable to only one specific drug or, alternatively, may be multi-residue in character. The chief value of screening methods is to enable large numbers of samples to be taken and tested quickly and cheaply. Those that give a presumptive positive reading can then be examined further in the laboratory. thus enabling expensive resources t o be targeted most usefully and the surveillance to be spread more comprehensively than would be the case if all samples had to be analysed by time-consuming methods in the laboratory. I t is. of course, vital that such screening methods should not produce false negatives perhaps as a result of age or inadequate storage of the kit. Mulri-residue screening merhods Veterinary drugs vary widely in molecular structure. chemical properties and biological activity. Hence. it is difficult to monitor for any single chemical feature

Sec. 2.21

The analytical approach

41

that would be an adequate indicator of the presence of the varied products on the market as residues in foods. Antimicrobial activity, or microbiological inhibition, is one such property which has been widely used. The tests are widely applicable and quite sensitive but results are only obtained following incubation, which takes several hours. Interference can occur from naturally inhibiting substances. The advantages and disadvantages of this approach are discussed further on p. 104. 2.2.1.2

Regulatory methods

I n contrast to screening methods, regulatory methods are quantitative and are performed in the laboratory, usually following presumptive positive results obtained during screening. The analytical procedures used must have been validated in terms of detection limit, recovery and repeatability. The detection limit must be one order below the M R L or regulatory action limit and recoveries and repeatability must satisfy the criteria discussed below (p. 42). The specificity must be sufficient to exclude other residues likely to be present and 'blank' tests must be performed on samples of a like nature whose history is such that the absence of the target residue can be guaranteed. 2.2.1.3 Reference methods

These methods are to be used in cases of dispute where legal action is envisaged. The procedures must be validated by collaborative study, preferably on an international basis. Specificity must be unequivocal and so established either by using mass spectrometry with adequate resolution. or by using more than one method in which the final determination step is based on quite distinct physico-chemical procedures. Thus t w o methods which employed chromatographic columns differing only in polarity would not provide unequivocal identification. However, results based on (a) GLC and.(b) HPLC which were in agreement could be regarded as satisfactory evidence of residue identity. The reference method should also be validated using certified reference materials whenever possible. Some workers have identified other types of methods using names such as surveillance methods and confirmatory methods. However, further division is of little additional assistance. Of major importance are the performance characteristics and validation data of the residue methods in use. 2.2.2 Performance characteristics of analytical methods Before considering the performance data of analytical methods it is necessary to define a number of parameters used in this type of work which often have different meanings assigned to them by different authors:

a component of the sample which is to be detected or determined. i.e. the veterinary residue of interest. Spec$ciry: the ability of a method to distinguish between the analyte and other constituents of the sample. These may be homologues. metabolites, isomers or even chemically unrelated substances which interfere at the detection stage of the method.

Analyre:

42

[Ch. 2

Analytical methodology

Limif of detection: the smallest concentration from which it is possible to deduce the presence of the analyte with reasonable statistical certainty. I t is arbitrarily taken to be the mean value of determinations on several blank samples plus three times the standard deviation of the mean. Blank samples are those samples known not to have been contaminated with the analyte. Sensifivify: defined as the ability of a method to discriminate between small differences in analyte concentration. This is often defined as the slope of the calibration curve. Generally, this parameter is of far less significance than the limit of detection in residue analysis. Scope: The applicability of a method should be clearly defined in terms of the analyte(s), the sample, e.g., liver, fat. urine, and the species of animal, the range of the determination and limit of detection. Limit of determination (or decision): some workers prefer to use this terminology which is defined as the mean of a number of blank samples plus five (or sometimes six) times the standard deviation of the mean. Accuracy: this is the difference between the true value and the determined value. In many cases, the true value will not be known unless a certified reference material is available. Precision: Repeatability is defined as intra-laboratory (within laboratory) variation and reproducibility as infer-laboratory or between-laboratory variations. Precision is obtained by collaborative studies using standard methods of validation of the results (ISO. 1986). Recovery tests: all methods should be checked by the addition of a known amount of analyte to a blank sample, so that the recovery of analyte when the fortified sample is put through the analytical procedure can be computed. Obviously this approach does not exactly reproduce the situation with naturally incorporated residues from feeding experiments. However, it is often the best that can be achieved. Care should be taken to add the analyte and then allow several hours (preferably overnight) for analyte-matrix interactions to occur before commencing the analysis. Table. 2.3 gives target recovery and precision values for residues present at different concentration ranges. Reference methods should meet these criteria.

Table 2.3 - Recovery and precision criteria for analytical methods used in residue

analysis Analyte level (P.P.b.)

Recovery (Yo)

Coefficient of variation ("/o)

2 100 10-100 < 10

85-1 10 75-1 10 65- 120

10 15 20

Sec. 2.2)

The analytical approach

43

Regulatory methods should also either satisfy the criteria or not be too far away from such a standard. They are not applicable to screening methods. Horwitz (1982) has derived an equation (2.1) linking the coefficient of variation with the level of analyte present from data obtained in a large number of collaborative studies of methods to determine major, minor and trace constituents in a wide range of materials.

where CV is the between-laboratory coefficient of variation expressed as per cent and concentration is expressed in negative powers of 10. Hence, knowing the concentration of analyte to be determined, it is possible to predict the coefficient of variation to be expected in a well-planned collaborative study. Where values outside the predicted limits are obtained, both methods and protocol for the study should be examined critically.

2.2.3 Analytical procedures The various stages in the determination of veterinary residues in foods are shown in Table 2.2. Whilst the analytical chemist should participate in any discussions relevant to stages 1 and 2, the main laboratory work commences with stage 3. When samples are collected at a location remote from the laboratory, they should be frozen and transported with solid carbon dioxide to reduce any loss of residue or degradation during transit. On arrival, the samples should be deep frozen at -20°C and protected from light until analysis. The complex nature of foods has already been referred to (p. 38). As it is essential for the portion of sample taken for analysis to be truly representative of the bulk too small a sample weight should be avoided. Animal tissues are complex mixturesof collagen, muscle proteins, elastin, fat, lipids and mineral constituents with water. Hence, in order to obtain a representative portion at least 1Og should be taken, if possible. I t may be desirable to homogenize a large portion of the tissue prior to analysis by mincing and/or treatment in a food processor, taking a smaller portion of t h e homogenized part for analysis. Homogenization can also be achieved concurrently with extraction (maceration). Sample treatment is an integral part of any analytical method and must be described in some detail. The need for enzymatic digestion must be considered at this point (p. 39).

2.2.3.I Extraction Separation of the residue from the bulk of the matrix is usually achieved by extraction using a solvent. Tumbling the finely divided sample in a solvent for 30 minutes to 1 hour may be satisfactory for feeding stuffs but is unlikely to be good enough for foods. More vigorous mechanical action is advisable in t h e latter case. Soxhlet extraction is very slow and seldom complete. The nature of the solvent selected for extraction is also critical. In general terms, polar residues are best extracted using polar solvents. A list of solvents in order of increasing polarity is

44

Analytical methodology

(Ch. 2

given in Table 2.4. Further information on the solubility of selected drugs in commonly used solvents can be found in Chapter 5 (p. 139). After extraction, the solvent is separated from the solid by filtration or by centrifugation. The presence of water and lipid material in the matrix is likely to cause major problems either at the extraction step or at later stages of the analysis. I n some cases it may be advisable to remove water by grinding the sample with anhydrous sodium sulphate crystals prior to solvent extraction. This has the added advantage that the grinding may further disrupt the cellular structure and hence increase penetration of the solvent and the extraction efficiency of the drug residue. On the other hand, it is important that the solvent should ‘wet’ the tissue. Some very dry materials, e.g. tea, may need to have water added prior to extraction in order to.reduce surface activity (Woodbridge and McKerrell. 1981). In the case of aflatoxins a two-phase extraction medium (water and chloroform) containing two immiscible solvents is preferred. Aflatoxins are not particularly soluble in either water or chloroform but the twophase system gives much better recoveries than either solvent alone. Lipid material, if present in the extract, nearly always causes problems at the detection stage whatever technique is being used. Hence, it is desirable to remove as much fatty matter as possible. If the residue is very polar, it may be possible to preextract the sample with hexane to remove fatsprior to extraction of the residue with a polar solvent. Alternatively, fatty matter can be removed at a later stage by column chromatography or by solvent-solvent partition. Any soluble proteins in the extract should be precipitated since they may cause emulsions at later stages of t h e method, thus lengthening the time for analysis and reducing the residue recovery obtained. After separation of solvent and matrix. the extract will contain only milligrams of dissolved material even from a 50-g sample so that a significant concentration of t h e residue has already occurred. The true efficiency of extraction can only be checked using radiolabelled compounds or isotopic dilution techniques. Compounds labelled with ‘‘C can be extracted in the usual way. The residue is then burnt to produce carbon dioxide. which is checked for residual activity by scintillation counting.

2.2.3.2 Clean-up The extract prepared as above will also contain many other compounds as well as the residue of interest. Some degree of ‘clean-up’ or purification is required before the final determination step (Table 2.2). The main techniques used are column chromatography and solvent partition. Column chromatography can be employed in several modes:

I i qu id-so I i d (adsorption ) ; liquid-liquid (partition); size exclusion (gel permeation, or molecular sieving). A further technique (immuno-affinity chromatography) is undergoing rapid development at the present time and offers great scope for the future. Dialysis has also been used as a purification step (Aerts etal.. 1990).

Sec. 2.21

The analytical approach

45

Table 2.4 - Elutropic series of commonly used solvents ii-Hexane Cyclohexane Benzene To1uene Diethyl ether Chloroform Ethyl acetate 1, I , 1-Trichloroethane Dichloromethane Pentan-3-01 Butan- 1-01 Propan-2-01 but an-2-01 Propan- 1-01 Acetone Ethanol Methanol Acetonitrile Water

Increasing polarity and dielectric constant

Conventional column chromatography uses glass columns packed with alumina, silica, Florisil or even carbon. The pH value and the moisture content of these materials can be critical. The mechanism of the reaction is not always fully understood. Empirical procedures have to be worked out and t h e process is often rather slow. Various bonded-phase materials have be prepared with groups such as -amino. -cyano, -0ctadecyl carbon and -phenyl combined with silica. However, the efficiency of separation achieved is very poor by comparison with similar materials of much smaller particle size employed in HPLC. Solid-phase extraction (SPE) is increasingly being used in this type of work. Liquid samples are passed through a bed of silica-based packing chosen to retain the analyte. Other materials are then removed with a solvent wash. The analyte is then eluted using a solvent of stronger polarity. This approach offers advantages in speed, low volume of solvents required and simplicity. Size-exclusion chromatography is used almost exclusively for the removal of very high molecular weight compounds, especially during the purification of antibodies. Solvent partitioning is an excellent method of removing fatty material from polar analytes since the distribution constant is very favourable. Where acetonitrile or methanol is used for extraction, partition against hexane or petroleum ether will remove fats. As the two phases have to be shaken and then left to separate, the procedure can be labour intensive and time consuming if large numbers of samples are involved. Emulsions may also cause problems at this stage.

Analytical methodology

46

[Ch. 2

2.2.3.3 Concentration If further concentration is required to achieve the required detection limit, this is usually effected by evaporation of solvent to a smaller volume. Care needs to be taken to ensure that losses do not occur by adsorption onto active surfaces of the glassware. Such losses, whilst not significant at higher levels, can be quite appreciable at the lower levels encountered during residue analysis. It may also be necessary to evaporate excess solvent at a low temperature under vacuum to prevent decomposition of the active compound. Protection from the light may also be necessary.

2.3 CHROMATOGRAPHY Even after the extensive clean-up operations described above, the extract is likely to contain many substances in addition to the target analyte. Further separation can be achieved using chromatographic methods. Separation is obtained by passing the mixture through a column containing two immiscible phases, one being stationary and the other mobile. Individual components of the mixture are then distributed between the two phases according to their differing chemical affinities. In the extreme case, substances insoluble in the stationary phase will pass rapidly through the column whereas soluble substances would not be eluted at all. In between these two extremes, most compounds will be partitioned between the two phases to differing extents and will therefore spend differing fractions of time in the two phases and, hence, pass through the column at differing speeds. The ratio of time in one phase to the time spent in the second phase is known as the partition coefficient. The stationary phase is usually a solid, or a liquid absorbed onto or chemically combined with a solid, whereas the mobile phase can be liquid (HPLC) or gaseous (GLC). In thin-layer chromatography (TLC) a finely divided solid (alumina or silica) is bound to a sheet or glass plate. The mobile phase (solvent) moves up the plate by capillarity and separation occurs by partition between active sites on the particles and the mobile phase. All three modes of chromatography have been widely used in veterinary residue analysis. 2.3.1 Thin-layer chromatography Fig. 2.1 shows a typical TLC experiment. Unknowns ( U ) and standards, S,,Sz, etc., are spotted onto the plate along a line A-B, the origin. The lower edge of the plate is lowered into a solvent inside a closed container. The solvent moves up the plate until i t reaches C-D.The plate is then removed and dried. A suitable visualization reagent is sprayed over the plate and the position of any spots is noted. An R f value is computed for each unknown and compared against standards run on the same plate, where:

R,.=

distance travelled by the spot distance travelled by solvent front

Some workers prefer to use R , values, where:

Sec. 2.31

47

Chromatography

D Solvent front

C

i

0

X

X

r

I

X

Sl

u,

+

s2

X

u2

I

s, Solvent

S1......S2......Ssetc

U,...... U2 etc

standard solutions unknowns

Fig. 2. I

R,=

I

s,

- TLC cxpcrimcnt

distance travelled by the spot distance travelled by a standard substance .

R, values fluctuate a little depending on experimental conditions, whereas such variations should not occur with R, values to the same extent. It is also possible to remove the spot, elute the compound and subject the eluate to further analysis by spectroscopy or other techniques to confirm its identity. On its own, TLC provides only presumptive identity of residues present and generally is only semi-quantitative when the intensity of the spots is compared visually against standards. Densitometers are available for use with TLC plates but the results obtained depend to some extent on the separation achieved, the shape of the spot and the absence of interferingcompounds. The technique isoften used as an additional clean-up step. In recent years, particles of smaller size (and narrower size distribution) have been employed, thus providing greater surface area and great efficiency and separating power. This approach is known as high-performance TLC and has been used extensively for the separation of sulphonamides. The plates are available commercially along with automatic spotting equipment and a densitometer detection system. Only very small sample loadings can be used.

48

[Ch. 2

Analytical methodology

2.3.2 Cas-liquid chromatography The sample is introduced into the column in the vapour phase. Hence this technique is only applicable to compounds that are stable at the column temperature and that are sufficiently volatile. Alternatively, non-volatile compounds can be determined if they can be made volatile by derivatization. This step increases the length and complexity of the analysis but at the same time introduces a degree of selectivity by the derivatization reaction. A schematic diagram of a gas chromatograph is shown in Fig. 2.2. The technique is capable of the highest degree of resolution (using capillary columns) and a range of detectors is available exhibiting both sensitivity and in some cases selectivity. Those most often used for residue analysis are described below. Detector

Flow

Chromatogram

Fig. 2.2 - Schcmiitic rcprescntntion of ;Igas chromatographic systcm.

2.3.2.1

Detectors

Most detection systems used in conjunction with a gas chromatograph work by monitoring some physical rather than chemical property of the gas stream emerging from t h e column. Changes in physical properties are readily converted into an electrical signal which can then be amplified and recorded to produce a chromatogram on chart paper. In the field of residue analysis, sensitivity is perhaps the most important property of a detector. Sensitivity (S) is defined as the response per unit concentration of analyte and would have the units mVkoncentration, where concentration is mg/cm'. Hence S = mV mg- cm3. S can be computed from a chromatogram using the formula:

'

A x F

S=

where A

F R, C M

R,xCxM = area of peak produced (cm'); = flow rate of carrier gas (cm-'/min);

= recorder sensitivity (cm/mV);

=chart speed ( c m h i n ) ; = mass of sample injected (mg).

The sensitivity of the detector affects the slope of the calibration graph; the more sensitive the detector the steeper the calibration line. Alternatively, sensitivity can

Sec. 2.31

Chromatography

49

be defined as the difference between two concentrations (C, and C,) which can be distinguished by the detector. Sensitivity is not the same as limit of detection. Whilst a low limit of detection (essential for residue work) cannot be achieved except with a sensitive detector, it does not follow that all sensitive detectors will necessarily have a low limit of detection. The limit of detection is defined as some function (usually two) of t h e background noise. If this is high, a low limit of detection cannot be achieved however sensitive the detector. Indeed the most sensitive detectors often do have a high background noise owing to small fluctuations in carrier gas flow rate or impurities present in the carrier gas. Hence these parameters must be strictly controlled to achieve the optimum limit of detection. Other characteristics that are important in a detector for gas chromatography include stability, linear range and selectivity. Stability encompasses both drift (by which the baseline varies slowly with time) and noise, indicated by rapid and random variations of the baseline. Linearity refers to the range over which the calibration curve is truly linear, i.e. the signal is proportional to the concentration (or mass) of analyte injected. For many detectors the linearity tails off at high concentrations as the detector becomes saturated. A wide linear range can be important since residue levels frequently vary in concentration from non-detectable to the occasional high level which may well be off-scale and outside the linear range of the detector. so requiring a repeat analysis. This is particularly important for automatic equipment left running unattended overnight. Selectivity is another important criterion since this assists in the clean-up of the extract required and ultimately in the reliability of the final result obtained. Many workers will only accept unequivocal identification of residues after confirmation by mass spectrometry. Cost and ease of use, whilst important in many situations, are of lesser significance in residue analysis since they form a very small fraction of the total. Ease of use and reliability could be important where automatic equipment is employed. Response time must be rapid so that sharp peaks are obtained. In essence, response time is conditioned primarily by detector geometry and in particular the 'dead' volume. The principles and characteristics of some detectors commonly used in residue analysis by GLC will now be discussed. Flame ionization detector The flame ionization detector (FID) is the most universally applied and useful detector in gas chromatography. It responds to all organic compounds apart from oxides of carbon and some simple compounds such as hydrocyanic acid and formic acid; it possesses high sensitivity. good stability and a wide linear range of response (around six ordersof magnitude). The eluent from the column is burnt in a hydrogen/ air flame, so ionizing any organic compounds present in the eluent. The detector contains two electrodes across which a potential is applied. Hence in the presence of ionized organic molecules the electrical resistance of the flame is decreased and the current between the two electrodes is increased. This change is then amplified and the signal fed into a recorder. The response is proportional to the number of carbon atoms in the molecule. The detector is consequently insensitive to water, inorganic compounds and gases such as nitrogen or helium used as the mobile phase. The flow

50

Analytical methodology

(Ch. 2

rates of the carrier gas and the combustion gases (hydrogen, air) must be optimized before use and the jet maintained in a clean state. As the organic molecules are destroyed in the hot flame, this detector cannot be used in-line with other detection/ identification systems such as infra-red or mass spectrometry unless a stream-splitter is incorporated at the exit point of the chromatographic column, so that only a small fraction of the gasstream passes into the FID, leaving the major fraction to be used in an ancillary detection system. One other drawback is that the detector completely lacks specificity. Two modifications to the basic design are available in an attempt to overcome this problem. Alkali pamk ionization detector This detector is also known as the thermionic detector or the nitrogen-phosphorus detector (NPD) and it consists of a solid alkali metal salt in the form of a bead fixed just above the flame. Potassium chloride or caesium bromide was used originally but rubidium sulphate finds favour in more modern forms of the detector. The collector electrode is often movable so that response to a particular hetero atom can be optimized. The detector exhibits enhanced response to organic compounds containing nitrogen, phosphorus or sulphur by comparison to the FID. The mechanism for this selectivity is still not clear and subject to dispute. A negative response can be produced by organochlorine compounds. Whilst the selectivity is very useful in parallel with an FID detector, the alkali-FID is far less robust and more difficult to use. Careful optimization of all the operating parameters is required before measurements are recorded. Flame photometric detector In this detector the photo-emission (chemiluminescence) from the flame is monitored instead of the electrical resistance (or conductivity) by a photomultiplier assembly. A hydrogen-rich cool flame is used to encourage the formation of molecular species such as S2 or HPO. The emissions are then monitored through interference filters (526nm for P, 394nm for S) by a low-noise photomultiplier tube. The detector possesses good sensitivity to S and P compounds and exhibits a stable response, being largely independent of small fluctuations in flame operating parameters. It is used mainly for pesticide residue analysis. Electron-capture detector The electron-capture detector relies on the ability of compounds to capture electrons (electron affinity). Hence, it records a loss of signal in contrast to the FID. The detector is extremely sensitive to halogenated compounds, conjugated carbonyls and aromatics. but insensitive to hydrocarbons, alcohols and simple saturated organic molecules. An ionizable carrier gas passes into a chamber containing a source of P-radiation (usually tritium (3H) or "3Ni) coated onto a foil. Slow electrons are produced and collected by one of two electrodes, across which a potential is applied. This produces a steady current. When a compound with a high electron affinity enters the chamber it reacts with the electrons and so reduces the standing current, giving a negative peak on the chromatogram. although by reversing the polarity the peak can be made

Sec. 2.31

Chromatography

51

to appear positive. This detector does not have a large linear range (about lo3),is easily contaminated and is not very robust. However. it does exhibit exceptional sensitivity and selectivity. It is widely used for the detection of organochlorine compounds. More recent designs of the detector employ a pulsed potential which is claimed to be more sensitive and more reliable. The tritium form of the detector is more readily contaminated and must not be used above 220°C owing to radioactive leakage. The "Ni source can be heated to 350°C and thus is easier to clean. Water and oxygen must be removed from gas lines. Electrolytic conductivity detector This detector is also known as the Coulson detector. I t depends on the measurement of the conductivity of pure water. Compounds in the column effluent are passed through a microfurnace where. with the assistance of a catalyst. S is converted to its oxides, chlorine to hydrochloric acid and nitrogen to ammonia. Such compounds are readily soluble in water and greatly increase its conductivity. Oxides of carbon. in contrast, are poorly absorbed and consequently the detector shows ar; enhanced response to analytes containing N , S or the halogens. 2.3.3

High-pressure liquid chromatography

This technique is often named high-performance liquid chromatography in manufacturers' and the scientific literature, but the above name is to be preferred as it is more descriptive of the separation process. The principles of separation are those described in 2.2.3.2 but the efficiency is increased greatly by using particles of smaller size (3-10 pm). This increases the surface area and hence, the frequency of interaction of the analytes between stationary and mobile phases during passage through the column. The reduction in particle size necessitates higher pressures to force the mobile phase through the column. Columns are typically 10-25 cm in length and about 4mm internal diameter. A pump is required which can develop a pressure of around 20k Pa (up to 10000 p.s.i.). A schematic diagram of the equipment is shown in Fig. 2.3. The most commonly used detectors in residue work are discussed below. HPLC is normally used for compounds that are involatile except at high temperatures, since the column is usually maintained at room temperature. or occasionally up to around 50°C. I t is also useful for the separation of analytes that are unstable at temperatures above ambient. The analyst can vary a number of experimental parameters in order to achieve better separation of a compound from other co-extractants. Among these are column length and diameter, stationary phase and temperature. but primarily the nature and flow rate of the mobile phase- unlike GLC, where relatively few gases are available for use as the mobile phase. More than one solvent can be used during the same chromatographic r u n , so that the polarity of the mobile phase can be steadily increased to elute the more polar constituents in a shorter time, giving better-shaped peaks (gradient elution). However, isocratic elution systems (single-solvent mobile phase) are generally easier to use and give more reproducible results. In GLC, a wider range of stationary phases can be employed and temperature programming can be used over a very wide range. Capillary columns also increase the separating power of the technique, although only

52

[Ch. 2

Analytical methodology

>

- Liquid pump

\

\

-

s

E

2. 0 E 0

o_ C

3 3

corder

2

processor (integrator)

+

Detector

1

Fig. 2 . 3 - Diagram ol an HPLC systcm.

small sample loading can then be used. However. the detectors used in gas chromatography are much more sensitive than those available for HPLC owing to the difference in the chemical nature of the two mobile phases (gases versus solvents). Furthermore, GLC is readily coupled to the mass spectrometer, giving the ultimate in specificity and sensitivity. Attempts have been made to couple HPLC to a mass spectrometer but with much less success. GLC and HPLC must be regarded as complementary techniques, but for drug residue analysis the latter is of greater importance since most drugs are involatile. Unlike GLC, in HPLC the two phases can be reversed. In normal-phase chromatography the stationary phase is a polar material (often silica) whilst the mobile phase is a non-polar hydrocarbon solvent. 1 n reverse-phase chromatography

Sec. 2.31

53

Chromatography

the column is packed with a non-polar stationary phase (often silica with a C18 hydrocarbon bonded onto its surface) and the mobile phase is a polar solvent such as methanol or acetonitrile in admixture with water (or buffer solution). Reverse-phase systems are generally more reproducible and, hence, more often used than the normal phase mode in drug residue analysis. 2.3.3.1 Detectors The ultraviolet (UV) detector is the most widely used detector in HPLC, similar in applicability and versatility to the FID used in gas chromatography. UV detectors cover the range 20W00nm and some instruments extend also into the visible region (400-700 nm). Thus nearly all organic compounds can be detected in this way. Below 200 nm. problems arise from the absorptivity of the solvent. The basic componentsof a single-beam detection system are shown diagrammatically in Fig. 2.4. The light

Radiation

Source

3,

Monochromator

+-’ Detector

I

Sample Cell

Fig. 2.1 - Layout o f a single beam UV/visihle spectrophotometer.

source is a deuterium lamp whose output is focused through a narrow slit onto the HPLC flow cell. Wavelength selection is achieved either with a monochromator (diffraction grating), or interference filter restricted to a given value, e.g. 254 nm. Little selectivity can be obtained at 254nm since most organic molecules absorb to some degree at this wavelength. Selectivity is then a function of the separation achieved by the chromatographic column. Monochromators permit a choice of wavelengths to be used; usually the most sensitive is selected. The design of the flow cell is critical. The volume is normally around 5-10 PI for maximum sensitivity and to prevent post column dispersion. The detector consists of a photomultiplier tube. The output from the lamp must be stable and this is sometimes hard to achieve. Hence. many instruments use double-beam optics where the lamp output is split into a sample beam and a reference beam. Any fluctuations in the lamp output are then cancelled out. Diode-array detectors enable measurements to be made at a number

54

[Ch. 2

Analytical methodology

of wavelengths simultaneously so that a complete spectrum can be scanned in a few milliseconds. Coupled with a microcomputer and suitable software. it is possible for the analyst to manipulate the data obtained and perform a number of calculations on the spectrum produced. Whilst most organic molecules absorb UV irradiation, only a small fraction subsequently re-emit the radiation at a longer wavelength. This phenomenon is known a s fluorescence. Hence. fluorescence detectors are more selective than UV detectors and usually more sensitive too as the radiation is emitted at right angles to the incident beam and, therefore, not 'flogged' by the background (Fig. 2.5). Both

Source -

Excitation monochromator

10 r L

Sample

Emission

lo = intensity of incident beam

c l Detector

If= intensity of fluorescent beam Fip. 2.5 - Layour of

ii

Ruorimctcr.

the excitation A,, and emission wavelength (A,,,,) can be controlled by a filter or monochromator increasing the specificity of the detector. Fluorescence is, however, subject to quenching by other co-extractants if present in the eluate. Compounds which do not exhibit fluorescence can often be broken down into molecules such as amines or phenols and then derivatised using dansyl chloride or fluorescamine, yielding a fluorescent compound.

2.3.3.2 Other detectors Whilst other detectors. e.g. refractive index, electrochemical, moving wire (or bett) and the mass detector. have been developed for use with HPLCequipment, their use is restricted to the determination of the major constituents of foodstuffs (sugars, lipids) since t h e y do not possess sufficient sensitivity for measurements at the p.p.b. level. Column efficiency and interpretation of results Fig. 2.6 shows a typical chromatogram that could have been obtained either by GLC or by HPLC. Qualitative identification is obtained by measuring the retention time t , and comparing this with the 1, of a standard substance injected immediately before (or after) the unknown using identical operating parameters. Confirmation can then be obtained by addition of a known amount of the suspected substance to a portion of 2.3.4

55

Chromatography

Sec. 2.3)

I

0

1

6

12

18

24

I

I

30

36

1

minutes

Identification of a peak by retention time (1,)

Area = H x W

Calculation of oeak area

-

lniection

Calculation of theoretical plates

Calculation of resolution

Fig. 2.6 - Interpretation of chromatograms.

the extract and re-injection. No additional peaks (or shoulders) should be seen on the chromatogram. Some workers prefer to use. as well, other chromatographic systems with columns of different polarities which produce a different value for 1,. However. it is preferable to obtain independent confirmation by using spectroscopy or another technique based on a different principle, since in many cases a change in polarity will induce only marginal changes to the chromatogram.

56

Analytical methodology

[Ch. 2

Quantitative measurements are obtained by computing the peak heights (or areas) and comparing against a calibration curve obtained by the separate injection of standard solutions containing different concentrations of analyte. For peaks which are Gaussian in shape, or very narrow, measurements either of peak height or area should produce equivalent results. Where the chromatographic separation is less gaod, measurements of peak area are more reliable than measurements of peak height. With modern chromatographic equipment, integration of peak areas is done electronically. However, it is always wise to check on the performance and linearity of the system under normal operating conditions using standard solutions. Reliance on electronic data alone can produce misleading results. A chromatogram must always be produced and examined visually. The efficiency of separation between components in a mixture is dependent on the column. Column efficiency is measured in terms of a concept known as ‘theoretical plates’, where each plate is equivalent to a single separation step in a solvent-solvent partition. The more theoretical plates, the greater the separating power of a column. Alternatively. the efficiency can be defined in terms of the height equivalent of a theoretical plate, which is simply the column length divided by the number of theoretical plates. These parameters can be computed from the chromatogram as follows:

where

= retention time of the peak; W =width of the peak at its base; W , =width of the peak at half its height (Fig. 2.6)

I,

Some workers also compute the resolution between 2 peaks where:

These parameters should be stated in standardized methods of analysis as guidance for the analytical chemist using the method for the first time. The performance of HPLC and GLC columns deteriorates with time, usually as a result of ‘poisoning’ with co-extractives which are not completely eluted off the column. Hence, it is a good idea when specifying a new method based on GLC or HPLC to identify a test mixture which the system should be capable of resolving. 2.4 MASS SPECTROMETRY

2.4.1 General principles Many large organic molecules are too complex to characterize in their natural states. One approach to solving this problem is to smash the molecule into smaller

Mass spectrometry

Sec. 2.41

57

fragments and by examination of the smaller pieces attempt to identify the parent molecule. One of the biggest 'hammers' available to the analytical chemist is known as a mass spectrometer. The essential components of such an instrument are shown diagrammatically in Fig. 2.7. The sample is introduced in the vapour state into an Slits

~~

Detector

Ion source Fig. 2.7 - Cornponcnts of a double-focusing mass spcctromctcr.

ionization chamber maintained at very low pressure ( torr). Electrons produced by a heated filament are accelerated to increase their energy and, hence, their ability to interact with the sample molecules (M). Such collisions normally produce a positive ion as follows: e-+M

M++2e-

M + is known as the molecular ion. Further collisions may induce fragmentation, splitting off small groups or even causing molecular scission. As the ion source region is maintained at a very high accelerating voltage, the positive ions are expelled from the source into the analyser, where they are separated according to their mass-tocharge ratios in a magnetic field. The path radius followed by an ion in the magnetic field is proportional to its momentum. Hence. by varying the accelerating voltage or the magnetic field strength it is possible to deflect individual ions along a defined path

58

[Ch. 2

Analytical methodology

into a collector slit. thus scanning the spectrum. The detector measures the relative abundance of the various mlz values. where m is the mass and z is the charge of the ion. I n most cases, z = 1 . Hence, m/z is equivalent to the relative molecular mass. 2.4.1. I Molecular ionization methods The energy required to remove an electron from an organic molecule is around 10-15eV (compared with an ionization potential of 5.2eV for sodium). In electron impact mass spectrometry, energies are usually fixed at 70eV. This is because the ionization efficiency increases steeply up to a value of around 50eV. Little change is observed between 50 and 75eV and the efficiency then falls slowly above this value. Hence 70eV represents the best compromise. This excess energy causes molecular vibrations outside the permitted elastic limits of the atoms, so leading to the rupture of bonds and fragmentation. Electron impact ionization does have some disadvantages. For some molecules fragmentation is complete and no molecular ion is obtained. This is a problem when trying to identify unknown molecules. I t is also difficult to distinguish between isomers. Obviously, compounds that are either thermally unstable or completely involatile cannot be examined by this technique. Other methods of ionization have therefore been devised. These include chemical ionisation, field ionization, field desorption and fast atom bombardment. When methane is ionized by electrons at low pressure, the following reaction takes place: CH,+e-

--+

CH: + 2 e -

A further reaction can occur when neutral methane molecules collide with molecular ions formed above:

CH; +CH,

-+

CH,+CH<

CH; is unstable and readily interacts with sample molecules by a protonation reaction as follows: CHT + M

-+

CH4 + (MH)'

where the ion (MH)' has an mlz value one unit greater than the molecular ion. Such quasimolecular ions (MH)' possess less internal energy than molecular ions M + produced by electron ionization, so that less fragmentation occurs. This results in a mass spectrum with a greater abundance of the molecular ion (MH') and fewer fragmentation peaks. The spectrum is thus easier to interpret. Obviously, this is a simplified account and other neutral molecule-reactant gas interactions can occur. In addition to methane, other reactant gases have been proposed, e.g. ammonia. In field ionization, sample molecules are introduced between an anode and cathode held close together, at a potential difference of around 10 kV. The high potential gradient attracts electrons to the anode and the molecular ions so formed to the cathode, where they pass through a small aperture into the mass analyser. Hence, they are focused to form a coherent beam suitable tor analysis. Both M and (MH)' +

Sec. 2.41

Mass spectrometry

59

ions can be formed but again less fragmentation is observed and a cleaner spectrum is obtained. Field desorption is a closely related technique which was developed for thermally unstable and involatile substances. The sample is placed directly on the surface of the electron emitter in the solid state and ions formed are then desorbed towards the cathode. Very little fragmentation occurs. Fast atom bombardment utilizes a stream of ionized rare gas molecules which impinge on the sample in the form of a solution applied as a monolayer to the surface of a matrix material. Positive and negative ions can be obtained but the spectrum may be contaminated by extraneous ions resulting from the matrix. High concentrations of molecular ions are produced. 2.4.1.2

Resolution

The resolving power of a mass spectrometer is defined as its ability to distinguish between two ions similar in mass by the relationship mlAm, where m is the mass to be measured and 4 m is the difference in mass between m and the next peak. Thus for a molecular ion of mlr 350. only a low resolving power is required to distinguish between this peak and another at mlz 351. In contrast, to distinguish between a peak of mlz 350 and another of mlr 350.035 would require a resolution of 10000. Such discrimination can only be obtained using a double-focusing instrument in which an electrostatic device is used to reduce the spread of kinetic energy values of ions with identical mlz values prior to separation in the magnetic field. Such instruments can be made with a resolving power up to 100000. Quadrupole instruments are now widely used since they are cheaper. more robust and easier to operate. They consist of an analyser section in which two pairs of parallel rods are connected to a DC voltage and a radio-frequency AC power supply. This system causes the ions to travel in a zigzag path between the rods so that only ions of one particular kinetic energy pass out through into the detector. Other ions collide with the rods so that t h e rods act as a molecular filter. Only low resolving powers can be achieved but the system is capable of fast scanning times, which is very useful in selective ion monitoring. 2.4.1.3

Combination with chromatographic techniques

The principal use of a mass spectrometer is to provide an unambiguous and unequivocal identification of an unknown compound. This can be achieved either by a very accurate measurement of the mass of the molecular ion or by a study of the fragmentation pattern in comparison with that produced by standard materials of known purity and origin. Obviously, this presupposes that the material examined in the mass spectrometer is a single pure substance. Spectra are complex enough without being further complicated by the presence of extraneous materials. e.g. coextractives. Hence. much work has been done to couple chromatographic techniques such as GLC or HPLC to a mass spectrometer. Thus, the separating power of chromatography is allied to the sensitivity and specificity of the mass spectrometer as a detector. Whilst attractive in principle, such a combination presents difficulties in practice since chromatographs and the mass spectrometer are inherently incompatible systems. The mass spectrometer has to operate at very low pressures and so cannot

60

Analytical methodology

(Ch. 2

be coupled directly to either G C or HPLC without an interface to remove most of the mobile phase. This must be accomplished without at the same time removing sample molecules eluting from the column in the mobile phase. Such interface systems and associated transfer lines used with GLC must be heated to prevent high boiling point materials condensing out, and the materials used must not catalyse destruction of the sample molecules by contact with active surfaces. Whilst a number of different GLC/ MS interface systems have been developed, most are now based on a jet separator. This relies on the differential diffusion between the lighter carrier gas molecules and the heavier sample molecules, so that the portion entering the mass spectrometer has lost most of the former without too much of the latter. Fortunately, the sensitivity of the mass spectrometer as a detector is seldom a limiting factor. For HPLC, a liquid mobile phase has to be removed. This is particularly difficult for aqueous systems. A moving belt interface has been described in which the eluent is sprayed onto an endless belt which passes through a vacuum chamber heated by infrared radiation. The solvent is progressively removed until finally the belt passes into the ionization chamber of the mass spectrometer. Alternatively, a thermospray device is available in which a small portion of the eluent is introduced via a capillary into the ion source of the mass spectrometer. Thermospray employs evaporation in a vacuum and ions are produced by interaction between sample molecules and inorganic ions. This can be supplemented by electron ionization using special filaments that do not burn out so readily. This is a rapidly developing field and much work remains to be done before a single system can be recommended. For a review see Games, (1986). Other mass spectrometric combination techniques include supercritical fluid chromatography/MS, capillary zone electrophoresislMS and MS/MS. These techniques are still undergoing development and to date have been little used in veterinary residue analysis. For a review of MS/MS see Rollins and Scrivens (1989). 2.4.2 Use of mass spectrometry in residue analysis This technique is extremely expensive, using equipment with a high capital cost and requiring specialist and highly qualified staff to run and maintain, in good working order. It can never be used as a general analytical tool and, hence, is employed when it is imperative that the identification of an analyte be unequivocal, e.g. in support of legal or regulatory action. Identification is effected by comparison of aspectrum with a reference spectrum not only at designated mass numbers but also to ensure that the ions are present in the correct relative abundance as indicated by the reference spectrum. This does, of course, imply that the sample extract is free from other coextractives as these too would show up in the sample chromatogram. Hence, mass spectrometry is normally used for residue analysis not on its own but in conjunction with another technique such as HPLC or GLC designed to remove co-extractants not so removed in the earlier chemical clean-up stages of the method. In such a situation the mass spectrometer is set up to monitor at one or two fixed m / t values only, instead of scanningover t h e whole spectrum. Here the instrument is being used simply as a detector, albeit a rather expensive one. However, this results in an increase of sensitivity over a full scan, so that detection limits are compatible with those achieved by ionization detectors in gas chromatography. In selected or single ion monitoring (SIM) amounts of analyte as low as picograms or even below

Sec. 2.51

lrnrnunoassays

61

can be detected. Monitoring more than one ion improves the specificity without losing too much sensitivity. Ions should be selected that are less frequently occurring and so less likely to arise from contaminants or co-extractants. Analysis by mass spectrometry is a specialist operation, usually, carried out by someone who spends his or her whole time working with the instrument. Examples of the use of this technique will be given in later chapters. A review of some applications of the technique in food analysis has been prepared by Cairns er al. (1989). by Gilbert (1987) and by Reid (1986).

2.5

IMMUNOASSAYS

The principal function of the immune system is to protect an animal from infection. Invasion by the infective organism stimulates the animal’s lymphatic system to produce antibodies against that particular agent or antigen. Such antibodies are specific for that one antigen and no other. I n humans, immunization against a given influenza virus is generally ineffective against any other type of influenza virus. It is this specificity of biological response which forms the basis of immunoassays. Unfortunately, only large molecules (greater than about 5000 daltons) can produce an immune response. smaller molecules being excreted through the kidneys or metabolized by the liver. Hence, most analytes (antigens) of interest to veterinary residue chemists must be coupled to a larger molecule (usually a protein) before injection into an animal for the production of antibodies. Glutaraldehyde is a bifunctional coupling reagent which links two compounds through their amino groups. Other reagents available include rn-maleidobenzoyl-N-hydroxysuccinimide ester and carbodiimide. Bovine serum albumin, keyhole limpet haemocyanin and ovalbumin are the most popular carrier proteins. The compound formed between the antigen. the bridging molecule and the carrier protein is known as a hapten, o r immunogen. Rabbits. mice, rats. hamsters and guinea pigs are the most commonly used laboratory animals where only small volumes of serum are required. For larger quantities pigs, sheep and donkeys are available. Many suitable antibody preparations are sold commercially. 2.5.1 Monoclonal antibodies Serum contains a large number of polyclonal antibodies specific for a large number of different antigens. Furthermore. the immunogenic response is variable and largely unpredictable. Therefore it is not possible to produce standard batches of antisera using the method discussed in outline above. Kohler and Milstein (1975) first described the production of monoclonal antibodies using in vitro hybridoma technology. In this way one can obtain antibodies that are specific against a single antigen, that are homogeneous and also can be produced in unlimited quantities from frozen cells. However, the experimental techniques involved require specialist knowledge and skilled personnel, and so are much more expensive. The finished product has the status and purity of an analytical reagent. In some cases, however, where a range of compounds similar in chemical constitution are required to be determined, a polyclonal antibody may be more suitable than a monoclonal product.

62

Analytical methodology

[Ch. 2

2.5.2 Principles of immunoassay lmmunoassays were first developed by Yalow and Berson (1959) primarily for use in the field of clinical chemistry. Since that time the technique has been applied to the determination of a wide range of analytes in foods and veterinary products. The reaction between an antibody (Ab) and its antigen (Ag) can be represented by the equation Ah + Ag

$

AbAg

At equilibrium the antibody-antigen complex is dissociating as fast as it is being formed since the binding is non-covalent. The degree of binding between the A b and Ag is known as the uvidiry or ufiniry, and is essentially the same as the association constant used in physical chemistry. Thus:

where [AgAb] [Ab] and [Ag] are the molar concentrations of the antigen-antibody complex. free antibody and free antigen respectively. The time taken to reach equilibrium depends primarily on the rate of diffusion but high-affinity antibodies will bind larger amounts of antigen than low-affinity antibodies.

2.5.3 Evaluation of antisera The avidity of an antibody is determined in practice by the production of a titration (or dilution) curve. Increasing dilutions of the antiserum are incubated with a constant amount of labelled antigen. Following incubation, the fraction of labelled antigen bound is determined at each dilution and a sigmoidal curve (A) (Fig. 2.8) is obtained. As expected. the highest binding occurs with the most concentrated solutions provided saturation is not reached. By convention, the dilution factor which binds 50 per cent of the antigen is known as the titre. If the experiment is then repeated with the addition of unlabelled antigen. a competition for antibody sites is set up. resulting in a second sigmoidal curve (B) known as a displacement curve. The degree of horizontal displacement is a measure of the avidity of the antiserum. The avidity can be calculated by means of Scatchard plots. The higher the avidity, the lower the limit of detection likely to be achieved on analysis. An indication of the speci3city of the antiserum can be obtained by preparation of a third displacement curve using homologues or chemicals closely related in chemical structure to the antigen. The closer this third curve is to the first one, the greater the specificity of the anti body. 2.5.4 Technique of immunoassay When an antibody is used for the determination of an analyte (antigen) a competitive assay is established between the antigen, a labelled form of the antigen Ag* and a limited amount of antibody. The equilibrium can be represented in the form:

Sec. 2.51

63

Immunoassays

90 80 -

70-

60a

0

P

> 50.-+ > .-c

' 8

Displacement curve

40Displacement curve + 560 ng CAP

30 20-

0

10-

0

0

Lf! c

0 0

0

z

c

p.

c

0

O

$9 c

0

m0 C

0 0 v

.-

y.. ' I ! r

.. F

0 C W N

..

c c

Antibody dilution Fig. 2.8 -Antibody

Ab

+ Ag i-Ag"

-..

c

LF! c

dilution and displacement curves lor CAP.

s AbAg + AbAg* + Ag + Ag* bound fraction free fraction

There the free and labelled antigens compete for the limited antibody binding sites. After incubation, when the above reaction has reached equilibrium, the free and antibody-bound antigen fractions are separated and the amount of labelled antigen in one of the fractions is determined. Using different known amounts of labelled free antigen, a calibration graph can be produced and the unknown antigen (unlabelled) in the original sample can be determined. The procedure has been reviewed by Blake and Gould (1984) and by O'Sullivan el al. (1979) and many others. In the early days, radioactive labels of antigens were used. For example, Yalow and Berson employed 12'1 for the determination of insulin and the technique was called radioimmunoassay (RIA). RIA has a number of disadvantages. such as the expensive counting equipment required. the essential safety requirements. the short half-life of some

64

Analytical methodology

[Ch. 2

isotopes and the difficulty of automating the separation step in the analysis. Although RIA is still used. enzyme immunoassays in which enzymes are used to label the antigen are becoming widespread and large numbers of applications in the food and veterinary field have been reported.

2.5.5 Enzyme-linked immunosorbent assays The basic reaction of classical immunoassay has been described in 2.5.4. After incubation of labelled antigen (of known concentration) and sample (containing an unknown concentration of unlabelled antigen) with a limited quantity of antibody, labelled and unlabelled antigens compete for a limited number of active sites on the antibody. The greater the quantity of unlabelled antigen (analyte) present in the sample, the smaller the quantity of labelled antigen that will bind to the antibody. Separation of free labelled antigen from bound antigen followed by addition of enzyme substrate to the bound fraction produces a colour depending on the enzyme label used. The intensity of the colour is inversely proportional to the concentration of analyte in the unknown sample. In practice the analyses are carried out on a 96-well microtitre plate. A dilute solution of specific antibody serum is added to each well and left to incubate under standard conditions. Excess solution is washed away. Samples and standards are then added individually to the wells in a random pattern, followed by enzymelabelled antigen and left to incubate. After incubation, the wells are washed, substrate is added and the colour is allowed to develop. The strongest colour will appear in those wells allocated to blank solutions. A calibration curve is prepared and unknowns determined by reference to this curve. Alternatively, a 'sandwich' assay can be carried out using a second antibody. Here. the plate is coated with specific antibody as before. The samples, standards and blanks are added and incubated. After washing, an enzyme-labelled antibody raised in a different species to the first antibody is added and allowed to incubate. The substrate solution is added and the reaction stopped when appropriate. A calibration curve is produced which gives a positive response as the concentration of antigen is increased. The most commonly used enzyme labels are alkaline phosphatase and peroxidase, which are available commercially in a pure state. Fluorescent labels may also be used, increasing the sensitivity still further.

Inevitably, space permits only a short description of each analytical technique. Many workers have spent a lifetime exploring just one single tedhnique. Hence, this account has concentrated only on the general principles, the advantages and disadvantages of each technique, with particular reference to residue analysis. Suggestions for a more detailed study can be found at the end of t h e book. The application of these techniques to the determination of veterinary products in animal feeding stuffs and to residues in foods are described in the following chapters.

Sec. 2.6)

References

65

REFERENCES Aerts, M. M. L., Beek, W. M. J. & Brinkman, V. A. Th. (1990) On-line combination of dialysis and column-switching liquid chromatography as a fully automated sample preparation technique for biological samples. J. Chromatogr., 500,453-468. Blake, C. & Gould, B. J . (1984) Use of enzymes in immunoassay techniques: a review. Analyst, 109,533-547. Cairns, T., Siegmund, E. G. & Stamp, J. J. (1989) Evolving criteria for confirmation of trace level residues in food and drugs by mass spectrometry. Mass Spectrom. Rev., 8, 93-1 17. Games, D. E. (1986) The combination of liquid chromatography and mass spectrometry. A d v . Mass. Spectrom. 10,323-342. Gilbert, J. (1987) (ed.) Applications of mass spectrometry in food science. Elsevier Applied Science, London. Horwitz, W. (1982) Evaluation of analytical methods used for regulation. J. Assoc. Off. Anal. Chem., 65,525-530. I S 0 (1986) Precision of test methods. International Organization for Standardization, I S 0 5725. Kohler, G. & Milstein, C, (1975) Continuous cultures of fused cells secreting antibody of predefined specificity, Nature (Lond.), 256,495-497. Nursten, H. E. & Williams, A. (1969) Volatile constituents of the blackcurrant, Ribes nigrum L. I : A commerical blackcurrant distillate. J . Sci. Food Agric., 20, 6 1 3-6 16. O'Sullivan, M. J.. Bridges, J . W. & Marks, V. (1979) Enzyme immunoassay: a review. Ann. Clin. Biochem., 16,221. Reid, W. J . (1986) Extraction and clean-up of contaminants and toxicants from food for mass spectrometric analysis: a literature review. Food Addit. Conturn., 3 ,

2.6

1-42.

Rollins. K. & Scrivens, J. H. (1989) MS/MS: applications a'nd future developments. Spectroscopy World, 1 , 2 6 2 9 . Woodbridge. A. P. & McKerrell, E. H. (1981) Work-up of crops and soils for residues of pesticides and their metabolites. In: Trace-organicsample handling, E. Reid (ed.) Ellis Horwood, Chichester, p. 128. Yalow, R. S. & Berson, S. A. (1959) Assay of plasma in solution in human subjects by immunological methods. Nature ( L o n d . ) ,184, 1643-1644.

Anthelmintics The name anthelmintic is derived from the Greek word ‘helminth’, meaning a worm Anthelmintics are therefore drugs acting primarily against intestinal worms, although many are active also against lung worms and liver fluke. A number of different types of worm have been described, differentiated by their morphology. Tapeworms are found mainly in the small intestine and they feed by absorption of nutrients from the host’s food. They are often flat and segmented. Hookworms cling to the intestinal wall. Flukes are flat and oval shaped. Some worms can be up to 50 cm long. As parasites these infections lead to reduced performance and growth of the animal and in some cases may cause mechanical obstruction of the gut. An example of gastrointestinal nematodes is shown in Fig. 3.1.

- especially intestinal worms.

Fig. 3. I

- Gastrointestinal nematodcs.

Both farm and domestic animals ingest material from the ground, soil o r pasture that has been contaminated with faeces containing eggs and larvae of helminths. Hence, they readily become infected and without a satisfactory treatment regime the

Sec. 3.11

Products on the market

67

cycle of expulsion and reinfection is perpetuated. Reinfection can occur within hours following treatment. (Pet animals are excluded from this discussion.) In the old days, carbon tetrachloride, Gentian Violet. quassia and thymol were used for treatment. These were essentially irritants designed to expel the parasites and had little specific action. Hence large, and possibly unsafe, doses were required. Even the advent of antibiotics brought little relief as these compounds are not very effective against worms. Obviously the substance used for treatment, whilst active against parasitic infections, must not harm the host animal. This rules out the use of many insecticides, although one or two products, e.g. dichlorvos, have a dual role. It is often not necessary to kill the worms; they can be paralysed and then ejected by normal bowel movements. Treatment is effected by injection or orally as a drench. Occasionally, the drugs are added to feeding stuffs or administered as a bolus, to provide a continuous slow release of active ingredient over a long period of time. Anthelmintics are used most frequently in spring and would not be given immediately prior to slaughter, thus reducing the likelihood of residues in meat products. Young animals (less than one year old) are more susceptible to parasitic infections than adults and are treated more frequently than adults, although anthelmintics are occasionally used prophylactically rather than therapeutically in sheep. Residues are most likely to be found in milk where the withdrawal periods have not been strictly observed, or in liver tissue since this is the target organ for metabolism.

3.1

PRODUCTS ON THE MARKET

Compounds in use on the U K market were surveyed by Watson (1983) and by the Steering Group on the Food Surveillance Working Party (1987). At that time the main compounds were levamisole and the benzimidazole group (albendazole, cambendazole, fenbendazole. oxfendazole and thiabendazole). The latter compound is also used for the post-harvest treatment of fruit and vegetables as a fungicide. ‘These and some closely related substances are listed in Table 3.1, which also contains some details of their chemical and physical properties, trade names and recommendations for use. Some preparations also contain copper or cobalt salts, but under normal conditions of use these elements are unlikely to give rise to problems in the human food chain. Whilst the mode of action and metabolism of anthelmintics is not fully understood, some are known to produce metabolites which can be as toxic as the parent compound. Some of the early products were reviewed by Ryan and McLeod (1979) and metabolism was discussed by Coles (1977). Levamisole is often administered as the luevo form of C,,H ,2N2Sor as a racemic mixture with the name tetramisole. It is used at 8 mg/kg orally or by subcutaneous injection, for cattle (not adult dairy), sheep, pigs, goats, geese and turkeys. Levamisole is particularly active against Ascaris lumbricoides but possesses poor activity against Trichuris spp. and pinworms. Many compounds contain the benzimidazole structure. This group is effective against a wider range of helminths than levamisole. For example, oxfendazole is recommended for the removal and control of lungworms (Dictyocaulus viviparus), stomach worms, barberpole worms (Huemonchus contortus and H. plucei), brown

68

[Ch. 3

Anthelmintics Table 3.l(a) - Anthelmintics Compound

Some trade namcs

Structural formula

[Chemical

Registry no. I

Valh;izcn . Zcntal

‘lH”

a> NHCOOCH,

N

I H

lCH,l,CHOCONH

C‘;imhcnd;izolc

[2hO07-SO-3~

Ascapil1;i. Bonlam. Bovicam. Canihct. Equivhcn. Novazolc. Novihcn. Porciim

I H

I

FI uk ivc r. Scponvcr

Dichlorvos (62-73-71

Astrohot. Atgard. Canogard

Fcnhcndazolc 1132 10-67-91

Panilcur

OH

CI

Sec. 3.11

69

Products on the market

Mol.

Usage and other data

Properties

LCg;ll status

weight

(UK)

C,,H,,N,O,S

265 m.p. 20tS-2100C. Col. cryst.: insol. Cattle. shccp 5-10 mglkg. Withholding I0 d shccp. I4 d cattlc in water: sol. in xiddhascs. Milk 72 h D M S O ;ind ecctic acid

PML

C,,H,,N,02S

302

m.p. 23S-240°C dcc.. w.cryst.; sol. in iilc.. DMF, sp. sol. in acctone. hcnzcnc: insol. iso-octane. H2O

Racing pigcons 30 mg/4(Nl g h.w. U V ,,,,,'1 232. 319 nm (HCI)

GSL

m . p . 218°C

Shccp. I 0 mgkg against Hukr Withholding 28 d

PML

C,H,CI,O,P

221

Liq.. h.p. 140°C, m i x . alc.

+

Cattle. pigs. horses

non-polar solvents

LD,,, 56-80 mdkg rats

C,,H,N,O,S

44h.S

m.p. I'L9-13O"C. cryst.

Cattle. pigs. shcep. horses .5-7.S

PML

mg/kg Withholding: milk 18 h. pigs I0 d. shccp. cattlc 8 d

C,,H,;NIO,S

299

m.p. 233 dcc.. sol. in D M S O ;

Cattle. shccp. goats. horses. pigs

insol. in H20

5 - 7 3 mg/kg Withholding: milk 72 h. mcat I4 d

PML

70

[Ch. 3

Anthelmintics Table 3.l(b) - Anthelmintics Compound [Chemical Registry n o . ]

Structural formula

Some trade names

H

I

Fluhcnd;izolc [ 3 1430- 15-61

Fluhcnol. Flumoxal. Flumoxane, Fluvcrmal

Ivcrmcctin [ iO2SS-86-71

Cardomec. Eqvalan. Ivomcc, Hc;irtgard. Mcctizan. Zimcctcrin

F O

C

O

See Fig. 3.2

Bioncm, Ccvasol. Cyvcrm. Lcwmisolc ( L form) Tctr;imisolc ( D L h r m ) Duphamisolc. Lcvacidc. Lcvadin. Lcvipor. N ilvcrm. Nilzan. 16595-so-s I Ridavcrm. Ripcrcol. Vermisolc

Mchendazolc [ 3 113 1-3971

Bantcnol. Equvurm. Lomper, Mchenvet, Noverme. Ovitelmin. Panrelmin. Telmin. Vcricidin, Vcrmirax. Vcrmox

~

csnm

N

~ /

N

H

c

o

o

c

N

I

0

0xCcnd;lzole 1537 16-SY-01

Autoworm. Dio. Equidin. Loditac. Rcpidose. Rycovet. Synanthic. Systamcx

II

""'7q

NHCOOCH,

H

H

3

Sec. 3.1 J

71

Products on the market

Mol. weight

Properties

Usagc and other data

Legal status (UK)

C l d 12F N;O;

313

m.p. 260°C

Pigs 80 g/lO() kg LD5,, > 2560 mgkg rats

PML

C,,H,,O,,

X7-l m.p. 155-157: sol. in MEK. insol. 1 % w/v soln cattlc (pigs) I ml per in sat. HICS. UV 238.245 50 (33) kg

B I:,

PML

Withholding 21 d

CllH,,N,S

203

Cl,,H13N,03 29.5

m.p. 87-89"C. 264-265"C (HCI); sol. in water. McOH; ~ l g tsol. . in EtOH, CHCI;, hexane

Cattle. sheep. pigs. 8 mdkg Withholding 3 d. milk 36 h

PML

m.p. 28X.S"'; sol. in formic; insol. in H 2 0 . ethanol. ether. CHCI,

Pheasants, partridge, waterfowl 120 p.p.m. in feed Chickens 64)p.p.m. in feed Withholding 14 d. May affect fertility LD5,,oral > 80 mgkg sheep. > 40 chickens

PML

Cattle. sheep. horses

m.p. 253°C dcc.

As bolus f ocattle. pigs 0.75 g/50 kg

PMU

Withholding I3 d LD5,,dogs > 1600 m g k g

POM

72

[Ch. 3

Anthelmintics

Table 3.l(c) - Anthelmintics Compound IC’hciniciil Registry no.]

Soinc triidc niimcs

Oxihcndiizolc 12055U-5S- I I

Anthclcidc. C;itovcl. Equitiic

Parhcndiizolc I1415S-S7-0)

H e I in ii t iic

Pipcriizinc I I S53J- Is-JI ;ilso phosph;itc. ;idip;itc iind citriitc s;ilts

Biozinc . Cit riizinc , Coopanc. Endorid. Lumhriciil. Vcrodid. Worm-Away. Wurmirazin

Thiiihcnd;izolc

Bovizolc. Eprofil. Equizolc. Mintczol. Ncmiipon, Martcct. Ranizolc. Thihcnzolc. Thiprazolc. Tccto

II JS-79-SI

(c> Structuriil lormu1;i

c’H’oa /

N

NHCOOCH,

I

NH

I

H

5

I

I S

1i.p. = hoiline point. m.p. = melting point. col. = colourlcss. cryst. = crystals. d = days. dec. = Jccoinposcs. h = hours. w. = white. Doscs arc typic;il valucs given ;is mglkg hody weight o f the animal. P O M = prcscriptic:n-only medicine. P M L = pharmaccutical merchants’ list. G S L = general sales list. Withholding = time (minimum) hctwccn end o l treatment and human consumption

Sec. 3.11

73

Products on the market

Mol. weight

Propcrtics

Us;igc and other data

I-cg;tl st ilt us

(UK)

Cl,Hl,N;O;

219

m.p. 230°C

Horses 10-IS mgkg

PML

Ruminants . pigs. poultry

C,Hl,,N?

86

m.p. I06OC. h.p. 146°C Strong hirsc. light-scnsitivc whitc crystallinc powder

Poultry. pigs I kg/4500 kg

GSL

C,,,H7NjS

201

m.p 30-4S"C. UV,,,,,, 29s (McOH) Fl.370c,,, 310,, in acid; sol in H?O. DMF. DMSO

Cattle. shccp 3-5 S/kg Horses 30 d227 kg LDo, > 3-8 d k g rahhits

PM L

370

m.p. 19YC. colourlcss pliltcs

Pigs. ciittlc. shccp. goats 0.75-1.S kdl00 kg Withholding 7 d. milk 3 d LD,,, > IS g/kg

PML

CI,HI,N,

O,S?

sol. = soluhlc. slgt. = slightly. misc. = miscihlc. insol. = insoluhlc. liq. = liquid. MEK = methyl ethyl kctonc. DMF = dimcthyl formamidc. DMSO = dimcthylsulphoxidc. McOH = methanol. H/CS = hydrocarhons. UV,,.,, = wavelength of maximum ahsorption in the U V . FI,,., = wavelength or cmission/cxcitation. LDsI, = dose of chemical to kill SO'%, of tcst animals.

74

Anthelmintics

[Ch. 3

stomach worms (Ostertagia ostertagi) intestinal worms, nodular worms (Oesophagosfomurn radiafurn) hookworms (Bunostonum phlebotomum) small intestinal worms (Cooperia pantata, C. oncophora, C . memasteri) and tapeworms (Moniezia benedeni). Most benzimidazoles are more potent than levamisole, enabling lower doses to be employed. Table 3.1 illustrates the various permutations of R , and R2 (substituent groups) that have been tested in an attempt to increase efficacy. More recently, the discovery of ivermectin has been described by Campbell et al. (1983) and by Baker and Swain (1989). This compound is a lactone disaccharide (Fig. 3.2) which is active against a broad spectrum of nematode and anthropod parasites, including strains which are resistant to levamisole and the benzimidazoles. It is a member of a new class of chemical compounds referred to as the avermectins and is now licensed for use in cattle, sheep, goats, reindeer, pigs, horses and dogs. The drug is excreted in the faeces and is inactivated on contact with soil particles. The avermectins are isolated from the mycelia of Streptomyces avermitilis. Compound B , is effective against a wide range of helminths in sheep and cattle in a single oral o r parenteral dose of 0.1 mg/kg. The active compound is a mixture of homologues, not less than 80 per cent of 22.23-dihydroaverrnectin B,, and not more than 20 per cent of 22,23-dihydroavermectin Blh. A comprehensive study of the metabolism of ivermectin has been published by Chiu et al. (1986). Whilst the parent compound was the major component identified in muscle tissue, liver contained a number of more polar compounds - probably hydroxylated derivatives. 3.2 ANALYTICAL METHODS 3.2.1 Levamisole Smith et al. (1976) published a method for the determination of levamisole residues in bovine milk based on GLC with a rubidium sulphate-modified flame ionization detector, since the molecule contains two nitrogen atoms and one sulphur. A detection limit of 0.01 p.p.m. was achieved and recoveries varied from 86 t o 113 percent over the range up to 2p.p.m. Marriner etal. (1980) used HPLC to determine levamisole in plasma and gastrointestinal fluids. They obtained recoveries of 80-95 per cent from plasma over the range 0.4-3.0 pg/2 ml and the results showed a good correlation with an unpublished GLC method. A more sensitive procedure was described by Woestenborghs et al, (1981) after a fairly extensive clean-up. They claimed a detection limit of 5 ng/ml of plasma, with recoveries of 79-86 per cent using an internal standard. Osterdahl ef al. (1985) determined levamisole in milk by extraction with methanol, clean-up on Extrelut columns and quantification using HPLC with a UV detector set at 220 nm. Recoveries of 78 f 7.1 per cent in the range 0.2-2.0 pg/ml were reported, with a limit of detection of 0.04 pg/ml. Benzimidazoles Austin et al. (1976) reported the separation of some benzimidazole compounds (mainly fungicides) using a home-made high-performance liquid chromatograph with very long columns and a variable-wavelength UV detector. Mourot et al. (1978) demonstrated the separation of cambendazole, fenbendazole, mebendazole, oxibendazole, parbendazole and thiabendazole using a Lichrosorb RP8 column and a 3.2.2

Sec. 3.21

Analytical methods

75

Fig. 3.2 -Structure of ivermectin.

Lichrosorb amino column. Gradient elution was required in some cases. A method for the determination of fenbendazole and its metabolites in urine, plasma, faeces and tissues was reported by Barker et af. (1986) based on HPLC with detection at 290nm. This work has now been extended so that eight benzimidazoles can be detected at the residue level in bovine liver (Barker etaf., 1990). Detection limits varied from 0.01 to 0.25 p.p.m. and recoveries were generally. better than 80 per cent. The authors found that liver tissue was non-homogeneous for samples as

76

Anthelmintics

(Ch. 3

small as 2.5 g. More consistent results were obtained by taking 10-50-g portions and using an aliquot for analysis. Long et al. (1990) have also described a multi-residue method for the determination of thiabendazole, oxfendazole, mebendazole, albendazole and fenbendazole in beef liver tissue. The sample was blended with a CIS packing material and compressed into a column. Only a 0.5-g sample size was required and no problems of inhomogeneity were encountered. The column was first washed with hexane, after which the benzimidazoles were eluted with acetonitrile and the extract was then purified on an alumina column. After evaporation to dryness, the residue was taken up in methanol, acidified with phosphoric acid and subjected to HPLC using a reversed-phase column and a photodiode detector. Recoveries from samples fortified in the range 100-3200 ng/g ranged from 52 to 104 per cent. Marti er al. (1990) adopted a similar approach which was applicable to eight benzimidazole compounds. The clean-up involved solvent partition and the use of C I S and Florisil cartridge purification prior to HPLC. Confirmation procedures requiring derivatization followed by GLC and G U M S were also described. Recoveries were determined at the relatively high levels of 0.1 p.p.m., although a detection range of 20-50 p.p.b. was claimed. Van den Heuval er ul. (1972) had previously reported a G U M S method for the identification of cambendazole and related compounds following the formation of trimethylsilane derivatives. Nerenberg er ul. (1978) used a radioimmunoassay procedure for the determination of oxfendazole in bovine, equine or canine plasma or serum. The valerate salt of oxfendazole was coupled to polylysine using the carbodiimide reaction for the production of antiserum from rabbits. The method could detect as little as 200 pg of oxfendazole per millilitre of plasma. Thc results obtained agreed with a “C radiochemical assay within k 20 per cent. Methods for thiabendazole were reviewed by Sawyer and Crosby (1980). TLC, GLC and HPLC methods have been described as well as the use of spectrofluorimetry. GLC with a sulphur-specific detector was found to be less sensitive. A GLClMS confirmatory assay for thiabendazole and its 5-hydroxy derivative down to 0.1 p.p.m. was reported by Van den Heuval er al. (19773. Tai er al. (1990) determined thiabendazole. the 5-hydroxy metabolite, fenbendazole and oxfendazole in milk by HPLC with a UV detector after extraction with ethyl acetate and a partition chromatographic clean-up step. Recoveries at the 10 ppb level were better than 80 per cent. ‘

3.2.3 lvermectin This compound is a large complex molecule (Fig. 3.2) and as such is not amenable to analysis by GLC. I t is not very sensitive to UV and so levels in tissues cannot be determined in this way. Tolan er al. (1980) described the conversion of ivermectin to a fluorescent derivative in an acetic anhydride-pyridine mixture. This reaction was used to determine nanogram quantities of ivermectin in plasma after clean-up on silica gel followed by reverse-phase HPLC. The same approach was reported by Tway et al. (1981) in work on cattle and sheep tissues. They were able to detect residues as low as 1-2 p.p.b., with quantifiable measurements at 10 p.p.b. Recoveries from liver, muscle, kidney and fat averaged 83 per cent. These workers found that

Sec. 3.41

Maximum residue limits in food

77

ivermectin was unstable in both acidic and alkaline media and that reaction vessels needed extensive cleaning and treatment with a silylating agent before use. These results were confirmed in later studieson cattle and pig tissue by Slanina eraf. (1989). Nordlander and Johnsson (1990) described an improved clean-up procedure using solid-phase extraction applied to pig tissues. Equally good detection limits and recovery values were achieved. Chiu er al. (1985) preferred a reverse isotope dilution assay with tritium-labelled compound, but this was applicable only above 60 p.p.b.

3.3

RESIDUES IN TISSUES

3.3.1 Levamisole The MAFF Working Party on Veterinary Residues in Animal Products (1987) reported results from the analysis of 50 samples of cattle liver obtained during 1984. No residues of levamisole were detected above 0.1 p.p.m. In 1986, Osterdahl e f a f . described a field trial in which a single intramuscular dose of 7mg of levamisole hydrochloride per kilogram body weight (b.w.) was administered to a herd of 42 milking cows suffering from lungworms. The drug was rapidly excreted in the milk with a half-life of about 5 hours. The peak concentration was found after 1 hour from administration and no residues could be detected after 29 hours following treatment. Hence, the recommended withdrawal time of two days appears to be quite sufficient to safeguard milk supplies. 3.3.2 Benzimidazole compounds In the UK National Surveillance Scheme (MAFF Working Party on Veterinary Residues in Animal Products, 1987) livers from 50sheep, 25 cattle and 25 calves were examined and found to be free from residues of selected benzimidazole compounds or their metabolites at levels above 0.05 p.p.m. Tai er al. (1990) reported results from a cow given 10 mg/kg b.w. of fenbendazole. The maximum concentration was found 28 hours after dosing, with no detectable residues after 76 hours.

3.3.3 Ivermectin Slanina ef af. (1989) have described a trial in which young male pigs were prescribed a single subcutaneous dose of 0.4 mg/kg b.w. The highest residue levels were found at the site of the injection. After seven days, higher concentrations were found in the liver than in kidney or muscle tissue. Only traces were found after 21 days. Cooking beef tissues containing ivermectin residues by boiling or frying resulted in an approximate 50 per cent reduction in ivermectin concentration.

3.4

MAXIMUM RESIDUE LIMITS IN FOOD

The FAO/WHO Joint Expert Committee on Food Additives has evaluated the risk of residues of certain veterinary drugs in the food chain. Of the anthelmintics, recommendations have been published for closantel, ivermectin and levamisole (FAOIWHO, 1990a). The recommendations are summarized in Table 3.2, although the committee called for further studies to be carried out, especially for levamisole.

78

[Ch. 3

Anthelmintics Table 3.2 - FAO/WHO recommendations for anthelmintic drugs

Drug

Closantel

Acceptable daily intake (mg/kg body weight) 0-0.03

Ivermectin

0-0.0002

Levamisole

0.003

Maximum residue limit (P.PJn.1 Sheep Bovine: muscle kidney liver Liver (all species) Fat (all species) Edible tissues and milk (all species)

1.5 0.5 2 1 0.015

0.02 0.01

A monograph has been prepared for albendazole (FAOIWHO, 1990b), which contains a comprehensive account of the chemical and physical properties of this compound and its metabolites. Pharmokinetic studies, residues and withdrawal times are also reported. Around half the dose administered to animals is excreted in the urine over the first six days although it is not clear what happens t o the remaining dose. Some metabolites have been identified, primarily the sulphone, sulphoxide and amino-sulphoxide. Analytical studies using ''C-labelled compound showed that > 80 per cent was extracted from tissues either with, or without, enzyme pretreatment following spiking. Animal studies confirm that bound residues are present ten days after dosing. After one day, residues as high as 30 p.p.m. in cattle have been detected but these fall rapidly to 1 p.p.m. after 20 days. Whilst atbendazole is not permitted in t h e USA and Italy, recommended tolerances in other countries vary from 0.5 to 5.0 p.p.m. The recommended withdrawal time ensures that only vanishingly small residues will occur in edible tissues.

3.5 REFERENCES Austin, D. J., Lord, K. A . & Williams, I. H. (1976) HPLC of benzimidazoles, Pest. Sci., 7,211-222. Baker, R. & Swain, C. J . (1989) Ivermectin: a drug for all seasons, Chem. Brir., 25, 692-696. Barker, S. A., Hsieh, L. C. & Short, C. R. (1986) Methodology for the analysis of fenbendazole and its metabolites in plasma, urine, faeces and tissue homogenates. Anafyt. Biochern., 155, 112-118. Barker, S. A., McDowell, T., Charkhian, B., Hsieh, L. & Short, C. R. (1990) Methodology for the analysis of benzimidazole anthelmintics as drug residues in Anal. Chem., 73,22-25. animal tissues. 1. Assoc. Off. Campbell, W. C., Fisher, M. H., Stapley, E. O., Albers-Shonberg, G. &Jacobs, T. A. (1983) Ivermectin: a potent new antiparasitic agent. Science, 221,823-828.

Sec. 3.51

References

79

Chiu, S. H. L., Buhs, R. P., Sestokas, E., Taub, R. & Jacob, T. A. (1985) Determination of ivermectin residue in animal tissues by HPLC-reverse isotope dilution assay. J. Agric. Food Chem., 33,99-102. Chiu, S . H. L., Sestokas, E., Taub, R., Buhs, R. P., Green, M., Sestokas, R., Van den Heuval, W. J. A., Arison, B. H. & Jacob, T. A. (1986) Metabolic disposition of ivermectin in tissues of cattle, sheep and rats. Drug Metab. Dispos., 14,590-600. Coles, G . C. (1977) The biochemical mode of action of some modern anthelmintics, Pest. Sci., 8, 536-543. FAO/WHO (1990a) Evaluation of certain veterinary drug residues in food. 36th Report of the joint FAOIWHO Expert Committee on Food Additives, World Health Organization, Geneva. FAO/WHO (1990b) Residues of some veterinary drugs in animals and foods. Monograph prepared by the 34th meeting of the joint FAO/WHO Expert Committee on Food Additives, F A 0 Food and Nutrition Paper 4112, Geneva. Food Surveillance Working Party (1987) Anabolic, anthelmintic and antimicrobial agents. Food Surveillance Paper No. 22, HMSO, London. Long, A. R., Malbrough, M. S., Hsieh, L. S., Short, C. R. & Barker, S. A. (1990) Matrix solid phase dispersion isolation and liquid chromatographic determination of 5 benzimidazole anthelmintics in fortified beef liver. J . Assoc. Off. Anal. Chem., 73,860-863. Marriner, S., Galbraith, E. A. & Bogan, J. A. (1980) Determination of the anthelmintic levamisole in plasma and gastro-intestinal fluids by HPLC. Analyst, 105,993-996. Marti, A. M., Mooser, A. E. & Koch, H. (1990) Determination of benzimidazole anthelmintics in meat samples, J . Chromatogr., 498, 145-157. Mourot, D., Boisseau, J . & Gayot, G., (1978) Separation of benzimidazole anthelmintics by HPLC. Anal. Chim. Acta, 99,371-374. Nerenberg, C., Runkel, R. A. & Matin, S. B. (1978) Radioimmunoassay of oxfendazole in bovine, equine or canine plasma or serum. J. Pharm. Sci., 67, 1553-1557. Norlander, 1. & Johnsson, H. (1990) Determination of ivermectin residues in swine tissues: an improved clean-up procedure using solid-phase extraction. Food Addit. Contam., 7 , 79-82. Osterdahl, B.-G., Johnsson, H. & Nordlander, I. (1985) Rapid Extrelut column method for determination of levamisole in milk using HPLC. J. Chromatogr., 337, 151-155. Osterdahl, B.-G., Nordlander, I. &Johnsson, H. (1986) Levamisole residues in milk from a herd of cows suffering from lungworms, Food Addif. Contam., 3, 161-166. Ryan, J. J. & McLeod, H. A. (1979) Chemical methods for the analysisof veterinary drug residues in foods. Part 1. Residue Rev., 71, 1-82. Sawyer, R. & Crosby, N. T. (1980) In: Developments in food preservatives: Analytical methods, R. H. Tilbury (ed.) Applied Science, London. Slanina, P., Kuivinen, J., Ohlskn, C. & Ekstrom. L. G. (1989) Ivermectin residuesin the edible tissues of swine and cattle: effect of cooking and toxicological

80

Anthelmintics

[Ch. 3

evaluation. Food Addir. Contam., 6 , 475-481. Smith, J . E., Parsarela, N. R. & Wyckoff, J . C. (1976) Determination of levamisole residues in bovine milk. J . Assoc. Off. Anal. Chem., 59,954-958. Tai, S. S.-C., Cargile, N. & Barnes, C. J. (1990) Determination of thiabendazole, 5hydroxy thiabendazole. fenbendazole and oxfendazole in milk, J. Assoc. Off. Anal. Chem.. 73,368-373, Tolan. J . C., Eskola, P., Fink, D. W., Mrozik, H. & Zirnmerman, L. A. (1980) Determination of avomectins in plasma at nanogram levels using HPLC with fluorescence detection. J. Chromatogr., 190,367. Tway, P. C., Wood, J. S. & Downing, G . V. (1981) Determination of ivermectin in cattle and sheep tissues using HPLC. J. Agric. Food Chern., 29, 1059-1063. Van den Heuvel, W. J. A . , Buhr, R. P., Carlin, J . R., Jacob, T. A., Konivszy, F. R., Smith, J. C., Trenner. N. R., Walker, R. W., Wolf, D. E. &Wolf, F. J. (1972) Combined G C and MS study of cambendazole and related compounds. Analyt. Chem., 44. 14-17. Van den Heuvel. W. J. A., Wood, J . S., Grovanni, M. D. & Walker, R. W. (1977) GLC/MS confirmatory assay for thiabendazole and 5-hydroxy thiabendazole, J. Agric. Food. Chem., 25,386389. Watson. D. H. (1983) Review of the concentrations of anthelmintic substances in animal food products. Food Chem.. 12. 167-177. Woestenborghs. R., Michielson, L. & Heykants, J. (1981) Determination of levamisole in plasma and animal tissues by GC with thermionic specific detection. J. Chromatogr.. 224.25-32.

Antibiotics

4.1

DEFINITION AND SCOPE

The word antibiotic is derived from the Greek words anti,meaning against, and bios meaning life. Paradoxically, antibiotics are now used most widely to protect human and animal life, but at the expense of lower orders in the animal kingdom. However, other groups of chemical agents are known which are also active against microorganisms in general, or more specifically against particular species of bacteria, fungi or viruses. Thus, antiseptics are compounds used in the treatment of human o r animal tissues (usually the skin) to kill or inactivate pathogenic micro-organisms. Examples of this group include acriflavine, chlorhexidine, iodine, quaternary ammonium compounds. heavy metals and salicylic acid. Disinfectants are similarly active against a range of common disease-producing micro-organisms and are usually bactericidal rather than bacteriostatic, and are applied to surfaces and equipment but not normally ingested. Whilst they do not kill all micro-organisms (especially bacterial spores) they generally reduce the level of contamination to an acceptable level (British Standards Institution, 1986). Some disinfectants are non-toxic to humans and animals, and can then be used as antiseptics. Nevertheless, most antiseptics and disinfectants are too toxic for internal, systemic use in human o r animal medicine and the active ingredient is used at a much higher concentration than is the case with antibiotics. Hence antiseptics and disinfectants are not incorporated into animal feeding stuffs or used in veterinary medicine on a continuous basis and so are unlikely to find their way into the food chain. However, some concern has been expressed over the use of iodo-compounds as antimastitis teat dips for cows and for the disinfection of equipment used in the dairy industry, possibly leading to high levels of iodine in the diet and problems with hyperthyroidism. Normally, dietary intakes of 150-200 pg of iodine per person per day are recommended and most diets supply sufficient of this trace element to satisfy normal metabolic processes through production of the hormone thyroxine. The chief sources of iodine in the diet are seafoods, foods containing the artificial colouring matter erythrosin and iodized salt. Results of a survey of British foods for iodine

82

Antibiotics

[Ch. 4

content have been published by Wenlock er al. (1982). They found that t h e average British diet contained a minimum of 255 pg of iodine per day and milk was identified as the most important individual source of the element. Winter milk contained five times the level of iodine found in summer milk, presumably resulting from the use of dairy concentrates. The use of iodophors as disinfectants or for mastitis control was thought to be only a minor source of iodine in the diet. Methods for the determination of iodine in foods have been described by Moxon and Dixon (1980). Antiseptics and disinfectants will not therefore be considered further in this review. The use of chemotherapeutic agents for the treatment of infectious diseases commenced with the discovery of the sulphonamides in the period 1930-5. These drugs were prepared synthetically and were found to have the ability to control bacterial diseases, especially septicaemias (blood infections). Their use was particularly widespread during the Second World War. Although Alexander Fleming had discovered penicillin in moulds in 1929 and had demonstrated its toxicity t o a wide range of micro-organisms, it was not until 1944 that the supreme importance of his discovery was realized and the drug was utilized as an antibacterial agent in human and, later, animal medicine. Thus, originally, the term antibiotic was ascribed to any product of microbial growth which was capable of killing or inhibiting at low concentrations the growth of other micro-organisms, in order to distinguish these newly discovered natural products from the sulphonamides, which were obtained synthetically and referred to as chemotherapeutic substances. However, this distinction has become blurred in recent years by the fact that many antibiotics are also produced synthetically, or by chemical modification of naturally obtained products. Hence, in this review the term antibiotic will be used to cover all antimicrobial products, including the sulphonamides and those products obtained from natural sources, but not arsenicals and the nitrofurans, which are discussed in later chapters. Together, antibiotics and chemotherapeutic substances are referred to as antimicrobials or antibacterials. Inevitably, some compounds are multifunctional and can be classed as antimicrobials, growth promoters or coccidiostats. An enormous number of antibiotics have been described in the literature but many are too highly toxic for clinical use and not all those developed for humans are suitable for use with animals. This account is therefore restricted to those compounds widely encountered in veterinary practice and animal husbandry. Whilst certain products have more than one function when added to animal feeding stuffs, in this review the discussion is restricted to those compounds which are primarily antibiotics and are not described elsewhere. A list of such compounds has been compiled in Table 4.1, along with information as to the source, chemical type, legal status and activity or function of the active ingredients. These aspects will be discussed in greater detail below. The therapeutic categories are generally those proposed by the US Adopted Names Council. 4.2 CLASSIFICATION

Antibiotics are low to medium (loo-1500) molecular weight compounds exhibiting a variety of chemical structures and, correspondingly, a diversity of chemical, physical

Syiithct ic Penicillin tnoulds+synthcsis Synt hctic

S. cittri1)ioricti.s

s. ~ i C I I f V S l I S

Synthctic

S.Jrctclicte

Ps. ~ t i ~ i r e s c ~ t ~ s

S. c.itrtrrr~~ro,rerrsic.itreir.~is

p-Lact ;im

Mncrolidc polythiiizolc Miicrolidc

Aminoglycosidc

Lincosaminidc Pol yet her

Aminoglycosidc Aminoglycosidc -

M. ptirprireit P. gri.veofrtlvto~r Syiithct ic E. coli S. Litrcv1tietisi.s

S. frrdicie

Pcptidc Aminoglycosidc

Glycoside complex

and rclatcd strains

Bit mhcrmycin

(E 712)

Synthetic and S. vetiezrtclrre S. Itcrritncltirii~rs

I

Pcptidc

B. sribtili.s, 13. lichetrifortni.s S. hiitti hergietisis

(Ravophospholipol) Chlormnphenicol Efrotoin ycin Friimomycin ( h m ycc t in) Gcntnmicin Griscofulvin 14iilquinol Intage n" Lincomycin Moncnsin (E 714) Mupirocin Ncoin ycin Nitrofurans Nosihcptidc 0lc;indomycin (E 710) Oxoliiiic acid Pcilicilliils Ronicliizolc (E 759)

I

Pcptidc

S. cii~riiiiirrs

1

-

I1

-

1

-

-

-

-

I1

-

1,11

-

S. rerrrhrnriiis Synthct ic

Apram ycin Arsenicals Avopnrcin (E 715) Bilcitracin (E 700)

-

Aminogl ycoside

Source

Product

POM POM PM L

POM POM

POM POM POM PML POM PML

POM

POM

-

PML

PML

PML

POM POM

Legal status EC UK nnncx

Cotiritiried irexi

Antih;ictcriel (for fish) Antih;ictcrinl Antihiictcrial pnge

Antibacterial Antifungal Antimicrohiel Immunization agent Antibacterial Antiprotozonl, nntihactcrial. ;intifungal. coccidiostat Antibacterial and growth promotcr Antimicrobial Antimicrobial Antimicrobial, growth promotant Antihactcrial

BroaG-spectrum nntihacterial Antibiotic growth promotant Entcric infcctions

Antibacterial

Antibacterial, growth promotant

Antibactcrial, growth promotant

Broad-spectrum antihactcrial Enteric infections. growth promotant

Activitylfunction

Table 4.1 - Some antibiotic substances used in veterinary practice and animal husbandry

00 W

Y

f h)

?

n

W J

Pcptidc

S. i~irgitritrc

Niipthiiccne derivativcs Mitcrolide

A mi nogl ycositlc

"lntiigcn is i i rcgistcrctl triitlc iiiiirk of Unifccds Intcrniition;il Lttl. P O M = prescriptioii-oiily iiicdicinc

(E711)

'Ihmulin 'l'ylosin ( E 713) Virginiiiniycin

Strcptoniycin Sulphoniimitlcs 1'ctr;icyclines

M;icrolidc

'rYPc

S. grisi~tts Synthctic Synthetic and S. trctrcofirt~ierr.r PI. tflltril~.v S. frccclicrc

S. trtt~hofirric~ta

Spiraniycin

( E 710)

Sourcc

Product

PML

I . I1

PML=pliiirm;iceuticiil merchants' list

POM

P OM P OM POM

PML

UK

I

I

iinncx

EC

Lcgal S t i l t l l S

Antihiictcriiil

A nt ihiic t c r iiil

Antihactcrial Antihactcriiil Antihiictcrial

Antihilctcrial. antirickcttsiac

Activi t ylfunct ion

Table 4.1 (conrinued) - Some antibiotic substances used in veterinary practice and animal husbandry

P

00 P

Sec. 4.21

85

Classification

and biological properties. Even in 1976, some 3000 compounds had been described and by 1980 this number had grown to 7000. so some system.of classification has become desirable. Attempts have been made to classify antibiotics in terms of their source. their mode of action or their chemical structure. Antibiotics are obtained from synthetic, natural or semi-synthetic sources, and a classification by source is usually based on the taxonomy of the producing micro-organisms. An example is given in Table 4.2 (Korzybski et al., 1978). However, it is felt that this approach is too

Table 4.2 -Classification Source/activity ~

~

I

11

111

IV V

of antibiotics according to source and activity" Number of compounds listed

~~

ACTINOMYCETALES Section A Macrolides B Active against Gram-positive organisms C Polypeptides D Broad-spectrum antibiotics E Active against acid-fast bacilli F Antifungal polyenes G Antifungal non-polyenes H Active against protozoa Active against plant and animal viruses I J Antitumour activity EUBACTERIALES A Genus Pseudomonas B Genera Micrococcirs , Streptococcus diploccus, Chromobacterium, Escherichia. Proteus C Genus Bacillus FUNGI IMPERFECTl A Genus Peiiicilliiim B Genus Aspergillus C Genus Fusariiim D Genera Gliocladium. Cephalosporiiim, Alternaria. Trichotheciiint . etc. BASIDIOMYCETES AND ASCOMYCETES LICHENS AND ALGAE

"Korzyhzki 1'1 trl. ( 1078).

41 121 116 219 28 91 90 35 35 110

17

23 82

49 31 12

71 53 9

86

Antibiotics

[Ch. 4

broad to be much use for analytical chemists, since the majority of substances are derived from the genus Acfinomycetes. Furthermore, some compounds can be produced by different and unrelated genera. Equally, the same genus may produce more than one antibiotic. The activity spectrum is of prime importance to clinicians, and classifications based on biological properties are widely encountered. Antimicrobials are often described as being effective against Gram-positive or Gram-negative organisms, or against both. This refers to a classification of bacteria based on the organism’s response when stained with a purple dye. The organism either retains or releases the dye on subsequent washings, so that Gram-positive organisms show up blue under the microscope whilst Gram-negative organisms appear red. Other classifications are based on differences in the mode of action of the active ingredient. Antibiotics are thought to function by interference in the synthesis and development of parts of the bacterial cell. They may prevent the formation of nucleic acids, or the synthesis of protein. Alternatively, they can attach themselves to the cell wall o r cell membrane and prevent essential cross-linking of the structure or promote the ingress of ions, thus destabilizing the whole structure and eventually causing complete rupture. However. the mechanism of action of some antibiotics is not yet fully understood and it is possible that some compounds can act in more than one mode. Hence a classification based on chemical structure is increasingly becoming more popular, now that the molecular formulae of more and more compounds have been elucidated. For the analytical chemist, a classification based on chemical structure is clearly the most appropriate. Chemical classification of antibiotics Antibiotics used in animal husbandry can be divided into the following chemical groups: (1) aminoglycosides; (2) 0-lactam compounds; (3) macrolides; (4) peptides; ( 5 ) sulphonamides (and trimethoprim); (6) tetracyclines; (7) miscellaneous, e.g. chloramphenicol, oxolinic acid; Each of these groups will now be considered in more detail and the principal characteristics of each described. Some physical and chemical properties of the more important antibiotics have been collected together in Table 4.3.

4.2.1

Aminoglycosides Examples of antibiotics in this group include apramycin, bambermycin, gentarnicin, lincomycin, neomycin and streptomycin. They are obtained from fungal sources (Table 4.1) and are complexes of several closely related structures. Some examples are shown in Fig. 4.1. Apramycin is a broad-spectrum antibiotic produced by a strain of Sfreptococcus tenebrarius. It consists of several components and is available in the chloride or sulphate form. The bambermycins (flavophospholipol) contain at least 4.2.1.1

Molecular formula

Molecular weight

477 463 449

GIH,,N5O, CaiH,iNjO, Ci,H~rNsO,

CI,,

Cz

454

CnHdhOi>

-

94-100 107-124

135-140 190-193

734

Fram ycetin (neomycin B) Gcntamicin C,

>do00

-

C5,H,NL0,, C,,H,,NO,,

Efrotomycin Erythromycin

I 145

360 >2000

2wd 245

>lOoOO

LD?,, valuc (mglkg)

Nonc

245-247

Melting point (“C)

151

c?iH.~iNPii 539 Complex I %lo peptidc Bacitrdcin A CNIHI,I,,NllOlhS 1421 Bambcrmycin 4 components: A. Bi. BL,C Chloramphenicol C I I H I Z C I ~ N ~ 0323 5

Apramycin Avoparcin

Compound

232.327 280

278

258

280.300

Water. alc. Water. McOH, DMF

+ 160

t 158

Watcr. pyridinc DMF

Alcohols

Coiiriiiued iiert page

Benzene, chlorinated hydrocarbons

Ac. ether, etc.

-

Benzene, pet. ether

Ether, CHCI,. Ac Benzene, CHCI,

Solubility in common solvents Fairly soluble Insoluble

Water Lower alcohols Watcr. DMF. DMSO

Very soluble

Water, McOH, EtOH -25.5 EtAC BuOH, EtAc. AC -78 Watcr, acids, alcs. Ether acetone, CHCI,, CHjCN +57 McOH, EtOH

+ 18.6 EtOH

-95

~ ~ m a x . [a]E (nm)

Table 4.3 - Properties of some antibiotics used in animal husbandry

f N

8’ 3

%

@

B

0

Y

88

Antibiotics

L

U

f 0

U

C 2-

U

c w

i

4

Molcculiir weight

200 Olh

Molcculiir formula

CIItlISNIO~ Cj,,HjjNO17

uv miix.

- 11)o -28

210

305

-46

luji;

2x2

nm

orgs=org;inic solvcn ts dil. =di lut c d =dcconiposcs

7(MM

I 09-203

130

(mdkg)

Melting point (“C)

LD,,, v;lluc

Watcr

Ether. hcnzcnc

Soluhility in common solvcnts Fairly soluhlc lnsoluhle

DMF=dimcthylTorm;imidc DMSO=dimct hylsulphoxidc (uJi;=spccific optical rotation ;it 2 5 ” for ~ sotlium ( D ) linc

CtIC1.i. McOH Water. iilcs. esters. ketones. hcnzenc. ether. c1ilnrin;itcd. HlCs

Very soluhlc

Table 4.3 (confin~ted) - Properties of some antibiotics used in animal husbandry

h)

P

3

6’

c

5

el

9

Y

90

Antibiotics

[Ch. 4

Apramycin

CH3

COOH

Bambermycin

NHCOCH,

HO

HO

HO NHCOCH3 Ho

I

NH

Moenomycin A Fig. 4.1 - Structural formulae of some aminoglycosides.

0

91

Classification

Sec. 4.21

Gentarnicin C, : R = R, = Me; R2 = H

Neornycin B.

R, = H R, = CH,NH2 R, = NH,

(y

I-

HOCH

-CONH

CH3CH2CH2

HO

I

CIH

H

I I I

H

Lincomycin

Fig. 4.1 (conrinued)- Structural formulae of some aminoglycosides.

92

Antibiotics

NH

\ C-

[Ch. 4

NH

Streptomycin

Fig. 4.I (conrinued) - Structural formulae of somc aminoglycosides.

four active components, named moenomycins A. B , , Bz and C, produced by S. bambergiensis and other related strains. A is the major component. Closely related in chemical composition is lincomycin, which is a free base but more stable as the hydrochloride hemihydrate. Neomycin consists of two amino sugars linked by a glycosidic bond. Gentamicin C, is a white amorphous powder, m.p. 102-108"C, soluble in water and polar organic solvents, and contains three saccharide units. Streptomycin A also contains three saccharide units linked through a glycosidic linkage. All are small, basic, water-soluble molecules possessing several primary amino groups. They are not very soluble in non-polar solvents and are not very absorbent in the UV. The aminoglycosides are broad-spectrum antibiotics active against both Gram-positive and Gram-negative organisms but not anaerobes or fungi. They are less active against Gram-positive bacteria than the penicillins or tetracyclines and are not active against streptococci. Aminoglycosides are not well absorbed from the alimentary tract or by topical application and so are usually administered parenterally. They are neurotoxic and potentially toxic to the kidney, and are thought to bind to bacterial ribosomes and inhibit protein synthesis. They can lead to an increase in resistant bacteria through mutation of the organism, producing altered ribosomes that no longer bind the drug involving enzymes that deactivate the drug and reduce its permeability. fl-Lactam compounds This group consists of the penicillins and the cephalosporins. The penicillins are a closely related group of compounds designated BT, N , G , 0,S, V etc., depending on the nature of the substituent groups, e.g., benzyl, phenoxymethyl, amino, isoxazolyl 4.2.1.2

93

Classification

Sec. 4.21

o r carboxy. Penicillin is obtained by adding phenylacetic acid to the fermentation broth. Many other compounds have been prepared by acylation of the 6-amino group. The similarity in chemical structure between the penicillins and the cephalosporins is shown in Fig. 4.2.

H

H CH3C = CHCH2SCH2CONH

CH3

jf $..

C-'

CH COOK

n U

Penicillin S Potassium

H

H

HOOCCH(CH,),CONH c

I U

CHlOCOCH3 COOH Cephalosporin C

Fig. 1.2- Structure of pcnicillins and cephalosporins.

In penicillin. the p-lactam ring is fused to .a five-membered thiazolidine ring, whilst for the cephalosporins the p-lactam ring is fused to a six-membered ring. The rings are not coplanar but are folded along the CS-N4 axis. The p-lactam ring is easily opened by acid hydrolysis (e.g. in the stomach) or by the action of penicillinase, which is produced by some strains of target bacteria as a defence mechanism. The cephalosporins are more stable, especially to enzymatic attack. The compounds are white, generally amorphous solids with no sharp melting points and they decompose on heating above 370°C. They are soluble in water; solubility in organic solvents depends on the nature of the substituent groups. The compounds possess characteristic infrared and nuclear magnetic resonance (NMR) spectra. Penicillins interfere in the development of the bacterial cell wall and are widely used. particularly for the treatment of mastitis. Following injection, the milk of treated cows can be contaminated with penicillin for several days. Such milk should be discarded as it cannot be

94

Antibiotics

[Ch. 4

made into cheese or yoghurt and might cause a reaction in sensitive individuals. Some farmers might seek to avoid such financial loss by the addition of penicillinase - an enzyme that will destroy residues of penicillin. It is not known what harm, if any. could arise from this practice. Penicillin G is weakly active against Gramnegative bacteria and is poorly distributed in tissues. It is, however, cheap and possesses low toxicity. Amino penicillins are more active against Gram-negative bacteria. Preparations are available in the form of tablets, powders, creams and injectable formulations. Cephalosporins act similarly to the penicillins but they have been employed only on a limited scale in veterinary medicine to date owing to cost. Macrolides Included in this group are erythromycin, nosiheptide, oleandomycin, spiramycin and tylosin. They consist of a large lactone ring with sugars (often amino sugars) attached. The structures of the compounds are shown in Fig. 4.3. Erythromycin is produced by Srreprococcus eryrhreus, found in soil. Three configurations (A, B and C) are produced during fermentation. A is the major component. Nosiheptide consists of yellow needles and is insoluble in water, but soluble in common organic solvents. Oleandomycin is a colourless, crystalline, basic substance, moderately soluble in water and polar organic solvents. Spiramycin has been separated into three components. Tylosin is soluble in water, lower alcohols, esters and ketones, as well as chlorinated hydrocarbons, benzene and ether. The macrolide antibiotics are active against Gram-positive organisms including staphylococci, particularly those which are resistant to penicillin. They are also used as growth promoters and act by interference with the synthesis of protein. They possess good tissue penetration and a long half-life. 4.2.1.3

4.2.1.4 Peptides The main compounds in this group are avoparcin, bacitracin (used usually as the zinc salt). efrotomycin and virginiamycin. These products are large peptide molecules which often contain D forms of amino acids, in contrast to naturally occurring proteins, which are built up from L-amino acids only. Avoparcin is a complex polypeptide which influences the composition of bacteria in the rumen so that less methane and acetic acid but more propionic acid are produced during digestion. This increases the net energy value of the feed to the animal and improves live-weight gain. Fig. 4.4 shows the structuresof avoparcin and bacitracin A , which isone of nine components of the commercial product. Virginiamycin is a mixture of two components designated M I and S , , which are both cyclic polypeptides and act synergistically when present in the optimum ratio of 4: 1. Bacitracin and virginiamycin are both white amorphous powders which are soluble in water and alcohol but insoluble in acetone. They are active against Gram-positive organisms and also act as growth promoters. Virginiamycin is effective against necrotic enteritis in broilers and against dysentery in pigs. The structural formulae of M ,and S , are also shown in Fig 4.4.

Efrotomycin Efrotomycin is a pale yellow solid (CSYHH8N2O2,J with a molecular weight of 1145. It has UV maxima at 232 and 327 nm. It is produced by Streptomyces lactamdurans and

4.2.1-5

Sec. 4.21

95

Classification

CH3 Erythromycin A

Oleandomycin

Fig. 4.3 -Structure

of some macrolide antibiotics.

96

[Ch. 4

Antibiotics 0

HN Nosiheptide

(cH3’2N OH

R

CH3

0

111

Spiramycins

Fig. 1.3 (cotrritiurd)- Structurc of some macrolide antihiotics

-COCHZCH

Sec. 4.21

97

Classification

CH3

0

1

CHO

h

nu

4

-OH

I

CH3

Tylosin

Fig. 4.3 (cotirititccd) - Structurc of somc macrolidc antibiotics.

is used as an antibiotic and growth stimulant in pig feeds with a minimum addition level of 4 p.p.m. and amaximum of 8 p.p.m-, reducing to6 p.p.m. over six months in age. The structural formula of efrotomycin is shown in Fig. 4.5. 4.2. I . 6 Sulphonamides The compounds most frequently used in animal husbandry are sulphanilamide, sulphacetamide. sulphadimidine (sulfamethazine) and sulphaquinoxaline. They contain the basic p-aminobenzene sulphonamide structure, which is closely related to aminobenzoic acid, an important factor in the vitamin B-complex.The sulphonamides are thought to act by displacing this compound and so interfering with the essential metabolic pathways of the target bacteria in the folic acid synthesis. Sulphadimidine (Fig. 4.6) and sulphaquinoxaline are used as feed additives. They are active mainly against Gram-positive bacteria but resistant strains can be produced. Some sulphonamides are active against Gram-negative bacteria and possess good tissue distribution especially if lipid soluble. They have long half-lives and are potentiated by the addition of trimethoprim. The latter cornpounds acts as an inhibitor of dihydrofolate reductases (Hitchings, 1961), thus enhancing the power of the sulphonamides and reducing the risk of resistant bacteria surviving and multiplying. Sulphaquinoxaline is used primarily as a coccidiostat, usually in combination with amprolium and ethopabate (see Chapter 5). 4.2.1.7

Tetracyclines Chlortetracycline and oxytetracycline are the best-known members of this group. The structure consists of a modified naphthacene ring as a basic skeleton, as shown in Fig. 4.7. The compounds are yellow crystalline substances with amphoteric properties. Chlortetracycline is soluble in aqueous solvents, especially above pH 8.5, but

(Ch. 4

Antibiotics

98 OH

ci-Avoparcin R = H 13-Avoparcin R = C l

C235

'1' J CHCH

CH,'

OH

CO

I - L-ILE - L-LEU- D-GLU

L

NH2

Structure of bacitracin A

Fig. 4.4 - Structure of some peptide antibiotics.

99

Classification

Sec. 4.21

0

Factor M:

\ NH CHa-CH-CH-

0

I I1

C-

I

/ \

CH2 0 CH2

CH2

I I I I /. ..

.

NH-CH-C-N-CH

I

\

I-

NCH, /

c=o

I

0 C

CH -NH

-C - C H - N

-C-CH

Factor S,(virginiamycin)

Fig. 4.4 (cotiibiired)- Structurc of some pcptidc a n t i h i o h

has only limited solubility in organic solvents. Oxytetracycline is soluble in both acidic and basic aqueous solutions. Oxytetracycline gives characteristic colour reactions with a number of reagentsand both show strong UV absorbance at 265 and 350 nrn. The tetracyclines are active against both Gram-positive and Gram-negative

An ti biotics

(Ch. 4 Me

HO

I

OH

Me0

0 CH;

I

Me0

HO

OMe

Fig. 1.5 - Structurc of cfrotornycin

organisms hy interference with protein synthesis. They are absorbed into the animal’s system more slowly than the penicillins but are well distributed in tissues and are also more slowly excreted. The compounds are complexed by calcium ions and. hence, residues become deposited in teeth and bones. Bacterial resistance has been observed following a course of treatment. 4.2.1.8 Miscellaneous compounds Chloramphenicol (CAP) is a powerful broad-spectrum antibiotic which is widely used in veterinary medicine and for the treatment of bacterial infections in poultry, cattle and pigs. The molecular formula of CAP is shown in Fig 4.8. The drug is used in human medicine for the treatment of eye infections but, otherwise, only as a last resort against resistant micro-organisms, since sensitive

Sec. 4.31

Problems with the use of antibiotics in feeds

101

CH3

Sulphadimidine

Sulphaquinoxaline

Fig. 4.6 - Structure of sulphadimidine and sulphaquinoxaline.

subjects may develop aplastic anaemia. Most countries therefore impose restrictions on the use of chloramphenicol and, in addition, stipulate maximum residue levels for CAP in food for human consumption. Oxolinic acid is widely used in fish farming for the treatment of diseases such as furunculosis and enteric red-mouth. I t is added to the feed at a level of 10 mg/kg body weight. The structural formula of the compound is shown in Fig. 4.9.

4.3

PROBLEMS WITH THE USE OF ANTIBIOTICS IN FEEDS

Whilst few would question the use of antibiotics for the treatment of sick animals, the addition of such compounds to feeds as prophylactics or as growth promoters is less easy to defend, especially in times of over-production. Furthermore, there is a possibility that residues of such compounds (or their metabolites) will persist in the animal and, hence, enter the human food chain. The presence of residues of antibiotics in milk may also inhibit the growth of organisms required for making cheese or yoghurt. Hence, most samples of milk are screened routinely before being used in such manufacturing processes. If man consumes animal products containing traces of an antibiotic, harmful effects may arise in exactly the same way as if an equivalent dose had been administered directly. Toxic effects are, however, unlikely since any residues will be present only at very low concentrations indeed, but allergenic reactions may be produced in sensitive or sensitized individuals. The

102

[Ch. 4

Antibiotics OH

0

0

OH

Chlortetracycline

OH

0

0

OH

CONH2

OH

Oxytetracycline Fig. 4.7 -Structure

of the tctracyclines

0

A

CHCl2

OH

OH

Ch loramp henicol

Fig. 4.8 -Structure

of chloramphenicol.

Sec. 4.41

Methods for the detection of antibiotics

103

0

C2H5

Oxolinic acid Fig. 4.9- Structurc oloxolinic acid.

principal hazardous effect is likely to be the development of resistant strains of bacteria which may be produced following the ingestion of subtherapeutic doses of antibiotics (Schothorst et a l . , 1978). Additional concern was aroused when it was discovered that this resistance could be transferred to other bacteria. Theoretically, this could include transfer of resistance from non-pathogenic organisms such as Enferobacfercloacae to pathogenic organisms, which would then not respond to normal drug treatment. Other effects could include disturbances to the ecology and flora of the digestive tract, possibly making the animal more subject to attack from other micro-organisms. 4.3.1 The Swann Report (1969) The problem was considered to be potentially so serious that a committee headed by Professor Michael Swann was appointed in 1968 to review the problem in the UK. The committee concluded that the administration of antibiotics to animals poses hazards to human and animal health unless carefully controlled (Swann, 1969). They therefore recommended that animal products should be carefully monitored and that penicillin and the tetracyclines should not be used for growth-promoting purposes in animals as they are widely used in the treatment of human diseases. In general. they proposed that only those products with little or no application as therapeutic agents in man or animals should be permitted for use without prescription. Therapeutic antibiotic preparations should only be available for use in animal husbandry if prescribed by a registered veterinary practitioner.

4.4

METHODS FOR THE DETECTION O F ANTIBIOTICS

The previous section has established the need to control levels of antibiotics in feeds and to monitor foods for the presence of antibiotic residues. As the levels present in foods are likely to be very low, very sensitive methods of detection are required. The diversity of chemical structures and properties of these compounds (4.2.1) demands

I04

Antibiotics

[Ch. 4

methods that are also discriminatory. For any monitoring programme to be successful. large numbers of samples must be taken and examined. Unfortunately, this requirement can be prohibitive in cost terms, especially when the analytical methods employed (e.g. mass spectrometry, radioimmunoassay) are expensive, both in terms of the capital equipment to be purchased and the specialist staff and facilities required to operate such equipment. Generally, these procedures are difficult to automate and hence cannot cope with the large numbers of samples resulting from a well-organized monitoring programme. The best approach is therefore t o use a cheap. sensitive. simple and rapid screening procedure on all the samples taken, even though the results obtained may not be, at that stage. unequivocal. Hopefully, only a small percentage of samples from this screen will indicate a presumptive positive. This reduced number of samples can then be examined more thoroughly by chemical methods possessing greater powers of sensitivity, specificity and discrimination. Generally. microbiological methods enable a large number of samples to be examined, but the methods detect the presence of inhibiting substances only and not necessarily their metabolites or degradation products. A positive result provides little o r no information as to the identity of the substance present. False negativescan also occur if residues are present to which the test is insensitive. On the other hand; chemical methods can detect both the active compounds and any degradation products, but the significance of the latter may not be known in termsof the hazard to human health. Chemical methods are often specific for single compounds (or single groups of compounds) only and, in addition, cannot cope with a large throughput of samples. This problem has been discussed more fully in Chapter 2, but it is particularly important with respect to antibiotics. A review of methods available for t h e monitoring of antibiotics in body fluids has been published by Rouan (1985). 4.4.1 Microbiological methods Whilst there are bioassays which are specific for individual antibiotics. these are of limited application in a general screening programme where the identity of the residues present is unknown. Such assays will not be included in this review. Most assays depend on the ability of antibiotics to inhibit the growth of a sensitive bacterial test organism. This is manifest by the failure to form colonies, i.e. a clear zone of inhibition is observed, o r by the suppression of the organism's normal metabolic processes, e.g. the production of acid or gas. Fig. 4.10 illustrates the formulation of zones of inhibition by avoparcin against a known test organism. Three different methods of extraction are compared. The use of methanol-hydrochloric acid is less good than either the official method (acetone-HCI) or 90 per cent acetonitrile-water soI u t ion. The theory of antibiotic inhibition zone formation has been discussed by Linton (1983). Zone size is determined by the interaction of two dynamic processes taking place simultaneously. These are (a) the growth of the test organism and (b) the diffusion of the antibiotic from its point of application. Following incubation of a seeded nutrient plate, the inoculum growth pattern follows the normal laws, namely an initial lag period followed by a logarithmic growth phase in which the time taken to double the number of organisms is approximately constant. The diffusion process is controlled mainly by the chemical and physical properties of the gel and the size

Sec. 4.41

Methods for the detection of antibiotics

105

Fig. 4. I 0 - Zones of inhibition produccd by avoparcin.

and ionic charge on the antibiotic molecule. In practice, the test will be affected by the time and temperature of incubation, the concentration of inoculum. the constituents of the medium - in particular its nutritional formulation - and the presentation of the sample as well as the sensitivityof the test organism to the various antibiotic residues that may be present. The size of inhibition zone produced under standard conditions is linearly related to the logarithm of the antibiotic concentration, as shown in Fig. 4.11. The point of intersection on the ordinate represents the minimum inhibitory concentration for a particular antibiotic-test organism combination. Only residue concentrations above this level can be detected. 4.4. I. I The Four-plate Test This protocol (Bogaerts and Wolf, 1980)was developed as a means of import control within the EC primarily to monitor residues of antibiotics in fresh meat from Third World countries for use at national borders. Hence, it is also known as the Frontier Post Test. The test involves diffusion on agar plates inoculated with Bacillus subtilis spores at pH values of 6, 7.2 and 8, together with a further plate inoculated with Micrococcus futeusat pH 8. Trimethoprim is incorporated into the pH 7.2 medium to enhance the test's sensitivity to sulphonamides. The formation of annular zones,of inhibition at least 2 mm wide to one or both micro-organisms indicates the presence of an antibacterial substance. Some workers (Corry etal., 1983) have found that only the pH 7.2 and pH 8 plates seeded with B. subtilis are essential for most surveys. The lower limits of detection achievable using the four-plate test (FPT) are shown in Table 4.4. Similar data were first published by Nouws et al. (1979). Clearly, the test possesses adequate sensitivity to most antibacterial substances apart from avoparcin, chloramphenicol, lincomycin and the nitrofurans. Whilst the test is ideal for the screening of a large number of samples, it is applicable to fresh meats only. Offals

106

[Ch. 4

Antibiotics

'I

10

20

30

40

50

mm2

Zone size (diameters2) Fig. 4. I I

- Rclation hctwccn thc s i x or an inhibition zone and antihiotic concentration.

and frozen pig kidney tissues have been found to give false-positive results owing to the presence of naturally occurring inhibitory substances (Smither, 1978). Hence. the test is cheap and simple to use, requiring no special equipment. It can detect the presence of a wide range of antibacterial substances but it cannot identify individual compounds. 4.4.1.2 The swab test on premises This test, developed in the USA, is specifically designed to be used by non-specialist inspectors in the slaughterhouse as a ioutine control method for meat and poultry. Slits are cut into the carcase and sterile cotton-wool swabs are inserted for 30 minutes to soak up the exudate. The swabs are then laid on prepared agar plates seeded with B. subtdis and incubated overnight at 29°C. The test has been described by Johnston eral. (1981). They found that the swab test on premises (STOP) had equal sensitivity to conventional test procedures for the detection of chlortetracycline, oxytetracycline, tetracycline, erythromycin, neornycin. penicillin, streptomycin and tylosin. Ninety-four per cent of all samples tested (n= 1780) gave comparable results by reference to standard procedures, the remaining samples being positive to STOP but negative by other tests. A variation of the test permits other residues such as virginiamycin and lincomycin to be detected. Other microbiological assay procedures for antibiotic residues have been reviewed by Katz (1986). Microbiological

Sec. 4.41

Methods for the detection of antibiotics

107

Table 4.4 - Limits of detection of the four-plate test and by electrophoresis to various antimicrobial substances Compound

FPT (Pgk)

Electrophoresis (I%>

~~

Avoparcin Bacit racin Chloramphenicol Chlortetracycline Erythromycin Lincomycin Monensin Neomycin Nitrofurans Oxytetracycline Penicillin Spiramycin Streptomycin Sulphadimidine Tetracycline Tylosin

7 1

10 0.1 0.1 0.2 14 0.2 40 0.5 0.02 0.3

0.5 7 (0.5“) 0.1 0.3

0.1 0.05 0.5 0.004 0.005 0.05 0.5 0.5

0.1 0.04 O.OO5-O.2 0.02 0.2 15

0.02 0.05

“In thc prcscncc of (rimethoprim.

methods generally lack specificity and so physico-chemical or immunoassay procedures are needed for confirmation of antibiotic identity. They also require incubation (usually overnight) and are not very reproducible. Only free antibiotic residues are detected, not bound residues. 4.4.2 Electrophoresis Electrophoresis is a method of separation in which charged molecules are caused to migrate in a buffered medium by the application of a high DC voltage. The high voltage generates an undesirable quantity of heat which has to be removed by a suitable cooling device, e.g. a cooled aluminium plate. Antimicrobial agents can be identified by differences in the distance migrated from a fixed point under standardized conditions in agar and agarose gels at pH values of 6 and 8. The positions of different antibiotics following electrophoresis are visualized by bio-autography using Micrococcus luteus and Bucillus cereus var. mycoides seeded into molten medium and overlayered onto the electrophoresis plate, prior to incubation for up to 24 hours at 30°C. Full details of the experimental procedure have been published by Smither and Vaughan (1978), who also tabulated the minimum amounts of antibiotic substances that can be detected (Table 4.4) along with the migration distance required for identification purposes. Behaviour in agar is quite different from that in agarose and is also dependent on pH value and inoculum. Such differences can be

108

Antibiotics

[Ch. 4

exploited diagnostically for the identification of unknown inhibitory substances although certain compounds very closely related in molecular formula could not be distinguished. 4.4.3 Thin-layer chromatography As an alternative to electrophoresis, antibiotics and related substances can also be separated and identified using thin-layer chromatography (TLC). The technique of bio-autography is again often used for the visualization of separated compounds, although spray reagents and spectroscopy are also available. However, it is not possible to separate all antibiotics on a single thin-layer plate and most workers have used several plates and solvent systems simultaneously to achieve satisfactory resolution. Neidert er af. (1987) described a scheme for the extraction of 14 commonly used substances from animal tissue using methanol, followed by acidifed methanol to recover residues of the tetracyclines and aminoglycosides. The methanol extract was further partitioned with chloroform to produce three separate extracts, each containing a defined group of antibiotic compounds. The extracts were then examined using three separate TLC solvent systems. Recoveries from tissues were claimed to be near quantitative and detection limits varied from 15 to 600 p.p.b., depending on the particular antibiotic tested. As early as 1969, Zuidweg et af. had published retention values ( R , ) of some penicillins, tetracyclines, neomycin, streptomycin and oleandomycin relative to penicillin G, following chromatography on Sephadex. However. this approach was qualitative and permitted only a separation into groups of antibiotics. A more complex system was described by Freres and Valdebouze (1973). They used two types of TLC plate, four solvent systems for elution, four extraction procedures and four test organisms at the visualization stage by bio-autography. In this way, they were able to identify all the commonly used antibiotics in animal feedstuffs at levels down to 5 p.p.m.; bacitracin was an exception, with a detection limit of 10 p.p.m. Other feed additives such as coccidiostats did not interfere. Bossuyt el al. (1976) studied 14 different antibiotics used for mastitis control. They were able to detect most compounds in the range 0.1-3 pg/ml, but only 15 pg/ml for neomycin. Other workers have concentrated on the separation of a restricted number of antibiotics in a given group. For example, Moats (1983b) published a semiquantitative method for penicillin G and cloxacillin in milk, whilst Asukabe er af. (1984) developed a procedure for the separation of the polyether antibiotics salinomycin and monensin using a derivatization reaction to produce a fluorescent compound for visualization. I n a later paper by the same authors (Asukabe et af., 1987) the technique of high-performance TLC was employed and the derivatization was extended to include lasalocid. A similar separation of four polyether antibiotics was reported by Owles (1984) using vanillin as the visualization reagent as an alternative to bio-autography. Residues in the range 3-100 p.p.m. were detected in feeds. Moats (1985) described a number of chromatographic methods for the macrolide antibiotics in tissues and milk using two-dimensional TLC with several visualization reagents. Similarly, TLC with bio-autography or colorimetric visualization reagents has been used to detect residues of monensin in animal tissues (Okada er af., 1980; Tihova and Peneva, 1982) and a collaborative study was undertaken by

Sec. 4.4)

Methods for the detection of antibiotics

109

the Analytical Methods Committee of the Royal Society of Chemistry (1986). A method for the determination of the macrolide antibiotics erythromycin, tylosin, oleandomycin and spiramycin has been published by Petz er al. (1987). The method was applicable to tissues, milk and eggs. Visualization was effected by bio-autography or with xanthydrol. Recoveries were in the range 71-96 per cent at 0.10.5 p.p.m. but o n l y 51 per cent from milk, at 0.02 p.p.m. Similar work was reported by Moats (1985). Oka eruf. (1987) used both TLC and HPLC for the separation and determination of eight tetracyclines. A combination of high-performance TLC and Cx-TLC plates was required for identification and UV densitometry was recommended for quantitative work. However, whilst these systems work well with standard mixtures, no data were presented for the recovery of these compounds added to feeds or residues spiked into animal tissue. Further work by this group has been reported (Ikai et al., 1987). Thomas and Newland (1987) examined four TLC systems for the determination o f vancomycin and some metabolites with particular reference to its constituents and stability. There is no doubt that TLC has many advantages for the detection of antibiotic residues in feeds and animal products. I t is particularly suitable as a screening test to be followed up by other detection systems, such as mass spectrometry, when presumptive positives are obtained. However, HPLC and immunochemical techniques are now being developed which, in coming years, will no doubt offer similar if not better advantages as screening tests. A comprehensive review of the methods available for the detection of sulphonamides in feeds and sulphonamide residues and metabolites in food has been compiled by Horwitz (1981). Early methods were based on the Bratten-Marshall diazotization reaction but were limited by background interferences and their inability to distinguish between individual compounds. Hence TLC was employed to separate sulphonamides prior to visualization. A screening test was published by Parks (1982) but recoveries were only 40-50 per cent. An improved version using fluorescamine for visualization and a densitometer for measurement was subjected to collaborative study (Thomas et al., 1983). Three sulphonamides were tested and recoveries were found to be better than 95 per cent. A further improvement was reported by Haagsma et al. (1984) using essentially the same technique. They were able to detect the presence of five sulphonamides at levels down to 0.05 p.p.m. in muscle and kidney tissues, following extraction with dichloromethane, clean-up on Sep-Pak cartridges and TLC. 4.4.4 Gas-liquid chromatography/massspectrometry GLC is not the prime method of choice for the determination of antibiotics, since the technique is applicable only to volatile compounds or to involatile compounds that can be made sufficiently volatile either by thermal degradation or by derivatization. A method for the determination of avilamycin residues in pig tissues, fat, blood, faeces and urine has been described by Formica and Giannone (1986). This requires alkaline hydrolysis to dichloroisoverninic acid, methylation and detection using an electron-capture detector. The method is sensitive down to 0.1 p.p.m. with recoveries around 85 per cent.

110

Antibiotics

[Ch. 4

GLC has been widely used for the determination of sulphonamide residues, usually in combination with mass spectrometry. Manuel and Stellar (1981) described a method based on extraction with acetonexhloroform, methylation and detection using an electron-capture detector. Satisfactory resolution between seven compounds was achieved and excellent recoveries of sulphadimidine (sulphamethazine) were obtained from pig tissues such as liver, kidney, muscle and fat. A number of papers reporting methods based on combined GUMS have been reported. Stout ef al. (1984) used chemical-ionization mass spectrometry for confirmation, since both the parent ion and fragment ions indicative of amines and sulphanil moieties were obtained. Again, satisfactory recoveries for sulphadimidine were obtained. Suhre et al. (1981) produced electron impact fragmentation patterns and used values of mlz 288 and mlz 227 for primary identification, since no molecular ion was seen. These fragments represent a loss of SOz and S 0 2 + H from the methylated molecule. A collaborative study of these procedures was reported by Malanoski er al. (1981). The GClMS approach provided the most reliable data, but GC on its own was also satisfactory under appropriate controlled conditions. Both methods were accepted as AOAC official first action status. Matusik et al. (1982) have studied the determination of sulphonamide metabolites. More recent studies have been reported by Paulson et al. (1985) and by Brumley ef al. (1983). A GUMS method for the determination of oxolinic acid in fish tissues has been described by Takatsuki (1991). Selective ion monitoring of ions at mlz 204,219 and 176 was practised and a detection limit of 1 p.p.b. was achieved. High-pressure liquid chromatography Since most antibiotics are relatively large, involatile and thermally unstable molecules, HPLC offers many advantages for their detection and determination. Unfortunately, many antibiotics have limited sensitivity to the detectors available for use with HPLC columns. Few antibiotics exhibit fluorescence, although most do absorb at specific wavelengths in the UV region of the electromagnetic spectrum. Thus most applications of HPLC to date in this field have been concerned with monitoring relatively high levels of antibiotics and their decomposition products during production, after extraction from fermentation broths, or in pharmaceutical preparations, and used to detect levels of impurities as well as the active ingredient, or for the monitoring of levels in serum to ensure optimal therapeutic levels and to avoid toxic reactions during clinical trials. A comprehensive compilation of applications described in the literature has been produced by Drucker (1987), although most of the substances described are not used in veterinary practice. Whilst much of this work is not concerned with the determination of residues of antibiotics in feeding stuffs or in animal tissues, the basic chromatographic conditions and parameters described by the clinical chemists provide a starting point for the development of new methods of analysis for trace levels in foods and feeds. New methods of extraction and clean-up will be required. together with an increase in sensitivity at the detection stage, which may be achieved by concentration of extracts or derivatization to a fluorescent product. One advantage over clinical analysis is that the acquisition of large amounts of sample (e.g. 50 g) usually presents no problem to the food chemist, whereas serum 4.4.5

Sec. 4.4)

Methods for the detection of antibiotics

111

samples are often limited in volume to 0.5 ml or less. The clean-up stage is a critical part of the analysis, since fat and proteinaceous material must be removed before the extract is added to the chromatographic column. Since some antibiotics bind to proteins, consideration must be given to whether measurement of free or total antibiotic concentration is required. Bioassay systems will generally only record free antibiotic, as the bound form would not be free to diffuse during the test. Chemical measurements of total antibiotic concentration can be obtained, provided the protein-antibiotic complex can be broken, perhaps by hydrolysis or enzymatic treatment, prior to analysis. Adsorption of some antibiotics on to glass surfaces has also been reported by Anhalt and Brown (1978). Since most of the published work on the determination of antibiotics by HPLC relates to clinical applications, only brief details of the techniques will be described. Even though antibiotics comprise such a wide diversity of chemical structures, there are a number of common features in the HPLC methods which have so far been developed. Thus most workers have adopted reversed-phase systems with octadecyl bonded phases predominating, or separations based on ion-pairing chromatography. Since many antibiotics possess a lower molecular extinction coefficient, derivatization reactions with o-phthalaldehyde, l-fluoro-2,4-dinitrobenzeneo r dansyl chloride are used to enhance sensitivity. Some key applications have been summarized in Table 4.5. A study of factors affecting the determination of p-lactam antibiotics by HPLC has been published by Huang et a/. (1991). A number of HPLC procedures have been published describing the determination of sulphonamides in animal tissues. UV detection has been carried out at several wavelengths, and Long et af. (1990) employed a photodiode-array instrument to detect eight sulphonamides in pork. Aerts et af. (1988) described a complex continuous flow technique to monitor for the presence of sulphonamides in eggs, meat and milk. A post-column derivatization step using dimethylaminobenzaldehyde was included and in most cases recoveries better than 80 per cent were achieved. The determination of neomycin in milk by HPLC was investigated by Shaikh and Jackson (1989). They used a reversed-phase column with an ion-pairing mobile phase. After post-column derivatization, a fluorimetric detector enabled levels down to 0.15 p.p.m. to be measured. Although a number of papers purport to show reliable methods for the determination of tetracyclines in animal tissues (Table 4.5), in most cases the chromatographic peak shapes are poor and recoveries are variable at the low levels encountered in residue analysis. Farrington er af.(1991) have recently exploited the reaction between tetracyclines and divalent metal ions to form chelates for clean-up of tissue extracts before determination using a standard HPLC procedure. The technique was satisfactory at the 50 p.p.b. level but more variable when extended to 10 p.p.b. It was tested with a wide variety of tissues. Whilst most antibiotics can be detected and determined by HPLC, few of the methods proposed have gained universal acceptance and few have been subjected to collaborative study. There is therefore still some way to go before reference methods based on HPLC will be available for most antibiotics.

u.p,

Fermentation Iwoth

Matrix

Oxolinic acid Pcnicillins G .V

Nosihcptidc Nystatin

Nconiycin

Griscofulvin

C,. cl:,.c2

Gcnt;iinicin

Erytlironiyciii A. B. C

Efrotoniycin

C p I M Sphcr, Cl,, X~lm C, Zorhiix

BuAc/huffe r

McOH

Powdcrs Tissue Milk St;ind;ird niixturcs Fish

Fcrincntation broths

DCM CHCI.,

Nuclcosil C,. 7 pin CH,,CNlCH,OIl/ acid Buffcr/McOH Lichrosorh RPX , 10 pni 20-SO0C

BufCcrlMcCN CIS Lic hrosorh SI- 100. CHCI,-TIIF. ~ t c . 5 Iiin ALI . ODs, 5 pin Buffcr. p H X c,, 5 ~ l n l Ion-p;iirlMeOH A q ./McOCl/THF DMSOIMcOH Vydac KP

Aq./McCN

Scriini Oiiitincnts

ClllCtS

Fccds

UV2,,-2,1,

cv

93% R. 1.6%

91-100'%, R RSD 6% RSD 0.6% RSD 1.4%

5 p.p. h.. SX-X5'% R

Nachtmann (1979)

White and Zarcmho (1981) Shaikh er nl. (1985) Shaikh idJackson (1989) Mcchlinski and Schaffncr ( 1974) H o r i i e/ n/. (19x7)

Hackitt and Dusci (1978) Tsuji cr ( I / . (1979)

Anhalt and Brown (107X) Barends C I ( I / . (1980) Bailcy and Brittain (1973)

Tsuji and Goetz (l97Xa) Tsuji and Goetz (W78h)

Strong (19x6)

Will er ( I / . (1980) Kcukcns er ( I / . (1986)

ODS

Er Ac/McCN Ail. or EtAc

BuffcrlMcOH iso. propano1 c t hc r/ McOH Aq.lMcOl1 BufCcdCH,CN

Tsuji and Rohcrtson (1975)

McGahrcn o ( I / . (19x3)

Rcfcrcncc

I-c Bcllc CI ( I / . (1979) Russcl (1978)

0.01 p.p.ni., 71% R

Pcrforniiince criteria

RP-2. I0 Iim NucIcosiI 10-N1-1

UV,,,

Dctection

McOl1

Uuffcr/McCN

Mobilc phase

Vigh and InczCdy (1976)

p-Bond;ip;ik, ionpair Clx,35°C Bondapak, CIS

Chrom;itogriiphy

Gr:itlicnt McOl-I/ UV,,, I)uffcr Micropiik-NIil 50°C Cyclohcx;inc/dioxiin UV2,

Ext riict ion

McCNlMcOl1 :1q./I I,PO, McCNIMcOl-1 Mobilc phwc Il-Botidapilk. CIS Powdcrs buffer or LiChrosorh RP-IX, 5 pi,70°C McCNlhuffcr Sephadcx/huffer Ion-pair. CIS Aq./MeOH Scruni McCN C,, Buffcr/McCN Scruni Pcrniaphiisc ETH CHClJhcxanc Fcrmcntation pro-

Milk Meat

Uiicitr;icin A - G I'h;irin;iccutic;il prcpwitioiis Chloriiniphcni- Iiitcrmcdiiitcs col Ph;iriii;icciiticals. aninial tissues

A\wp;ircin

Compound

Table 4.5 - HPLC of antibiotics

z.t:

E

a

f.

1 3

--

Sec. 4.41

Methods for the detection of antibiotics

113

F= lluorcscciicc tlctcction OPA=o-phtli;il;ildchydc DNFB=tlinitrofluorol~ciitlchydc

ODS=C,, RP= rcvcrsc phiisc

Vitginiiiiiiyciii

V;inroinycin

'l'ylosin

HCllEDTA

R = rccovcry RSD= rcliitivc standard dcviation CV=cocflicient of variation

Mohilc phasc

Dctcction

UV,,, C2, C,. C,,, BUf fc rl S-I0 Iim dicth;iiiol;iminc HCllMcCN Polymcric. 5-10 itin PhosphoriclMcOLil UV,,,, MeCN Mg gluconiitc Pellioncx CP-128 EDTA/bullcr/EtOH UV,,, Ph;irm;iccuticiils 'Tissues EDTAlbuffcr RP-8, 10 F m MeOHlMcCN UV,,,, McCN CI, BufferlMcCNI UV,,, Mciit. eggs McOH uv,,, Fcrnicntalion broth Affinity coluinns Ultriisphcrc ODS. BuffcrlMcCN S pm gradient Piircnt acid degrxlii4 systems uv,.,, tion ~ir(iilucts N . PhiisclR. Phasc UVXJ Livcr McOl-llhuffcr

Plasiiiii, urine. tissues l'issucs. scriini

Chromatogr;iphy

Table 4.5 (continued)- HPLC of antibiotics

l'ct rxylincs

Extraction

Matrix

Compound

6I-X3"/u R

Ashworth (1985)

80% R Q 0. I p.p.ni. 83-IoWu R

ei

id.

'Thomas and Newland ( 1987) Gottschiill CI t i / . (19x7)

( 1987)

Folcnii-Wasscrmen

Butrctfield el a/. (1975) Ikai el id. (1987) Moats (1985)

Motits (1986)

Rcfcrcncc

Performance cr i tc r i ii

t:

B

ir=. z

c P

L

Sec. 4.51

Residues in tissues

115

4.4.6 Card Tests Immunoassay kits are now produced commercially in the form of a card supplied with reagents, which makes the test ideal for quick screening in the field. The antiserum raised against a specific analyte (see 2.5) is bound to a support, which is usually a fibre-glass matrix. The card has small windows through which the reagents and sample or standard solutions can be added by pipette. The sample (or standard) is first added and allowed to react with the antibody absorbed onto the support. A solution of analyte-nzyme conjugate is then added. If analyte was present in the unknown, some of the binding sites will have been blocked. Free sites will react with analyte-enzyme complex. Addition of substrate produces a reaction with the enzyme and a colour. The strength of the colour is inversely proportional to the analyte concentration. The test is quick and easy to perform as a check on the presence or absence of residues. Assays have been developed for chloramphenicol (CAP), gentamicin, neomycin, sulphamethazine and tylosin. Detection limits fall in the range 1-50 p.p.b. The analyte must first be extracted from the tissue into solution. I n some cases a simple partition to remove fat is advisable.

4.5 RESIDUES IN TISSUES Whilst there are many analytical papers reporting the development of methods of analysis for antibiotic residues in tissues. few of these papers describe the incidence of residues present in food products on the market. The most comprehensive survey was carried out between 1977 and 1979 by Smither et al. (1980). These authors examined a total of 5442 home-produced meat samples and found that only 34 (0.63 per cent) showed any inhibitory activity in t h e FPT. Subsequent examination by electrophoresis established that only two of the samples actually contained true antibiotic residues. Twelve samples contained a naturally produced inhibitory substance and had therefore given a false-positive reading in the FPT. Of 972 imported meat and offal samples examined, 85 gave a positive result in the FPT and were subsequently shown to contain no antibiotic residues. In a later survey carried out between 1980 and 1983, some 3400 animals (cattle, calves, pigs and sheep) were examined and positives were found in about 1 per cent of animals; sheep showed a lower incidence than cattle or pigs (MAFF, 1987). Antimicrobial activity was detected more frequently 'in kidney tissue than in the meat. Sulphadimidine was detected in 40 out of 339 kidney samples taken from calves and pigs and an incidence of 21 per cent was found in pig kidneys. Levels found in pig kidneys ranged from 0.01 to 6.0 p.p.m. Small amounts of tetracycline residues were found in fish but no residues of chloramphenicol were detected in kidneys from cattle, pigs or sheep. Similar results were reported in a later report. although a steady fall in the numbers of samples containing more than 0.1 p.p.m. of sulphadimidine was noticed. More widespread use of the tetracyclines was also reported. The effects of cooking and cold storage on residues of ampicillin, CAP, oxytetracycline, streptomycin and sulphadimidine were investigated by O'Brien et al. (1981). They found that, in geeneral, the effects were varied but usually very small.

116

Antibiotics

[Ch. 4

The Codex-recommended ADIs and MRLs for benzyl penicillin and oxytetracycline are given in Table 4.6(a). In the main these limits are determined primarily by the limit of detection that can be achieved by existing analytical methodology. Some UK recommended limits are given in Table 4.6(b).

Table 4.6(a) - Codex recommended ADls and MRLs AD1 MRL mglperson per day (all species) (p.p.m.)

Antibiotic Benzylpenicillin

0.03

Oxytetracycline

(LO.003

0.05 liver, kidney, muscle 0.004 milk 0.1 muscle 0.3 liver 0.6 kidney 0.01 fat 0.1 milk 0.2 eggs

Table 4.6(b) - UK Veterinary Products Committee recommended MRLs (p.p.m.) Tissue ~~~~

~

Chloramphenicol Chlortetracycline Neom ycin Oxytetracycline Sulphonamides (total) Tetracycline

~

~

~

~~

0.01 0.05 0.5 0.25 0.1 0.5

Milk

Eggs

0.01 0.02 0.15

-

~~

0.1

0.1

0.1

0.05 0.2 0.3 0.1 0.3

REFERENCES Aerts, M. M. L., Beek. W. M. J . & Brinkman, A. Th. (1988) Sulphonamides in egg, meat and milk using post-column derivatization with dimethylaminobenzaldehyde. J. Chromatogr., 435 97-1 12. Alawi, M. A. & Russel, H. A. (1981) A simple, sensitive and specific HPLC amperometric screening method for trace levels of sulphonamides in liver, kidney. and muscle tissues. Chrornatographia, 14, 704706. Analytical Methods Committee (1986) Collaborative study of methods for the detection of residues of monensin in chicken tissues. Awulyst, 11 1, 1089-1093.

4.6

Sec. 4.61

References

117

Anhalt, J. P. & Brown, S. D. (1978) High performance liquid chromatographic assay of aminoglycoside antibiotics in serum. Clin. Chem., 24, 1940-1947. Ashworth. R. B. (1985) Liquid chromatographic assay of tetracyclines in tissues of food-producing animals. J . Assoc. Of5 Anal. Chem., 68, 1013-1018. Asukabe, H.. Sasaki,T., Harada, K.-I., Suzuki, M. & Oka, H. (1984)Fluorodensitometric determination of polyether antibiotics. J. Chromarogr., 295,453-461. Asukabe, H., Sasaki,T.. Harada. K.-I., Suzuki, M. & Oka, H. (1987) Simultaneous fluorodensitometric determination of polyether antibiotics. J. Chrornatogr., 396,261-271. Bailey, F. & Brittain, P. N. (1973) High efficiency liquid chromatography in pharmaceutical analysis. J. Chromatogr.,83,431-437. Barends, D. M., van der Sandt, J. S. F. & Hulshoff, A. (1980) Micro determination of gentamicin in serum by high performance liquid chromatography with ultraviolet detection. J . Chromatogr., 182,201-210. Bens, G. A., van den Bossche, W. & de Moerloose, P. (1979) Separation and determination of components of spiramycin in bulk powders and in pharmaceutical preparations by high performance liquid chromatography. Chromatographia, 12,294298. Bogaerts. R. & Wolf, F. (1980) A standardized method for the detection of residues of anti-bacterial substances in fresh meat. Fleischwirtschaft, 60,672-673. Bossuyt. R., Penterghem, R. van & Waes. G. (1976) Identification of antibiotic residues in milk by TLC. J. Chromatogr., 124, 37-42. British Standard 5283 (1986) British Standards Institution, London. Brumley, W. C., Min. Z., Metusik, J . E., Roach, J. A. G., Barnes, C. J., Sphon, J. A. & Fazio, T. (1983) Identification of sulfonamide drugs in swine liver by collision-induced dissociation/mass analyzed ion kinetic energy spectrometry. Anal. Chem.. 55. 1405-1409. Butterfield. A. G., Hughes, D. W.. Wilson, W. L. & Pound, N . J. (1975) Simultaneous high speed liquid chromatographic determination of tetracycline and rolitetracycline in rolitetracyline formulations. J . Pharm. Sci., 64,316320. Corry, J. E. L., Sharma. M. R. & Bates, M. L. (1983) In: Antibiotics: assessment of antimicrobial activity and resistance, Russell, A. D. & Quesnel, L. B. (eds). Academic Press, London, pp. 349-370. Drucker, D. B. (1987) Microbiological applications of high-performance liquid chromatography. Cambridge University Press. Farrington. W. H. H.,Tarbin. J.. Bygrave, J. &Shearer, G . (1991) Analysisof trace residues of tetracyclines in animal tissues and fluids using metal chelate affinity chromatography/HPLC. Food Addit. Contam., 8. 55-64. Folena-Wasserman. G.. Sitrin, R. D., Chapin, F. & Snader, K. M. (1987) Affinity chromatography of glycopeptide antibiotics. J. Chrornatogr., 392,225-238. Formica, G . & Giannone. C. (1986) Gas chromatographic determination of avilamycin total residues in pig tissues, fat, blood, feces, and urine. J. Assoc. Off. Anal. Chem., 69.763-766. Frtres. D. & Valdebouze, P. (1973) MCthode d’identification des antibiotiques dans les aliments pour animaux par chromatographie en couche mince. J . Chromafop-.. 87, 300-304.

1 I8

Antibiotics

[Ch. 4

Ghebre-Sellassie. I . . Hem.. S . L. & Knevel. A. M. (1982) Separation of.penicillin and its major degradation products by ion-pair reversed-phase high-pressure liquid chromatography. J . Pharrn. Sci.. 71. 351-353. Gottshall. D. W.. Gombutz. C. & Wang. R. (1987) Analysis of tissue residues and comparative metabolism of Virginia mycin in rats. turkeys, and cattle. J . Agric. Food Chem., 35. 900-904. Haagsma. N.. Dieleman. B. & Gortemaker, B. G. M . (1984) A rapid thin-layer chromatographic screening method for 5 sulfonarnides in animal tissues. Ver. Qirurf..6. 8-12. HiiagSma. N . & Van de Water, C. (1985) Rapid determination of 5 sulphonamides in swine tissues by high-performance liquid chromatography. J . Chromarogr., 333, 2%-26 1 . Hackrtt. L. P. & Dusci. L. J . (1978) Determination of griseofulvin in human serum using high-performance liquid chromatography. J . Chromarogr., 155,206208. Hitching. G . H. (1961) A biochemical approach to chemotherapy, Trans. N Y Acud. Sci.. 23. 700-708. Horii. S . . Yasuoka. C. & Matsumoto, M. (1987) High-performance liquid chromatographic me!hod for the simultaneous determination of oxolinic, nalidixic and piromidic acids in cultured fish. J . Chrornarogr.,388,459-461. Horwitz. W. (1981) Analytical methods for sulfonamides in foods and feeds. 1. Review of methodology. J . Assoc. Off. Anal. Chem., 64, 104-130. Huang. H.-S.. Wiu, J.-R. & Chen. M.-L. (1991) Reversed-phase HPLC of amphoteric P-lactam antibiotics: effects of columns. ion-pairing reagents and mobile phase pH on their retention times. J . Chromarogr.. 564, 195-203. I k a i . Y . . Oka. H . . Kawamura. N.. Yamada, M., Harada, K.-I. & Suzuki, M . (1987) Systematic simultaneous analysis of residual tetracyclines in animal tissues using TLC and HPLC. J . Chrornatogr., 411.313-323. Johnston. R . W.. Reamer. R. H., Harris. E. W.. Fugate, H. G . & Schwab, B. (1981) A new screening method for the detection of antibiotic residues in meat and poultry tissues. J . Food Protectioti. 44, 828-831. Kiitz, S. E. (1986) Microbiological assay procedures for antibiotic residues. In: Agriculritrui trses of uttrihiorics. Moats, W. A. (ed.) ACS Symposium Series 320, American Chemical Society, Washington. DC, pp. 142-153. Kennedy. J . H. (1978) High performance liquid chromatographic analysis of fermentation broths: cephalosporin C and tylosin. J . Chrornatogr., 16,492-495. Keukens. H . J.. Beck. W . M . I. & Aerts, M. M. L. (1986) High-performance liquid chromatographic screening and confirmation methods for chloramphenicol residues in meat with off-line cartridge sample clean-up and on-line diode array UV-VIS detection. J . Chrornatogr.. 352.445-453. Korzybski. T.. Kowszyk-Gindifer, 2.& Kurylowicz, W. (1978) Antibiotics: origiti, /witire uiid properties. American Society for Microbiology. Washington, DC. Lebelle. M. J.. Young. D. C . , Graham. D. C . , & Wilson. W. L. (1979) Highperformance liquid chromatographic determination of chloramphenicol and 2amino- I-(IT-nitropheny1)-1.3-propanediol in pharmaceutical formulations. J . Chromurogr.. 170. 282-287. Linton. A. H. (1983) In: A~itibiotics:assessmetit of anrirnicrobial acriviry and

Sec. 4.61

References

119

resistance, Russell, A. D. & Quesnel, L. B. (eds) Academic Press, London, p.

19. Long. A. R., Hsieh. L. C., Malbrough, M. S., Short, C. R. & Barker, S. A. (1990) Multiresidue method for the determination of sulfonamides in pork. J. Agric. Food Cliem., 38,423426. MAFF (1987) Anabolic, anthelmintic and antimicrobial agents. 22nd report of the Steering Group on Food Surveillance, HMSO, London. Malanoski, A. J.. Barnes, C. J . & Fazio, T . (1981) Comparison of 3 methods for determination of sulphamethazine in swine tissues: collaborative study. 1. Assoc. Off. Anal. Chem., 64. 1386-1391. Manuel, A. J . & Stellar. W. A. (1981) Gas-liquid chromatographicdetermination of sulfamethazine in swine tissues: collaborative study. J. Assoc. Off. Anal. Chem.. 64, 794-799. Matusik, J . E.. Barnes. C. J.. Newkirk, D. R . & Fazio, T. (1982) Evaluation of 3 methods for recovery of sulfamethazine metabolities from swine tissue. J . Assor. Off. Atiul. Cliem.. 65. 828-834. McGahren, W. J . . Leese. R. A., Barbatschi, F., Morton, G . O., Kuck, N. A. & Ellestad, G . A. (1983) Components and degradation compounds of the avoparcin complex. J. Aiitibiot., 36, 1671-1682. Mechlinski, W. & Schaffner. C. P. (1974) Separation of polyene anti-fungal antibiotics by high-speed liquid chromatography. J. Chromarogr., 99,619-633. Moats, W. A. (1983a) Determination of penicillin G , pencillin V. and cloxacillin in milk by reversed-phase high-performance liquid chromatography. J. Agric. Food Chem., 31.880483. Moats. W . A. (l983b) Determination and semi quantitative estimation of penicillin G and cloxacillin in milk by TLC. J . Agric. Food Chem., 31, 1348-1350. Moats, W. A. (1984) Determination of penicillin G and cloxacillin residues in beef and pork tissue by high-performance liquid chromatography. J. Chromarogr., 317,311-318. Moats. W. A. (1985) Chromatographic methods for t h e determination of macrolide antibiotic residues in tissues and milk of food producing animals. J . Assoc. Off. Attul. Chem.. 68. 980-984. Moats. W. A. (1986) Effect of the silica support of bonded reversed-phase columns on chromatography of some antibiotic compounds. J. Chromatogr., 366,69-78. Mourot. D., Delepine, B., Boisseau, J. & Gayot, G . (1978) Reversed-phase highpressure liquid chromatography of spiramycin. J. Chromatogr., 161,386-388. Moxon, R. E. D. & Dixon. E. J . (1980) Semi-automatic method for the determination of total iodine in food. Atialyst, 105,344-352. Munns. R. K.. Shimoda, W.. Roybal, J . E. & Viesra, C. (1985) Multiresiduemethod for determination of 8 neutral p-lactam penicillins in milk by fluorescence-liquid chromatography. J. Assoc. Off. Atial. Chem., 68, 968-971. Nachtmann. F. (1979) Automated high-performance liquid chromatography as a means of monitoring the production of penicillins and 6-amino penicillanic acid. Chrotnatographia. 12.380-385. Neidert, E., Saschenbreker. P. W. & Tittiger, F. (1987) Thin layer chromatographic/ hioautographic method for identification of antibiotic residues in animal tissues. J. Assoc. Off. Atial. Chem.. 70, 97-200.

120

Antibiotics

[Ch. 4

Nouws, J . F. M.,van Schothorst, M. & Zir, G . (1979) A critical evaluationof several microbiological test methods for residues of antimicrobial drugs in ruminants. Arch. Lebensmittel Hygiene, 30, 1-40, O'Brien, J. J . , Campbell, N . & Conaghan, T. (1981) Effect of cooking and cold storage on biologically active antibiotic residues in meat. J. H y g . Camb., 87, 5 1 1-523. Oka, H., Ikai, Y., Kawamura, N., Uno, K., Yamada, M.. Harada, K-I., Uchiyama, M., Asukabe, H. & Suzuki, M. (1987) Determination of 8 tetracyclines using thin-layer and high-performance liquid chromatography. J. Chromatogr., 393, 265-274. Okada, J., Higuchi, I. & Kondo, S. (1980) Determination of the disappearance rate and residual levels of monensin in chick tissues by quantitative thin-layer bioautography. J. Food Hyg. SOC.(Jpn),21, 177-183. Onji, Y ., Uno, M. & Tanigawa, K. (1984) Liquid chromatographic determination of tetracycline residues in meat and fish. J. Assoc. Off. Anal. Chem., 67, 1135-1 137. Owles, P. J. (1984) Identification of monensin, narasin, salinomycin and lasalocid in pre-mixes and feeds by thin-layer chromatography. Analyst, 109, 1331-1333. Parks, 0. W. (1982) Screening test for sulfamethazine and sulfathiazole in swine liver. J. Assoc. Off. Anal. Chem.,65,632-634. Parks, 0. W. (1984) Evidence for transformation of sulfamethazine to its N4glucopyranosyl derivative in swine liver during frozen storage. J. Assoc. Off. Anal. Chem., 67,566569. Patthy. M. (1983) Trace analysis of sulfaquinoxaline in animal tissues by highperformance liquid chromatography. J. Chromatogr., 275, 115-125. Paulson, G. D., Mitchell, A. D. & Zaylskie, R. G. (1985) Identification and quantitation of sulfamethazine metabolites by LC and GC-MS. J. Assoc. Off. Anal. Chem. 68, 1000-1006. Petz, M., Solly. R., Lymburn, M. & Clear, M. H. (1987) Thin-layer determination of erythromycin and other macrolide antibiotics in livestock products. J. Assoc. Off. Anal. Chem.. 70,691-697. Rouan, M. C. (1985) Review: antibiotic monitoring in body fluids. J. Chromarogr., 340,361400. Russel, H. A. (1978) Uber die Bestimmung von Chloramphenicol in tierischen Geweben durch HPLC. Chromatographia, 11,341-343. Schothorst. M. van, Leusden, M. van & Neuws, J . F. M. (1978) Antibiotic residues: regulations, tolerances and detection in the EEC. J. Assoc. Off. Anal. Chem., 61, 1209-1213. Seymour, D. & Rupe, B. D. (1980) High-pressure liquid chromatographic determination of sulfamethazine residues in beef tissues. J . Pharm. Sci., 69,701-703. Shaikh, B. &Jackson, J. (1989) Determination of neomycin in milk by reverse phase ion-pairing HPLC. J. Liq. Chromafogr.,12, 1497-1515. Shaikh, B., Allen, E. H. & Gridley, J. C. (1985) Determination of neomycin in animal tissues, using ion-pair liquid chromatography with fluorimetric detection. J. Assoc. Off. Anal. Chem., 68,29-36.

Sec. 4.61

References

121

Sharma. J. P. & Bevill, R. F. (1978) Improved high-performance liquid chromatographic procedure for the determination of tetracyclines in plasma, urine and tissues. J . Chromatogr.. 166, 213-220. Smither, R. (1978) Bacterial inhibitors formed during the adventitious growth of micro-organisms in chicken liver and pig kidney. J . Appl. Bacteriol., 45. 265-277. Smither. R. & Vaughan, D. R. (1978) An improved electrophoretic method for identifying antibiotics with special reference to animal tissues and animal feeding stuffs. J . Appl. Bacteriol., 44.421329. Smither. R., Lott, A. F., Dalziel, R. W. & Ostler, D. C. (1980) Antibiotic residues in meat in the UK; an assessment of specific tests to detect and identify antibiotic residues. J . t f y g . , Camb., 85, 359-369. Stout, S. J . , Stellar, W. A., Manuel, A. J., Poeppel. M. 0. & Da Cunha. A. R. (1984) Confirmatory method for sulfamethazine residues in cattle and swine tissues, using gas chromatography-chemical ionization mass spectrometry. J . Assoc. Off. Anal. Chem.. 67. 142-144. Strong. J . D. (1986) Determination of efrotomycin in feeds by HPLC, Analyst, 111, 853-855. Suhre, F. B . , Simpson, R. H. & Shafer, J . W. (1981) Qualitative/quantitative determination of sulfamethazine in swine tissue by gas chromatographic/electron impact mass spectrometry using a stable isotope labelled internal standard. J . Agric. Food Chem. 29.727-729. Swann Report (1969) Joint Committee oti the use of Antibiotics in Animal Husbandry and Veterinury Medicine. HMSO. London. Cmnd 4190. Takatsuki, K . (1991) GC-MS determination of oxolinic acid in fish usingselected ion monitoring. J . Chromatogr., 538, 259-267. Terada. H., Asanoma, M. & Sakabe. Y. (1985) High performance liquid chromatographic determination of penicillin G in animal tissues using an on-line precolumn concentration and purification system. J . Chromatogr.. 318, 299-306. Thomas. A. H. & Newland, P. (1987) Chromatographic methods for the analysis of vancomycin. J . Chromatogr.. 410,373-382. Thomas. M . H . . Epstein. R. L., Ashworth. R. B. & Marks, H. (1983) Quantitative thin layer chromatographic multisulfonamide screening procedure: collaborative study. J . Assoc. Off. Anal. Chem.. 66, 884-892. Tihova, D. & Peneva, V. (1982) A rapid thin layer chromatographic method for the determination of residual quantities of monensin in biological material. Vet.Med. Nauki. 19.52-56. Tsuji, K. & Goetz, J . F. (1978a) High-performance liquid chromatographic determination of erythromycin. J . Chromatogr. 147,359-367. Tsuji, K . & Goetz. J . F. (1978b) Elevated column temperature for the highperformance liquid chromatographic determination of erythromycin and erythromycin ethylsuccinate. J . Chromarogr., 157. 185-196. Tsuji, K. & Robertson, J. H. (1975) Improved high-performance liquid chromatographic method for the polypeptide antibiotics and its application to study the effects of treatments to reduce microbial levels in bacitracin powder. J . Chromarogr.. I 12,663-672.

122

Antibiotics

[Ch. 4

Tsuji, K . , Goetz, J . F., van Meter, W. & Gusciora, K. A. (1979) Normal-phase highperformance liquid chromatographic determination of neomycin sulfate derivaJ. Chromurogr.. 175. 141-152. tised with l-fluoro-2,4-dinitrobenzene, Vigh, G. & Inczedy, J . (1976) Separation of chloramphenicol intermediates by highperformance liquid Chromatography on MicroPak-NH1 columns. J . Chromafogr., 129, 8 1-89. Vilim, A. B., Larocque, L. & Maclntosh, A. I . (1980) Screening procedure for sulfamethazine residues in pork tissues. J. Liq. Chromurogr.. 3 , 1725-1736. Wal. J.-M.. Peleran J.-C. & Bories, G . F. (1980) High-performance liquid chromatographic determination of chloramphenicol in milk. J . Assoc. Off.Atial. Chem., 63, 1044-1048. Wenlock, R. W., Buss. D. H . , Moxon, R. E. & Bunton, N . G. (1982) Trace nutrients. 4. Iodine in British food. Br. J . Nutr., 47, 381-390. Whall, T. J. (1981) Determination of streptomycin sulfate and dihydrostreptomycin sulfate by high performance liquid chromatography. J. Chromatogr.. 219, 89-100. White, E. R. & Zarembo, J . E. (1981) Reverse phase high speed liquid chromatography of antibiotics, 111. Use of ultra high performance columns and ion-pairing techniques. J. Anlihiot.. 34.836-844. Zuidweg, M. H.J.. Ostendorp, J . G . & Bos C. J. K. (1969) Thin-layer chromatography on Sephadex for the identification of antibiotics. J. Chromafogr., 42, 5 52-5 54.

Coccidiostats

5.1

COCCIDlOSlS

Coccidiosis is a highly contagious infection of an animal caused by parasitic microbial organisms (protozoa) collectively known as coccidia, belonging to the genus Eirneriu in the class Sporozoa. Over 600species of coccidia have been identified but only nine are known to infect poultry, which are most susceptible owing to the warm humid atmosphere present in intensive rearing units on modern farms (Fig. 5.1). The most pathogenicspecies in chickens are E. tenefla.E . necarrix, E. maxima and E. brunetti. In addition to poultry, coccidiosis also affects pigs, cattle, sheep and game birds. However, the disease is usually less of a problem in animals other than chickens since they are reared less intensively with less chance of infection. These protozoa are intracellular parasites of epithelial tissues and are found both in vertebrates and in invertebrates, but are more common in the former. They are transmitted by faecal infection, where they exist in a highly resistant form known as the oocyst. When oocysts are swallowed the membrane is damaged, releasing sporozoites which penetrate the epithelial cells and multiply rapidly in both asexual and sexual cycles. Some enter the bloodstream and so are transmitted t o the liver and kidney. The reproductive cycle takes about seven to ten days and the parasites can multiply around 100000-fold in that time before being excreted. In its acute form coccidiosis rapidly causes death, but even in the subacute form the condition results in poor weight gain and reduced egg production. A closely related disease, particularly in turkeys, is known as histomoniasis or blackhead. It results from infection by the protozoal flagellate Hisfornonusmefeugridis and, unless treated, rapidly results in death. Hence, chemotherapy is practised using drugs prophylactically to control these diseases. So far it has not been possible to produce vaccines givingeffective immunity against all likely pathogenic strains. In any case, vaccination would present problems in practice as such large numbers of birds are involved (p. 22). Good management and hygiene also help to prevent the spread of the disease.

124

Coccidiostats

[Ch. 5

Fig. 5. I - An intensive rearing unit for poultry. Photograph kindly supplied hy thc Institute of Animal Physiology and Genetics Research, Edinburgh Research Station. Roslin. Midlothian.

The drugs used to control coccidiosis must have a wide spectrum of activity and must be used at such a level which does not allow resistant strains to be developed. At the same time t h e drug must not be toxic to the animal and should be rapidly metabolized so that residues in edible tissues are kept to a minimum. Whilst this problem could be controlled using mandatory withdrawal periods, under practical farming conditions such restrictions may not always be observed. As so many coccidiostats are available, many farmers switch from one compound to another to prevent the development of drug resistance over the years. Hence, most poultry are fed with feeds containing drugs for the whole, or majority, of their lives. Thus the

Sec. 5.21

Coccidiostats in use

125

health of the animals and the absence of residuesin edible tissuescan only be ensured by the availability and use of analytical methods for the determination of drugs in feeds and residues in tissues.

5.2

COCCIDIOSTATS IN USE

The major coccidiostats have no common chemical structure and therefore there are no group tests that can he used to screen either for compounds in a feed or for residues in the food. This is in complete contrast to the antibiotics discussed in the previous chapter, which can be detected, although not identified. on the basis of their antimicrobial activity. A semi-quantitative method for the identification of 25 drugs in animal feeding stuffs has been published by Cody eraf. (1990) and will be discussed in more detail later. Some compounds also possess antibiotic or antibacterial activity in addition to their role as coccidiostats. These products, e.g. the sulphonamides (apart from sulphaquinoxaline), have already been discussed in Chapter 4 . Other compounds, e.g. avoparcin, carbadox, flavomycin, halquinol, narasin, nitrovin, salinomycin, tylosin, tiarnulin, virginiamycin and zinc bacitracin, are classed as growth promoters and are described in Chapter 6. This chapter concentrates on those compounds whose primary function and use is as a coccidiostat and includes acinitrazole, amprolium, arprinocid, buquinolate, clopidol, decoquinate, diaveridine, dimetridazole, dinitolmide, ethopabate, furazolidone, halofuginone, ipronidazole, lasalocid, methylbenzoquate, monensin, nicarbazin, nitrofurazone, pyrimethamine, robenidine, ronidazole and sulphaquinoxaline. Not all these compounds are actively used today although many are still licensed. Some information on the compounds has been collected together in Table 5.1. The uses and methods of analysis for some individual compounds will now be discussed. Named compounds Acinitrazole (Cyzine) This compound is used in the range 150-500 p.p.m. in turkey feed for the prevention and treatment of histomoniasis. A seven-day withdrawal period is advised to ensure that residues will be C O . 1 p.p.m. in tissues. The compound is metabolized to 5.2.1

5.2.1. I

N-(5-amino-2-thiazolyl)acetarnide.

Only methods based on polarography have been described for this compound. However, the technique is not reliable in the presence of organic co-extractants and would not be satisfactory for the determination of residues in foods. Amprolium Amprolium possesses limited activity against E. maxima and E. mivati and therefore is often used commercially in admixture with ethopabate (Amprolmix) or with both ethopabate and sulphaquinoxaline (Pancox). The normal dose is 125 p.p.m. of amprolium and 8 p.p.m. of ethopabate in feeds fed to day-old chicks up to three days before slaughter. Similar rates are used for turkeys.

5.2.1.2

[Ch. 5

Coccidiostats

126

0

I

I

I W

0 W

r 2

? J 5.

0

n

I

Sec. 5.21

127

Coccidiostats in use

n

E

0

8

128

Coccidiostats

z, 0

[Ch. 5

Sec. 5.21

Coccidiostats in use

I30

[Ch. 5

" X

Sec. 5.21

Coccidiostats in use

131

132

Coccidiostats

z,

0

(Ch. 5

Sec. 5.2)

Coccidiostats in use

133

Analytical methods for amprolium are currently unsatisfactory. The compound is highly charged and therefore only sparingly soluble in most organic solvents. It is usually extracted from feeds using aqueous methanol. Co-extractants are then removed by chromatography on an alumina column. On elution from the column, amprolium is reacted with 2,7-naphthalene diol, potassium ferrocyanide, potassium cyanide and methanolic sodium hydroxide to produce a purple colour measured at 530 nm (The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations, 1985). The limit of detection is only 40 p.p.m. and nitrofurazone interferes. The method requires the use of dangerous reagents, is time consuming and gives low recoveries from feeds. A more recent HPLC method for amprolium in poultry feeds (Vanderslice and Huang, 1987) uses post-column oxidation to a thiochrome derivative followed by fluorescent detection (Acx 339 nm, h,., 432 nm). Near- quantitative recoveries were obtained at 228 p.p.m. An alternative ion-pair HPLC method has been reported by Kentzer et al. (1988). No suitable methods are available for the determination of residues in tissues. 5.2.1.3 Arprinocid

This is a broad-spectrum coccidiostat, now withdrawn from the market for cornmercia1 reasons. An HPLC method for arprinocid in feeds in the range 30-120 p.p.m. was studied by the Analytical Methods Committee (1988). The method involves extraction with chloroform, passage through a silica cartridge and determination by reversed-phase HPLC using UV detection at 254 nm. Recoveries were satisfactory, except for feeds containing fish-meal or pelleted products. No methods are available for the determination of arprinocid in foods. Buquinolate Formerly used in feeds at 82-110 p.p.m.. often in association with arsenicals or antibiotics, the compound is tautometric at the 1,4 position. I t permits drug resistant strains to develop and is now little used. It has low toxicity, and a zero withdrawal period results in residues in tissues as low as 0.1 p.p.m. in muscle and 0.4 p.p.m. in liver. Analytically, the compound is extracted with chloroform, purified on an alumina column and hydrolysed with alkali to produce a more fluorescent compound (Cox et al. (1967).

5.2.1.4

5.2. I .5 Clopidol (metichlorpindol),Coyden This drug is administered to chickens, pheasants and partridge continuously at a rate of 125 p.p.m. until five days before slaughter. For rabbits the recommended dose is 200 p.p.m. In admixture with methylbenzoquate (Lerbek) the recommended composition is 100 p.p.m. clopidol and 8.35 p.p.m. methylbenzoquate for chickens and turkeys, and double this dose of each compound for rabbits. Clopidol is particularly active against E. [enella,E. necarrix, E. brunetti, E. maxima, E. acervulina and E. mivari. A method for the determination of clopidol in feeds was reported by Kutschinski in 1968 based on GLC. This method required the use of toxic reagents (diazomethane, benzene) and so HPLC is now preferred as no derivatization step is required. Kutschinski found that sample size was important to achieve good repeatability, 50 g

I34

Coccidiostats

[Ch. 5

being preferred to 10 g. No losses on storage were observed over 17 weeks. Soderhjelm and Andersson (1979) preferred an alumina column for clean-up prior to reversed-phase HPLC and U V detection at 254 nm. Good recoveries and repeatability were achieved. A spectrophotometric method was studied earlier by the Analytical Methods Committee (1974). All methods use alkaline methanol for extraction, as clopidol is insoluble in most common solvents except alcohol, or strong acids and bases. No methods have been published for the determination of clopidol in food products. 5.2.1.6

Decoquinate

Along with buquinolate and methylbenzoquate, this compound possesses the basic quinolone structure. Quinolones are highly active and possess low toxicity to man, so that only short withdrawal times are required. The metabolism of decoquinate has been studied by Craine ef ul. (I971), w h o found that the compound was rapidly excreted in the faeces without production of metabolites. In a separate study by the same team (Kouba ef ul., I97 1 ) residues in tissues reached a plateau after three days. Higher levels were found in liver and kidney than in muscle or skin. It is used at a level of 30 p.p.m. in feeds and to prevent the development of resistant strains can be mixed with arsenicals or antibiotics. A method for decoquinate in feeds was examined by the Analytical Methods Committee (1975a). Following extraction using 1 per cent calcium chloride solution in methanol, partition into chloroform and clean-up on a Florisil column, the extract was examined spectrotluorimetrically. Buquinolate and methyl benzoquate, being similar in chemical structure, interfere. although more than one such compound would not normally be present in t h e same feed. The method is applicable in the range 5-60 p.p.m. but care must be taken to check the activity of the Florisil used in t h e clean-up stage. 5.2.1.7 Diaveridine This compound is used primarily as a synergist with sulphaquinoxaline o r o t h e r sulphonamide drugs. A method for the detection of residues of both drugs in hen eggs and chicken tissues using HPLC has been published by Sakano ei al. (1981). Detection limits down to about 0.02 p.p.m. were achieved with recoveries in the range 53-78 per cent. 5.2.1.8

Dimetridazole

The drug is used in turkey feed in the range 125-500 p.p.m. to prevent histomoniasis and in pig feeds to prevent scouring. I t can be used in combination with other antimicrobial drugs but a five-day withdrawal period is required to ensure no residues are present in edible tissues. Dimetridizole is metabolized to form the 2hydroxy compound. An HPLC method for the determination of dimetridazole in pig feeds was published by Roybal el al. (1987). After extraction with methanol, the extract was examined on a C18column and the compound detected at 320 nm. Recoveries were almost theoretical over the range 0.1 to 93 p.p.m. A method of confirmation using capillary GC/MS has been described by Morris ef af. (1987).

Sec. 5.21

Coccidiostats in use

135

In 1985 the Analytical Methods Committee published a collaborative study of an HPLC method for residues in chicken tissue obtained following a trial where animals were given 250 p.p.m. in their feed up to slaughter. Only very low residue levels were detected in liver and in leg muscle but 23 p.p.b. was found in breast muscle. 5.2.1.9 Dinitolmide This compound is a coccidiostat added to animal feeds at 125 p.p.m. for chickens and between 125-187 p.p.m. for turkeys. It is active mainly against E. reneffu but also acts as a preventative against E. necarrix, E. acervulina and E. maxima. I t has been used in admixture with a number of other compounds and antibiotics. I t is metabolised to 3-amino,5-nitro-o-toluamide in chickens. This metabolite is bound to tissue constituents unless released by digestion with ficin. The parent compound and its metabolite can be extracted from tissues with acetone, subjected to clean-up on an alumina column and determined colorimetrically (Smith er af., 1961; Thiegs et u f . ,

1961).

Ethopabate This additive is active especially against E. muximu and E. brunetti, but not against E. renefla. Hence, it is usually incorporated into mixtures with amprolium and sulphaquinoxaline. Feeds contain only small amounts of ethopabate in the range 4-8 p.p.m. It can be determined in feeds down to 2 p.p.m. by extraction with aqueous methanol, followed by acidification and partition into chloroform. This extract is washed first with alkali, then with water before concentration and hydrolysis with hydrochloric acid. The free amine thus formed is diazotized and coupled with N-2aminoethyl-1-naphthylamineand the compound extracted into butanol. The absorbance is measured at 555 nm (The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations. 1985). 5.1.1.10

5.2. I . I I Furazolidone and Nitrofurazone These substances are added to animal feeds in the range 8-220 p.p.m. to stimulate growth and for the prevention and control of disease. Adverse reactions have been observed both in man and in animals. Furazolidone is thought to be a carcinogen and so no detectable residues are permitted in edible tissues in some countries. The compound is unstable to light and is also rapidly metabolized to a number of products, which are excreted in the urine. However, radiolabelled studies found that some of the activity could not be extracted from the tissues and was possibly bound to DNA (Vroomen et al., 1986). A method for the determination of furazolidone in feeds was published by Jones er al. in 1978. The drug was extracted with acidified methanol and then partitioned into dichloromethane. Determination was achieved by HPLC with UV detection at 360 nm. Recoveries generally fall in the range 90-100 per cent for commercial pig and poultry feeds. A similar approach was recommended by Cieri (1979). Several workers have reported methods for the determination of the furazolidones in animal products. Vilim and Maclntosh (1979) used HPLC to determine

136

Coccid iostats

[Ch. 5

nitrofurazone in milk. Following a simple extraction with ethyl acetate the compound was determined at 365 nm after separation on a C18column. The detection limit was 5 p.p.b. but recoveries were only 57-67 per cent owing to protein binding. Confirmation of identity was achieved by El mass spectrometry. Results from two cows treated with 200 mg of nitrofurazone were included. After six milkings, residues were found to be below 5 p.p.b. Methods using reversed-phase HPLC for the determination of the nitrofuran derivatives in tissues have also been reported by Hoener et a[. (1979). Sugden er al. (1983) and by Winterlin eral. 1981. Giovanni et af. (1987) determined furazolidone in eggs on sale in the market; 90 per cent of samples tested gave a positive result. The mean content found was 74.5 k 64.2 p.p.b. The maximum level found was 276.5 p.p.b. In some samples, residues of chloramphenicol were also present. Aerts et al. (1990) have reported a complex dialysis and column-switching automated procedure that can detect nitrofuran residues at levels in the range 1-5 p.p.b. with recoveries of 75-90 per cent for meat and eggs. An HPLC method for the determination of furazolidone in salmon tissue was developed by Samuelsen (1990). This compound is used particularly in Japan in fish breeding as a growth promotant and for the control of disease. The method described could detect levels down to 5 p.p.m. with a recovery approaching 95 per cent. 5.2.1.12

Halofuginone (Stenorol)

This compound is usually incorporated into poultry feeds as the hydrobromide at a concentration of 3 p.p.m. I t should not be fed to laying birds, guinea fowl, ducks o r other game birds. A five-day withdrawal period is advised for broilers and seven days for turkeys. The substance is active against E. renella, E. necatrix, E. acervufina, E. brunerri and E. maxima in broiler chickens and E. maleagrimiris, E. adenoides, E . gallopavonis, E. meleagridis and E. dispersa in turkeys up to 12 weeks of age. It is incorporated in a gelatin-based coating in a maize starch base. Hence methods of extraction from feeds require treatment with a hot aqueous medium to dissolve this coating prior to partition into an organic solvent. The determination of halofuginone as the free base in feeding stuffs has been reported by the Analytical Methods Committee (1983a) based on the method published by Anderson el al. (1979). After extraction with ethyl acetate and partition into hydrochloric acid, the compound was concentrated using a macroreticular resin. HPLC with a U V detector was used to determine the final concentration of halofuginone. Recoveries were better than 80 per cent, although slightly lower levels of halofuginone were found in pelleted feeds and after storage for two months. A similar .approach was used by the Analytical Methods Committee (1984) to determine residues of halofuginone in chicken tissue (liver, kidney, breast muscle, skin and fat) down to a level of 0.1 p.p.m. Sep-Pak C18cartridges were used for clean-up prior to HPLC on a reverse-phase column. Experiments with ‘‘C-labelled compound established that the extraction from liver was 84 per cent complete, whilst that from kidney was 93 per cent complete. For the entire method, recoveries in the range 64-74 per cent were obtained and were considered satisfactory for this type of work. Results from a feeding trial in which chickens were fed a commercial feed containing 3 p.p.m. of halofuginone produced tissues after slaughter containing

Sec. 5.21

Coccidiostats in use

137

lower than expected levels of the drug. Liver was found to contain about 0.2 p.p.m. with 0.15 p.p.m. in kidney. Levels in muscle and fat were much lower, e.g. 0.02 p.p.m. 5.2.1.13 lpronidazole This compound is recommended for the treatment of blackhead in poultry and dysentery in pigs by incorporation into feeding stuffs at a level of 40-80p.p.m. It also improves weight gain and feed efficiency. Up to 250 p.p.m. has been used to control outbreaks. A four-day withdrawal period is advised to ensure residue levels below 2 p.p.b. in tissues. The compound is unstable in the light and in the animal it is metabolised to l-cu,cu--trimethyl-5-nitroimidazole. Ipronidazole is determined in feeding stuffs by extraction with toluene, partition into acid and back-extraction into alkaline toluene before separation and detection by gas chromatography with an electron-capture detector. Dimetridazole and ronidazole do not interfere (Analytical Methods Committee, 1983b). The method of Roybal et al. (1987) can also be used.

5.2. I . I4 Lasalocid (A vatec) This drug is added to broiler chicken feeds as the sodium salt for the prevention of infections caused by E. necatrix, E. tenella, E. acervulina, E. brunetti, E. maxima and E. mirvati. Likely infections in turkeys include E. meleagrimitis, E. gallopavoris, E. adenoides and E. dispersa. It belongs to the group known as ionophores, as a result of its ability to combine with. monovalent and divalent ions. This property enables water-soluble ions to pass through lipophilic cell membranes present in the parasites, so changing internal osmotic pressures and causing the death of the organism. Lasalocid is added to feeds in the range 75-125 p.p.m. The drug is non-toxic and rapidly metabolised in the animal. No withdrawal period is required in the USA. N o strains resistant to lasalocid have been detected. Lasalocid is also used as a growth promotan't in cattle (see Chapter 6). The compound can be determined in feeding stuffs by HPLC using a fluorescence detector. The method is very rapid since the feed can be extracted directly with mobile phase and then a portion of the extract is transferred to the chromatographic column. Theoretical recoveries were achieved over the range 8-120 p.p.m., with a coefficient of variation as low as 2.68-3.35 per cent. 5.2.1.15 Maduramicin ammonium This substance is obtained as the ammonium salt of a polyether monocarboxylic acid produced by Actinomadura yumaensis. It is permitted in chicken feeds at a level of 5 p.p.m. but its use is prohibited within seven days before slaughter. It must not be fed to equines. The sodium salt (C47H7YHa017) has also been prepared. Maduramicin acts to control coccidiosis resulting from infections of E. necarrix, E. tenella, E. acervulina, E. brunetti, E. maxima and E. mivati. It is generally active against Grampositive and Gram-negative organisms. The compound should not be confused with maduramycin (C28H2201,,) produced by Actinomadura rubra. The drug can be determined in feeding stuffs at levels of 5 p.p.m. following extraction, derivatization with dansylhydrazine and chromatography on a reverse-

138

Coccidiostats

[Ch. 5

phase column with a fluorescent detector (Gliddon etal., 1988). The compound is not particularly sensitive to a UV detector. This method employs dichloromethane for extraction in which molecular sieves are added to reduce the moisture content of the feeding stuff which, otherwise. would lead to reduced recoveries. 5.2. I . 16 Methylbenzoquate (Nequinate) Statyl This compound is a broad-spectrum coccidiostat added to poultry feeds at around 10 p.p.m. I t is often used in conjunction with other coccidiostats, especially clopidol (metichlorpindol), incorporated at 125 p.p.m. A method for the determination of methylbenzoquate in feeds has been published by Merson etal. (1985). The drug was extracted using 2 per cent methane sulphonic acid in methanol, as most other organic solvents are not very effective (Table 5.2). After partition into chloroform, interferents are removed by ion-exchange chromatography and a second partition into chloroform. The determination is completed by HPLC on a reversed-phase column and a UV detector at 265 nm. The detection limit was 1 p.p.m. and recoveries of greater than 95 per cent were obtained at 5-10 p.p.m. 5.2.1.17

Monensin (Romensin, Rumensin) and other ionophores (narasin, salinomycin) Monensin is a natural product produced by the fermentation of Streptomyces cinnamonensis. Like lasalocid it affects the transfer of sodium and potassium ions through the cell membranes. It also has a dual role both as a coccidiostat in poultry and as a growth promotant in cattle. I t is rapidly absorbed, metabolized and excreted, but a three-day withdrawal time is recommended for poultry. It is used in poultry feeds as a coccidiostat up to 110 p.p.m. Kline et al. (1970) proposed a microbiological assay for the determination of monensin in feeds using Bacillus subtilis, whilst Golab et al. (1973) described a colorimetric procedure based on the reaction with vanillin. Donoho and Kline (1968) used a semi-quantitative thin-layer bioautographic method for t h e determination of monensin in tissues and the procedure was later modified by Okada et a / . (1980). Tihova and Peneva (1982) used p-anisaldehyde as the visualization reagent whilst Owles (1984) reported a TLC method that would identify separately monensin from lasalocid, narasin and salinomycin. T h e Analytical Methods Committee (1986) examined several of these methods but no one technique was preferred. Levels of monensin down to 0.1 p.p.rn. could be detected but recoveries from fat were generally low. The separation of the four ionophores on a TLC plate was described. An ELISA method for monensin in cattle plasma was developed by Heitzrnan etal. ( 1986). Okada et a f . (1980) also investigated the disappearance rate of monensin from chicken tissues following administration of 80, 100 or 120 p.p.m. in the feed. N o residues in liver. muscle or kidney were detected at 24 hours or more after withdrawal, or in fat after 48 hours following withdrawal. Narasin is used similarly in feeds up to a level of 60-80 p.p.m. but a withdrawal period of at least five days before slaughter is advised. It is active against E. ucervulina, E. brunetti, E . maxima. E. mivati, E. necatrix and E. tenella.

B.p.1. ("C) UV cut-off (nm)

DChl = dichloronicthiinc

+ + + = > 90'%rccovcrcd + + = > 75% rccovcrcd

Acinitrazolc Aniproliuni Arprinocid Buquinoliitc Cirhadox Clopidol Dccoquinatc Diavcridinc Diinctridazolc Dinitolinidc Ethopahatc Furnzolidonc Hiilofuginonc Ipronidazolc Met hylbcnzoquatc N ifursol Nit rofurazonc Nit rovin 0l;iquindox Pyrimethiiininc Rohcnidine Ronidiizolc Sulpliiidiinidinc Sulpliiinitriin Su1phiiquinox;iliiie

Drug

-

+++ +++ +++ +++ ++

+

-

++ +++

-

++

+

++ +++ +++ +++

rccovcrcd - = < SO"% rccovcrcd DMF = dinicthylk~rniniiiitlc

+ = S0-75'%

- - = < 10'% rccovcrcd

+++ -+++ +++ +++ _+++ +++ +++ +++ +++ + +++ +++ ++

+ + +++ +++ + +++ +++ +++ +++ +++ + +++ __ +++ +++ + +++ +++ +++ +++ +++ +++

+++ __ +++ + ++

+

+++ +++

_-

+ + +++ ++

62 245

82 190

56 330

--

Chioroforin

Acctonitrilc

Acetone

solvcllt

++ +++ +++ +++ ++ +

-_

++ + +++ +++ +++ +++ +++ +++ +++ ++ ++

+++ -_ +++

233

42

DCM

Table 5.2 - Extraction of drugs by various solvents at a concctitrntion of 40mg/l

+++ +++

+++ +++ +++ + +++ +++ +++ +++ +++ + ++ + ++ +++ +++ ++ +++ ++ + ++ ++ +++ +++

I53 268

DMF

-

+++ +++ +++ +++ +++ +++ +++ +++ ++ +++ +++ _+++ +++ +++ +++ +++ +++ +++ +++ + +++

205

Mct hanoll watcr 50:50

W 9

-

(D

5l

-.a

140

Coccidiostats

[Ch. 5

Salinomycin is added to chicken feeds in the range 5&70 p.p.m. and also needs a withdrawal period of five days. The ionophores are extremely toxic to horses. 5.2.1.18 Nicarbazin Nicarbazin is an equimolecular mixture of 4.4’-dinitrocarbanilide (DNC) and 2hydroxy-4.6-dimethylpyrimidine(HPD). It is used in chicken feeds at a level of 100-125 p.p.m. and is fed continuously up to four weeks of age. The mixture is active against E. necatrix, E. tenella, E. acervulina, E. maxima and E. brunetti. It should not be fed to breeding or laying hens owing to adverse effects on shell colour. yolk pigmentation and hatchability. The US FDA permits a residue level of 4 p.p.b. in uncooked chicken muscle, liver, skin and kidney. To achieve this level a withdrawal period of seven to nine days is required. Macy and Loh (1984) have developed an HPLC method for the determination of both constituents of the drug in feeding stuffs and in pre-mixes. The DNC fraction is detected by UV at 340 nm following chromatography on a CIScolumn. The HPD constituent is determined using the same chromatographic system but with the UV detector set at 305 nm. Recoveries of 101 per cent and 87 per cent respectively were obtained for the two fractions. A method for the detection of DNC in eggs has been published by Vertomrnen et al. (1989). Samples were extracted with acetonitrile after acidification with acetic acid. Clean-up was effected using Bond-Elut solid-phase columns and the eluent examined by reversed-phase HPLC and a UV detector at 360 nm. Recoveries varied from 88 to 116 per cent, over the range 2.5-25 p.p.b., the coefficient of variation being better than 5 per cent above 10 p.p.b. 5.2. I . 19 Nitrofurazone See furazolidone, section 5.2. I . 12. 5.2.1.20 Pyrirnetharnine This drug contains the pyrimidine structure and is closely related to arnprolium, diaveridine and ethopabate. It is a constituent of Supracox. along with sulphaquinoxaline, amprolium and ethopabate, and has also been used with sulphaquinoxaline alone in a product, known as Whitsyns. In poultry and rabbit feeds, the drug is present at a concentration of 5 p.p.m. It is almost insoluble in water and only slightly so in alcohol or ethylene glycol. Determination of pyrimethamine in feeds can be achieved with GLC (Cala et al., 1972) using an electron-capture detector down to 0.1 p.p.m. with 86 per cent recovery. Confirmation was achieved by using “C-labelled drug and by G U M S . Alternatively, the procedure of Harris et al. (1977a) can be used, and the method has been evaluated by the Analytical Methods Committee (1981). A TLC procedure for the determination of pyrimethamine in tissues has been published by De Angelis et al. (1975). 5.2.1.21 Robenidine (Cycostat) This compound is fed to poultry at a level of 33 p.p.m. and is effective against all the major species of Eimeria. I t is also used to prevent intestinal coccidiosis in rabbits in

Sec. 5.31

Multi-detection methods for coccidiostats

141

the range 50-66 p.p.m. A six-day withdrawal period is required and the drug should not be fed to laying hens and it may also taint the flesh of broilers. It has been used in conjunction with arsenicals. A method for the determination of robenidine in feeds has been described by the Analytical Methods Committee (1975b). It involves extraction with acidified acetone, purification o n a basic alumina column and spectrophotometric determination at 440 and 550 nm. The difference in absorption of these two wavelengths is related to the concentration of robenidine. Although the method is sensitive down to 3 p.p.m.. grass meal, nitrofurazone, acinitrazole and dinitolmide may cause interference. 5.2.1.22 Ronidazole This drug is used to control histomoniasis infections in poultry by addition to feed at a level of 60 p.p.m. I t is a carbamate and forms yellow crystals which are soluble in many solvents but are unstable in basic solutions. Methods based on polarography or TLC are available for its determination in feeds. A GLC method was published by Harris et al. (1977b) and this was evaluated by the Analytical Methods Committee in 1980. An HPLC method was studied in 1983 (Analytical Methods Committee, 1983~). Hot methanol was used for extraction prior to clean-up on a combined Florisil-alumina column. A reversed-phase column and a UV detector set at 308 nm completed the separation and detection stage. Eighteen laboratories participated in the evaluation. 5.2.1.23 Sulphaquinoxaline

Sulphaquinoxaline is usually employed in combination with amprolium and/or ethopahate or with diaveridine to combat various intestinal disorders of poultry and cattle. The .compound is metabolized by acetylation in the animal and binds to proteins. I t is excreted in the urine, faeces and milk and residues are also found in edible tissues. The earlier methods of analysis for sulphaquinoxaline in feeds were based on the Bratton-Marshall reaction and therefore lacked specificity. The determination of sulphaquinoxaline in tissues by HPLC has been reported by Patthy (1983). Separate procedures were devised for muscle tissues and for liver. Alkaline urea was used to improve the extraction. The assay was tested over the range 20-1000 p.p.b. Satisfactory recoveries were achieved throughout the range but the precision was naturally better at levels above200p.p.b. The method was applied in a study in which broilers fed the drug were tested for residues for one to ten days post-treatment. It was found that a withdrawal period of seven days was necessary to reduce residues in muscle and liver down to 10 p.p.b.

5.3 MULTI-DETECTION METHODS FOR COCCIDIOSTATS Some attempts have been made to devise a qualitative test to identify coccidiostats and similar compounds in animal feeding stuffs. Hammond and Weston (1969) devised a procedure for the detection of 17drugs in feeds using TLC with two solvent

I42

[Ch. 5

Coccidiostats

systems and five detection agents. This scheme was modified and extended by the Analytical Methods Committee in 1978. Some of the drugs tested are no longer in regular use and others have come on to the market since that time. Hence in 1990 Cody er ul. worked out a scheme using HPLC for separation and identification which could be applied to 25 drugs used as prophylactics or growth promoters. In this work the propensity f o r six different solvent systems to solubilize the drugs was first examined. The results of this study are given in Table 5.2 in qualitative terms. All six solvents appeared to solubilize between 15 and 20 of the drugs to at least 80 per cent under t h e idealized test conditions used. However, acetonitrile was preferred since it gave fewer problems at later stages of the determination. Better recoveries were obtained when 5 per cent of water was added to the extractant. Removal of coextractants was effected by passage through a silica cartridge. The identification of extracted drugs was carried out with t h e aid of two chromatographic columns and five different mobile-phase systems. An example of the chromatographic separation achieved is shown in Fig. 5.2. Thirteen animal feeds containing different combinations of the drugs were prepared and used to test the method. All the drugs present were correctly identified; no peaks were wrongly assigned in the 'blank' feeds. 3. Clopidol 4. Ronidazole

5. Dirnetridazole

6. Nitrofurazone 8. Sulphadimidine 9. Diaveridine

10. Furazolidone 11. Dinitolmide

12. Acinitrazole 13. lpronidazole 14. Ethopabate 15. Sulphaquinoxaline 16. Arprinocid

17. Halofuginone

c c

b

L

Fig. 5 . 2 - Chron1;itogr;im showing thc stpilriition of I 4 drugs

Sec. 5.31

Multi-detection methods for coccidiostats

>

3

P)

5 .-E

I

f? In 0)

a

F

143

I44

Coccidiostats

[Ch. 5

In the above study, a UV detector set at 254 nm was used to identify ?he drugs. Obviously this is not the wavelength of maximum sensitivity for all drugs in the scheme. Hence further discrimination and an increase in sensitivity could be obtained by making measurements at other wavelengths for selected compounds. The absorption of drugs at various wavelengths in the range 210-300 nm is illustrated in Table 5.3. Such a system is designed to detect the presence of undeclared medicinal additives in feeding stuffs. It can be used diagnostically where animals have died unexpectedly, to check that the feed contained only declared additives and that no mistakes had been made at the feed mill. It is sufficiently sensitive to pick up accidental cross-contamination from previous batches and could be easily extended to form the basis of a multi-detection procedure for residues in foods. Where known additives are to be identified, the rather complex procedure can be simplified considerably.

5.4 REFERENCES

Aerts. M. M. L., Beek, W. M. J. & Brinkman, U. A. Th. (1990) Determination of nitrofuran residues in edible products. J . Chrornatogr., 500, 453-468. Analytical Methods Committee (1974) The determination of clopidol in animal feeds. Analyst, 99,233-238. Analytical Methods Committee (1975a) The determination of decoquinate in animal feeds. Analyst. 100.6-3-67. Analytical Methods Committee (1975bj The determination of robenidine in animal feeds and pre-mixes. Analyst, 100,668-674. Analytical Methods Committee (1978) Identification of prophylactic and growthpromoting drugs in animal feeding stuffs. Analyst, 103, 5 13-520. Analytical Methods Committee (1980) Determination of ronidazole in animal feeds by GLC: a collaborative study by the EEC Committee of Experts. Atzalw. 105, 161- 164. Analytical Methods Committee (1981j Determination of pyrimethamine in animal feeds. Analyst, 106, 1208-1209. Analytical Methods Committee (19834 Determination of halofuginone hydrobromide in medicated animal feeds. Analyst, 108, 1252-1256. Analytical Methods Committee (1983b) Determination of ipronidazole in animal feeds. Analyst, 108, 106-108. Analytical Methods Committee (1983~)Determination of ronidazole in animal feeds by HPLC. Artalyst, 108, 1521-1524. Analytical Methods Committee (1984) Collaborative study of a method for the determination of residues of halofuginone in chicken tissue. Analyst, 109, 171-1 74. Analytical Methods Committee (1985) Collaborative study of a method for the determination of dimetridazole residues in chicken tissue. Analyst, 110, 1391-1 393.

Sec. 5.41

References

145

Analytical Methods Committee (1986) Collaborative studies of methods for the detection of residues of monensin in chicken tissues. Analysr. 111, 1089-1093. Analytical Methods Committee (1988) Determination of arprinocid in poultry feeds by HPLC. Analyst. 113.903-906. Anderson, A.. Christopher, D. H. & Woodhouse, R. M. N . (1979) Analysis of the anti-coccidial drug, halofuginone. in chicken feed using GLC and HPLC. J. Chromatogr., 168,471-480. Cala. P. C., Trenner, N. R., Buhs, R. P., Downing, G. V., Smith, J. L. & Vanden Heuvel. W. J . A. (1972) GLC determination of pyrimethamine in tissue, J. Agric. Food Chem.. 20,337-340. Cieri, U. R. (1979) HPLC detection and estimation of furazolidone and nitrofurazone in animal fats. J. Assoc. Off. Anal. Chem., 62. 168-170. Cody, M. K., Clark, G. B., Conway, B. 0. B. & Crosby, N. T. (1990) Identification of medicinal additives in animal feeding stuffs by HPLC. Analyst, 115, 1-8. Cox, P. L.. Hollifield, R. D. & Heotis, J . P. (1967) The spectrofluorometric determination of buquinolate in poultry tissue and eggs. Poultry Sci., 46, 680-686. Craine, E. M., Kouba, R. F. & Ray. W. H. (1971) The disposition of decoquinate-"C administered orally to chickens. J. Agric. Food Chem., 19, 1228-1 233. De Angelis, R. L., Simmons, W. S. & Nichol, C. A. (1975) Quantitative TLC of pyrimethamine and related diaminopyrimidines in body fluids and tissues. J. Chromatogr., 106. 41-49. Donoho. A. L. and Kline, R. M. (1968) Monensin, a new biologically active compound. VI1 T-L bioautographic assay for monensin in chick tissues. Anrimicrob. Agents Chemother.. 763-766. Giovanni. F. De, Cortesi, M. L. & Catellani, G . (1987) Residuesof chloramphenicol and furazolidone in eggs on the market, Indusrrie Alimentari, 26, 362-364. Gliddon, M. J . , Wright, D., Markantonatos, A. & Groth, W. (1988) Determination of maduramicin ammonium in poultry feeds by HPLC, Analyst, 113, 813-816. Golab. T.. Barton, S. J . & Scroggs, R. E. (1973) Colorimetric method for monensin. J. Assoc. Off. Anal. Chem., 56, 171-173. Hammond, P. W. & Weston. R. E. (1969) The detection of prophylactic drugs in animal feeding stuffs by TLC, Analyst, 94.921-924. Harris, J. R., Baker, P. G. & Munday, J . W. (1977a) Improved method for the determination of pyrimethamine in poultry and rabbit feeding stuffs by GLC. Analyst, 102, 873-876. Harris, J. R., Baker, P. G . & Alliston, G . (1977b) Determination of ronidazole in pig and turkey feeds. Analyst, 102,580-583. Heitzman. R. J . , Carter, A. P. & Cottingham, J . D. (1986) An ELlSA assay for residues of monensin in plasma of cattle. Br. Vet. J., 142. 516523. Hoener, B. A., Lee, G . & Lundergan. W. (1979) HPLC determination of furazolidone in tissue. J. Assoc. Off. Anal. Chem., 62, 257-261. Jones. A. D.. Smith, E. C.. Sellings, S. G . & Burns, I . W. (1978) Determination of furazolidone in pig and poultry feeds by HPLC. Analyst, 103, 1262-1266. Kentzer. E. J., Cottingham, L. S. & Smallidge, R. L. (1988) lon-pair reverse-phase

I16

Coccidiostats

[Ch. 5

HPLC determination of amprolium in complete feeds and premixes. J. Assoc.

Off. Anal. Chetn., 71, 251-255. Kline. R. M., Stricker. R. E.. Coffman, J. D.. Bikin. H. & Rathmacher, R. P. (1970) Microbiological assay of monensin in chicken rations. J. Assoc. Off.Anal. Chem.. 53,49-53. Kouba, R. F., Craine, E. M. & Ray. W. tl. (1971) The presence of residues in the tissues of rats receiving decoquinate orally. J. Agric. Food Chem., 19, 1234- 1237. Kutschinski, A. H. (1968) GLC determination of clopidol in poultry feeds. J. Agric. Food Chem., 16.913-915. Macy, T. D. & Loh, A. (1984) Liquid chromatograplhic determination of nicarbazin in feeds and premixes. J. Assoc. Off. A n d . Chem.. 67, 11 15-1 117. Martinez. E. A. & Shimoda, W. (1985) Determination of monensin sodium residues in beef liver tissue by liquid chromatography of a fluorescent derivative. J. Assoc. Off. Anal. Chem., 68. 1149-1153. Merson, G . H. J., Hill, L. A. & Johnson. S. F. (1985) Determination of methyl benzoquate in poultry feeding stuffs using HPLC. Analyst, 110, 761-764. Morris, W. J., Nandrea, G. J . , Roybal, J. E., Munns. R. K., Shimoda, W. & Skinner, H. R. (1987) Quantitative confirmation of dimetridazole and ipronidazole in swine feed by capillary G U M S with multiple ion detection,J. Assoc. Off. A nul. Chem ., 70.630-634. Okada. J., Higuchi, I . & Kondo, S. (1980) Determination of the disappearance rate and residual levels of monensin in chick tissues by quantitative thin-layer bioautography. J. Food Hyg. SOC., (Jpn), 21, 177-183. Owles, P. J . (1984) Identification of monensin. narasin, salinomycin and lasalocid in premixes and feeds by TLC, Analyst, 109, 1331-1333. Patthy. M. (1983) Trace analysis of sulfaquinoxaline in animal tissues by HPLC. J. Chromarugr.. 275, 115-125. Roybal, J . E., Munns, R. K., Hurlbut, J . A., Shimuda. W., Morrison, T. R. &' Vieria. C. L. (1987) Rapid LC determination of dimetridazole and ipronidazole in swine feed, J. Assoc. Off. Anal. Chem., 70,626-630. Sakano, T., Masuda, S. & Amano, T . (1981) Determination of residual diaveridine and sulfaquinoxaline in hen's egg, chicken plasma and tissues by HPLC. Chem. Pharm. Bull.. 29, 2290-2295. Samuelsen, 0. B. (1990) HPLC determination of furazolidone in Atlantic Salmon (Salmosalar) tissue, J. Chromatogr., 528,495-500. Smith, G. N.,Thiegs, B. J . & Swank, M. G . (1961) Determination of 3S-dinitro-otoluamide (zoalene) in chicken tissues. J. Agric. Food Chem., 9 , 197-201. Siiderhjelm, P. & Andersson, B. (1979) The assay of the coccidiostat clopidol in animal feeds by HPLC. J. Sci. Food Agric., 3 0 , 9 3 4 6 . Sugden, E. A., Maclntosh, A. I. & Vilirn, A. B. (1983) HPLC determination of furazolidone and nitrofurazone in chicken and pork tissues. J. Assoc. Off. Analyr. Chem., 66,874-880. The Feeding Stuffs Regulations (1988) S.I. 1988 No. 396. HMSO, London. The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations (1985) S.I. No. 273, HMSO, London.

Sec. 5.41

References

I47

Thiegs. B. J.. Smith. G . N . & Bevirt. J . L. (1961) Determination of 3-amino-5-nitroo-toluamide (anot) in chicken tissues. J. Agric. Food Chem.. 9 , 201-204. Tihova. D. & Peneva. V. (1982) A rapid T L C method for the determination of residual quantities of monensin in biological material. Vet.-Med. Nuirki. 19, 52-56. Van d e r Slice, J . T. & Huang, M-H. A. (1987) L C determination of amprolium in poultry feed and p r e m i x e s using post column chemistry with fluorometric detection. J. Assoc. Off, Arid. Chrm.. 70,920-922. Vertommen. M. H . , Van der Laan, A. & Veenendaal-Hesselman. H . M . (1989) H P L C screening method for low levels of nicarbazin in eggs with off-line cartridge sample clean-up. J. Chromurogr.. 481.452-457. Vilim. A. B . & Maclntosh. A. 1. (1979) H P L C determination of nitrofurazone in milk. J. Assoc. Off. A w l . Cheni.. 62, 19-22. Vroomen, L. H . M.. Berghnians, M-C. J., van Leeuwen, P . . van d e r Struijs. T . D. 9.. de Vries, P. H . U. & Kuiper. H. A. (1986) Kinetics of “C-furazolidone in piglets upon oral administration during 10 days and its interaction with tissue macro-molecules. Food Addit. Cotifam..3.33 1-346. Winterlin. W . , Hall, G . & Mourer. C. (1981) Ultra trace determination of furazolidone in turkey tissues by liquid partitioning and HPLC. J. As.soc. Off. A r i d . Ckem., 64, 1055-1059.

Growth promoters and hormones

6.1 MECHANISMS OF GROWTH PROMOTION

Growth promoters and hormones, whilst quite separate classes of compounds, are here considered together since they are both administered to animals to improve the rate of growth of the animal and, hence, the feed conversion efficiency. Both classes of compounds could not themselves be regarded as nutrients yet, when added to an animal’s feed, or by implantation in the case of some hormones, they cause muscle tissue to be accumulated more quickly, with less feed consumed per pound of weight gained. There are thought to be three main mechanisms to account for this phenomenon, depending on the particular compound used: (1) Action of antibiotics (antimicrobials) (see Chapter 4): these compounds affect‘

the normal microflora present in the gastrointestinal tract, thereby increasing the number of beneficial micro-organisms present and so improving digestion and absorption of nutrients. (2) Action of polyether ionophores in ruminants: the microflora present in the rumen are able to digest coarse cellulosic and fibrous materials that are indigestible for simple-stomach animals. The efficiency of this fermentation process can be improved by certain compounds such that the products of digestion contain more beneficial volatile fatty acids such as propionic acid and less methane (normally expelled in the animal’s breath). Propionic acid is used in carbohydrate metabolism. (3) Action of hormones: these substances can be given in the feed but are more usually implanted in the animal’s ear so that the active substance can be released slowly over a long period of time into the bloodstream. The ear is chosen as it is not normally consumed by man and so there is little danger of relatively high concentrations of a highly biologically active material entering the human food chain. The word ‘hormone’is derived from a Greek word meaning to stimulate. Hormones are secreted naturally by a number of glands (e.g. pituitary, ovary,

Sec. 6.31

Antimicrobial agents as growth promoters

149

testis, thyroid and adrenal glands). They have a profound effect on body growth, sexual characteristics and behaviour.

6.2

DEFINITIONS

Before considering the compounds in more detail, some definitions and terms used in the literature are presented to assist understanding of the differences between products on the market in some countries and their effects: Anabolics: these substances affect the metabolism of an animal in such a way as to increase protein deposition. They can be natural or synthetic. Anabolism: reactions by which cell components are synthesized from organic and inorganic precursors. (c.f. catabolism). Androgens: androgens (e.g. testosterone, 19-nor testosterone) are responsible for the growth of the male sex organs. They also increase protein deposition and produce less fat in the carcase. Catabolism: reactions which involve the enzymatic degradation of organic compounds, usually by hydroxylation, oxidation or reduction. Endogenous: compounds naturally present in mammals. Exogenous: compounds produced synthetically. (c.f. xenobiotics). Hormones: non-nutritive compounds secreted by glands directly into the bloodstream to stimulate the activity of other organs in the body. Oestrogens: these compounds are responsible for the development and maintenance of the female sex organs and the regulation of the menstrual cycle in primates and the oestrous cycle in other mammals (e.g. diethylstilboestrol, hexoestrol, dienoestrol. oestradiol-170 and zeranol). Progestins: prepare the uterus for implantation and maintenance of pregnancy (e.g. progesterone). Steroids: hormones secreted by the adrenals. ovaries or testes. Xenobiotics: substances which occur naturally but in another species from the one under study.

Some definitions of animals: Bull: male cow, non-castrated; or 'entire'. Capon: castrated cock bird (from the Greek kapon, to cut) Cull cows: animals too old for breeding, being fattened before slaughter. Heifer: young female cow, before calving. O x : gelded (castrated) male cow. Steer: young male ox.

6.3 ANTIMICROBIAL AGENTS AS GROWTH PROMOTERS Most public concern over the use of drugs in animal husbandry has centred round the administration of antibiotics and hormones for the sole purpose of increasing meat

Iso

Growth promoters and hormones

(Ch. 6

production (section 4.3). particularly when over-production is costing large sums of money merely to store the unwanted excess (section 1.3). Whilst few would question the use of therapeutic doses of drugs to maintain healthy, disease-free stock. the addition of subtherapeutic levels has caused concern, although residual levels of drugs in animal products would be expected to be even lower than when using therapeutic doses. As early as 1955, Coates er al. showed that small amounts of penicillin (around 10p.p.m.) in the feed produced a noticeable increase in the growth of young chickens. This stimulated research into the effects of a whole range of antibiotics on the growth of poultry, pigs and cattle. However, following the Swann Report (4.3.1) only those substances little used in human medicine were permitted as growth promoters in animal husbandry. The treatment was found to be much less effective in ruminants than in single-stomach animals. The mode of action of antibiotics in producing accelerated growth has been reviewed by Visek (1978). He concluded that antibacterial agents modify the microflora in the gastrointestinal tract, although there is no quantitative evidence for changes in bacterial species as the organisms involved are mainly anaerobic and could not be examined by routine culturing methods. The increase in growth over untreated animals observed has reached 30 per cent, but 10 per cent is perhaps more typical. The wide difference in chemical structures of compounds known t o be active in this way suggests that the observed effect is not the result of an increase in the production of nutrients such as vitamins or other physiologically active chemicals.

6.3. I Rumen digestion modifiers In ruminant animals (cattle, sheep) the reticulo-rumen complex stomach is essentially a large fermentation organ for the digestion of cellulosic materials. The liquor contains billions of micro-organisms such as bacteria and protozoa, which break down the organic matter in the feed to simple molecules such as ammonia, steamvolatile fatty acids (e.g. acetic, propionic and butyric), as well as the gases carbon dioxide and methane. Some of these chemicals are absorbed through the rumen wall into the bloodstream. whilst others are used by the microbes as a source of food and for the synthesis of complex molecules. e.g. protein. Excess gases have to be removed by eructation, otherwise bloat results. Compounds such as avoparcin and monensin-sodium were found to increase liveweight gain by around 10 per cent (Table 6.1) and to improve the feed conversion ratio. These changes are thought to result from a modification of the reticulo-rumen digestion processes by which the production of methane, acetic acid and butyric acid are reduced by about 5-15 percent. There is a corresponding increase in the proportion of propionic acid, resulting in more available energy and greater glucose production by the liver. Digestion is then completed by passage through the omasum, abomasum and duodenum. I t has been estimated that 75-80 per cent of the cattle in the USA are fed on feeds containing monensin. 6.3.2 Ionophores lonophores are antibiotics produced from various species of Srreptomyces by fermentation. They promote the transfer of cations into bacterial cells which in turn produces an osmotic pressure which can only be equalized by ingress of water. This

Sec. 6.31

Antimicrobial agents as growth promoters

151

causes swelling of the bacterial cell, eventual disruption of the cell structure and failure to multiply. Hence, ionophores possess anticoccidial properties and are active against the major species of Eiineria without producing resistance. Ionophores also act as dietary enhancers in both ruminants and pigs and possibly chickens too. They act against Gram-positive inflammatory bacteria which destroy the intestinal wall and limit nutrient absorption. They also enhance digestion in the rumen of cattle and in the intestines of pigs. Ionophores such as monensin, narasin and salinomycin are toxic to horses and adult turkeys. They should not be used in conjunction with tiamulin as adverse reactions have been observed. 6.3.3 Chemical properties and methods of analysis Compounds commonly used as non-hormonal growth promoters are listed in Table 6.1, although they are also regarded as antibiotics or coccidiostats. Avoparcin, bambermycin, tylosin, virginiamycin and zinc bacitracin have already been discussed in general terms in Chapter 4, whilst lasalocid and monensin are reviewed in Chapter 5. More specific information on their chemical properties together with methods of analysis are presented here. Substances acting by hormonal action are treated in 6.4.

6.3.3.1

Arsanilic acid

C,H,AsNO,, mol. wt. 217 Organo-arsenicals have been added to feeding stuffs for many years as growth promotants and to control scour in pigs. Lead arsenite has been used as an orchard spray. However, the principal source of arsenic in the diet is fish. where the element occurs as arsenobetaine or arsenocholine. Contamination of the environment by arsenic arises from the burning of coal, from volcanic eruptions, mining waste and metal smelting. The use of arsenicals in animal feeds can give rise to small residues in poultry and pig livers. The Feeding Stuff Regulations (1988) impose a maximum limit for arsenic of 2 p.p.m. in ‘straights’ except for products from fish-meal. grassmeal or sugar-beet pulp. Total arsenic is readily determined by digestion with a mixture of nitric and sulphuric acids. conversion to the hydride and determination using carbon-furnace atomic absorption spectrophotometry (Evans et ul., 1979). The UK Working Party on the Monitoring of Foodstuffs for Heavy Metals (1982) found that the average dietary intake per day was only 89 pg, about one-quarter of the FAO/WHO recommended maximum.

Ahchcm

Gctroxcl Mcc;idox

Biimhcrniyciii"

Carhiidox

Fcdiin Roxzirsonc

Olaquindox Phcn yliirsonic acid

Niiriisin Nitrovin

Mupirocin

El;incohiin Roincnsin Bactodcrin Eismycin Montehan Pa yzonc Pcnt iizonc

Hiilqiiivct Ouimohr Ouiviilin, etc. Aviitcc

Monc iisi n"

LiisiiIocid"

Hiilquinol

-

M;ixus Avotm

Aviliimyciii Avop;ircin"

Coppcr

-

Tradc niinics

Awinilic ;icid

Compound

Cheminex Cyanamid IC1, Coopcrs

P.Hand

Elanco

-

-

PM L -

-

PML

PM L

Rochc Elenco P. Hand

Synt hctic

-

Squihh

Synthctic Synthetic

Synt hctic

S. aurcufncictrs

P . flriurc.scciis

s. cirll~fltlru~rel,.s;s

S. Insalieiisis

Synthctic

PM L

U KASTA

Arscnical

Pol yether Nitrofuran

Antihiotic

lonophore

lonophore

Ouinoxiilinc dcrivativc Sulphatc or hiisic carbonatc Chlorinatcd quinolinol

POM Synthctic

A mi noglycosidc

PM L

Polycthcr Pc pt i dc

A . B. Chcmiciils P. Hand Hoechst

s. cll~rdillrls

S . viridor/rrotirugtire.~

Arscniciil

TYPC

PML PML

Synthctic

Sourcc

Elaiico P. Hiitid Cynniiinid

POM

Product liccncc Lcg;d holdcr/rn;irkctcd hy status (UK)

Table 6.1 - Non-hormonal growth promoters

Pigs Pigs Poultry

Broilers Turkeys Broilers Turkcys Cattlc Pigs Rroilcrs Calvcs Poultry

Pigs

Pigs

Pigs Turkcys Cattlc Pigs Poultry Rahhits Pigs

Liimhs

Chickens Pigs Pigs Broilers Cattle

C o r h u e d trexr pngc

25- loo 25-37.5 50

75- 125 90-125 100- 120 I00 120-300 mg/day 70 25-40 I0

100-600

15-35

1(b-20 u-16 1-25 1-20 2-4 55

7.5-15 l.S-40 I(L-20 5-40

10-40

u p to 100

Usc in feeding stuffs Animal Lcvcl (p.p.m.)

Alhac

R . = Rcici1ltr.s.

" SCC iilso Tiihlc

5-50 5-20 5-50

.%SO

20-50 u p to 20 5-Ioo Pigs Tu r kc ys Broilers Calvcs, Iamhs Pigs R;i hhi ts Turkeys Pcptidc

20 20-50 Calvcs

Broilers

Pcptidc

10-40

30-40

5-50

60 30-40

Pigs

Calvcs Lambs Kids Piglets Pigs Pigs

Broilers Pigs

Use in feeding stuffs Animal Level (p.p.m.)

Miicrolidc

SCCalso Tuhlc 4.1. 5. I.

R . lichcriifoniii.s

PML

I'

S. virgirriiic

PML

P. Hiind G. Roscn Rousscl

S. frcrilicie

PMUPOM

Elanco P. Hiind P. H i d Smith, Klinc Bccchiim

-

Sulphur-pcptide

s. lilreyilllrerl.sis Plerrro~irstiiridi.s

POM

Macrolidc

s. nlllbo~fiicior.s

PM L

RhBncPoulcnc

Leo

Polyethcr

s.crlbits

PM L

TYPC

Source

Hocchst P. Hand

Product licence Lcgal holdcr/markctcd hy Stiltus (UK)

POM = prescription-only mcdicinc. P. = ~ . ~ ~ ~ l l ~ / ~ J l l ? ~ l l ~ i l . ~ . PML = phiirmaccuticiil merchants' list. S. = S~riproriiyccs.

Zinc lwcitriicin"

Virginiiimycin"

Thiopcpiiii Ti;imuli n (its hydrogen Tumar ii ic ) Tylosi 11"

Tiiimu t i n Dyniilin Dcniigiird Tyliiinix 'ryi;tsui Eskiilin StSfiiC

Coxistac siicox Siilgiiin Snlocin R o v m ycin Foromxidin

Siilinomycin

Spiriimyciii

Triitlc niiincs

Compound

Table 6.1 (coritirtued) - Non-hormonal growth promoters

[Ch. 6

Growth promoters and hormones

I54 6.3.3.2 A vilamycin

CI

HO

(o$T3 0.-

H

H,C

-c

'.OH

\

0

[11051-71-11 This substance is a polyether complex produced by Srreptomyces viridochromogenes. Avilamycin A is the main component but other closely related structures have been isolated. The compound (C,,H,,C120,,) has a molecular weight of 1402. I t forms colourless needles with a m.p. of 181-182°C and U V maxima are shown at 227 and 286 n m . Avilamycin has only recently been approved for use in feeds in the UK. I t is added to pig feeds at a level of 20-40 p.p.m. for animals up to 4 months old and at 10-20 p.p.m. for the period between 4 and 6 months. No withdrawal period is required but the compound should not be mixed with other antibiotics or growthpromoting substances. A GLC method to determine residues in pig tissue has been proposed by Formica and Giannone (1986). The compound (and metabolites) are converted by alkaline hydrolysis to dichloroisoeverninic acid. After partition into chlorinated solvents and clean-up on a silica-gel column, the derivative is methylated and determined by GLC using an electron-capture detector. Recoveries from muscle, liver and kidney in the range 0.3-1 p.p.m. fell within the range 70-95 per cent. Feeding trials established that 93 per cent of the compound is excreted in the faeces within 72 hours and no residues were detected in edible tissue above 0. I p.p.m.

Sec. 6.31

Antimicrobial agents as growth promoters

155

6.3.3.3 Avoparcin (see Fig. 4.4) This compound is a glycopeptide antibiotic active against Gram-positive organisms which is also used as a growth promotant in cattle, pig and poultry feeds. A 5 per cent improvement in efficiency of milk production has been claimed. I t is a white, hygroscopic, amorphous solid with no definite melting point, consisting of two components:

a, Cx,,HI,IICIN,,03A, Mol. wt. 1911, [a]z$- 96°C

p, C,,,Hl(,0C12N~,03,,, Mol. wt.

1936, [a]$ - 102°C

The powder is soluble in water, dimethylformamide, dimethylsulphoxide and moderately so in methanol. Solutions are fairly stable in the pH range 4-8. The UV maximum is 280 n m in neutral or acidic solutions and 300 nm in basic solutions. The LD5,, value is > 10000 mg/kg. No withdrawal period is required.

6.3.3.4 Barnberrnycin (see also 4.2.1 and Fig. 4.1) This compound is also known as flavomycin, flavophospholipol, or moenomycin. It is a complex of four active components known as moenomycins A , B,,Bz and C; A is the major constituent. I t is produced by Srrepromyces bamberigiensis and a number of other related strains. It is a colourless, amorphous solid with no definite melting point, decomposing above 200°C. I t is soluble in water, methanol and dimethylforrnamide but less so in ethanol. propanol, ether and ethyl acetate. I t is insoluble in benzene and chloroform. The substance has a UV maximum in water at 258 nm and is slowly decomposed in both acidic and alkaline solutions. The LD5,, value is > 2000 mg/kg. The drug is widely used in the UK and no withdrawal period is required, but methods of analysis currently available are most unsatisfactory.

6.3.3.5 Carbadox

C II H I ( , N 4 0mol. 4 , wt. 262

[6804-07-51

This drug forms minute yellow crystals with a m.p. of 239-240°C. It is insoluble in water but is soluble in chloroform and methanol. and exhibits UV maxima at 236,

156

Growth promoters and hormones

[Ch. 6

251,303,366and 373 nm. The compound is light sensitive and in the animal is rapidly metabolized to quinoxaline-2-carbonic acid and other compounds. It is added to pig feeds at a level of up to 50 p.p.m. to promote growth and to control dysentery and enteritis. It should only be fed to pigs up to 4 months of age and a withdrawal period of 28 days is recommended. The compound is known to inhibit DNA synthesis and some metabolites may be more toxic than the parent compound. FAO/WHO (1990) have recommended MRLs of 0.03p.p.m. in liver and 0.005 p.p,m. in muscle tissue. An HPLC method for the determination of carbadox in feeds has been described by Lowie eral. (1983). The compound is extracted using a mixture of water, acetonitrile and methanol, then purified on an alumina column and determined by HPLC using a reversed-phase system and a detector at 365 nm. Residues in tissues are determined as the metabolite, and a GLC method has been published by Lynch and Bartolucci (1982)in which a propyl ester derivative is formed. An optimized method for carbadox residues and metabolites has been studied by Binnendijk et al. (1991). 6.3.3.6 Copper Certain salts of copper (e.g. CuS0,CuC03, Cu(0H)J are added to pig feeds to check the enteritis which frequently affects young animals. Sheep are very sensitive to copper, so such feeds must be kept separately, and effluent from pig farms should not be discharged to land on which sheep graze.

6.3.3.7 Halquinol

Y

X

Y

OH

[8067-69-41 This substance is obtained by the chlorination of 8-quinolinol and contains three structurally related components (see above). 5,7-dichloroquinolin-8-olis the main component. It forms chelates with many cations forming coloured solutions suitable for spectrophotometric determination. The Analytical Methods Committee (1981) evaluated one such procedure using iron(II1) chloride to produce a green solution with an absorption maximum at 685 nm. The GLC method of Cowen and Heyes (1976)was not recommended.

Antimicrobial agents as growth promoters

Sec. 6.3)

157

6.3.3.8 Lasalocid (see Chapter 5) 6.3.3.9 Monensin (see Chapter 5) 6.3.3.10 Mupirocin OH

[ 12650-69-01

C2h H 4 10 ,

This naturally occurring compound is produced by Pseudomonas fluorescens. It is active against Gram-positive bacteria such as staphylococci and streptococci and against some Gram-negative bacteria of lesser importance. The calcium salt is used in pig feeds as a growth promotant. There are no published chemical or specific methods for its detection in feeds or foods. Mupirocin has a molecular weight of 501 (and forms crystals with a m.p. of 77-78°C. It has a UV maximum at 222 nm.

6.3.3. I 1 Narasin

COO-Na,

C43H,,O,

I

CH:

[55 134-13-91

An ionophore antibiotic used as a coccidiostat to control infections in broiler chickens caused by E. acervulina, E. brunetti, E . maxima, E. mivati, E . necatrix and E. tenella. It is added to feeds at a level of 70 p.p.m. as a growth promotant. A fiveday withdrawal period is required. It should not be fed to horses, turkeys, other avian species or to laying birds, or used in conjunction with tiamulin. Narasin is a polyether antibiotic produced by Streptomyces aureofaciens, with a molecular weight of 765. It crystallizes from acetone with a m.p. of 9&100"C and exhibits a UV maximum at 285 nm. It is insoluble in water but soluble in most organic solvents.

IS8

Growth promoters and hormones

[Ch. 6

6.3.3.12 Nitrovin

[804-36-41

C,,H ,?NhOh.mol. wt. 360

This compound occurs as blackish-violet crystals with a m.p. of 217°C (dec.). It is used as a growth promoter in animal feeds for chickens, turkeys, pigs and calves at concentrations varying from 10 to 25 p.p.m. in the feed. Although the compound is thermally stable even at elevated temperatures, low recoveries have been reported from aged feeds and from pelleted feeds by comparison with the meal from which the pellets had been produced. The compound has now been withdrawn in the EC. The determination of nitrovin in feeds has been examined by the Analytical Methods Committee (1991). They found that the statutory method (The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations, 1985) gave low results and they preferred a method based on the work of Chen et al. (1985) using HPLC. This produced excellent chromatography and reliable recoveries in a wide-ranging collaborative study, although results for pellets were still slightly lower than those from t h e meal. 6.3.3.13 Olaquindox 0

t

t 0

C,IH 13N301

[23696-28-81

Like carbadox. this substance is used as a growth promotant in starter and/or grower rations. but not in finisher feeds. I t is added in the range 25-100 p.p.m. and is used up to four months old. The compound is rapidly absorbed from thekut and the majority is excreted in the urine. A number of metabolites have been identified. It is considered to be a genotoxic agent (FAO/WHO, 1990) but the available data were insufficient to allocate an AD1 value, or MRL levels in tissues. However, with good veterinary practice no residues that might be harmful would be produced. The compound has a molecular weight of 263 and exists as pale yellow crystals with a m.p. of 209°C (dec.). It is slightly soluble in water and some organic solvents. A method for the determination of olaquindox in feeds has been evaluated by the Analytical Methods Committee (1985). The drug was extracted using acetone and

Sec. 6.31

Antimicrobial agents as growth promoters

159

water. the extract filtered and the determination completed by HPLC and U V detection at 393nm. Precautions must be taken to prevent decomposition of olaquindox by light, and the method is subject to interference by nitrovin. The determination of olaquindox residues in pig tissues has been reported by Nagata and Saeki (1987). They used acetonitrile for extraction. alumina column clean-up followed by reversed-phase HPLC with detection at 350 nm. Recoveries were 66-74 per cent in the range0.29.05 p.p.m. A detection limit of0.02 p.p.m. was stated.

6.3.3.14 Salinomycin

~12H7001 I

[53003- 10-41

This compound is active against E. ucervulina, E. brutiefti. E . maxima, E . mivati, E. tiecarrix and E. retiellu. I t is added to broiler feeds at a level o f 60 p.p.m. As a growth promoter. it is added to pig feeds at a level of 30-60 p.p.m. (up to 4 months of age) and thereafter at 15-30 p.p.m. It should not be fed to turkeys or to horses o r used in admixture with tiamulin. A five-day withdrawal period is required in Europe but not in the USA. The compound has a m.p. of 113°C and a U V maximum at 284 nm. Its molecular weight is 75 I . The sodium salt is also used. A TLC method has been developed for the identification and determination of t h e ionophores monensin. narasin. salinomycin and lasalocid in feeding stuffs (Owles, 1984). HPLC and TLC methods for salinomycin in chicken tissues have been developed by Dimenna et al. (1989). By HPLC, 0.02 p.p.m. in skin or fat and 0.M5 p.p.m. in liver could be determined. Iso-octane was preferred to methanol for extraction since much cleaner extracts were obtained. After clean-up on a silica column. a derivative was prepared using pyridinium dichrornate to form an a.0unsaturated ketone with a A,,,;,, at 225 nm. The system can also be used to determine narasin. The method was used to study ionophoric activity in a number of feeding trials using various antibiotic combinations. Salinomycin levels found in muscle and fat were very low but those in liver approached the tolerance limit of 1.8 p.p.m.

6.3.3.15 Spiramycin (see Chapter 4 and Fig. 4.3) This drug is used as a growth promoter in the feeds of calves, kids, lambs. pigs. turkeys and other poultry (except layers) but not rabbits. It is added at a level to provide 5-50 p.p.m. of spiramycin activity. There is no withdrawal period but the drug should not be fed to laying birds, adult breeding stock or to adult ruminants.

160

Growth promoters and hormones

[Ch. 6

6.3.3.16 Thiopeptin

[ 12609-84-61 This substance, produced by Streptomyces luteyamensis. consists of several components of which p is the major. I t exists as faint yellow crystals which decompose at 219-222°C. It is soluble in dioxane. dimethylsulphoxide, dimethylformamide, pyridine and chloroform but insoluble in diethyl ether, benzene, hexane and water.

Sec. 6.31

Antimicrobial agents as growth promoters

GsH,,N04S. mol. wt. 494

161

[ 55297-95-5) Fumarate [55297-96-61

This drug is administered to animals as the bifumarate salt. I t can be added to the feed or to the drinking water. It is used as a growth promoter and to control dysentery in pigs. The compound is crystalline and melts at 147-148°C. I t is added to give a concentration of 30-40 p.p.m. (as the fumarate). A five-day withdrawal period is required. I t must not be used in conjunction with monensin, narasin or salinomycin. The determination of tiamulin in animal feeds has been described by Howard and Cowen (1982). They used a mixture of ethyl acetate and hexane with sodium carbonate to extract the compound as the free base. This was then back-extracted into tartaric acid solution prior to examination by HPLC. The substance has a very low molecular absorption in the U V , hence large volumes are injected on-column, but this does not appear to disturb the chromatography. Recoveries of 97 per cent were achieved at 10 p.p.m. as well as a good correlation with a microbiological method over the range 30-200 p.p.m. 6.3.3.1 7 Tylosin (see Chapter 4 and Fig. 4.3) This antibiotic is obtained from Srreptomyces frudiue. I t forms crystals from water with a melting point of 128-132°C. The [algvalue is - 46°C and the U V maximum is found a t 282 nm. The compound is soluble in lower alcohols. esters and ketones. chlorinated hydrocarbons, benzene and diethyl ether. I t is stable in the pH range 4-9. The hydrochloride melts in the range 141-145°C. Phosphate and tartrate salts are used in commerce. Tylosin is added to pig feeds in the range 10-40 p.p.m. and can be mixed with sulphadimidine to control enteritis, dysentery and respiratory infections. No withdrawal period is required for pig feeds containing tylosin alone. whereas nine days is essential if sulphadimidine is also present. Only microbiological inhibition tests have been used for detection in feeds. 6.3.3.18 Virginiamycin (see Chapter 4 and Fig. 4.4) This antibiotic is a mixture of two active components designated M and S. The commercial product contains 75 per cent M and 5 per cent S:

M -C28H3sN307,decomposes at 165-167”C [a]” - 190°C. UV maximum 216 nm; S - C,,H,,,N,O ,,,.m.p. 24&242”C, [a]g’ - 28”. UV maximum 305 n m .

162

Growth promoters and hormones

[Ch. 6

The mixture is an amorphous white powder which decomposes at 138-140°C. It is sparingly soluble in water and dilute acid. I t dissolves in alkalis but is rapidly deactivated. It is also soluble in methanol, ethanol, acetic acid, ethyl acetate. chloroform and benzene. It is insoluble in ligroin (high boiling, light petroleum). The substance is used in poultry. pig and cattle feeds in the range 5-50 p.p.m. mainly in the early weeks of life. N o residues have been found in edible tissues and consequently no withdrawal period is necessary. A method for the determination of virginiamycin in feeds by HPLC has been published by Saito e t a / . (1989). The authors used methanol for extraction and detected the main component (M) only with a UV detector at 235 nm. A recovery rate of 93 per cent and 87 per cent was obtained at 20 p.p.m. and 10 p.p.m. respectively. Good correlation with a bioassay method was reported.

6.3.3.19 Zinc bacitracin (see Chapter 4 and Fig. 4.4) This antibiotic is usually added to feeds as the zinc salt, which is stable to heat. The manganese and sodium salts have also been prepared, although little used. I t is a cream-coloured powder which is soluble in water. methanol, ethanol and ethyl acetate. It is active primarily against Gram-positive organisms and three major active components ( A , B and F) have been identified. A number of minorcomponents, e.g. B , . B2, C, D. E, F,, F2and G have also been identified. A - Cf,HI,,3N1701f,S. mol. wt. 1423; B - C h 5 H I O I N l 7 O l hmot. S , wt. 1409. valine replaces isoleucine; F- Cf,5H,,7Nlh017S.mol. wt. 1407. a degradation product of A .

The UV maximum is at 250 n m ; a weak fluorescence isshown (Icx 292, h,,, 325). The substance is used as a growth promotant and to increase egg production. It can be added to feeds for poultry, calves, lambs. pigs and animals bred for fur. excluding rabbits. in the range 5-100 p.p.m. I t should not be used for adult breeding stock or for lactating cattle. No withdrawal period is required.

6.4 HORMONES AS GROWTH PROMOTERS

It has been known for many years that the sex of an animal affects itsgrowth rate and carcase composition. male animals growing faster and producing a leaner carcase than females. The sex hormones were an obvious cause of such differences. Nevertheless. it is normal practice, especially in the U K , tocastrate male cattle which are being kept for beef production in large herds. The animals are then more docile and more easily managed, but removal of the testes and the loss of the hormone testosterone produces a carcase intermediate between that of an entire male and a female. The increased proportion of fat makes the carcase less valuable in today’s health-conscious market, where every effort is being made to reduce intake of animal fats. Hence, experiments began in which artificial and natural hormonal substances

Sec. 6.41

Hormones as growth promoters

I63

were given to animals in an attempt to replace the loss of carcase quality resulting from castration. Beef and veal production in EC countries is now around 8 million tonnes. Prior to the EC ban on the use of hormones, 50-60 per cent of beef cattle in the UK were implanted with anabolic steroids, whilst in France 70 percent of calves and 50 per cent of steers were so treated. This produced a market of around $25 million for hormonal products in the EC. In the USA, 90 per cent of beef cattle are treated with hormones. I t has been estimated that the use of hormonal implants can improve farmers’ margins by up to f 3 0 a head for steers and f 15 a head for heifers. The first compounds used were the synthetic stilbenes (Fig. 6.1). Initial experiments showed that these compounds could increase the rate of growth of both cattle (Dinusson er al.. 1950) and lambs (Andrewser al.. 1949). Diethylstilboestrol (DES). hexoestrol and zeranol all possess oestrogenic activity along with the naturally occurring sex hormone oestradiol. Trenbolone and testosterone both possess androgenic properties. and the effect of using these substances can he seen in Table 6 . 2 . However. the most effective growth promotion results in steers and veal calves were obtained with a mixture of an oestrogen and an androgen. DES also exhibits oestrogenic activity in humans. Two cases in which children were affected allegedly as a result of consumption of food containing hormone residues were highlighted in the popular press, thereby increasing public concern. Since 1970. it is claimed that 3000 young people have been affected by premature breast enlargement, early menstruation and high oestrogen levels in the blood, although conclusive evidence for the presence of hormones in the food was not obtained. In a well-publicized incident in Italy, abnormal breast development in baby boys was observed and this was attributed to the consumption of canned vealbased baby foods containing residual quantities of hormones. An evaluation of the risk to health of these hormones has been published by IARC (1979). DES was found to be carcinogenic in a number of animal studies, producing tumours principally in oestrogen-responsive tissues. Data frpm human studies suggest that DES administered to women during pregnancy resulted in a n increased risk o f endometrial cancer and in cervical adenocarcinoma in exposed daughters. Following this work, the use of the stilbenes DES. hexoestrol and dienoestrol was reviewed and their administration to food-producing animals was subsequently prohibited in the EC in 1982. However, the use of hormonal substances such as oestradiol, progesterone and testosterone for therapeutic purposes continued since these compounds were naturally occurring and normal constituents of the body. Two synthetic compounds, trenbolone and zeranol were also permitted since there was no evidence of any adverse effects in use. A scientific committee was established by the E C to review the use of all these compounds, but before their report could be published a total ban on the use of all hormonal substances for growth-promoting purposes was imposed (see Chapter 8). 6.4.1 Mode of action The action of synthetic and natural hormones stimulates the pituitary gland to secrete growth hormone, although interactions between oestrogens and androgens are not fully understood. With DES, only the trans isomer is active and differences

[Ch. 6

Growth promoters and hormones

164

Table 6.2 - Effect of anabolic agents used as implants

Treat men t

Live-weight ga i nfd ay

Increase over controls ( O/O 1

Animals

790

-

Steers

860

+8

Steers

910

+ 14

Steers

990

+ 25

Steers

I050

+ 32

Steers

(g)

Controls (no treatment ) Trenbolone acetate (300 rng) Zeranol (36 rng) Hexoestrol (60 mg) Trenbolone acetate (300 mg) + hexoestrol (45 mg)

~~~~

~

~

Increase in weight compared to controls (kg)

DES (25 mg) Oest radiol ( 2 0 mg) Ze ra n o I (36 rng) Testosterone (200 mg) + oest radiol (20 rng) Trenbolone acetate (140 rng) + oestradiol ( 2 0 mg) Progesterone (200 mg) + oestradiol (20 mg)

4.9-9.1 4.1

0.5-3.4 7.6-9.7

9 .O-15.8

4.6-7.6

Veal calves

Sec. 6.41

Hormones as growth promoters

165

between oral administration and implantation in the ear may also occur. Whilst oral administration, via the feed, maintains a constant level of active compound in the animal, some compounds are metabolized in the rumen and gut before absorption. Active compounds are formulated as esters (acetate, benzoate, propionate or palmitate). The ester moiety is rapidly hydrolysed and the active substance may then be conjugated to glucuronic acid or as the sulphate, which increases water solubility and elimination in the urine or faeces. The metabolism of anabolic agents in cattle has been reviewed by Rico (1983) and their distribution in tissues by Heitzman ( 1 983). The latter showed that the half-life following intramuscular injection of 300 mg trenbolone acetate was only 15 days in cattle. This meant that the levels of active ingredient in the plasma would fall too quickly for sustained growth, as opposed to therapeutic purposes. Hence, compressed pellets with the active ingredient impregnated into a silicone rubber matrix were preferred since these can be placed in a non-edible part of the animal such as the ear, to release a small amount of active compound over a long period of time. Heitzman (1979,1983) showed that this technique increased the half-life from 15 days to 60 days. Absorption is delayed even further by the use of implants containing a mixture of oestradiol and a second steroid, which leads to a greater improvement in the rate of live-weight gain. Following administration to cattle, anabolic agents undergo metabolism as follows, prior to elimination in the milk, urine or faeces (Rico, 1983): oestradiol-17p progesterone testosterone zeranol

+ +

+ +

oestradiol-17a pregnanediol epitestosterone zearalanone

The lowest concentrations are found in the muscle and fat, with slightly higher levels in t h e kidney and liver. Much higher concentrations can be detected around the site of implantation (ear) but such tissue is normally discarded at slaughter. The effects of zeranol implants on carcase quality have been studied by Unruh eral. (1986). Treated bulls produced a carcase with increased palatability scores, probably the result of increased fat thickness, marbling and greater tenderness resulting from a delay to the maturation process. The compounds that have been used are shown in Fig 6.1. In practice. administration is normally by implants containing androgens alone for female animals and a mixture of oestrogens and androgens for castrates and young animals.

6.4.2 Chemical properties of hormonal growth promoters 6.4.2.1

Dienoestrol (see Fig. 6.1)

c ,sH I S 0 2

(84- 17-3)

This compound has a molecular weight of 266 and forms minute needles from dilute alcohol. These have a m.p. of 227-228°C. They are freely soluble in alcohol,

Growth promoters and hormones

166

[Ch. 6

Hexoestrol

Dienoestrol

Fig. 6 . I - Structurc of thc stilbcncs

methanol. ether, acetone and chloroform but are insoluble in water. Under reduced pressure the crystalssublime; the sublimate has a slightly higher m.p. The hormone is oestrogenic. 6.4.2.2 Diethylstilboestrol (see Fig. 6. I ) C I sH2002

[56-53-11

DES appears under many names. It has a molecular weight of 268 and forms small plates from benzene with a m.p. of 169-172°C. DES is soluble in alcohol, diethyl ether and chloroform but insoluble in water. The dipalmitate salt (C5,)H,,,0,) has a m.p. of 77-78°C. Diphosphate, dipropionate and disulphate salts were formerly used for their oestrogenic action. 6.4.2.3 Hexoestrol CISH2202

(also known as Synthovo, Cycloestrol; see Fig. 6.1)

[ 84- 16-21

This compound has a molecular weight of 270 and crystallizes as needles from benzene. but as thin plates from dilute alcohol, with a m.p. of 185-188°C. I t is

Sec. 6.41

Hormones as growth promoters

167

soluble in diethyl ether, acetone, alcohol and methanol, only slightly soluble in benzene and chloroform, and insoluble in water. The diacetate salt has a m.p. of 137-139°C and the dipropionate a m.p. of 127-128°C. All possess oestrogenic activity. 6.4.2.4

Oestradiol

HO

&

This is another compound possessing oestrogenic activity. It has a molecular weight of 272 and forms prisms from 80 per cent alcohol solution with a m.p. of 173-179°C and UV maximum at 225 and 280 nm. The compound is soluble in alcohol, acetone, dioxane and many other organic solvents, but insoluble in water. I t has been used in many forms in the past, e.g. benzoate, propionate, dipropionate, hemisuccinate, heptanoate. undecanoate and valerate. 6.4.2.5 Progesterone 0

II

0

dPe

This substance is secreted during the latter half of the menstrual cycle and prevents ovulation when pregnancy occurs. It has a molecular weight of 314 and exists in two crystalline forms of equal activity: a-orthorhombic prisms, m.p. 127-131°C and 0orthorhombic needles, m.p. 121°C. I t is soluble in acetone, alcohol and dioxane but insoluble in water. The U V maximum occurs at 240 nm.

168

Growth promoters and hormones

[Ch. 6

6.4.2.6 Testosterone

0

[58-22-01

C,,H2X02

Testosterone is an androgen. It has a molecular weight of 288 and forms needles from dilute acetone solution with a m.p. of 155°C.The needlesare soluble in ethyl alcohol, diethyl ether and most organic solvents, but insoluble in water. The UV maximum appears at 238 nm. The hormone was used in the form of the acetate, propionate o r isobutyrate salts. 6.4.2.7 Trenbolone (Finaplix)

Trenbolone acetate

[ 10161-33-81

CIXH2202

This compound has a molecular weight of 270 and exists in the crystalline state with a m.p. of 186°C. U V maxima are observed at 239 and 390nm. The acetate salt is usually employed in implants which have an anabolic action. This forms crystals with a m.p. of 9697°C. 6.4.2.8 Zeranol (Ralgro, Ralabol, Ralone) OH

CIXH2005

0

Me

[55331-29-81

This substance has a molecular weight of 322. Mixtures of isopropanol-water yield two crystalline diastereoisomers: the more soluble form has a m.p. of 146-148°C whilst the less soluble isomer melts at 178-180°C. The compound exhibits UV maxima at 218,265 and 304 nm.

Sec. 6.41

Hormones as growth promoters

169

Analytical methods for hormones The earlier methods for the determination of hormones in feeding stuffs and animal tissues have been reviewed by Ryan (1976). In the main, methods for feeding stuffs were based on extraction with chloroform, partition into an alkaline aqueous phase and colorimetric determination. A limit of detection of 10 p.p.m. was achieved. More sensitive procedures based on fluorescence detection were also available, but none of these methods was suitable for the determination of residues in animal tissue. Bioassay techniques were used for screening but were found to be slow, laborious, of poor sensitivity and were unable to discriminate between different hormonal substances. Modern methods for screening utilize GLC or immunoassay principles. Tests are often carried out on the urine of live animals since levels of hormones can be ten times higher in body fluids than in tissues. Nevertheless, there is a need to detect the illegal administration of hormones to animals by determinations on carcases post-slaughter, or for imported products where body fluids are not available. Methods for hormones in animal tissues are more complex since levels of analyte are much lower and problems caused by co-extractants are much greater. A survey of current methodology is now presented. Some workers have developed methods applicable to one compound only, whilst others have preferred multiresidue procedures. Whilst it is often quicker to screen body fluids (e.g. bile, plasma or urine) for the presence of hormones, this review concentrates on the detection of residues in animal tissues. Radioimmunoassay is the most sensitive and cheapest method for the routine monitoring of tissues for hormonal residues (Jansen ef al., 1985). The methods available have been reviewed by Hoffmann (1978). 6.4.3

6.4.3.I Diethylstilboestrol Abraham et al. (1972) described the production of specific antibodies against DES and claimed that quantities as low as 0.25 ng could be detected. Gridley ef al. (1983) published an even more sensitive method for DES residues in bovine liver. Lawrence and Ryan'( 1977) preferred to use GLC. They prepared heptafluorobutyryl derivatives (HFB) of DES and then compared the efficiency of electron-capture and electrolytic conductivity detectors. They were able to detect 1-2 p.p.b. of DES in beef liver. Day el al. (1975) used GLC/MS to confirm the identity of DES residues since RIA and GLC can give only presumptive positive results. The proposed method was long and tedious. It involved enzymatic digestion of the DES conjugates, purification, followed by esterification to form a chloro-derivative, which was measured by electron-capture GLC. Confirmation was effected by MS, measuring the 4-chloro-derivative at an m/zvalue of 488. Van Peteghem ef af.(1987) used GLC/ isotope dilution MS for the determination of'DES residues in meat samples.

6.4.3.2 Other anabolics Other compounds have been determined in a similar way to the methods proposed for DES. Harwood et al. (1980) described an RIA method for hexoestrol residues in tissues of cattle and sheep in which 0.02-0.1 p.p.b. could be detected. Concentrations found at various periods after implantation were also recorded. A GLC method in which HFB derivatives were prepared was used by Tobioka and Kawashima (1981). Recoveriesof 72 per cent were claimed and the detection limit wasO.l p.p.b.

170

Growth promoters and hormones

(Ch. 6

Hoffmann and Rattenberger ( 1977) described the determination of testosterone in tissues from veal calves. bulls and heifers as well as in milk. They used RIA with antiserum obtained from rabbits. Satisfactory recoveries were obtained with quantities in the range 100-600 pg. A chemiluminescent method for 17a-methyltestosterone was proposed by Jansen eral. (1988). More recently. the determination of nortestosterone has been reported by Van Ginkel er al. (1989) using immunoaffinity chromatography followed by HPLC or GLCIMS. Dixon and Russell (1986) used a monoclonal antibody to determine residues of zeranol in cattle tissues following treatment with Ralgro. Levels below 0.4 p.p.b. could be detected in muscle. fat, liver and kidney. Recoveriesvaried within the range 69-72 per cent. Residue levels in cows treated with Ralgro (36 mg) were determined 70 days after implantation. Chichila et al. (1988) preferred capillary GLC/MS to quantify residues of zeranol and its metabolites in muscle, liver and kidney tissues from cattle and were able to detect quantities in range 0.1 p.p.b. to 1 p.p.m. After treatment with P-glucuronidase, the extraction was performed in a ternary phase system of hexane, acetonitrile/buffer and dichloromethane. Zeranol was present in the middle phase. After anion-exchange chromatography, the extracts were derivatized and examined by GLC/MS. Recoveries were around 50 per cent. A similar three-phase solvent system was employed by Hsu etal. (1988) to determine trenbolone and its metabolite in bovine tissues. Solid-phase extraction with C l S and silica cartridges removed some co-extractives and HPLC reduced matrix interference even further prior to determination by GLCIMS. A limit of detection of 0.5 p.p.b. in liver and muscle tissue was achieved. A number of authors have recommended procedures for the detection of a number of anabolic residues in a single analysis. Laitem etal. (1978) used pentafluorobenzoyl chloride to prepare perfluoro esters of DES, dienoestrol and hexoestrol residues in cattle tissues. The esters were then determined by G L C with an electron-capture detector. Stan and Abraham (1980) were able to determine seven oestrogenic drugs by formation of trimethylsilyl ethers and determination using GLC/MS. Tuinstra et al. (1983) also employed G U M S but preferred gel-permeation chromatography or Extrelut columns at the clean-up stage. HPLC separations mere then carried out prior to derivatization and determination. Although the procedure was developed specifically to detect the presence of hormonal compounds in urine. the techniques could be readily adapted to tissue analysis. Residues of hormones in tissues Samples of quadrupeds slaughtered in the UK since 1980have been examined for the presence of stilbene residues (Working Party on Veterinary Residues, 1987). In 1981 (before the ban on the administration of stilbene compounds to animals) over 8 per cent of samples were declared positive. This percentage fell rapidly in the following years so that by 1985 less than 0.5 per cent of samples tested were found to contain stilbenes. Even so the levels found were very low, being below 1 p.p.b. in most cases. The survey covered cattle. calves. pigs and sheep. Some capons and imported veal calves were also examined but no confirmed positives were obtained. Some samples were also tested for the presence of trenbolone and its metabolites. Positive findings were recorded in very few samples and then only at levels very close

6.4.4

Sec. 6.51

Bovine somatotropin

171

to the limit of detection. Residues of zeranol were detected in some samples of meat from cattle and calves probably as a result of the animals consuming feeding stuffs contaminated with zearalenone, which is known to occur in some cereal products. However, concentrations of zeranol in meat were in all cases less than 1 p.p.b. Positive findings of progesterone in the fat from male animals and of testosterone in the plasma of female animals were also reported but the levels found were not considered to differ significantly from naturally occurring concentrations. Residues of hormones in animal tissues following treatment by implantation have been reported by some authors in papers whose primary purpose was to demonstrate the efficacy of a new analytical procedure. Heitzman (1986) has shown that 6-30 per cent of the dose present in the implant remains at the site, dependingon the dose and time since implantation. Hence, it is important that such tissues do not find their way into the human food chain. Heitzman (1986) has also determined levels of zeranol and hcsoestrol in animal tissues following treatment. The liver and kidney are the main target organs and residues are normally below 1 p.p.b. - further rcashurancc. particularly when combined with the findings of the Working Party on Veterinary Residues (1987) reported above. 6.5

BOVINE SOMATOTROPIN

I t has been known for many years that a natural hormone known as somatotropin stimulates growth and lactation in farm animals. However, until recently the hormone has only been available in small quantities from slaughtered animals. Following t h e development of recombinant DNA technology in the 1970s. it has now become possible to produce large quantities of some somatotropins at relatively low cost. Average milk yields per cow in the UK have increased by around 2 per cent per year over the last 20 years as a result of breeding and improvements in the nutritional quality of feeds. Experiments using bovine somatotropin (BST) suggest that milk yields of treated animals could be increased by 20-40 per cent. BST is a complex polypeptide with a molecular weight of 22000 secreted by the pituitary gland. It is species specific, so that injections of BST into other animals, including humans. would produce no noticeable effect. No residues in milk or meat products are likely to occur and, in any case, the synthetic product is indistinguishable from the natural hormone. One problem is that for maximum increase in milk yield daily injections of the hormone would be required. This is not very practical on a large dairy farm. Experiments are in progress to develop a slow-release product to obviate the necessity for daily injections. When fed ora1ly.the compound is inactivated. Some objections to the use of the hormone in this way have been raised by animal sympathizers who claim that repeated injections could 'burn the animal out'. Whilst there appear to be no short-term problems in the administration of the hormone, its effect on long-term reproductive efficiency has not yet been fully established. If the practice is approved, it may be necessary to draw up a code of practice to regulate the commercial exploitation of this product. Work is now proceeding on the development of similar hormones for use in pigs and poultry. Stahly (1990) has shown that porcine somatotropin depresses the

I72

Growth promoters and hormones

[Ch. 6

voluntary feed intake and stimulates the growth of the major proteinaceous tissues such as muscles, internal organs. skin and bone. Fatty tissue is reduced by somatotropin administration. Energy maintenance requirements are increased, possibly because the animal has less fat to keep itself warm. An ELISA method for the determination of BST in blood and milk has been published by Zwickl er al. (1990). They prepared a polyclonal anti-BST antiserum from rabbits and used this to bind BST present in the sample. The bound BST was determined by addition of a biotin-anti-BST antibody complex and reaction with horseradish peroxidase-labelled avidin D: 0.2 ng/ml could be detected in milk. Recoveries from milk were better than 95 per cent. 6.6

P-AGONISTS

Following the ban on the use of stilbene and other hormonal products, together with the development of highly sensitive methods of analysis for the detection of residues of such compounds in animal tissues. attention has turned to the possible use of other agents for promoting live-weight gain in cattle. One such group of compounds are known as P-agonists. Clenbuterol

NH;,

<-> f->

CHOH CH2 NH C(CH3)3

CI

Cimaterol

NH2

CHOH CH2 NH CH(CH&

Sal butamol CHOH CH2 NH C(CHJ3

Ractopamine CHOH CH2 NH CH CH3 (CH2)2 Fig. 6 . 2 - Structurc of somc p-agonists

Sec. 6.71

References

173

Originally clenbuterol was recommended for the treatment in horses of pulmonary disease and bronchospasms resulting from allergies and infections. However, studies showed that the compound also possessed so-called repartitioning activity, in which the fat content of a carcase is reduced and the muscle fraction is increased. Animal studies have been reviewed by Hanrahan e f u l . (1986). In view of current consumer preference for leaner meat, the use of such compounds could be clearly attractive to t h e meat industry. Compounds used in some countries include clenbuterol, cimaterol, salbutamol and ractopamine. Their structures are shown in Fig. 6.2 and are similar to the naturally occurring catecholamines such as adrenaline. Although t h e compounds are known as P-agonists, their mode of action is not fully understood. They appear to interact with P-receptors on the cell membrane, reducing protein and lipid breakdown and stimulating lipolysis (Warriss, 1990). Experiments with animals have shown that clenbuterol can reduce the fat content of the carcase by about 20 per cent in cattle and sheep, and by smaller amounts in pigs and poultry. The cross-sectional area of the longissimus dorsi muscle is increased by amounts ranging from 11 to 43 per cent (Hanrahan ef uf., 1986). Similar results have been obtained using cimaterol and ractopamine (Cromwell, 1988). The dose level administered to the animal has only a small effect on its growth within a given range. For example. pigs are usually fed 0.01-5 mg/100 kg bodyweight per day. corresponding to around < 0.1-10 p.p.m. in the feed. Hence, residues in animal products would only be expected to occur at very low levels. Work is currently under way to develop methods of analysis based on HPLC and GLC/MS that are capable of detecting residues at a level of 1 p.p.b. and below. A specific radioimmunoassay for clenbuterol has been published by Delahaut etal. (1991). 6.7

REFERENCES

Abraham, G . E., Reifnian, E. M., Buster, J . E., Stephany, J . D. & Marshall, J . R. (1972) Production of specific antibodies against DES. Anal. Lefr.. 5,479-486. Analytical Methods Committee (1981) Determination of halquinol in pre-mixes and medicated feeding stuffs. Analysf, 106, 105-1 13. Analytical Methods Committee (1985) Determination of olaquindox in medicated animal feeds by HPLC. Anulysr. 110,75-77. Analytical Methods Committee (1991) Determination of nitrovin in medicated animal feeds by HPLC. Analysf, 116,415420. Andrews. F. N.. Beeson. W. M. & Harper, C. (1949) The effect of stilbestrol and testosterone on the growth and fattening of.lambs. J . Anim. Sci., 8,578-585. Binnendijk, G. M., Aerts. M. M. L.. Keukens, H. J. & Brinkman, U. A. Th. (1991) Optimization and ruggedness testing of the determination of residues of carbadox and metabolites in products of animal origin: stability studies in animal tissues. J . Chrornufogr.,541,401410. Chen, J . , Wang, F. & Yang, S. (1985) Determination of growth stimulator nitrovin in animal feeding stuffs by HPLC. Fenxi Huaxue, 13, 935-937, Anal. Absir., 1986.48.7G15. Chichila. T. M. P., Silvestre, D., Covey, T. R. Sr Henion, J . D. (1988) Distribution of zeranol in bovine tissues by selected ion monitoring capillary GC-MS. J . Atiul. Toxicol., 12, 310-318.

174

Growth promoters and hormones

[Ch. 6

Coates, M. E., Davies. M. K. & Kon. S. K. (1955) The effect of antibiotics o n the intestine of the chick. Br. J. Nutr., 9, 110-1 19. Cowen, T. & Heyes. W . F. (1976) The determination of chlorhydroxyquinoline in medicated pig-feeds. 11. UV batching assay and GLC assay for rnono- and dichloro components. Anulysf, 101, 167-173. Crornwell, G. L. (1988) Repartitioning agents- what's ahead. In: Biotechnology in the feed itidusfry, Proc. Alltech's 4th Annual Symposium, Lyons, T. P. (ed.). Alltech Technical Publications, Kentucky, pp. 23-36. Day. E. W., Vanatta, L. E. & Sieck, R. F. (1975)Theconfirmation of DES residues in beef liver by GC-MS. J. Assoc. Off. Anal. Chem., 58.520-524. Delahaut. Ph., Dubois, M.. Pri-Bar, I.. Buchman, O., Degand, G. & Ectors, F. (1991) Development of a specific radioimmunoassay for the detection of clenbuterol residues in treated cattle. Food Addit. Contam., 8, 43-54. Dimenna, G. P., Lyon, F. S., Thompson, F. M., Creegan, J. A. & Wright, G . J . (1989) Effect of antibiotic combination, dosing period, dose vehicle. and assay method on salinomycin residue levels and their ionophoricity in chicken tissues. J. Agric. Food Chem., 37, 668-676. Dinusson, W. E.. Andrews. F. N. & Beeson, W. M. (1950)The effect of stilbestrol, testosterone, and thyroid alterations on growth and fattening of beef heifers. J. Anim. Sci.,9, 321-328. Dixon. S. N . & Russell. K. L. (1986) Radioirnmunoassay of the anabolic agent zeranol. IV. The determination of zeranol concentrations in the edible tissues of cattle implanted with zeranol (Ralgro). J. Vet. Pharmacol. Ther., 9 , 9 6 1 0 0 . Evans. W. H.. Jackson, F. J . & Dellar, D. (1979) Evaluation of a method for determination of total Sb. As and Sn in foodstuffs using measurement by AAS with atornisation in a silica tube using the hydride generation technique. Analyst, 104. 16-34. Food and Agriculture Organization (FAO/WHO) (1987) Residues ofsorne velerinury drugs in otiimals and foods. FAO, Food and Nutrition paper, no. 41, Rome. Food and Agriculture Organization (FAO/WHO) (1990) Evaluation of certain veterinary drug residues in food. WHO Technical Report Series 799, WHO, Geneva. Formica. G . & Giannone, C. (1986) GLC determination of avilamycin total residues in pig !issue. fat. blood, feces and urine. J. Assoc. Off.Anal. Chem., 69, 763-766. Gridley, J . C., Allen, E. H. & Shirneda, W. (1983) Radioimmunoassay for DES and the monoglucuronide metabolite in bovine liver, J. Agric. Food Chem., 31, 202-296. Hanrahan, J . P., Quirke. J . F., Bowmann. W., Allen, P., McEwan, J. C., Fitzsirnons. J. M., Kotzian, J . & Roche, J . F. (1986). P-Agonistsand their effects on growth and carcass quality. in: Recent advances in animal nutrition, W. Haresign 8r D. J . A. Cole (eds). Butterworths, London, pp. 125-138. Hanvood, D. J . , Heitzman, R. J . & Jouquey, A . (1980) A radioimrnunoassay method for the measurement of residues of the anabolic agent. hexoestrol, in tissues of cattle and sheep. J. Vet. Pharmacol. Ther.. 3,245-254. Heitzman. R. J . (1983) The absorption, distribution and excretion of

Sec. 6.71

References

175

anabolic agents. J. Anim. Sci., 57, 233-238. Heitzman, R. J . (1986) Residues in animal products. In: Recent advances in animal nurrition, W. Haresign & D. J. A. Cole (eds). Butterworths, London, pp. 157- 176. Heitzman, R. J. & Harwood. D. J. (1983) Radioimmunoassayof hexoestrol residues in faeces, tissues and body fluids of bulls and steers. Vet. Record, 112, 12U-123. Hoffmann, B. (1978) Use of radioimmunoassay for monitoring hormonal residues in edible animal products. J. Assoc. Off. Anal. Chem., 61, 1263-1273. Hoffmann. B. & Rattenberger. E. (1977) Testosterone concentrations in tissue from veal calves, bulls and heifers and in milk samples. J. Aiiirn. Sci., 46.635-641. Howard, D. & Cowen, T. (1982) Determination of tiamulin hydrogen fumarate in animal feeds using HPLC. Analyst, 107, 319-323. Hsu, S. H., Eckerlin, R. H. & Henion, J. D. (1988) Identification and quantitation of trenbolone in bovine tissue by GLC-MS. J. Chromarogr., 424, 219-229. IARC (1979) Monographs on the evahation of the carcinogenic risk of chemicak to humans, Vol21, Sex hormones (ii). International Agency on Cancer, Lyon. Jansen, E. H. J. M., Van den Berg, R. H.. Van Blitterswijk, H., Bothmiederna, R. & Stephany. R. W. (1985) A highly specific detection method for DES in bovine urine by radioimmunoassay following HPLC. Food Addir. Contam., 2,271-281. Jansen, E. H. J . M., Van den Berg, R. H., Zomer, G . & Stephany, R. W. (1988) A chemiluminescent immunoassay for 17a-methyltestosterone. Food Addit. Contum., 2.47-53. Laitem, L., Gaspar, P. & Bello, I. (1978) Stable derivatives for the GC determination of synthetic anabolic stilbene residues (DES, dienestrol and hexestrol) in meat and organs of treated cattle at the sub-ppb (10") level. J. Chromatogr.. 156, 267-273. Lawrence. J. F. & Ryan, J. J . (1977) Comparison of E-C and electrolytic-conductivity detection for GLC analysis of HFB derivatives of some agricultural chemicals. J . Chromurogr., 130,97-102. Lowie. D. M., Teague, R. T., Quick, F. E. & Foster, C. L. (1983) HPLC determination of carbadox and pyrantel tartrate in swine feed and supplements. J. Assoc. Off. Anal. Chem., 66,602-605. Lynch, M. J. & Bartolucci, S. R. (1982) Confirmatory identification of carbadoxrelated residues in swine liver by GC-MS with selected ion monitoring. J . Assoc. Off. Anal. Chem., 6 5 , 6 7 0 . MAFF (1982) Survey of arsenic in food. In: 8th Report of the Steering Group on Food Surveillance, HMSO, London. Nagata, T . & Saeki, M. (1987) Determination of olaquindox residues in swine tissue by HPLC. J. Assoc. Of& A n d . Chem., 70, 706-707. Owles, P. J . (1984) Identification of monensin, narasin, salinomycin and lasalocid in premixes and feeds by TLC. Anulysr, 109, 1331-1333. Rico, A. G. (1983) Metabolism of endogenous and exogenous anabolic agents in cattle. J. Anim. Sci., 57, 226-232. Ryan, J . J. (1976) Chromatographic analysis of hormone residues in food. J. Chromurogr., 127,5349. Saito, K . , Horie, M., Hoshino, Y., Nose, N . & Nakazawa, H. (19S9) HPLC

176

Growth promoters and hormones

[Ch. 6

determination of virginiamycin in premixes and feeds. J. Liq. Chrumatugr, 12, 373-38 1 . Stahly. T. S. (1YYO) Impact of somatotropin and beta-adrenergic agunistson growth, carcass composition and nutrient requirements of pigs. In: Recent advances in ariimul tiiifrifioti, W. Haresign & D. J . A. Cole (eds). Butterworths, London, pp. 103-1 12. Stan. H.-.I. &L Abraham. B. (1980) Determination of residues of anabolic drugs in meat by GC-MS. J. Chruinurugr., 195. 231-241. Tobioka, H. &L Kawashima, R. (1981) GLC determination of hexestrol residues in Anal. Chem., 64. 709-713. adipose tissue. J. Assoc. Off. The Feeding Stuffs Regulations (1988) HMSO, London. The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations 1985, S.I. no. 273, HMSO, London. Tuinstra. L. G. M. Th.. Traag, W. A., Keukens, H. J . & van Mazijk, R. J . (1983) Procedure for the GC-MS confirmation of some exogenous growth-promoting compounds in the urine o f cattle. J. Chromarogr., 279, 533-542. Unruh, J. A.. Gray, D. G. & Dikeman, M. E. (1986) Implanting young bulls with zeranol from birth to slaughter ages: 11. Carcass quality, palatability and musclecollagen characteristics. J. Atzim. Sci., 62, 388-398. Van Ginkel. L. A., Stephany, R. W.. Van Rossum, H. J., Van Blitterswijk, H., Zoontjes, P. W., Hooijschuur. R. C. M. & Zuydendorp. J. (1989) Effective monitoring of' residues of nortestosterone and its major metabolite in bovine urine and bile. J. Chromarogr., 489,95-104. Van Peteghem, C. H.. Lefevere, M. F., Van Haver. G. M. & De Leenheer, A . P. (1987) Quantification of DES residues in meat samples by GC-isotope dilution MS. J. Agric. Food Chem., 35, 228-231. Visek. W. J . (1978). The modeofgrowth promotion byantibiotics,J. Anim. Sci., 46, 1447- 1469. Warriss, P. D. (1990) Beta-andrenergic agonists for pigs: development and commercial aspects. Feed Compounder, 10(5), 62-64. Working Party on Veterinary Residues in Animal Products (1987) Atiuholic. uritltelmiriric urid anrimicrobial agents, 22nd Report of the Steering Group on Food Surveillance, paper no. 22. HMSO, London. Zwickl. C. M., Smith. H. W. & Bick, P. H. (1990) Rapid and sensitive ELlSA method for the determination of bovine somatotropin in blood and milk. J. Agrir. Food Chrm., 38, 1358-1362.

Other contaminants Despite the attraction of so-called ‘natural‘ or ‘organic’ farming methods. the use of some synthetic chemicals is probably essential to secure the production of an adequate supply of food for the needsof the world population (see Chapter 1). Thus. fertilizers are needed to boost the growth of plants and othercrops. whilst a variety of chemicals are approved as additives in feeding stuffs for animals to improve the rate of conversion of carbohydrate and vegetable protein to animal protein. Similarly. other chemicals are required to prevent wastage of crops, either pre-harvest or postharvest, whilst medicinal products are used in animal husbandry to prevent losses of animals by disease. Inevitably, some of these chemicals will find their way into the human food chain. either directly as in pesticide residues on food crops such as vegetables, fruit. cereals, etc.. or indirectly following the consumption of residues on such crops or added to feeds and consumed by animals whose tissues are subsequently eaten by humans. This chapter examines the contaminants that find their way into t h e human food chain adventitiously as well as the methods of analysis available for their detection and quantification. The emphasis will be laid upon those residues which arise from the use of chemicals in animal husbandry. although the references quoted will also provide an insight into those residues which are present as a result of the direct use of chemicals in agriculture generally.. but unrelated to animal husbandry. Contaminants will only be found in minute quantitiessince the animal acts as a highly efficient filter and destroyer of active residues. This increases the problems for the analytical chemist. who has to contend with a wide variety of chemicals and matrices which require methods of analysis that are ultra-sensitive and highly specific. The role and effects of residues of pesticides. trace elements, mycotoxins, tranquillizers and some biological contaminants will now be reviewed.

7. I

PESTICIDES

It has been estimated that some 30-50 per cent of crops worldwide are lost to pest damage even before harvest, and without the use of pesticides this loss would be

Other contaminants

178

(Ch. 7

perhaps 30 per cent higher (MAFF. 1984). Since pesticides are designed to kill certain living organisms. public opinion and medical experts have demanded restrictions on their use and controls to safeguard the food supply. Spraying operations may also result in drift, thus endangering operatives, bystanders and the surrounding environment. The acute and chronic toxicity of many of these compounds has resulted in the adoption of maximum residue limits (MRLs), which reflect a standard achievable under good agricultural practice, together with recommended acceptable daily intake levels (ADls), which ensure that nobody is subjected to any unacceptable risk during a normal life-span. I n the UK, the use of pesticides was subject to a voluntary code of practice known as the Pesticides Safety Precautions Scheme, instituted in 1954. This required a company wishing to sell a product for use on human foods to produce evidence of residue data on both crops and soils. Approved products can then only be used for designated crops under controlled conditions of safety known as good agricultural practice. Over the years. public safety has been assured by an extensive monitoring programme in which retail foods were sampled, cooked as necessary, and then analysed for residues of pesticides to check that such residues found are within safe concentrations. Despite the fact that this voluntary system of control has worked very well for many years, it has now been replaced by a more formal system of enforcement through legislation. The Food and Environment Protection Act 1985 Part 111 has been enacted 'to regulate pesticides and substances, preparations and organisms prepared or used for the control of pests or for protection against pests'. In particular, in Section 16 of the Act we find: 16 - ( I ) The provision of this Part of this Act shall have effect (a) with a view to the continuous development of means (i) to protect the health of human beings, creatures and plants; (ii) to safeguard t h e environment; and (iii) to secure safe, efficient and humane methods of controlling pests

... (2) (k) specify how much pesticide or pesticide residue may be left in any crop, food or feeding s t u f f . . . The first part of these provisions is included in the Control of Pesticides Regulations 1986. Maximum residue limits have been incorporated into legislation through the Pesticides (Maximum Residue Levels in Food) Regulations 1988. An abridged version showing some of the main provisions is shown in Table'7.1. The E C have adopted similar residue limits (a) for cereals and (b) for foods of animal origin as shown in the table. A separate Directive is concerned with residues of pesticides on fruit and vegetables. Only the more important compounds have been included in Table 7.1. The Regulations and Directives should be consulted for a more authoritative and complete statement of the legal position. In addition to the loss of crops resulting from damage by pestsor vermin, animals themselves suffer from the effects of external parasites such as ticks. mites. fleas,

Sec. 7.11

179

Pesticides

Table 7.1 - Some pesticide residue limits (p.p.m.) adopted by the U K

Dieldrin (including aldrin) DDT (including TDE. DDE) Endrin HCB HCH a

Cereals

Animal products"

Milk

0.01

0.02

O.O( 16

0.05 0.01 0.01 0.02

1

0.04

0.05 0.2 0.2

0.008

0.1

0.004

2

0.003 0.008

B Y Heptachlor (including epoxide) Dichlorvos Pyret hrins Malathion

0.1 0.01 2 3

0.01

8

Adapted from EC Directives S61362 ccrcals and 86/3h3 animal products and the U K Pcsticidcs (Maximum Rcsiduc Lcvcls in Food) Rcgulations. " Expresscd as p.p.ni. fat.

warble fly and maggot fly. Such infestations feed on the blood and others may also transmit protozoal infections via the bloodstream. I t has been estimated (Brander, 1986) that such losses can amount to $500 million in the USA and perhaps $7 billion worldwide. In the early days of farming. palliative treatment involved the use of preparations containing derris. sulphur. arsenic or nicotine; but relatively high concentrations were required for the treatment to be effective. with consequent risk to both operatives and animals. Insecticides such as dieldrin. y-HCH (lindane) or DDT (dichlorodiphenyltrichloroethane), developed in the 1950s. were found to be more selective against animal parasites and consequently could be used at much lower concentrations. Furthermore, they were retained in the wool for several weeks following treatment, thus providing a continuous protection against re-infection. Animal parasites of the class Arachoida (e.g. ticks and mites) or the class lnsecta (flies, lice, fleas) pass through a number of stages in their life-cycle from egg. larva, pupa to adult. Hence, any programme of control needs to be effective against each individual stage for maximum protection. Treatment is effected using dusts, suspensions or emulsions; the latter applied by dipping or spraying. Even so, resistance to individual compounds can occur and may be transmitted genetically. Hence. it is good practice to vary the active substance in the formulation or, alternatively. use more than one active compound in admixture. The best known and most widely used compounds are DDT. y-HCH (lindane or y-BHC) and hexachlorobenzene (HCB). Theoretically HCH can exist as eight geometrical isomers. The technical product consists in the main of four of these isomers but its use in the EC countries has now been prohibited in favour of lindane, which is the y-isomer alone. and is preferred as it is the least persistent of the isomers

180

Other contaminants

[Ch. 7

and has lower mammalian toxicity. However, the persistence of t h e organo-chlorine insecticides gave rise to problems for wildlife in terms of reduced fertility and thinning of their eggshells. Furthermore, such compounds were found to be concentrated in fatty cells and were not metabolized. There was thus a danger that these substances could gradually spread and accumulate throughout the whole food chain. Many compounds initially approved for use were therefore subsequently withdrawn, or severely restricted in their approved applications. They were replaced by organo-phosphorus compounds. which were found to be equally effective although not so persistent. Whilst organo-phosphorus compounds are more acutely toxic to man than the organo-chlorine compounds, they are rapidly metabolized and excreted in the urine. In recent years synthetic pyrethroids based on the naturally occurring pyrethrins have been introduced and flumethrin has been approved for use in sheep-dips. These compounds are effective insecticides and have low mammalian toxicity. The structures of some of these compounds are shown in Fig. 7.1.

7.1.1 Pesticide residue surveys The exposure of a population to pesticides in the food supply can be measured in several ways:

(1) total diet studies (called market basket surveys in the USA and Australia); (2) duplicate diet studies; (3) analysis of individual foods; (4) by calculation, using data on the total annual production of each substance. The organization of total diet studies in the UK was described by Harries eral. in 1969 and major reorganizations to the scheme were initiated in 1978 (Buss and Lindsay) and in 1983 (Peattie eral.). The types and quantities of food purchased are based on information obtained from the UK National Food Survey. Samples of food are' purchased at fortnightly intervals, then prepared and cooked as appropriate. For ease of analysis, it is convenient to divide foods into groups, each food in a particular group having a similar chemical composition. Originally there were seven groups but in 1975 this was increased to nine and in 1981 to 20 groups. Changes to the sampling scheme should be made as infrequently as possible since the main purpose of total diet studies is to identify trends in exposure over a number of years rather than worry too much about absolute concentrations detected in any one sample. Likewise, it is advisable to use the same methods of analysis and the same designated laboratories to ensure that perceived trends are real and not artefacts brought about by changes in sampling, analytical techniques, methods, equipment or reagents. The total diet approach inevitably means that any food containing a relatively high residual level of a given pesticide will be masked by t h e dilution effect of admixture with other foods that do not contain any of the same residue. Residue levels may thus appear to be reassuringly low and hence will not indicate the exposure of the person who is on a special diet, for either medical reasons or personal preference and may consequently be eating a food with relatively high levels of residues. The principal advantage of a total diet study is that it provides the

Sec. 7. I ]

Pesticides

181

CI

CI

DDT

-,,-I3KC

Parathion

Fenthion

Fensulfothion

Demeton-methyl

Me Me

CN Cypermethrin

Me Me

Br2C=CHA

C

O

O

~

H

~

o

/

O

CN Deltamethrin

Fis. 7. I - Structurcs of some pesticides uscd for animal treatment.

I s2

[Ch. 7

Other contaminants

CN Fenvalerate CI CH(CH&

Me M e

C12C =CH

A C O O C H 2 a

0'

/o

Permethrin Fig. 7. I (corr/itrctet/)- Structure5 of w m c pesticides uscd f o r animal treatment

maximum information on mean population exposure from a relatively small number of analyses. Analysis of each food separately would impose an unacceptable demand on scarce laboratory resources and lead to high costs. However, not all foods are included in a total diet study and no account is taken of differences in dietary habits. In the USA. separate total diet studies are regularly carried out for infants, toddlers and adults. since the first two groups may present a special risk. I t is essential to supplement total diet studies by analyses of individual foods and to pay particular attention to staple foods in the diet. Selective studies on individual foods are particularly useful when the contaminant is applied in agricultural practice to a few commodities only. An alternative approach to total diet studies involves the examination of duplicate diets in which selected persons are asked to prepare a replicate of all meals t h e y consume. This approach is particularly suitable for individuals thought to be at special risk, e.g. infants. the old, vegans or diabetics. Calculations based on total production are often limited by a lack of accurate data. For example. the total tonnage of a pesticide manufactured in a given country divided by the total population gives an estimate of the mean exposure and intak.e. Such calculations can be erroneous since there are often non-food uses for the product and it may also not be possible to separate sales of the product for home use from those for export. Equally, an allowance must be made for imports. No allowance can be made for natural occurrence or contamination or, on the other hand, for losses during processing and cooking. However, it may be possible to achieve an approximate confirmation of the exposure levels obtained independently by analysis in total diet studies. 7. I. I. I UK results The latest results of the U K government rnonitoringprogramme in which nearly 4000 samples were examined in the year 1988-89 for a whole range of pesticides have

Sec. 7. I ]

183

Pesticides

recently been published (MAFF, 1990). Sixty-four per cent of all samples contained no'detectable residues. Of those samples found to contain residues, 34 per cent were at a level below the MRL; only 2 per cent of samples contained residues above the MRL. Five hundred and fifty-six samples of animal feeding stuffs were analysed. N o residue was found in 434 samples (78%) but 7 samples did contain residues above the MRL values. Some MRLs for organo-chlorine and organo-phosphorus compounds are given in Table 7.2.

Table 7.2 - Some maximum residue limits (p.p.m.) for pesticides in animal products. as approved by the Codex Alimentarius Commission

Dieldrin DDT HCB y-HCH Demeton-S-methyl Diazinon Ethion Fenitrothion Pirimiphos-methyl

Carcase meat

Milk

Eggs

0.2 7

0.15 1.25 0.5 0.2 0.05 0.5 0.5 0.05 0.05

0.1 0.5

1

2 0.05 0.7 2.5 0.05 0.05

1

0.1 0.05 0.2 0.05

Poultry meat

7 1 0.7 0.05

-

0.2

-

7.1.1.2 USA Market basket surveys The organization of the FDA pesticides monitoring programme has been described by Reed er al. (1987). The objectives of this programme are (a) to monitor domestic and imported food in order to check compliance with the tolerances imposed under the Food. Drug and Cosmetic Act, and (b) to gather information on the incidence and levels of pesticide residues in the food supply. The tolerance value represents the maximum residue level expected from the registered use of the pesticide. Tolerances are published in the Code of Federal Regulations, Title 21 Section 193 for foodstuffs and Section 561 for animal feeds. For example. DDT is permitted at a level of 100 p.p.m. in peppermint or spearmint oils, 80 p.p.m. in dried hops. 6 p.p.m. in crude soyabean oil. but only at 1.25 p.p.m.in the fat of dairy products and milk. Such tolerances are designed to provide no unacceptable risk to health. The total diet survey is carried out four times each year at 12 locations, sampling table-ready food. Each 'basket' contains 234 individual foods chosen to represent the typical US diet. Separate samples of infant and toddler diets are prepared. Comprehensive survey data covering the period 1977-80 have been published by Gartrell er ul (1983. Residues of a-HCH, pp'-DDE. dieldrin, heptachlorepoxide, HCB. yHCH. rnethoxychlor and octochlor epoxide were found in dairy products but at

184

Other contaminants

(Ch. 7

average concentrations of less than 1 p.p.b. The meat, poultry and fish group contained 18 residues, the most significant being 2-ethylhexyldiphenylphosphate (at 98.5 p.p.b.) and 2-chloroethyl linoleate (at 14.5 p.p.b.). Average residue levels of 4.8 p.p.b. of pp'-DDE and 3.3 p.p.b. of dieldrin were also detected. all other residues being at 1 p.p.b. or below. Malathion (29.9 p.p.b.) was the major residue detected in grains and cereal products and also in fats and oils (16.7 p.p.b.). Overall pp'-DDE. dieldrin and malathion were the compounds most frequently detected but even so daily intakes of these compounds were calculated to be well below F A 0 1 W H O acceptable levels. Little change in residue levels has been noticed since 1977. 7. I . 1.3 Other surveys Results on Dutch total diet samples were reported by De Vos ef al. (1984). Samples of 126 different food items were examined in the two-year period 1976-78. Pesticides, PCBs. bromide, heavy metals, arsenic and selenium were detected in a number of samples but mostly at levels below Dutch tolerance limits and well below the ADI. The results obtained were compared with work carried out in Australia, Canada, New Zealand, Spain. the UK and the USA. Japanese results were published by Matsumoto el al. (1987). They examined 'foods collected over the period 1977-85 and, in general, obtained residues similar to those found in USA studies, except that intake of malathion in the USA was seven times greater than in Japan and dieldrin and heptachlor were eight and sixteen times greater respectively. In contrast, intakes of P-HCH, pp'-DDD and HCB were significantly lower in the USA than in Japan. N o explanation could be advanced to account for these differences.

Analytical methods for the determination of pesticide residues Pesticides and related substances, e.g. metabolites, exhibit a wide variety of chemical and physical properties. Furthermore, they may occur in samples of food or the environment, which also possess a wide variation in their composition and properties. In most cases, any such residues will only be present in minute amounts. All of these considerations present many problems for the analytical chemist who is asked to develop rapid. cheap, multi-residue techniques which are reliable and accurate. despite the fact that the interpretation and significance of the results obtained will be inexact and possibly controversial. Sampling protocols are normally agreed in advance between t h e interested parties. I t is important that the analyst makes the fullest possible contribution to such discussions. The pretreatment of samples prior to analysis must also be agreed. Inedible portions. e.g. bones in fish, will probably be discarded. Any washing process must be specified and carefully controlled. The highest concentrations of pesticides are found on the surface of the produce. Hence, peeling will greatly lower the levels found on analysis. Washing is much less effective. Heat does not destroy organo-chlorine compounds but cooking may remove such compounds from meat and poultry by leaching of the fat. Organo-phosphoruscompounds are systemic but are alkali labile. Generally. cooking and preparation removes 50-95 per cent of the residue. The treated product will then need to be homogenized by maceration or grinding. Commodities such as fresh meat or milk deteriorate rapidly if not analysed 7.1.2

Sec. 7.21

Trace elements

185

immediately or stored at - 20°C. Some organo-phosphorus compounds are very labile and this can be accelerated by pretreatment processes. Exposure to direct sunlight and metallic surfaces should be kept to a minimum. Contamination from the laboratory environment. reagents. equipment or plasticizers in particular must be avoided and checked by the analysis of 'blank' samples. Analytical methods for pesticide residues comprise extraction. clean-up (i.e. removal of co-extractives) and detection steps. Acetone, acetonitrile and hexane are the most commonly used solvents for extraction. Anhydrous sodium sulphate is often added to remove water and reduce emulsion formation. Partition into other solvents is often practised to remove fats or plant material. Further purification is then effected by column chromatography using Florisil. alumina or silica gel prior to separation and detection by GLC using selective detectors such as the ECD, AFID or FPD. I t is essential that presumptive results of the presence of identified residues are confirmed, if possible, by an alternative technique based on a different physicochemical principle. Many workers rely on a separate GLC column containing a stationary phase of different polarity to that used in the first column, but this approach is limited in its validity and discrimination. Capillary columns increase the separating power available and two detectors used in parallel can also provide confirmatory evidence. Chemical derivatization techniques may be appropriate in some cases but G U M S offers the only unequivocal confirmation of identity where resources permit, although it is probably not sensitive enough to detect the lowest levels that may be found by other means. Consideration must also be given to analytical quality control to establish satisfactory standards of repeatability, recovery and limit of determination. The Committee for Analytical Methods for Residues of Pesticides and Veterinary Products in Foodstuffs examined the available procedures for the determination of organo-chlorine compounds in animal fat and eggs and recommended the method described by Telling el al. (1977). This method enabled HCB to be determined at the same time as other residues which could be detected down to 5-10 p.p.b. I t was less sensitive for DDT and related compounds. which could only be detected above 20-30 p.p.b. The lipophilic properties of the organo-chlorine pesticides make them more difficult to extract from animal fats in comparison with fruit and vegetable products. Inevitably, the extract contains more interfering co-extractives which have to be removed by chromatography on an alumina column prior to determination by GLC. In the USA, the Mills procedure (AOAC, 1990) using Florisil is preferred. 7.2 TRACE ELEMENTS The use of fertilizers to increase crop yields is well known and normally does not give rise to problems of contamination in the resulting food supply, though concern has been expressed regarding the increasing concentrations of nitrates and cadmium found in the environment, allegedly from fertilizer sources. The use of sewage sludge containing toxic elements or micro-organisms as a fertilizer on cultivated land has also been questioned. These dischargesdo contain useful quantitiesof nutrients such as nitrogen and phosphorus. but not potassium, and the sludge also acts as a conditioner to improve the soil structure. especially on sandy soils, being a good

I86

Other contaminants

[Ch. 7

source of organic matter. However, sewage sludge may also contain a number of heavy metals from industrial discharges which, whilst often essential at low concentrations. can exhibit toxic effects at higher levels. Arsenic, cadmium, lead and mercury may be hazardous even at relatively low concentrations. Generally, heavy metals are unlikely to be removed by leaching, leading to a build-up in the soil, where they may be ingested by grazing animals. Some elements, e.g. copper, nickel and zinc, are toxic to plants and cadmium is readily translocated in plant tissues (Royal Commission Report, 1979). Copper is toxic to sheep and many trace elements are toxic to fish when leached into watercourses. Nevertheless, many of these inorganic elements are known to be essential to human and animal life. Deficiencies can cause problems unless corrected by supplements added to the diet. Deficiencies or excesses of inorganic elements may reduce the productivity of livestock. The subject has been reviewed extensively by Underwood (1981). Whilst the function of mineral constituents in the diet is still imperfectly understood, it is now thought that 22 elements are essential for life, although in some cases the evidence is by no means conclusive since it is very difficult to feed an animal on an artificial diet which is totally deficient of trace quantities of a given element over a long period. The list of essential elements contains seven macro-constituents, i.e. calcium. phosphorus, potassium, sodium. chlorine, magnesium and sulphur, together with 15 trace elements, i.e., iron, iodine, zinc, copper, manganese, cobalt, molybdenum, selenium, chromium, tin, vanadium, fluorine, silicon, nickel and arsenic. These elements are thought to perform three functions in the body (Underwood, 198 1 ): (1) as structural components of organs and tissues. e.g. calcium, phosphorus.

fluorine and silicon in bones and teeth; (2) as constituents of body fluids required to maintain osmotic pressure, acid-base balance and membrane permeability, e.g. potassium, sodium, calcium, magnesium and chlorine, (3) as constituents or activators of enzyme systems, e.g. iron, copper, zinc, cobalt, manganese, molybdenum and selenium. Where deficiencies of any of the above elements occur. the problem can be removed by additions to compound feeding stuffs. Alternatively, deficiency in cobalt is often corrected by spraying over grassland, thus entering the animal's diet during grazing. On the other hand, some elements cause problems when present in excess. Such excesses are not easily removed from an animal's diet, although the effect may be ameliorated by the addition of other, protective, elements. Included in the group of potentially toxic elements are arsenic, cadmium, copper, fluorine, mercury, molybdenum, selenium and zinc. Whilst all elements are toxic if present in sufficient quantity, the preceding elements are often toxic at very low concentrations even though they also appear to be essential to life. The dividing line between toxicity and nutrient requirement is often very narrow. For example, selenium in the form of selenite or selenate may exhibit toxicity at levels above 2 p.p.m., whereas concentrations below 0.05 p.p.m. may produce deficiency symptoms. The toxicity level of an

Sec. 7.21

I87

Trace elements

element is frequently affected not only by the type of animal but also by the presence of other constituents also present in, or absent from, the diet. For example. only 25 p.p.m. of copper may cause poisoning in sheep (especially when molybdenum and sulphur are deficient). whereas pigs and cattle are more tolerant. Indeed. copper is used as a growth promotant in pig feeds up to 175 p.p.m. At the same time. copper exerts a protective action in t h e case of toxicity to molybdenum. The presence of calcium ameliorates toxicity to zinc and, perhaps surprisingly, mercury affords protection against poisoning by selenium. Other dietary constituents may also be important. Selenium is now thought to act as a substitute for vitamin E in the diet. The maximum concentrations of individual inorganic elements permitted in animal feeding stuffs in the UK and the EC are shown in Table 7.3; the more Table 7.3 - Prescribed limits for trace elements in feeding stuffs Element

Feed

Arsenic

Straights Except lucerne. grass. sugar-beet pulp Phosphates, fish-meals Mineral Complete Straights (vegetable) (animal) Phosphates Mineral Complete (not young animals) Straights Grass-meal. lucerne, clover Phosphates Yeast Complete Mineral Straights Fish-meal Complete

Cadmium

Lead

Mercury

Maximum content (p.p.m.) referred to a moisture content of 12%

-3 4 10

12

2 1

2 10 5 1 10

40 30 5 5 30 0.1 0.5 0.1

important of these elements in animal husbandry will now be considered in more detail. Methods of determination of trace elements in organic matter generally follow the same principles, although many variations in individual procedures have been recommended. The subject has been reviewed comprehensively by Crosby (1977) and by Reilly (1980). Validated methods have been published by the Analytical Methods Committee (1991) and by the AOAC (1990).

188

Other contaminants

(Ch. 7

Arsenic Arsenic trioxide is obtained by roasting naturally occurring ores. The toxicity of arsenicals makes these compounds ideal for use as insecticides, weed-killers and wood preservatives, although paradoxically medicinal uses for both humans and animals have been reported in past years. Arsenic occurs widely throughout the environment, being present in some mineral ores and released during coal burning, and may be thought of as a natural constituent of seafoods. Fish which live close to the sea bed, such as plaice. dabs. flounder and skate, generally contain higher levels of arsenic than most other fish, apart from carp and whelks. The trivalent form of the element is more toxic than the pentavalent state. Arsenates are rapidly excreted from the body by the kidneys,whilst arsenites bind to tissue proteins and accumulate in body tissues such as hair, liver and muscle. Arsenicals are now little used in human or animal medicine, except for the control of E . coli infections, or as growth promotants in some animal feeds. Small amounts of arsenic derived from natural sources may be found in animal feeding stuffs containing fish-meal. The Arsenic in Food Regulations (1959) imposed a general limit of 1 p.p.m. for most foods, and up to 2 p.p.m. is permitted in the majority of animal feeding stuffs. In the UK, a survey of foods for content of arsenic has been reported (MAFF, 1982a). Most fish contained < 5 p.p.m. and a level of 10 p.p.m. was only rarely exceeded. Pig and chicken livers showed consistently elevated levels, although still close to the limit of detection. Samples of fish were first ashed with magnesium nitrate up to 500°C overnight to convert organically combined arsenic to the pentoxide. Other samples were digested with a combination of nitric and sulphuric acids and then examined by atomic absorption spectrophotometry, after conversion to the hydride using sodium tetrahydroborate. The determination of arsenic in foods has been discussed by Evans et al. (1979). They were able to obtain recoveries of added arsenic in the range 88-103 per cent at a level of 0.095 pg. The application of this method to individual foods and total diet samples showed that only very low levels of arsenic were being ingested by the average population in the UK. The intake was calculated to be 89 pg per person per day, which gives an adequate margin of safety over the recommended AD1 of 50 pg/kg body weight (equivalent to 3.5 mg for a 70-kg adult). Methods for the determination of total inorganic arsenic in fish products have been described by Brooke and Evans (1981). Daghir and Hariri (1977) reported a trial in which an organo-arsenical compound was fed to chickens at two levels (50 and 100 p.p.m.) for 15 weeks. An accumulation of arsenic was observed, reaching a maximum in weeks 4-6. The concentration then slowly decreased and had reached negligible proportions in two weeks after withdrawal of the drug from the feed. 7.2.1

7.2.2 Cadmium This element is obtained as a by-product of zinc or lead smelting and is also used for plating, in alloys and as a pigment. It is found at low concentrations in fertilizers derived from phosphate rock. Uptake of cadmium from the soil by plants results in oral intakes that have given cause for concern in one area of t h e UK which lieson the site of disused zinc and lead mines. Whilst the population was advised to refrain from consumption of locally grown crops, samples of animal products such as milk, chicken or eggs were found to contain no higher levels of cadmium than products

Sec. 7.21

Trace elements

189

obtained from other parts of the UK. Cigarette smoke is another major source of cadmium. Such exposure leads to an accumulation of cadmium in the body, since the biological half-life is at least ten years. Cadmium is known to be toxic to the kidney in man but general exposure levels do not cause concern. Less than 10 per cent of ingested cadmium is absorbed. the remainder being excreted via the kidney. A study of UK total diets published in 1983 (MAFF) suggests that the mean daily intake of cadmium is below 20 jig per day. The major contribution to this total came from animal offal and shellfish. containing up to 0.4 p.p.m. Slightly higher intakes have been reported in the USA and Japan but these are still well below the provisional tolerable weekly intake of 400-500 jig recommended by FAO/WHO. Methods of analysis of foods for cadmium are based on digestion with acids followed by chelation and solvent extraction. Determination can be completed using flame, or carbon furnace. atomic absorption spectrophotometry, or using inductively coupled plasma emission spectroscopy. Concern over pollution of the environment has led the E C to control levels of cadmium in animal feeds as shown in Table 7.3. 7.2.3 Copper Copper occurs in the earth's crust in several different forms and is widely used in industry as a result of its desirable physical and electrical properties. Copper is an important constituent of a number of different enzyme systems in man and animals. It is also used as a fungicide and as a growth promotant in pig feeds. There is a propensity for shellfish (especially oysters) to accumulate the element, and uptake from soils by certain plants is known to occur. Fish and algae are sensitive to copper, as are sheep: other mammals and man are much less sensitive. The determination of copper in foods is usually performed after acid digestion by atomic absorption spectrophotometry. or colorimetrically using diethyldithiocarbamate reagent. The limit of detection varies between 0.05 and 0.02 p.p.m. The major sources of copper in the diet are cereals, meat, fruit and vegetables. Offals again contain much higher levels than muscle tissue. High concentrations can be found in crab. lobster and tomato ketchup. A study of the UK diet suggested (MAFF 1981) that the average daily intake was < 1.8 mg, very slightly below t h e value suggested by WHO as adequate. 7.2.4 Lead The major source of environmental pollution arises from the use of lead compounds as 'anti-knock' agents in motor fuels. Concentrations of lead in soils fall rapidly with distance from major roads. Soluble lead compounds can be translocated through plant tissues. Levels in soils may also be increased by the use of sewage sludge. Early surveys of lead in foods showed that canned foods were a major contributor to the UK diet (MAFF, 1982b). Modern canning techniques no longer require the use of lead solders. Results reported in 1982 showed that the mean daily intake was 0.7mg per week - well below the FAOIWHO level for adults of 3mg per week. Reductions in lead additives in petrol in recent years should further reduce the exposure of the population (particularly children) to lead pollution. The maximumpermitted concentration of lead in food was reduced from 2 p.p.m. to I p.p.m. in

190

Other contaminants

[Ch. 7

1980. Methods of analysis are based on acid digestion, chelation and solvent extraction. followed by atomic absorption spectrophotometry. giving a limit of detection i n the range 0.01-0.05 p.p.m. Slightly higher levels of lead are permitted in animal feeding stuffs (Table 7.3). However. lead contamination is not normally a problem and few feeds are tested for this element. In 1989 a consignment of rice bran was contaminated during shipment from Burma to Belgium. On arrival in Belgium the product wassold and reprocessed into animal feed in Holland. Some of this product was imported into the U K (2000 tonnes) and fed to cattle in the Midlands. Wales and south-west England. Many cattle died but emergency powers were taken to ensure that cattle. beef, milk and dairy products from affected farms did not enter the human food chain. U p to 9000 p.p.m. was found in some samples of feed. 7.2.5

Mercury

This element has been used by man for many years on account of its special physical and chcmical properties. Uses have included the 'silvering' of mirrors and as an amalgam in dental restoration work. I t is also used in thermometers. barometers and a s an electrode in the chlor-alkali industry, which subsequently discharges contaminated effluents into the sea. In recent years the perils of exposure to mercury vapour have become recognized. It readily forms stable organo complexes with methyl and sulphydryl groups. which can interfere in biological systems. Methylation can occur in sediments at the bottom of a lake or sea and the resulting organo-mercurial is rapidly taken up by living organisms such as plankton, so entering the food chain. Organo-mercury compounds were formerly used extensively as seed dressings and chiefly affected wildlife. although occasional cases of poisoning in humans have been reported. Saha and McKinlay (lY73) showed that normal agricultural use of dressed seed did not affect levels of mercury in wheat. However, in the U K the use of mercury-based seed dressings will no longer be approved after March 1992. The presence of mercury in animal feeding stuffs can arise either from wheat grown from treated seed, or from the use of fish-meal as ingredients. Compound feeds should not contain more than 1 p.p.m. (Table 7.3). The relationship between concentrations of mercury in the feed and levels in animal products has been investigated. Smart and Lloyd (1963) found that both total and organo-mercury accumulated in eggs, more being found in egg-white than in the yolk. Seller a!. (1974) later attributed this to binding by the protein ovalbumin. A case in which 14 members of a family ate eggs from chickens fed mercury-treated seed grain was reported by Enplender er ril. (1980). Blood mercury levels were found to cotrelate well with the number of eggs consumed. Phenyl mercury was found in samples of the grain at a level of 9.1 p.p.m.. with total mercury at 13.0 p.p.m. The eggs contained 3.0 p.p.m. of total mercury in the yolk and 4.5 p.p.m. in the white, whilst muscle tissue contained 0.86 p.p.m. (leg) and 1.48 p.p.m. (breast). Higher concentrations were found in offal. However, methyl mercury levels predominated over phenyl mercury in the eggs. despite a 9:1 ratio in favour of the phenyl compound in the grain. Fortunately, the accidental contamination of the feed was discovered before serious harm to the family occurred.

Sec. 7.21

Trace elements

191

In the U K some 213000 tonnes of fish-meal are used annually in the production of animal feeding stuffs, approximately two-thirds being incorporated into poultry feed and one-quarter in pig feeds. Worldwide. around 25 million tonnes of fish are processed other than as fresh, frozen. smoked or canned products (Windsor and Barlow. 1981). This source can produce trace quantities of mercury in animal productssince up to0.4 p.p.m. is permitted in fish-meal. Surveysof total diet samples in the UK (MAFF. 1987b) have shown that the dietary intake of mercury is between 2 and 3 pg per day. of which 1 pg per day arises from fish. The highest concentrations are found in fish. shellfish. mushrooms (which can take up mercury from the soil), cereals and offal. Intake of methyl mercury is low. at 1 pg per day on average. and these figures are generally well below the FAO/WHO provisional tolerable weekly intake levels of 0.3 mg (total mercury) and 0.2mg (organic mercury). The determination of mercury in foods and feeds requires considerable care and skill. since losses can easily occur during the pretreatment of the sample to remove organic matter. In 1977. the Analytical Methods Committee proposed a method for fish based on treatment with sulphuric acid. nitric acid and hydrogen peroxide (AMC. 1977). Excess peroxide was removed by boiling and addition of potassium permanganate. A portion of the digest was then treated with hydroxylammonium chloride and tin(ll) chloride solutions before aeration through the cell of an atomicabsorption spectrophotometer fitted with a cold cathode mercury lamp. Concentrations down to 1 p.p.b. could be detected in some cases. Methyl mercury is measured using GLC. as described by Westoo (1967). 7.2.6 Selenium At low concentrations. selenifim acts to destroy peroxides. I t is a constituent of glutathione peroxidase. I t is thought to control muscular dystrophy or white muscle disease in conjunction with vitamin E. It may also ameliorate the toxic effects of cadmium and mercury. At higher levels it is toxic, giving rise to 'blind staggers' in cattle grazing on selenium-rich soils. Addition of selenium to the diet increases selenium levels in milk and eggs but not fat. The verysmall range spanningdeficiency and toxicity levels has stimulated the development of methods of analysis to determine selenium in foods. The AOAC fluorimetric method was critically examined by Michie er ul. (1978). Most problems occur during digestion to remove organic matter. Unless oxidizing conditions are maintained throughout. selenium can be lost as the hydride. which is very volatile. Tetravalent selenium is then reacted with 2.3-diaminonaphthalene reagent. and then examined in a fluorimeter. Levels of selenium in UK goods have been published by Thorn er a!. (1978). Fish and nuts contained the highest concentrations of selenium. An average daily intake of 60 pg per person was computed; this value was somewhat lower than corresponding levels reported for other countries. Summary of data for essential nutrients in ruminants Hansard (1983) has summarized the requirements of ruminants for certain essential trace nutrients (Table 7.4). This shows the typical levels found in feeds. the percentage absorption by the animal and likely concentrations in selected animal tissues. Vos er al. (1987) compared levels of arsenic. cadmium. lead and mercury in

7.2.7

0.03-0.3 5-8

Cobalt Copper Iodine Iron Manganese Molybdenum Nickel Selen i um Zinc

0-I0 60-300 500-900 0.2-10 0.9-1.0 0-50 1540

Range in forage 3-5 1-2 30-50 21 .o 15.0 20.0 12-18 10-40 10-50

(I%)

Absorption

3.3 0.14.3 I .o-2.0 0- 1 .o 0.05 50

Variable

0.2 5-10

Muscle

1 .w 0. I 2.5 70

9.0 2.5

0.25 70-80

Liver

Concentration (p. p. in .)

(1.005 0.1-0.2 0.5-0. 1 0.3-0.6 0.03 3.20 0.03 0.03 3.3

Milk

5-10

> 100 8-10 1000

0.06-0.15 25-40

50-900

100 50- 100 500

Unknown

> 50

Toxic level (p.p.m.1 0.05-1.0 5-10 0.2 35 20 0.01-1 .o

Estimated requircment (P.P.m*1

Summary o f data for selected microminerals in ruminants: absorption, tissue concentration. dietary requirements and toxic levels with range of level in forages

Esse n t ia I rnicromineral

Table 7.4-

7

z

9

Mycotoxins

Sec. 7.31

I93

meat. livers ilnd kidneys of cattle slaughtered in the Netherliinds in the period 1980-85. N o clear trends were observed apart from ;I fall in the lead concentration in kidneys. The values found were compared with those reported for other countries.

7.3 MYCOTOXINS The word 'mycotoxin' is derived from the Greek words 'mykes' (a fungus) and 'toksikon' (ii poison). Mycotoxins are therefore toxic metabolites produced by fungi. usually moulds. Several hundred toxic compounds have hecn isolatcd from moulds but o n l y a small proportion are toxic to mammals. Over the years a number of causal associations between human health iind mycotoxins havc been made but the evidence is only convincing in the case o f ergotamines produced by Clavicq~s pirrpirrca infestations o n rye and wheat. and for islanditoxin from fcriic~illiirm i.slutidicirtn contamination of rice. Nowadays. the most important mycotoxins arc the atlatoxins produced by A.slwr,qillit.s /luvir.s, ochratoxins from Pcwicillitm viridicutum and the trichothecenes isolated from a number of Firsariirm species. These and some other toxins are listed in Table 7.5. The structures of the aflatoxins are shown in Fig. 7.2 and some other Table 7.5 - Some toxigenic moulds and associated toxins

Species A .,puvrr.s

A . oclrrtrcwrs

A . rwsicdor F. griit~iirieurirm F. ro.seiitn

F. s1,orotrichioitle.s P. cirritiirm P. expunsum P. islrtidic~rim P . viridicu/iim

A Hi) t ox i ns Ochratoxin

S te rig ma t ocyst i n Deoxynivalenol Nivalenol Zeiirii lenone Diacetoxyscirpenol T-2 toxin Citrinin Pat u I i n Luteoskyrin Ochratoxin

0.4-3.5 (ducklings) 28 (rats) 8 (guinea pigs) 55 (rainbow trout) > 800 (mice) 46 (mice) 41 (mice)

-

0.4 (pigs) I .2 (pigs) 35 (mice) 10-15 (mice)

-

A , = A.vp(v~,gi//ii.v. F . = F i t w r i i i i u . P. = Pmici//iiini.

mycotoxins in Fig. 7.3. These moulds may contaminate plant products during growth. at harvest or during post-harvest storage. Fungal growth occurs o n l y under conditions of favourable temperature and humidity. Optimum temperatures are 2540°C for Aspergilliis and Pctzicillium species and. hence. contamination is more

194

[Ch. 7

Other contaminants

0

0

15 16

0

0

Fig. 7 . 2 - Structurcs of thc ;iH;itoxins

frequently observed in tropical climates. F~r.sariumspecies grow at lower temperatures and so can be found in temperate zones. To prevent fungal growth in sensitive commodities, the product should be dried so that its water activity is below 0.7. This state can be tested by the use of cupricchloride crystals (CuCI,H20). If not more than 50 per cent of such crystals liquefy over a period of a few hours when enclosed in an atmosphere containing a sample of the food. then the product should be safe from mould growth.

Sec. 7.31

195

My cotoxins

@ + ,CO OH

\

/ 0

CH3 CH3

/

0

HO

CH3

Citrinin

Zearalenone

Penicillic acid

Sterigrnatocystin

R l R , R , R g OH

OAc” OAc OCOC4H9

OH

OAc OAc H

OH OH

OH H

OH

OH

..... T-2Toxin

................... Diacetoxyscirpenol

OH OH

................ Nivalenol

;p@--IT R;

................ Deoxyriivalenol

70

‘r7

’51

CH,

17

--H R:,

R:,

Fusarium trichothecene mycotoxins

Fig. 7.3

- Strocturcs 01sonic othcr niycotoxins

Toxicity of mycotoxins Ergotism was probably the first documentated case of mycotoxin poisoning. The disease was also known as ‘holy fire’ and was characterized by necrosis and gangrene 7.3.1

1Y6

Other contaminants

[Ch. 7

caused by the consumption of grain contaminated with CIwiceps p i r r p r e r i . Overwintered mouldy grain in Russia during the Second World War gave rise to alimentary toxic aleukia. and niouldy yellow rice in Japan similarly produced symptomsof vomiting, convulsions and general paralysis as a result of contamination with various species of Perticilliirm. Such symptoms are probably characteristic of trichothecene poisoning. However. it was not until the early 1960s when large numbers of young turkeys died in the UK that mycotoxicoses began to be systematically investigated. As the causative agent was then unknown. the disease was referred t o its turkey->( disease. Eventually. the source of the toxin was traced to a consignment of Brazilian groundnut meal found to he contaminated with A .PUVIIShence. the name 'aflatoxins'. Analysis of the extracted meal revealed the presence of f o u r components; two possessed ii blue fluorescence and two a green fluorescence at different points on the TLC plate. Accordingly. these compounds became known as aflatoxins 0 , .Bz. GI and G 2 .Their structures were later established and are shown in Fig. 7.2. Further work showed that when compound B , , was consumed by dairy cattle it appeared as the4-hydroxylated derivative in the animal's milk and wascalled aflatoxin M , . Toxicological studies showed that B, is a carcinogen in many species when ingested at very low levels, and associations between the incidence of liver cancer in humans and aflatoxins i n the diet have been made by many authors. Thus, the use of preserved cows' milk for baby foods led governments to impose strict limits on the permitted levels of aflatoxins in animal feeding stuffs and on food consumed by humans. A detailed survey of current legislation has been prepared by Van Egmond (1989). Ochratoxin has been identified as a probable cause of nephropathy in pigs in Denmark and as a possible cause of endemic nephropathy in the Balkans (Krogh, 1977). Analytical methods and the results obtained have been reviewed (Crosby. 1984). 7.3.2 Aflatoxins Since aflatoxin B , is a potent hepatocarcinogen in many species of animals, much effort has been expended to develop reliable methods of analysis and to use these methods to survey a large n m b e r of foods and animal feeding stuffs. Chemically the aflatoxins are bisfuranoisocoumarin structures (Fig. 7.2) with high melting points. They are reasonably stable structures except in alkaline media. which open up the lactone ring. Hence. ammoniation has been proposed as a method of detoxification of contaminated food for use in animal feeding. Treatment with hypochlorite followed by acetone is recornmended for the decontamination of equipment in the laboratory. Analytical methods for the determination of aflatoxins have been surveyed by Stoloff (19x2). Most procedures employ an organic solvent, e.g. chloroform, methanol, acetonitrile or acetone, in admixture with water for extraction. This extract is then purified by column chromatography and examined using TLC or HPLC. I n recent years the methods have been improved by using postcolumn derivatization with saturated iodine solution to enhance the sensitivity of t h e final measurement. More rapid clean-up procedures have been developed and methods based on immunoassay can be used either as an aid to clean-up or as a test kit for screening purposes. To improve the analytical data produced. numerous

Sec. 7.4)

197

Tranquillizers

collaborative studies have been organized (Patey el ul. 1991) and reference materials containing certified levels of atlatoxin M , in milk powder can be purchased. Results of food surveillance studies for mycotoxins in the UK diet were published in 1980 and in 1987a (MAFF). The second report showed that levels of M ,in milk supplies have fallen considerably in the period since 1979. Animal feeding stuffs were found to contain levels of B , up to 400 p.p.b. arising from ingredients such as palm kernel expeller cake and groundnut. The Feeding Stuffs Regulations (1986) established limits for levels of B , in animal feeds as follows: Straight feeds Complete feeds for cattle (except dairy cattle) Complete feeds for pigs and poultry (except young animals) Other complete feeds Complementary feeds for dairy cattle

50 p.p.b. 50 p.p.b. 20 p.p.b. 10 p.p.b. 1 0 p.p.b.

Therefore, most foods and feeds in the developed world now contain amounts of atlatoxins which are very low indeed and pose no threat to man or animals. I t is unlikely that any significant progress can be made in the future. Monitoring will still be required to ensure that levels do not increase. 7.3.3 Ochratoxin Ochratoxin A is the most toxic of compounds in this group. Its presence in pig feeds arises mainly from cereals. I t causes kidney damage in pigs to the extent that visible abnormalities are readily detected at the slaughterhouse. Methods of analysis for ochratoxin in foods have been published by Hunt er af. (1979, 1980). These methods involved enzymatic digestion, dialysis and HPLC with post-column derivatization. A limit of detection of 1 p.p.b. can be achieved. Few foods or feeds in the UK contain detectable levels of ochratoxin A. 7.3.4 Trichothecenes This group consists of a large number of compounds produced by Fusarium species. They are found particularly on cereals. Canadian wheat in 1980 was contaminated with deoxynivalenol up to 8500 p.p.b. Contamination also occurred in 1981 and 19x2. Some UK-grown cereals have been shown to contain small amounts of the trichothecenes. Methods of analysis have been developed by Gilbert er af. (1983).

7.4

TRANQUILLIZERS

Tranquillizers are administered to animals for sedation prior to anaesthesia or in preparation for transport to market. Stress in animals is known to produce a deterioration in meat quality and pigs, in particular, are most likely to become stressed during transportation. Some compounds available for use are shown in Fig. 7.4 and Table 7.6. In general most compounds are metabolized rapidly within the

Other contaminants

[Ch. 7

F-o-s0

Azaperone

Acepromazine CH3

'/y\;

&

OH

CH,

H

I

H Carazolol

Chlorprothixene

Fig. 7.4 - Structures ol'somc triinquillizcrs.

Tranquillizers

Sec. 7.41

H

199

CH3

Xylazine

CH3

Chlorpromazine

i

,)

H3C

N' I

CH3

Propriopromazine

animal's body; any residues are concentrated in the liver and/or kidneys. Doses administered fall in the range 0.05-0.3 mg/kg body weight and recommended withdrawal periods are usually one to seven days. Liver and kidneys should be discarded if tranquillizers have been administered shortly before slaughter. Laitem er uf. (1978) used GLC to determine residues of tranquillizers in meat tissues. Those compounds containing sulphur were detected with a Rame photometric detector at 394 nm. Other techniques such as TLC, HPLC and GUMS were used for non-sulphur-containing tranquillizers. The compounds were extracted from a 5-gsample of meat with acetone-sulphuric acid. The extract wascentrifuged, made alkaline and active substances were were partitioned into hexane. Recoveries were only 50-60 per cent but nanogram quantities could be detected. Rogstad and

-91

7J

ate 51 mazine

azine

-8]

61 e 91 327 298

Conducton, Suacron

Rompan

Many names

442

Atravet, Plegicil, Notensil, Soprontin Stresnil, Suicalm

256

220

Colourless crystals, m.p. 140-142"C, sol. in dil. acids, benzene, acetone, chloroform. Sparingly sol. in pet. ether. Insol. in water, alkalis Crystals, m.p. 236239°C

Crystals, m.p. 179-180°C

356 429

Crystals, m.p. 234235°C Oily liquid, amine odour

335 319

P-Adrenergic blocker

Orange-coloured oil, b.p. (0.5 mm) 220-240°C Yellow crystals from ethylacetate, m.p. 1 3 5 1 3 6 ° C soluble in water Crystals, m.p. 73-75°C

326

Vetranquil

azine

Properties

Molecular formula

Molecular weight

Trade names

d and ber]

Table 7.6 - Compounds used as tranquillizers

h

-

Sec. 7.51

Probiotics

20 I

YndestiId (1981) used both packed and capillary columns along with a nitrogenselective detector. They tested samples containing 40-800 ng of tranquillizers and achieved a recovery o f 93 per cent. A limit of detection of 4 p.p.b. was reported. A TLC method for the determination of propiopromazine in pig tissue was described by Olling et d. (1981). The tissue was homogenized. ground with anhydrous sodium sulphate and extracted with petroleum ether in a Soxhlet apparatus. Further clean-up was effected by solvent partition and the resulting extract was evaporated to dryness using a Danish-Kuderna iipparatus. TLC was carried out on polyamide plates and a fluorescence sciinning densitometer was used for quantification. giving limits of detection in the range 2 to I0 p.p.p. Adsorption onto glass surfaces was found to be a problem but recoveries were generally around 75 per cent. The distribution of propiopromazine in pig tissues following administration wits studied. A method for the simultaneous detection of xyliizine. azaperone, acepromazine. propionylpromazine and chlorpromazine in kidney and meat was developed by Etter et al. (1984). Reverse-phase HPLC with a UV detector was used and levels down to between 5 and 10 p.p.b. could be detected.

PROBlOTOlCS Following public concern over the widespread use of antibiotics in animal husbandry and the possibility of residues of such compounds entering the food chain. other methods for the control of diseases in livestock production have been investigated. All animals have a complex mixture of micro-organisms in their gut flora. Some 10'' organisms may be present therein. including over 400 different species of bacteria. The mixture is often characteristic for each species of animal. The population of micro-organisms is generally fairly stable despite host interactions. expulsion by peristalsis and antimicrobial chemicals present in the feed. The gastrointestinal tract of an animal contains beneficial species as well as pathogens. I n the past. antibiotics were used to kill off the latter organisms to maintain a healthy animal but in some cases beneficial organisms are killed as well. Reduction in beneficial organisms may slow down the animal's recovery and reduce its overall performance. Probiotics are designed to increase the numbers of beneficial species. so 'crowding out' and reducing the effects of any pathogens present. Probiotics are therefore defined as microbiological feed supplements which affect beneficially the host animal by improving its intestinal microbial balance. Probiotics may contain live cells or. alternatively, may consist of bacterial stimulants. The beneficial species present in the gastrointestinal tract are mainly lactic acid-producing bacteria, which by lowering the pH value of the medium prevent the proliferation of many pathogenic species such as Escherichia coli. Live cultures may consist of a single species or mixtures of two or more species. The most common organisms employed are Stre~?tococcit.s/creciitm,Lactobacillirs ucidophilus. Bacillirs sithtilis and Srreptococcits cerevisiue. These live organisms should then flourish and overwhelm any pathogens present by depriving them of nutrients. I n this wily better feed utilization should result. removing the need for either antibiotics or growth7.5

202

Other contaminants

[Ch. 7

promoting agents. This is seen as a more natural mode of animal husbandry which gives no problems from residues entering the food chain. The exact mixture of cultures will vary from animal to animal. Generally most success is achieved by feeding the products to very young animals up to weaning. to assist in t h e establishment of desirable gut Hora and offer protection during periods of stress. Other probiotics contain live yeast cultures or bacterial stimulants. The former are fed to ruminants only and appear to stimulate feed intake and digestibility of the diet by increasing the numbers of cellulolytic bacteria within the rumen. Increased volatile fatty acid production has been observed along with reduced methane levels. Bacterial stimulants consist of mixtures of vitamins. trace elements and co-factors in a rumen mixture designed to stimulate the growth of beneficial bacteria. They exert a buffering effect on the intestinal pH value which. above 8,promotes the growth of pat hogens. The mechanism of action of many of these products is not yet fully understood. At present their use is not controlled by licence since no medicinal claims are made by the manufacturers. It is claimed that the cost involved in using the products is saved by the reduction in antibiotics and similar chemicals required. Whilst some field trial results have varied there appears to be agreement that t h e products are most beneficial to very young animals or those under stress. 7.6

BOVINE SPONGIFORM ENCEPHALOPATHY

This disease was first recognized in the UK i n 1986. although a similar disease in sheep and goats called scrapie has been known for over 200 years. The disease is more popularly known as 'mad cow disease'. Scrapie affects the brains of sheep and goats producing distinctive pathological lesions in the tissues and symptoms such as staggering gait. The causative agent has not yet been identified but is most likely to be some type of virus. Over 2000 cases of bovine spongiform encephalopathy (BSE) were identified in the UK in 1988, covering nearly 1700 farms mainly in the south-west of the country. Affected cattle, totalling 26000, have had to be slaughtered and cremated. Concern has increased dramatically in the last few years because it was thought that as the symptoms were confined to sheep and goats there was little chance of the agent getting into the human food chain and affecting man. Creutzfeldt-Jakob disease, however, has similar symptoms in humans. This disease occurs throughout the world, although BSE is confined largely to the UK at present. The source of disease in cattle is thought to be the feeding to cattle of ovine protein contaminated with the scrapie agent. The incubation period could well be anything from two to eight years. and the sudden appearance of the disease in cattle may have been the result of a change in the treatment of ovine waste introduced at about that time. Each year in the UK some 600 million poultry. 15 million pigs. 20 million sheep and 4 million cattle are slaughtered. This results in an animal byproducts industry which has to process around 1.75 million tonnes of waste per year. The process reduces the volume three-fold t o give 400000 tonnes of protein meal and 250000 tonnes of animal fats and tallow. wort1 :;rdund f 100 million. Some 9 million

Sec. 7.71

Salmonella

203

tonnes of animal waste are processed in the EC. The rendering industry was also implicated in the salmonella-in-eggs scare. with the result that it is under great pressure from consumers to justify its piocedures and processes. In the late 1070s the industry switched from a batch process to a continuous process which employed somewhat lower temperatures and a reduction in the use of solvent extraction. I t has been suggested that the agent responsible for scrapie could survive this newer process. although there is no independent evidence to support this view. Furthermore. similar processes are used in other parts of the world where BSE has n o t t o date been identified. The issue is complicated by the fact that there is no diagnostic test for the causative agent and also that it appears necessary for an animal to receive a fairly high dose before it becomes infected. Further pressure o n the rendering industry has come from aesthetic arguments from consumer-s who do not support the feeding of animal protein to animals who are natural herbivores. Nevertheless. if processed waste protein were to be banned from a11 animal feeds. a huse disposal problem would arise which would increase costs to the industry. and ultimately the consumer. as well as posing problems for safe disposal in the environment. Current research is now under way to determine if the infection can pass from older cattle to the young. At present this seems unlikely as outbreiiks have bccn restricted to only a few animals in a herd. unlike foot and mouth disease. Infections in laboratory animals have required large doses and infection planted directly in the brain or blood cells. In the meantime, protein derived from ruminants cannot be used in cattle feed. although this restriction does not apply to poultry or pig feeds. Restrictions have also been placed on slaughterhouses to reduce the chances of crosscontamination from affected animals. Brain. spinal cord, spleen. intestines and thymus tissues cannot now be used asconstituents of food. although offal from calves under 6 months old is excluded from this ban. Such products are not now used in compound feeding stuffs. The latter provision isonly voluntary but has been adopted by the industry to allay public fears over the wholesomeness of products fed to ;in i ma Is. Much work remains to be completed before we have a thorough knowledge of the causative agent. its ability to infect animals. its propensity to cross from one species to another and. hence. the precautions necessary to protect the human species. I n t h e meantime. sensible and pragmatic controls have been implemented. In July 19SK t h e feeding of ruminant-based protein to cattle was banned and certain offals are now banned from use in baby foods. Milk and carcases from infected animals cannot be used for human food. 7.7 SALMONELLA

Over 56000 cases of food poisoning were reported in the U K during 1990 and it is possible that the actual incidence is around ten times the number of reported cases. In I972 the number of reported cases was only around 5000. S o l m m 4 l r r infections are responsible for a large percentage of the cases reported. reaching ;I peak of 2s per cent in 1987. Poultry carries :I heavy load of bacterial contamination. especially in the intestines. There is therefore a great opportunity for infection to occur in slaughterhouses and in the home. The bacteria are killed if the meat is properly cooked but

204

Other contaminants

[Ch. 7

danger arises when uncooked meat is kept near t o cooked meat. so allowing crosscontamination to occur during handling or from cutlery. surfaces etc. Whilst around 1700 strains of Sulmonellu have been identified, the species which present the greatest danger to human health are S. typhimiirium and S . enteritidis. The former is found in unchlorinated water supplies and the environment generally, but the latter is specific to poultry and is not normally present in cattle. There is no doubt that in recent years the numberofcasesof food poisoning has been rising and it seems likely that many of these result from consumption of products from the poultry industry. Nevertheless it was the statement by Mrs Edwina Currie MP - UK government Health Minister - in November 1988 that focused media attention to this problem. Mrs Currie stated that 'most egg production was infected with Salmonellu'. The public interpreted this statement to mean that eating eggs was dangerous. Egg consumption plummeted for a time, although production and consumption have now almost recovered to former levels. S . enteritidis was found in some eggs, although paradoxically more frequently in eggs from free-range production than from battery operations. This raised the question as to the real source of the infection. Sulmoriella could be present in the feed, the drinking water, the environment or transmitted from the breeding birds. Meat and bone meal as an important ingredient of poultry feeds was a prime suspect but the product is heat treated during processing and data from Prosper De Moulder (Wilson, 1990) showed that in a properly operated plant contamination with salmonellu was very low and in fact lower than other ingredients such as soya o r fish-meal. Furthermore. the serotypes of sulmorzellu found were not S. enteritidis. Contamination could well arise from the breeding environment, from drinking water, poor hygiene and husbandry, or faeces. Vertical transmission from breeding stock to eggs has been demonstrated. Hopper and Mawser (1988) examined a flock of 60000 birds and found ovarian or oviduct infection in a small number of birds who had produced infected eggs. In modern production units faecal contamination of eggshells is unlikely to be a significant route for infection. The UK government has taken a number of measures to combat this problem. All businesses processing animal proteins have to register with MAFF, whether o r not the product is used in animal feeding stuffs. Products used in feeds must be sampled and checked by analysis by authorized laboratories for the presence of Sulmonella. Codes of practice for the control of Sulmonrllu in animal by-products have also been published. Meat and bone-meal now no longer contains poultry offal, which is only used for pet foods. Proscribed material such as brain, spinal cord, spleen, thymus, tonsilsand intestinesis not used in the production of meat and bone-meal. Rendering plants operate under conditions designed to kill Sulmonellu. As a further check on its performance. tests for Closrridiu s.p.p. are carried out since these are more heat resistant than Sulmonellu, so if the tests are negative one can be sure that Sulmonellu will not be present either.

REFERENCES Analytical Methods Committee (1977) Determination of mercury and methylmercury in fish. Analyst, 102,769-776. 7.8

Sec. 7.81

References

205

Analytical Methods Committee (1979) Determination of small amounts of selenium in organic matter. Aticily.sr, 104, 778-787. Analytical Methods Committee (1991) Officicil, sturidardised und recommended methods ofutiu1ysi.s. 3rd edn, C. A. Watson. (ed). Royal Society of Chemistry, (in press). Arsenic in Food Regulations (1959) S.I. no. 831. HMSO. London; amended in 1960 by S.I. no. 2261 and in 1973 by S.I. no. 1052. Association of Official Analytical Chemists (1990) Officiul methods of Analysis, 15th edn, K . Hclrich (ed.). Association of Official Analytical Chemists. Arlington, VA.

Brander. G . C. (1986) Chemiculs for utiimal heulrh control.. Taylor & Francis. London. p. 94. Brooke. P. J . & Evans. W . H. (1981) Determination of total inorganic arsenic in fish, shellfish and fish products. Atialyst. 106, 514-520. B u s . D. H . & Lindsay. D. G . (1978) Reorganisation of the U K total diet study for monitoring minor constituents of food. Food Cosrnet. Toxicol., 16, 597-600. Control of Pesticide Regulations (1986) S.I. no. 1510. HMSO, London. C'roshy. N . T. (1077) Determination of metals in foods: a critical review. Analyst. 102.225-268. Crosby, N. T. (1984) Review of current and future analytical methods for the determination of mycotoxins, Food Addit. Contum., 1, 3 9 4 4 . Daghir. N . J. 6t Harris, N. N. (1977) Determination of total arsenic residues in chicken eggs. J . Agric. Food Chem., 25, 1009-1010. De Vos. R. H., van Dokkurn. W., Olthof. P. D. A., Quirijns, J. K., Muys, T. & van der Poll. J . M. (1984) Pesticides and other chemical residues in Dutch total diet samples. June 76-July 78. Food Chern. Toxicol., 22, 11-21. Englender. S. J.. Landrigan. P. J . & Greenwood. M. R. (1980) Organic mercury exposure from fungicide-contaminated eggs. Arch. Environ. HIrh., 35,224228, Etter. R . . Battaglia. R . , Noser, J. and Schuppisser, F. (1984) Nachweis von 'Tranquilizern in Nieren und Muskelfleisch (Determination of tranquillizers in kidney and meat samples. Miti. Gehiete Lehetisti. Hyg., 75, 447-458. Evans, W . H.. Jackson. F. J. 6t Dellar, D. (1979) Evaluation of a method for determination of total Sb, As and Sn in foodstuffs using measurement by AAS with atomisation in a silica tube using the hydride generation technique. Analyst. 104. 16-34. Food and Environment Protection Act (1985) Ch. 48. HMSO, London. Gartrell, M. J . , Craun. J. C.. Podrebarac, D. S. & Gunderson, E. L. (1985) Pesticides, selected elements and other chemicals in adult total diet samples: October 1979 - September 1980. J . Assoc. Off. Anal. Chem., 68. 1184-1 195. Gilbert. J.. Shepherd, M. J. &L Startin, J. R. (1983) A survey of the occurrence of the trichothecene mycotoxin deoxynivalenol (vomitoxin) in U K grown barley and imported maize by combined GC-MS. 1.Sci. Food Agric., 34, 86-92. Hansard. S. L. (1983) Micromineralsfor ruminant animals. Nirir. Abs. Rev. Series B , 53, 1-24. Harries. J. M., Jones. C. M. c(r Tatton, J . O'G. (1969) Pesticide residues in the total diet in England and Wales. 1966-7. I -Organisation of a total diet study.,/. Sci. Food Agric., 20.242-245.

700

Other contaminants

(Ch. 7

Hunt. D. C.. Philp. L. A . bi Crosby. N . T. (1979) Determination of ochratoxin A in .. pig s kidney using enzymic digestion. dialysis and HPLC with post-column dcrivatisation. Antr!\*.st. 104. 1171-1 175. Hunt. D. C. McConnie. B. R. & Crosby, N. T. (1980) Confirmation of ochratoxin A by chemical derivatisation and HPLC. Arrcrlysr. 105. 89-90. Krogh. P. ( 1977) Ochratoxin A residues in tissues of slaughter pigs with nephropathy. N o r ( / . VOI. M e t / . . 29. 402-405. Laitcni. L. Bellow. I . & Gaspar. P. (1978) GLC determination of tranquiliser rcsiducs in body fluids and in the meat of slaughtered animals. J . Cliromutogr.. l56..177-.3?9. Matsumoto. H . . Murakanii. Y . . Kuwabara. K..Tanaka. A. & Kashimoto. T. (1987) Accragc ditily intitkc o f pesticides and PCBs in total diet samples in Osaka. Jitpat~.Bttll. E t / i . i r o i l . COtlti1tti. Toxicol.. 38. 954-958. Michie. N . D.. Dison. J . ti Bunton. N . G . (1978) Critical review of the A O A C Huorometric method for determining selenium in foods. J . Assoc. Off. Awl. ( . l / ( ~ t t / . 61. . 18-51. Ministry o f Agriculture. Fisheries and Food ( 1980)Sirriyy ofrwycotoxins i r i the U K . Food Survcillance Paper no. 1. HMSO. London. Ministry o f Agriculture. Fisheriesand Food (1981) Surtvy ofcopperuridziricitifood. Food Surveillance Paper no. 5. HMSO. London. Ministry o f Agriculture. Fisheries and Food (19%) Survey of nr.sertic in food. Food Surveillance Paper n o . X. HMSO. London. Ministry o f Agriculture. Fisheries and Food (1982b) Survey of leuti it1 food. Food Survcillirnce Paper No. 10. HMSO. London. blinistry o f Agriculturc. Fisheries and Food (1983) Sirrvey ofcutlrniirrn itifood. Food Sur\.cillancc Paper n o . 12. HMSO. London. Ministry of Agriculture. Fisherics and Food (1984) 13rh Reporr of the Sreeririg Group of1 Food Sitr.i-eil/trrrc.e.Food Surveillance Paper no. 14. HMSO. London. Ministry o f Agriculture. Fisheries and Food ( 1987a) Mycoroxitis. Food Surveillance Pitper n o . IS. HMSO. London. Ministry o f Agriculture. Fisheries and Food (1987b) S i r n q of mercury infood, Food Survcillance Paper n o . 17. HMSO. London. Ministry of Agriculture. Fisheries and Food (1990) Report of fhe working purry 011 pcsticitlc resitiirc.s: 19SS-9. Supplement to issue no. 8 (1990) of The Pesticides Register. HMSO. London. Olling. M . . Stcphany. R . W. & Rauws. A. G . (1981) The determination of propiopromazine in animal tissue. J . Vet, P/?urinucol. Thercrp.. 4. 291-294. Patcy. A. C.. Sharman. M . & Gilbert. J . (1991) HPLC determination of aflatoxin lcvcls in peanut butters using an immunoaffinity column cleanup method: A n d . Chem., 7 4 . 76-81. international collaborative trial. J . Assoc. Off. Peattie. M . E.. Buss. D. H.. Lindsay. D.G. %I Smart. G. A . (1983) Reorganisation of the British total diet study for monitoring food constituents from 1981. Food C'ltcm. Toxicot., 21. 503-507. Pesticides (Maximum Residue levels in food) Regulations (1988). S.I. no. 1378. HMSO. London.

Sec. 7.81

References

207

Reed. D. V., Lombardo., P.. Wessel, J. R.. Burke, J. A. & McMahon. B. (1987) The FDA pesticides monitoring program. J. Assoc. Off. Anal. Chem., 70, 59 1-595.

Reilly. C. ( 1980) Metul co,ituminutiori of food. Elsevier Applied Science, Barking; 2nd edition in preparation. Rogstild. A. & Yndestad. M. (1981) Analysis of xylazine in biological material by GLC using packed and capillary columns. J. Chromutogr., 216, 350-354. Royal Commission on Environmental Pollution. Seventh Report (1979) Agriculture u ~ i d p o l l i ~ t i oCmnd. ~ i . 7644. HMSO. London, p. 161. Saha. J . G . & McKinlay, K. S. (1973) Use of mercury in agriculture and its relationship to environmental pollution, Toxicol. Envirorz. Chem. Rev., 14, 27 1-290. Sell. J . L.. Guenter, W. & Sifri, M. (1974) Distribution of mercury among components of eggs following the administration of methylmercuric chloride to chickens. J. Agric. Food Ckem.. 22. 248-251. Smart. N . A. & Lloyd. M. K. (1963) Mercury residues in eggs, flesh and liversof hens fed on wheat treated with methyl mercury dicyandiamide. J. Sci. Food Agric., 14. 734-740. Stoloff, L. (1982) Analytical methods for aflatoxins: an overview. In: Environmetitul carciriogen.~: selected methods of anulysis, Vol. 5 , Some mycotoxins. IARC Sci. Publ. no. 44. H. Egan (ed.). International Agency for Research on Cancer, Lyon. pp. 33-62. Telling. G. M.. Sissons, D. J . & Brinkman. H. W. (1977) Determination of organochlorine insecticide residues in fatty foodstuffs usinga clean-up technique based on ii single column of activated alumina.. 1. Chromatogr.. 137.405423. Thorn. J.. Robertson, J.. Buss. D. H. & Bunton, N. G. (1978) Trace nutrients: selenium in British food. Br. J. Nutr., 39. 391-396. Underwood. E. J . (1981) The mineral nutritioii of livesrock, (2nd edn.) Commonwealth Agricultural Bureau. Slough. Van Egrnond. H. P. (1989) Current situation on regulations for mycotoxins: overview of tolerances and status of standard methods of sampling and analysis. Food Addit. Cotitam.. 6.139-188. Vos. G . . Hovens. J. P. C. 6t Delft. W. V. (1987) Arsenic, cadmium, lead and mercury in meat, livers and kidneys slaughtered in The Netherlands during 1980-5.. Food Addit. Cotirum., 4. 73-88. Westoii, G. ( 1967) Determination of methylmercury compounds in foodstuffs. Acra. Chem. Scunrf.. 21. 1790-1800. Wilson, S. (1990) What future for meat and bone meal? The Feed Compounder, lO(6). 64-68. Windsor. M. & Barlow. S. (1981) Introduction tofishery by-products. Fishing New Books, Farnham.

Legislation Lcgislation is ;I complex subject not made any easier by the convoluted and contorted language used by lilwyers. European legislation (EC) often suffers during translation into the English language since this is done by linguists and legal experts who are not always expert in the technicalities of animal feeding stuffs. The following is a simple account of the important features of current legislation which affects the work of a food analyst involved in the determination of veterinary residues. References are made to the original texts. which should be consulted for an authoritative view.

8.1

DEVELOPMENT OF FOOD LEGISLATION IN THE UK

The UK has been a pioneer in the field of food legislation from the thirteenth century onwards. when an Act was passed to protect the purchaser against short weight in bread. Over the years. adulteration became the major weapon in t h e armoury of dishonest traders. Even the food industry has not been exempt from such malpractices and in the very early days expensive commodities such as tea. coffee. spices. flour and sugar were regularly subject to adulteration with cheap diluents or substitutes. a s diverse a s sand. alum, spent leaves. acorns, water and black lead. During these times. the Guilds were responsible for maintaining the purity of staple commodities in the U K . but there were no really reliable methods of food analysis, although microscopy was a valuable tool for the identification of adulterants. The problem wasexacerbated by the gradual shift of the population from the countryside into urban areas and the effect of the Industrial Revolution. This meant that increasing numbers of people no longer prepared their own food but instead consumed products sold by manufacturers. As a result of the publicity given to these malpractices. the first Adulteration of Food and Drink Act was enacted in 1860. This allowed local authorities to appoint public analysts but few. in fact, did so. In 1872. drugs were included in t h e scope of the Act and the appointment of analysts became mandatory. Inspectors were empowered to procure samples for analysis. However. enforcement remained variable and following further discussions Parliament passed

Sec. 8.21

Current legislation in the UK

209

the 1875 Sale of Food and Drugs Act, which contains the basis of our current law. In 1968. the Medicines Act was promulgated so that there was no longer any need to link the control of drugs with food as in the Food and Drugs Act 1955. then extant and subsequently replaced by t h e Food Act 1984. In turn, this latter Act has been replaced by t h e Food Safety Act 1990. Similar developments in food legislation have occurred in other countries, e.g. the USA.

8.2

CURRENT LEGISLATION IN THE UK

8.2.1 The Food Safety Act 1990 This Act places an obligation on food manufacturers to provide the consumer with food that is safe. wholesome and. in addition, ensures that the consumer is not misled about the character or quality of the product purchased through false or misleading claims on labels. It is also designed to protect the honest trader from less honest competitors. In particular, the Act states (Part 11, Section 7):

( I ) Any person who renders any food injurious to health by any of the following operations, namely: (a) adding any substance to food; (b) using any substance as an ingredient in the preparation of food; (c) abstracting any,constituent from the food; and (d) subjecting the food to any other process or treatment; shall be guilty of an offence.

Regard shall be had not only to the probable effect of that food on the health of a person but also to the probable cumulative effects. These provisions date back to 1872 and have seldom been invoked over the years. However. they would cover the case of deliberate sabotage of foods which has been become a problem in recent years. (2) Consumer protection (Part I 1 Sections 14 and 15) is ensured by the statement: Any person who sells to the purchaser's prejudice any food which is not (a) of the nature. or (b) of the substance. or (c) of the quality, demanded by the purchaser, shall be guilty of an offence. These requirements date back to 1875 and are far reaching. Most prosecutions were brought under this section of previous Acts. The Act also empowers ministers to make regulations covering the composition of food. This may include the use of additives in foods and the prohibition of any contaminant in the preparation of food. Statutory Instruments have been issued covering the use of antioxidants, artificial sweeteners, colours, emulsifiers and stabilizers. flavours and preservatives. Contaminants subject to regulation include

210

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[Ch. 8

arsenic. fluorine. lead and pesticides, although the latter are regulated under the Food and Environment Protection Act 1985. The Meat and Meat Products (Hormonal Substances) Regulations 1989 prohibit the sale of meat from any animal which has had hormonal substances administered to it. The regulations also specify conditions for the analysis of suspected products. Wider powers concerning analysis of animals and fresh meat are embodied in the Animals and Fresh Meat (Examination for Residues) Regulations 1988. These Regulations cover all residues of substances (including metabolites) that have a pharmacological action. Any prosecution would have to be based on the general food safety regulations since at present no residue limits are stated. In addition to the above legislative controls. all meat for human consumption must be inspected as laid down in the Meat Inspection Regulations 1963. but these relate to disease and hygiene and do not encompass analysis for drug or hormone residues. 8.2.2 The Food and Environment Protection Act 1985 This Act authorizes the issue of emergency orders by ministers to prevent the consumption of food rendered unsuitable for human consumption by 'an escape of substances' - to use the formal wording of the Act. These powers were used in 1989 and 1990 when a consignment of animal feed imported into the UK was found to be contaminated with lead. (7.2.4). The orders restricted t h e slaughter of cattle in a designated area. together with the use of animal products from the area for human food. The Act could also be used to prevent a hazard to human health following contamination by radioactivity or an industrial accident. The Act also regulates the use of pesticides. At present in the U K consumers are protected indirectly from drug residues in foods by legislative conirols on animal feeding stuffs, veterinary medicines and medicated feeding stuffs. Together. these regulations cover the manufacture and supply of animal feedings stuffs and, like legislation covering human foods, have been in force for many years. The Regulations cover the labelling. marketing and nutritional aspects of feeding stuffs as well as the use of additives and contaminants. The main provisions of legislation pertinent to feeding stuffs will now be described. A detailed review of the appropriate legislation up to 1987 has been prepared by Williams (1987).

8.2.3 The Agriculture Acts 1970 and 1986 Only Part IV of the 1970 Act relates to feeding stuffs; the provisions apply also to fertilizers but this a p e c t will not be considered further here. The Act lays down an obligation on the seller to provide the purchaser with a written statement prescribing the nature of the material and instructions for its storage and use. Furthermore, the seller warrants that the product is fit for its purpose and that it contains no deleterious ingredients. The Act also makes provision for sampling and analysis and for limits of variation from the statutory declaration. The Act was amended in 1972 by Schedule 4E of the European Communities Act 1972, to comply with the accession of the UK to the European Economic Community in 1973. This had the effect of inserting a new Section 74A which enables the UK to honour its obligations to enact EC Directives into its national legislation. Further

Sec. 8.ZJ

Current legislation in the UK

21 I

amendments hilve been passed so that the definition of animal now includes pet animals. and feeding stuffs now include pet foods. The Agriculture Act 1986 is concerned primarily with the provision of services and goods connected with agriculture and the countryside, together with fees and charges to be levied for such services or goods (including those for veterinary purposes). Otherwise. this Act does not impinge on animal husbandry or veterinary residues in food. 8.2.3. I

Regulations issued under the Agriculture Act (1970) (a) The Feeding Stuffs Regulations (1988) as amended (1989)

New feeding stuff regulations have appeared at regular intervals as required to implement EC Directives emanating from Brussels. The latest amendment, which ciimc into force on December 1 1990, applies only to non-medicated products and modifies the set of regulations issued in 1988. The major change is the introduction of an cquation for the calculation of the metabolizable energy of pig and ruminant feeds based o n analytical determinations of certain components of the feed. together with thc requirements of EC Directive 9044 as they affect limits of variation. The principal purpose of the regulations is to control the marketing and nutritional content of animal feeding stuffs, as well as limiting the content of undesirable substances such as arsenic, cadmium. fluorine. lead, mercury, nitrates. aflatoxins. hydrocyanic acid. theobromine, vinylthiooxazolidone. volatile mustard oil. gossypol and various impurities of botanical origin. Limits for organochlorine pesticides in feeding stuffs were introduced in the 1988 Regulations (see Chapter 7). However. control of most veterinary residues is exercised through parallel legislation issued under the Medicines Act 1968. (b) The Feed Stuffs (Sampling and Analysis) Regulations 1982

This Statutory Instrument defines the methods to be used to take iin official sample of an animal feeding stuff or pet food in order to check the validity of the sti~tutory dcclaration. Detailed analytical methods are laid down for the determination o f moisture. oil. protein. fibre. sugar. ash, trace elements. vitamins. miscellaneous constituents and some contaminants, in accordance with various EC Commission Directives. Two amendments have been issued but these are n o t concerned with veterinary residues. 8.2.4 The Medicines Act 1968 This legislation lays down a framework for the control, safety. quality, efficacy and use of drugs in human and animal medicine. A Medicines Commission was set up to oversee a number of activities including the practice of veterinary medicine through the work of the Veterinary Products Committee, which is charged with responsibility for advising on the safety and use of all drugs administered to animals. I n addition, the British Pharmacopoeia Commission is responsible for the quality of drugs. I t published in 1985 the British Phurmucopoeiu (Veterinury). which is a compendium o f monographs for preparations used in veterinary medicine. The

212

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Legislation

monographs contain the chemical structure of each compound, methods for identification and assay, together with notes on action, use and storage requirements. The manufacture, sale and supply of an animal feeding stuff containing a medicinal product are controlled by Section 40 of the Medicines Act - as amended by section 13 of t h e Animal Health and Welfare Act 1984. This section enabled ministers to issue Regulations for the control and sale of medicated feeding stuffs, to require registration of manufacturers with the Royal Pharmaceutical Society of Great Britain, and in Northern Ireland with the Department of Agriculture for Northern Ireland. and to charge registration fees to recoup the cost of enforcement. The register is divided into two parts. Part A relates to incorporation of medicinal products at a level below 2 kg per tonne and Part B for incorporations at o r above 2 kg per tonne. Detailed codes of practice covering good manufacturing practice, quality control. personnel and training, documentation. premises and equipment have been issued and are available from the Ministry of Agriculture, Fisheries and Food.

8.2.4.1

Regulations issued under the Medicines Act

(a) The Medicines (Feeding Stuffs)(Limits of Variation) Order 1976 This specifies tolerance levels for medicinal products based on the level of incorporation i n t o the feeding stuff. Thus, up to 50 p.p.m., a limit of variation as high as 50 per cent is allowed. whereas at an incorporation rate of over 5 per cent only 10 per cent tolerance is permitted (Table 8.1). An offence is committed if the level of medicinal

Table 8.1 - Limits of variation on medicinal products incorporated into animal feeding stuffs

Limit of variation 70

Products

Level of incorporation

Ant he Im in t ics Antiblackhead drugs Anticoccidial drugs Anti-microbial substances Antiscour agents Arsenicals Growth promoters (except Cu) Hormones Tranquillizers

1. Up to SO mg/kg 2. 50-500 mg/kg 3. 500 mg/kg-0.5% 4. 0.5-5% 5. >5'X

50 40

Copper

I . Up to 200 mg/kg 2. >200mg/kg

50 30

30 20 10

Sec. 8.2)

Current legislation in the UK

213

product in a feed determined by analysis is found to be greater than the specified limit of variation from the declared value on the label. (b) The Medicines (Veterinary Drugs)(General Sale List) Order 1984 This Statutory Instrument includes a list of medicinal products which can be sold with reasonable safety without the supervision of a pharmacist. It includes, however, products such as amprolium for use with pet birds or pigeons only, as well as a wide range of chemicals and natural products not normally considered as drugs. The products remain subject to the provisions of the Medicines Act 1968 with regard to matters such as licensing, labelling, packaging and advertising. (c) The Medicines (Veterinary Drugs) (Pharmacy and Merchants’ List) (no. 2) Order 1989 The latest amendment came into force on 3 January 1991 as Statutory Instrument 1990 no. 2496. I t updates and replaces all four 1989 orders (relating to veterinary drugs. veterinary drugs in animal feeding stuffs aand horse wormers) which may be sold by pharmacists and registered agricultural merchants and saddlers. (d) The Medicines (Veterinary Drugs) (Prescription Only) Order 1991 This order specifies descriptions and classes of veterinary drugs which can only be administered by a veterinary practitioner, or under his direction. It also controls the retail sale of such products which can only be sold in accordance with a prescription supplied by a veterinary practitioner. (e) The Medicines (Medicated Animal Feeding Stuffs) Regulations 1989 as amended ( 1 990) These regulations prohibit the use of medicinal products in animal feeding stuffs except in accordance with a product licence, an animal test certificate o r a written direction given by a veterinary practitioner. The regulations also prohibit the sale of such feeding stuffs except as directed. Registration as described in 8.2.4 is required by these regulations. (f) The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations 1985 These regulations prescribe methods for the sampling and analysis of medicated animal feeding stuffs to check compliance with the statutory declaration. Methods of analysis are specified for acinitrazole, amprolium, avoparcin. buquinolate, clopidol, copper, dinitolmide, ethopabate, flavophospholipol, furazolidone, monensin, nicarbazin, nifursol. nitrofurazone, nitrovin, oleandomycin, sulphaquinoxaline, the tetracycline group. tylosin, virginiamycin and zinc bacitracin. However. many of the methods specified are out of date and have been replaced in modern control laboratories by procedures based on HPLC as described in Chapters 4 , 5 and 6. The above methods still must be used in cases of dispute.

214

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Legislation

8.2.5 Standard withdrawal periods Thc Mcdicines (Labelling of Medicinal Products for Incorporation in Animal Fceding Stuffs) Regulations 1988 require the label of medicated feeding stuffs to include. amongst other things, a statement of the required withdrawal period. When :I verterinarian prescribes the use of medicated products outside the recommendation specified on the data sheet, the withdrawal periods indicated in Table 8.2 should be used. Table 8.2 - Standard withdrawal periods for drugs administered to food-producing animals in the UK

Animal product Meat: sheep and cattle pigs poultry. rabbits Milk: cows. goats, sheep Eggs:

Withdrawal period (days)

28 10

7 7 7

8.3 EC LEGISLATION EC legislation is concerned. in common with that of most other legislative authorities throughout the world. with the quality, efficacy and safety in use of chemical substances in agriculture from the standpoint of their effects on (a) animals. (b) humans and (c) the environment. However, in addition to such laudable objectives. the EC is also concerned that the regulations should not differ amongst the different member states (Belgium. Denmark, France, Germany. Greece, Ireland. Italy. Luxembourg, Portugal, Spain. the Netherlands and the UK). Differing legislation or technical standards distort the conditions of competition in products that are the subject of common market organization and, hence, could produce a barrier to intraCommunity trade. Therefore. most EC Directives in food and agriculture are introduced with a view to the harmonization (or unification) of differing standards throughout member states, so permitting the free circulation of goods. The principal legislation affecting feeding stuffs and veterinary residues is listed in Table 8.3. along with references to the Official Jourtzal of the European C'omtniiriifie.s, which is the authoritative text for all such legislation. Council Directive 90/167 controls the preparation, marketing and use of mediated feeding stuffs. Those directives which seek to control (directly or indirectly) levels of residues in human food will now be considered in more detail. In particular. this will include directives dealing with additives. undesirable substances and hormones. Such

Council Council Commission Council Council Cornmission Commission Council Couiicil Council Council Council Commission Council Council Council Council Commission Commission Commission Cou nci I Commission Council Council Council Commission Commission Council Commission Commission Commission Commission Council Council Council Commission''

Skinding committees

"Community Decisions, not Directives.

Dctcction of rcsiducs

Vctcrinary products in fccdingstuffs

Ccrtnin products

Miirkcting. compounds

Undcsirahlc substances

Additivcs L;itcst amciidmcnt Anncxcs Anncxcs amcndnicnt Guidclincs Horinoncs

CouncillCominission

Bricf titlc 20. 7.70 15. 10.6X 24. 9.76 23. I I .70 29. I 1.84 12. 4.91 19. 4.91 16. 2.X7 31. 7.81 16. 7.85 31.12.85 14. 7.87 18. 2.X8 7. 3.88 17. 5.88 25. 4.90 17.12.73 1.12.76 28. 7.83 3. 6.86 21. 7.86 I . 4.87 19.10.87 2. 4.79 22. 1.90 27. 6.80 31. 3.87 30. 6.82 26. 7.84 6. I I .us 10. 7.x5 2x. 10.86 28. 9.81 28. 9.81 26. 3.90 I4.II.UY

701372" 6M36 I 76179I" 701524 X41587 911248 911249 x71153 811602 851358 851649 x714 lo" XXlIY6" 8WI46 88/299 90121X" 74/63 76l934 831381 861299 86/354 871238 871519 791373 90144 801695 871235 821471 x41443 851509 851382" 861530 811851 8 11852 90/ 167 891610 I'

Diltc

Dircctivc

-

21. 5.88 8. 5.90 I I . 2.74 Botanical impuritics 31.12.76 13. 8.X3 Hg, pets As, Pb, F, Hg, aflatoxin B, I I . 7.86 Aflatoxin. B,,lahclling 2. 8.86 Cd 25. 4.87 Pcsticidc residues 27.1o.w 6. 4.79 Declaration and 1;ihclling 31. 1.90 Tolcraiiccs 22. 7.80 14. 4.87 21. 7.82 Urea, amino acids 14. 9.84 Tryptophan 23. I I .ns 14. 8.X5 Corididn yeasts Bactcria, mcthioninc 7.1 I .X6 Authorization and marketing 6.1 1. X I 6 . I 1 3 1 Analytical, pharniacotoxicology clinical standards 7. 4.90 Mcdicatcd feeding stuffs 2.12.89 Rcfcrencc methods, national laboratories

16. 3.88

7. 3.x7 7. 8.81 23. 7.85 31.12.x.5 11. 8.X7 12. 4.xx

18. 5.91 18. 5.01

9.10.76 14.12.70 8.12.84

Liitcst consolidated version Efrotam ycin Assessment of additives Stilbcncs prohibitcd Supplementary Prohibition Methods of analysis. criteria UK plan for examination of residues Prohibition Trade in animaldmcat BST prohibition

Feeding stuffs Vetcrinary Animal nutrition

3 .ox. 70

L I701I L255123 L279135 L270/I L3 I91 13 L12411 L 124143 L 64/19 L222132 L191146 L3X2122X L223118 LO94122 LO701I6 L12W36 LI w 2 7 L 38/31 L36412O L222/3I L 189140 L2 I2127 L I 10125 L304138 L 86130 L 27/35 L 188123 L102154 L2 I3lX L24512 I L3 14125 L217.27 L3 I2189 L31711 L3 17116 L 92/42 L351139 18. IO.OX

Comments

Diitc

O.J. no.

Table 8.3 - EC legislation on animal feeding stuffs and residues in food

!2 vl

m c,

r0

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[Ch. 8

directives cannot be enforced without agreed and tested methods of analysis. Whilst a number o f procedures for selected analytes have been agreed over the years. the current position is still far from satisfactory. However, the Commission is now actively considering the requirements and performance criteria of procedures for the sampling and analysis of foods and feeds being marketed within the Community. Directive 86/469/EEC is concerned specifically with the examination of animals and fresh meat for the presence of a wide range of residues arising from the use of agrochemicals and is discussed in more detail below. Nevertheless, many of the approved Community methods of analysis are now in urgent need of revision since there have been many improvements in analytical chemistry over the last few years. 8.3. I The Additives Directive (70/524/EEC) This Directive specifies the compounds or substances which can be incorporated into an animal feeding stuff, and at which levels. The introduction to the Directive contains the following clauses:

- Whereas satisfactory results depend to a large extent o n the use of appropriate good-quality feeding stuffs . . . - Whereas animal feeding increasingly involves the use of additives . .. .

- Whereas, as a general rule. 'additives'

means substances which improve both the feeding stuffs in which they are incorporated and livestock production; whereas, for this reason, antibiotics should also be regarded as additives since, when used in small quantities. they have a physiological nutritional effect, although when used in large quantities they have a medicinal effect . . . - Whereas. furthermore, certain purely medicinal substances such as coccidiostats should. during a first stage. be regarded in relation to feeding-stuffs as additives Hence, unlike in U K legislation. no legal distinction is made at present between medicinal additives and other compounds used for nutritional o r formulation purposes. although hormones were initially excluded and subsequently made the subject of a separate directive. Premixtures were included in the legislation from the start. The legislation contains a positive list of substances which were authorized for use in animal feeding. The compounds were listed in two Annexes. For inclusion in Annex I , a substance: (a) must have a favourable effect on the characteristics of those feeding-stuffs or on livestock production when incorporated in such feeding-stuffs; (h) at the level permitted in feeding-stuffs it must not endanger animal o r human health nor harm the consumer by altering the characteristics of livestock products; (c) must be capable of being controlled qualitatively and quantitatively; (d) at the level permitted in feeding-stuffs. treatment or prevention of disease is excluded (apart from substances in Annex 1 (d)); (e) for serious reasons concerning human or animal health, must not be restricted to medical or veterinary purposes.

Sec. 8.3)

EC legislation

217

A supplementary list of compounds (Annex I I ) was permitted under certain safeguards for a period of five years. This Directive, and in particular the Annexes to the Directive, have been amended many times. The latest version of the Directive (84/587/EEC) was published on 8 December 1984. following its adoption on 29 November 1984. The above clauses were not changed significantly but an Annex 111 was included specifying the minimum conditions which must be fulfilled by manufacturers. A consolidated version of the Annexes was published on 12 September 1985 in a Commission Directive (85/429/EEC), but the Annexes have been modified several times since. The latest modification is described in Commission Directive 90/412/EEC. Each Commission Directive refers to the preceding amendment so that it is possible to record all changes made since the previous consolidated version of the Annexes was adopted. In order to check whether additives comply with t h e principles of efficacy and safety to man, animals and the environment, member states require manufacturers to supply a dossier or monograph giving technical details of their trials concerning an additive proposed for inclusion in the Annexes. This requirement in Article 9 of the Directive (84/587/EEC) has been expanded into Council Directive 87/153/EEC. fixing guidelines for the assessment of additives in animal nutrition. The guidelines encompass the identity, characterization and use of the additive, studies concerning its efficacy and toxicity, as well as metabolism, excretion and residues in foods. Additives intended for use only in pet foods need not be subjected to such an exhaustive testing programme as those designed to be fed to livestock from which are derived products to be used for human consumption. Qualitative and quantitative methods of analysis for the determination of the additive, in premixtures and feeding stuffs must be provided. along with methods for the determination of residues of the additive in animal produce. 8.3.2 The Undesirable Substances Directive (74/63/EEC) As in the U K , there is a list of undesirable substances which are not permitted in animal feeding stuffs, where they could affect animal or human health. Maximum permitted levels are specified. Most concern has arisen from the presence of aflatoxin B , present in some batches of groundnuts, palm kernel or copra used as ingredients of feeding stuffs for dairy cows. In the animal, aflatoxin B, is metabolized to a more soluble form (aflatoxin M I ) ,which has been detected at very low levels in cows' milk. Proposals have now been agreed in the EC to amend the Undesirable Substances Directive further by including maximum limits for residues of pesticides (Table 8.4) and cadmium (Table 8.5). These topics are considered in greater detail in Chapter 7. 8.3.3 The Hormones Directive (81/602/EEC) Pressure from consumers to prohibit the use of hormones as growth promoters has been increasing over the years. Following discussions within the European Parliament and in the Economic and Social Committee, the Commission made a proposal to Council which was adopted on 31 July 1981. This Directive prohibits the administration to certain farm animals of substances having a thyrostatic action or substances having an oestrogenic, androgenic or gestagenic action. I t also prohibits

218

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Table 8.4 - Limits for pesticide residues in animal feeds (p.p.m)

Aldrin, dieldrin Camphechlor (Toxaphene) Chlordane DDT Endosulfan

Endrin Heptachlor Hexachlorobenzene (HCB) Hexachlorocyclohexane (HCH) a-isomer p-isomer

y-isomer

All feeds, with the exception of: fats All feeds

0.01 0.2 0.1

All feeds. with the exception of: fats All feeds, with the exception of: fats All feeds, with the exception of: maize oilseeds complete feeds for fish All feeds, with the exception of: fats All feeds, with the exception of: fats All feeds, with the exception of: fats All feeds, with the exception of: fats Compound feeds with the exception of feeds for dairy cattle Straight feeds, with the exception of: fats All feeds. with the exception of: fats

0.02 0.05

0.05 0.5 0.1

0.2 0.5

0.005 0.01

0.05 0.1

0.2 0.01

0.2 0.02 0.2 0.01 0.005 0.01 0.1 0.2 2.0

Council Dircctivc 87/519/EEC.

the marketing of 'treated animals or meat from treated animals. An exception was made in the use of such products for therapeutic use and for certain reproductive functions. Stilbenes and their derivatives were totally banned. In effect, this Directive only prohibited those products which were already banned by member states. since a decision on the use of oestradiol 17-p. progesterone, testosterone, trenbolone and zeranol was postponed. Even though these hormones were subsequently found to be harmless to humans when used under controlled conditions, the Council adopted a further Directive (85/649/EEC) on the 31 December 1985, which prohibited the use of all hormonal substances for fattening purposes. This Directive then became the subject of an action in the European Court ( U K v. Council ofrhe EEC) since, the UK argued. the Directive was adopted under Article 43 of the Treaty establishing the European Economic Community and not under both Articles 43 and 100 as for all other legislation connected with animal husbandry and. in

Sec. 8.31

EC legislation

219

Table 8.5 - Limits for cadmium in animal feeds and phosphates Commodity

Straight feeds of vegetable origin Straight feeds of animal origin (except feeds for pets) Phosphates Complete feeds for cattle. sheep and goats (except calves. lambs and kids) Other complete feeds (except feeds for pets) Mineral feeds Other complementary feeds for cattle, sheep and goats Phosphates (raw material)

Maximum content (p.p.m) (at a moisture content of 12%) 1

2 10 1

0.5 5 0.5

15

Council Dircctivc S7/23S/EEC.

particular. Directive 81/602/EEC. This change had the effect that approval could be obtained by qualified majority voting in place of the unanimity required under Article 100. This argument was initially rejected by the European Court's Advocate General but subsequently supported on procedural grounds in a later judgement and, consequently, Directive 85/649/EEC was declared void. The Court's judgement rested solely on the finding that the Council of Ministers had infringed itsown rules of procedure. However, the Council of Ministers re-affirmed its decision to ban the use of hormones and Directive 881146 was agreed. 8.3.4 Sampling and Analysis of Feeds The basic Directive was adopted by Council on 20 July 1970 (Table 8.3). This was followed by a series of Commission Directives laying down detailed methods of analysis for selected nutrients and medicinal additives. Those of most interest to the residue chemist are indicated in the table. However, many of the procedures are now over 20 years old and better methods are available. as discussed in earlier chapters. I t is to be hoped that the EC will find the time and resources to revise these methods in the near future. 8.3.5 Sampling and analysis of Foods for veterinary residues Whilst the Community has promulgated controls on the trade of animals, meat and meat products both within and from outside over a number of years, it was the adoption of the Hormones Directive (81/602) which gave an impetus to the need for a common position on the examination and sampling to detect residues in such products. Directive 86/469/EEC established sampling levels and frequency according to the type of residue. The specific groups of residue are shown in Table 8.6. Directive 85/358/EEC required member states to control the prohibition of certain

220

Legislation

[Ch. 8

Table 8.6 - Residue groups

A.

GROUPS COMMON TO ALL MEMBER STATES Group I (a) Stilbenes, stilbene derivatives, their salts and esters (b) Thyrostatic substances. (c) Other substances with oestrogenic, androgenic or gestagenic action, with the exception of substances in Group 11. Group I1 (a) Inhibitors Antibiotics. sulphonamides and similar antimicrobial substances (b) Chloramphenicol

B.

SPECIFIC GROUPS Group I: Other medicines (a) Endo- and ectoparasitic substances (b) Tranquillizers and 0-blockers (c) Other veterinary medicines Group 11: Other residues (a) Contaminants present in feeding stuffs (b) Contaminants present in the environment (c) Other substances

hormones and thyrostats. This recognized that there were no agreed Community reference methods of analysis for such substances but that results obtained by radioimmunoassay, TLC or GLC would be recognized if confirmed by an official laboratory. Subsequently by Decision 87/410/EEC the Commission gave equal status to results obtained by HPLC. mass spectrometry and spectrometry (infrared. diode array). This Decision contained a detailed Annex which laid down criteria of acceptability for. inter ulia, accuracy and precision, calibration curves, interferences and the interpretation of the results obtained by individual analytical techniques. Commission Decision 89/61O/EEC gave a list of the national reference laboratories authorized to carry out such work andupdated the definitions and criteria to be used in reference methods of analysis for residues. A further revision is under consideration and a manual of reference materials and methods is being prepared. Thus a complex and detailed uniform legal framework has been established within the members of the Community and this framework is constantly being improved and re-assessed. However, much less attention has been paid to enforcement standards within the different national organizations. 8.4

LEGISLATION IN THE USA

In the early years, food laws were the responsibility of the individual states. The first national food and drug law was passed in 1906. This attempted to prohibit adulteration and brought about improvements in hygiene and labelling. but modern

Sec. 8.41

Legislation in the USA

22 1

legislation stems from the Federal Food, Drug and Cosmetic Act passed in 1938, which set standards for food composition and prescribed limits for poisonous or deleterioussubstances in foods. At this time, the government was required to prove a substance was harmful before its use could be restricted. Subsequent amendments in 1957 (relating to pesticides), 1958 (food additives) and in 1960 (colours) introduced t h e important principle that the safety of ingredients must be established before their use. Effectiveness was introduced in 1962. The 1958 amendment is better known as the 'Delaney clause' and has been the subject of considerable debate. It states that, 'no additive shall be deemed safe if it is found to induce cancer when ingested by man or animal'. This wording precludes any exercise of scientific judgement, however unrealistic the feeding trials of an additive may have been in relation to normal consumption by humans. It means that whatever the benefits conferred by an additive in food, its use is precluded at any level if it is a carcinogen, even though the demonstrable carcinogenic activity in animals only occurs at levels several orders of magnitude greater than normal human consumption. However, balancing benefit and risk is somewhat arbitrary without clear guidelines. Generally, a 'no-observedeffect level' is calculated for each additive on the basis of data collected from animal feeding trials. A further, arbitrary, safety factor of 100 is then incorporated in deciding permitted tolerance levels in foods. However, for carcinogens this approach cannot be adopted because of the Delaney clause and because they usually lack a noobserved-effect level. In such cases. methods of risk assessment have been developed based on animal data and epidemiological studies. These may conclude that the perceived risk of an additive at the normal levels found in foods is likely to produce (say) one case of cancer in a million as a result of the population ingesting the additive over a whole lifetime. Someone then has to take the decision as to whether such a risk is acceptable or not. One in a million may be an acceptable risk to some people but not so to others. The US approach to carcinogens is an absolute legal prohibition and permits n o flexibility or decision making on a case-by-case basis. The problem has been exacerbated by the ability of analytical chemists to detect lower and lower levels of residues over the years. Thus. at one time. the use of diethylstilboestrol (a carcinogen) in animal feeding stuffs was permitted following an amendment of the Delaney clause, since residues of DES could not be detected in animal tissues. The development of radioimmunoassay and mass spectrometry has meant that much lower concentrations of DES can now be detected and residues have been found in liver tissue of treated animals. Hence, the use of DES as a growth promotant is now no longer permitted. Unlike in the EC countries, hormonal substances are still authorized for use as growth promotants in cattle production. American regulations can be found in the Code of Federal Regulations (CFR) published by the Office of the Federal Register, National Archives and Records Administration. The Code is divided into 50 titles. each covering a broad area subject to Federal Regulation. The CFR is prima facie evidence of the text of the original documents and it is revised annually. Food and drugs are covered by Title 21. which is published in nine volumes covering parts 1-1316. Some of the most relevant sections are listed in Table 8.7. Of particular interest are the tolerances for drug residues in foods. The more important substances are listed in Table 8.8. For some

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Legislation

[Ch. 8

Table 8.7 - Code of Federal Regulations (USA)

Title 21 : Food and Drugs Part n o .

Subject

200-299 20 1 .lo5 225

Good manufacturing practice (GMP) for drugs Veterinary, drugs, labelling GMP for medicated feeds

500-599 501 505 509 5 10 510.450 556 558 561 564 573 583 589

Animal food labelling Required warnings. withdrawal periods Unavoidable contaminants in animal feed New animal drugs Sulphonamide residues Tolerances for residues of new animal drugs in food New animal drugs for use in feed Tolerances and pesticides in animal feed Definitions and standards for animal feed Food additives permitted in animal feed Food substances generally recognized as safe in feed Substances prohibited from use in animal food or feed

compounds a range is quoted as the tolerance depends o n the particular animal and tissue involved. This aspect is covered in greater detail for clopidol. as an example, in Table 8.9. The concept of zero tolerance is dependent on the particular analytical method selected for the determination. In the CFR, the method of analysis is described in full experimental detail, where a zero tolerance is required.

8.5 CODEX ALIMENTARIUS COMMISSION Food laws in many developing countries reflect their primary need to ensure an adequate supply of safe and wholesome food of adequate nutritional content for a rapidly expanding population. Pesticides are more widely used and under less rigorous systems of control than in the developed world. Food hygiene to prevent outbreak of disease is another major problem. Furthermore, the climate often increases the risk of spoilage on storage and increased wastage of scarce resources. Together these factors can cause problems to Western nations particularly over exports from developing countries. Many countries in Africa and Asia have regulations which reflect their history in colonial times, although more up-to-date legislation is being introduced. Frequently, progress is inhibited by a lack of administrative, scientific and technical personnel required to enforce such new legislation. In an attempt to facilitate world trade, whilst protecting the health of the consumer, member governments of the Food and

Codex Alimentarius Commission

Sec. 8.51

Table8.8-Code of Federal Regulations: tolerances for residues of new animal drugs in food Drug

Tolerance (p.p.m.)

Ampicillin Amprolium Apramycin Arsenic Bacitracin Buquinolate Carbadox Chlortetracycline Clopidol Decoquinate Dichlorvos Dimetridazole Erythromycin Ethopabate Fenbendazole Furazolidone Gen tam ici n Halofuginone 1pronidazole Ivermectin Lasalocid Levamisole Monensin Neomycin Nequinate N ica rbazi n Oleandomycin Oxytetracycline Penici IIi n Robenidine Streptomycin Sulphanitran Tetracycline Tiamu I in Tylosin Virginiamycin Zeranol

0.01 0.5 -2.0 0.1 -0.4 0.5 -2.0 0.5 0.1 - 0.4

zero zero - 4.0 0.02 - 15.0 1.0 -2.0 0.02 - 0.1

zero 0

-0.125

0.5 - 1.5 0.8 -20.0

zero 0.1 -0.4 0.1

zero 15 0.3 -7.2 0.1 0.05 0.15 - 0.25 0.1

4.0 0.15 0.1

- 3.0

zero - 0.05 0.1 - 0.2

zero zero 0.25 0.4 0.05 - 0.2 0.1 - 0.5

zero

223

224

Legislation

[Ch. 8

Table 8.9- Code of Federal Regulations: tolerances for residues of clopidol in food

A-

B

-

C -

DE-

In cereals, grains. vegetables and fruits: 0.2 p.p.m. In chickens and turkeys: (i) 15 p.p.m. in uncooked liver and kidney (ii) 5 p.p.m. in uncooked muscle tissue

In cattle, sheep and goats: (i) 3 p.p.m. in uncooked kidney (ii) 1.5 p.p.m.. in uncooked liver (iii) 0.2 p.p.m. in uncooked muscle tissue I n swine: 0.2 p.p.m. in uncooked edible tissues In milk: 0.02 p.p.m. (negligible residue)

Agriculture Organization and the World Health Organization of the United Nations agreed to set up a Joint FAOlWHO Codex Alimentarius Commission to coordinate food standards throughout the world. An extensive programme has been undertaken and standards covering the composition, labelling, additives, contaminants, hygiene, sampling and analysis for a number of commodities have been prepared. A large proportion of these standards have already been accepted by member governments. A new Codex Committee on Residues of Veterinary Drugs in Foods held its first meeting in October 1986. An ud hoc Working Group on Methods of Sampling and Analysis has also been established. Once again several papers have been produced setting o u t general criteria of acceptability to be applied to sampling schemes and methods of analysis. There are few differences of substance between the E C and Codex criteria. Perhaps the most urgent requirement at the present time is an agreement on priorities and the adoption of specific methods for use in laboratories.

8.6

REFERENCES

British Phurmucopoeiu (Vererinury) 19c15, HMSO, London, with subsequent amendments. Williams, D.R. (1987) Anirnulfeeding stuffs legishion ofrhe U K : a concise guide, Butterworths, London.

8.6.1 Recent UK Legislation The Food Safety Act, 1990. HMSO, London, Chapter 16. The Food Act, 1984. HMSO, London, Chapter 30. Meat Inspection Regulations 1963. S.I. 1963 no. 1229, HMSO, London. Animals and Fresh Meat (Examination for Residues) Regulations 1988. S.1. no. 848, HMSO, London Meat and Meat Products (Hormonal Substances) Regulations 1989, S.I. no. 2133, HMSO, London.

Sec. 8.61

References

225

Agriculture Act 1970. HMSO, London, Chapter 40. European Communities Act 1972. HMSO, London. Chapter 68. The Agriculture Act 1970. Amendment Regulations 1982, S.I. no. 980, HMSO, London. The Agriculture Act 1986. HMSO. London. Chapter 49. The Feeding Stuffs Regulations 1988. S.I. no. 396, HMSO. London. The Feeding Stuffs (Amendment) Regulations 1989. S.1. no. 2014. HMSO, London. The Feeding Stuffs (Sampling and Analysis) Regulations 1982. S.I. no. 1144. HMSO. London. The Feeding Stuffs (Sampling and Analysis) (Amendment) Regulations 1984. S.I. no. 52, HMSO, London. The Feeding Stuffs (Sampling and Analysis) (Amendment) Regulations 1985. S.I. no. 1 119. HMSO, London. The Animal Health and Welfare Act 1984. HMSO. London. Chapter 40. Medicines Act 1968. HMSO, London. Chapter 67. The Medicines (Feeding Stuffs Limits of Variation) Order 1976. S.I. no. 31, HMSO. London. The Medicines (Veterinary Drugs) (General Sale List) Order 1984. S.I. no. 768, HMSO, London. The Medicines (Veterinary Drugs) (Prescription Only) Order 1991. S.1. no. 1392, HMSO. London. The Medicines (Medicated Animal Feeding Stuffs) Regulations 1989. S. I . no. 2320, HMSO, London (Amended 1990, S.I. no. 1210). The Medicines (Animal Feeding Stuffs) (Enforcement) Regulations 1985. S.1. no. 273, HMSO. London. S.6.2 EC Legislation See Table 8.3 for titles. reference numbers, dates an'd reference to the Official Journal of the Europeati Communities. 8.6.3 USA Legislation Thiscan be found in the Code of Federal Regulations. Part 21. published annually by the Office of the Federal Register, National Archives and Records Administration, US Government Printing Office, Washington, DC.

Conclusions 1. The need to use chemicals in animal husbandry will continue well into the future. So-called 'organically grown' animal products will comprise only a small fraction and specialized corner of the market, limited by the price differential. Medicinal additives will continue to be used both for the therapeutic and prophylactic needs of animals. Similarly, the use of chemicals (fertilizers and pesticides) in the production of food for animals and humans will be maintained. Hence, humans will have to cope with residues of these chemicals both in the food chain and in the environment.

2. Levels of chemicals added to animal feeding stuffs are known and generally well controlled, although the recent contamination by lead highlights the need for eternal vigilance. Analytical methods have been developed to monitor the presence of most medicinal additives, although current statutory methods are largely outdated and should be replaced by methods based on HPLC. Methods' for some antibiotics are less than satisfactory and more resources need to be spent in this area.

3. Analytical methods for residues of medicinal additives in animal tissues are being developed but there is no consensus as to the best method to use for individual residues. Few methods have been validated by international collaborative study trials. In most cases, the methods have been tested only by fortification of test samples in the laboratory with the specified analyte. This procedure, whilst the best available in most cases. does not mirror the natural situation where animals ingest medicinal products in their feed. Many such methods exhibit a wide variation in recovery values, oftcn at levels below 70 per cent. Hence, there is still some way to go before satisfactory methods become available. 4. The importance of biotechnology for the future of the agriculture and food

industries is only being recognized very slowly. Improvements have been made over t h e years in both animal husbandry and crop growing by selective breeding.

Ch. 91

Conclusions

227

However, such changes are slow to produce results. Genetic engineering technology, DNA manipulation and embryonic transfer techniques have the potential to speed up this process quite dramatically. The use of probiotics and enzymes in feed technology is still only in its infancy in terms of commercial development. All these aspects could pose problems in the future for the analytical chemist. 5 . Concerns raised by BSE and BST have appeared only in recent years but could have far-reaching effects on the industry. The causative agent in BSE is still uncharacterized. A trend towards compulsory declaration of ingredients in quantitative terms looks unstoppable. This will pose considerable enforcement problems. not least for the analytical chemist.

6. The UK government has established an Expert Group on Animal Feeding Stuffs to review the regulation of the whole industry. Many of the problems raised in this book fall within the terms of reference of this committee, which is charged with looking at the legislation affecting medicated feeding stuffs and the compositional aspects of feeds. The whole industry, the public and the enforcement agencies will await the conclusions of this review with some eagerness. The committee have the opportunity, and the responsibility, to ensure that the public is reassured and that a suitable regulatory framework exists for the industry to flourish in future years.

10 Suggestions for further reading

GENERAL

Brander, G. C. (1986) Chemicals for animal healrh control. Taylor & Francis. London. Human and animal disease control, uses of antibacterials, antibiotics, anthelmintics, pesticides, coccidiostats, growth promoters, hormones, legal aspects. No information on analytical methods. Budavari, S. (ed.) (1989) The Merck Index: an enclopedia of chemicals, drugs and biologicals, 11th (edn.). Merck, Rahway, NJ. Chemical and physical data on individual compounds, references to synthesis, structure determination and efficiency in animal trials. Ewing, W. & Haresign, W. (1989) Probiotics UK. Chalcombe, Marlow. Mounsey, H. G. (ed.) (1990) Handbook ofmedicinalfeedadditives,9th (edn.) HGIW Publications, Bakewell. NOAH (1990) Compendium of data sheets fer veterinary products 199&1. Datapharm Publications, London. Stark, B. A . & Wilkinson, J. M. (1989) Probiotics: theory and applications. Chalcombe, Marlow.

CHAPTER 1: AGRICULTURAL PRACTICE

Minshull, G. N . (1990) The new Europe into the 1990s, 4th edn., Hodder & Stoughton, London.

CHAPTER 2: ANALYTICAL METHODOLOGY

Denney. R. C. & Sinclair, R. (1987) Visible and ultraviolet spectroscopy. Analytical chemistry by open learning. Wiley, Chichester.

Ch.

lo]

Suggestions for further reading

229

Dickes, G. J. & Nicholas, P. V. (1976) Gas chromatography in food analysis. Butterworths, London. Hill, H. C. (1972) Introduction to mass spectrometry, 2nd edn. Heyden, London. Johnstone, A. & Thorpe, R. (1982) fmmunochemisrry in practice. Blackwell, Oxford. Lindsay. S . (1987) High performance liquid chromatography. Analytical chemistry by open learning. Wiley, Chichester. Macrae, R. (1988) H P L C in food analysis. Academic Press, London. Morris, B. A. & Cliford, M. N. (eds) (1985) Immunoassays infoodanalysis. Elsevier Applied Science, London. Morris, B . A., Clifford, M. N. & Jackman, R. Immunoassays for veterinary andfood analysis - I. Elsevier Applied Science, London. Roitt, 1. M. (1984) Essential immunology, (5th edn.) Blackwell. Oxford. Stahl. E. (1966) Thin-layer chromatography: a laboratory handbook. Allen 8c Unwin, London. Tijssen, P. (1985) Practice and theory of enzyme immunoassays. Elsevier, Amsterdam. Willett, J . E. (1987) Gas chromatography. Analytical chemistry by open learning. Wiley, Chichester. Zlatkis, A. & Kaiser, R. E. (eds) (1977) HPTLC: high performance thin-layer chromatography. Elsevier, Amsterdam. CHAPTER 4: ANTIBIOTICS

Drucker,' D. B. (1987) Microbiological applications of high-performance liquid chromatography. Cambridge University Press, Cambridge. Moats, W. A. (ed.) (1986) Agricufturaf uses ofantibiotics. ACS Symposium Series 320, American Chemical Society, Washington, DC.

P;igc nunihcrs in h l d type indiciitc thc 1tw;ition oT the strucrural formulac of namcd compounds

itcccptahlc daily intitkc (ADI). 178. 184. IS8 ;in t ihiorics. 6 I6 arsenic. 151. 188 oliiquindox. I58 iiccpromazinc. 198. 2(Ml. 201 ;icinitr;izolc. 125. 126. 139. 141, 142. 143 additivcs in fccds. 9. 20. Z I . 33 iitliitoxins. 23. 29. 44. 193. 194. 196-197 B,.limits in rccds. 197 dccontiimination. 196 legislation. I96 moulds producing. 193, I96 rlc, 196 inlhcndazolc. 67.68. 76. 78 aininoglycosidcs. 86. 90. 91. 92 ;impicillin. I 1.5 iiinprolium. 125. 126. 133. 135. 139. 140. 143. 213 nninholic agcnts. 140. I63 ;in;ilysis clciin-up. 40.44 cxtriiction. 37.39. 4.344. 4.5 sensitivity. 37. 39. 42. 10-1 spccilicity. 37. 39. 41. 104 stitgcs in. 39-41 ;inalytical mcthods itccuriicy. 39. 12 critcriii of. 42 detection limit. 42 dctcrmin;ition limit. 42 multi-residue Tor drugs in fccd. 40. 141 rcfcrcncc. 41 rcguliitory. 41. 43 screening. 40 viilidntion. 41 mthclmintics. 9.20. 3 5 . 6 7 8 . 212 iictivu ingredients. 68-73 chcmic;il/physic;il propcrtics. 68-73 FAOlWHO limits Tor. 77-78 mct;ibolism. 67. 74. 78 ;intihiotics (;intihiictcrials). Y. 20. 21. 35. 81-1 16 ils growth promotcrs. 83-84. 1 0 1 . 103. I4X. 150

definition of.XI-X2 clectrophorcsis. 107 glc. 109-I 10 hplc. I I(L1I-l inhibition zoncs. lO4-lO6 mcthods. 103-1 IS tlc. IOprl09 anti hodics . 6 1-64. antigens. 61-64 ant isc p t ics. X I -X2 apramycin. X3.86.87.90 arprinocid. 125. 126. 133. 139. 142. 143 arsanilic acid, 151. iS2 arsenic. 179. 184. 186. 1x8. 191-193.210 limits in feeds. 151. 187. 1x8 arsenicals. X3. 133. 134. 141, 151. 188. 212 avcrmectins. 74 avilamycin. 109. 152. 154 avoparcin. X3. X7.94.98. 125. 150 detection limits. 10s. 107 four-platc rest, 105. 107 growth promotant. 152. 155 hplc. I I2 inhihition zoncs. 104-105 azapcrone. 198. 200. 201 hncitracin. 83.81.94.98. 125. 153. 162 detection limit. 107. I08 hplc. 112 tlc. lox hamherrnycin. X3.86.87. 90. 1.52. 15.5 hcnzimidazolcs. 67.75.76 mcthods. 71-76 rcsiducs. 7.5. 77 hcta-agonists. 172- 173 hctiAiictam compounds. 92. 93. 94 hplc of, 112-1 I4 BHC. 179. 181 bolus. 67. 71 bovine. somatotropin. 171 mcthod. I72 hovinc spongiform cnccphalopathy. 9. 30. 202-203

huquinolare. 125. 127. 133. 134. 139. 143 cadmium. IXS. 1x6. IXX-189, 191-193

Index limits in Iced. 187.219 camhcndazoic. 67.68.74. 76 c;trazolol. 198.2OU carhiidox. 125. 139. 143. 152. 155

MRL. I56 ccphitlosporins. 92.93.94 chlorirmphcnicoi. 83. 87, 100. 102. 105 card tcst. I 15 dctcction limits. 107 four-plate tcst. I07 hplc. 112

MRL. I16 rcsiducs. I 15 chlorpromazinc. 119. 200. 201 chiorprothixcnc. 198 chlortctracyclinc. 88. 102. I06 detection limits. 107

MRL. 116 chromatogr;tphy. 45. 46 clean-up. 44 glc. 46. lo()-I I 0 hplc. 45-46. I I(I-I 1.5 tlc. 46. 10s-IOY cimiitcrol. 172-1 73 clcnhutcrol. 172-173 clopidol. 125. 127. 13.3-134. 138. 139. 142. 143 tolcranccs in food. 224 closnntcl. 68. 77 cloxacillin. I08 hplc. I13 cohalt. 67. I86 coccidiosis. 13-125 coccidiostiits. 20. 35. 108. 12.3-144 multiresiduc method. 125 cooking. cffcct of. antihiotics. I 15 ivcrmectin. 77 coppcr. h7. 186. 1x7. I89 its growth promoter. 23. 152. 156. IS9 cypcrmcthrin. 181

p.p’DDD. IS4 p.p‘DDE. 183. 181 DDT. 179. /XI. 183, 185 dccoquinatc. 125. 127. 134. 139. 143 dcltamcthrin. 181 dcmcton-Smcthyl. 181. I83 Dcrris. 179 di;tvcridinc. 125. 127. 134. 139. 110. 141, 142. 143 dinzinon. I83 dichlorvos. 67.68. I79 dicldrin. 179. 183. IS4 dicnoscstrol. 140. 103. 16.5-166 dicthylstilhocstrol. 14Y. 163. Ih$. 166. 221 methods. I69 dimctridasolc. 125. 128. 1.34-135. 137. 139. 142.

I43 dinitolmidc. 125. 128. 139. 139. 141. 142. 143 disinfcctants. 81 iodo compounds ;IS,81-82 drug rcsiducs. .swrorder ir~dividrcu/nuttied ~~oltl/~f~llfld.s

23 1

EC agricultural policy. 1.5 Dircctivcs. 215 cxccss production. 15. 21.23 mcmhcr statcs. 21. 214 self-sufficicncy. 21-23 statistical data. 19. 21-22 cfnotomycin. 83. 87. 94.97. 100 hplc. I I2 cndrin. 179 crythromycin. 87.94.95 dctcction limits. 107 hplc. 112 tlc. lo9 cssential clcmcnts, 1x6. 191-193 cthion. I83 cthopahatc. 125. 128. 135. 139. 140, 142, 143 fchantcl. 68 fccding stuffs. 9. 17. 2.5.37 additives in. 33-36. 186 dcfinitions of. 27-28 ingrcdicnts in. 25.27.29.30.31.33 production

(EEC),31-33 (UK).30 regulations. 27.29 straights. 26.28.30 fcnhcndazolc. 67.68.74.75.76.77 fcnitrothion. 183 fcnsulfothion. 181 fenthion. 181 fcnvalcratc. 182 flavomycin. 90. 125. 155 Hiivophospholipol. see hamhermycin fluhendazole. 70 food composition of. 38.43 deficiency (malnutrition). 17, 18 excess production. 15 stocks. (EC). 23 UK output. 21.26 yiclds. 26 Food and Environmcnt Protcction Act. 178 Four-Platc Test. IOS framomycin (framycctin). 83.87 furazolidone. 125. 128. 13.5-136.139, 142. I43 gcntamicin. 83, Sh. 87.91 hplc. 1 I2 glc. 41. 46. 48-51. 52. 53, 54.56.59. 60 dctectors. 48-Sl AFID. SO. 74. 1x5 conductivity. 5 I . I69 ECD. SO. IW. 110. 137. 140. 154, 169. I85 FID. 49.53 FPD. 50. 185. I99 Gram-ncgativc hactcria. 86.92.94.97.99. 137.

I57 Grim-positive hactcria. 86.92,94.97.99. 137. 151. 15s. 157. 162 griscofulvin. 83.88

232

Index

hplc. I I 2 growth promoters. 9. 20. 35. 94. 101. 125. 135. 137. 142. 148-162.201. 221 halofuginonc. 125. 129. 136. 139. 132. 143 hdoquinol. 83. 125. 152. 156 HCB. 179. 183. 184. IS5

11-HCH. 179, 1x3 f3-HCH. 170. 181 ./-HCH. 179. 183 heavy mct;ils ( . s c ( ~ c i l . ~ oAs. . Cd. Hg. Ph). X I . 1x4.

I 86 hclminths. hh hcptachlor cpoxidc. 179. 183. I84 hcxocsotrol. 149. 10.3. 164. 166. lh7 methods. I69 residues. 170-171 histomoni;isis. 123. 131. 141 hormones. 9.35. I4S-I4Y. 162-171.210 hcplc. 41.45.46. 51-56. 59. hO column cflicicncy. 54-56 detectors. 53 Huorcsccncc. S4

uv. 53-51

of itntihiotics. I I(t-I I3 im muno;ixs;i ys. 4( 1. 6 1-64 intagcn. 83 iodine. 81-82 ionophorcs. 137. 138. 140. 138. 150-151. 157 tlc method. 13s ipronidazolc. 125. 129. 137. 139. 142. 143 ivcrmcctin. 70. 74.75. 76-77 1iis;ilocid. 125. 129. 137. 138. 152 ICild. ISh. 189-190. 191-193. 210. 226 in feeds. 187. I00 Icv;imixolc. 07.70. 74 methods. 74 rcsiducx. 77 lincomycin. 83. Sh. SS. 91 detection limit. 107 Four-pl;itc test. 105. 107 lindiinc. 179 cow disease (BSF). 9. 202 miiduriirnicin iimmonium. 130. 137 mahthion. 170. IS4 miiss spectrometry. 41. 40. .SO. 52. 5661. 109. I85 antihiotics. 104. 109. 110 DES. 169 fur;izolidonc. 136 molecular ionization. 57-58 resolution. 59 testosterone. 170 trcnholonc. I70 zcriinol. 170 maximum residue limits (MRLs). 40.41. 178 anthclmintics. 77-78 antihiotics. I I6 carhadox. 156 ch1or;imphenicol. 101 mild

olaquindox. 158 pcsticidcsi 183 mehcndazolc. 70. 74. 76 medicinal additives. 9. 34-35. 37 types. 35 world market. 20-21. 35 mercury. 186. 190. 191-193 in feeds. 1x7. 190 in fishmeal. IY(L191 in food. 190 metabolism ( w e ulso tinder nunird compounds). 3Y.61.67.75.7R.124 hormones, I65 pesticides. 181) methoxychlor. 1x3 methyl henzoquatc. 125. 130. 133. 134. 138, 139.

I43 metoscrpate. 2OU monensin. 83. 125. 130. 138. Ihl detection limit. 107 growth promotant. 150-152 tic. 108. 159 monoclonal antibodies. 61 mupirocin. 83. 152. 157 myrotoxins. 177. 193-197.195 narasin. 125. 138, 151. 152. 157, 159. 161 neomycin. 83. X6. 88.91 dctcction limit. 107 hplc. 111. 112

M R L . 1 I6 tlc. 108

nicarhazin. 125. 140 nickel. I86 nifursol. 139. 143 nitrofurans. 83. 105. 141 detection limit. 107 nitrofurazone. 12.5. 131. 133. 135-1315. 139. 142.

I43 nitrovin. 125. 139. 143. 152. 158. 159 nosihcptide. 83. XX. 93,96 hplc. I12 nystatin. I12 ochratoxin. 195. 197 octochlor cpoxide. 1x3 oestradiol. 149. 163. IM. 165. 167 oestrogcn. 139 olaquindox. 139. 143. 152. 158-159 oleandomycin. 83. XS. 94.95 hplc. I12 tlc. lox. I09 organochlorine compounds. 51. 179, 183. 183,

IX5.21 I organophosphorus compounds. 179. 183. 1x4. 185 oxfendazolc. 67. 70. 76 oxihcndazole. 72. 74 oxolinic acid. 83.88. 101, 103 gc-ms. I I 0 hplc. 112 oxytctracyclinc. XX. 97.99. 102. 106 detection limit. 107

Index MRL. I I h rcsiducs on cooking. 1 IS

piirathion. 181 p;irahcnd;izolc. 72,74 penicillin. X3.88.92-94. 103. IS0 ADI/MRL. I I6 dctcction limit. 107 hplc. I12 tlc. 10s pcnicilliniisc. 93. 94 pcrmcthrin. 182 pcsticircs. 9. 17. 21.35.37. 177-lX5.210.226 limits. 179. 218 methods, 1x4-185 residues. SO. 177 surveys. IX(Ll84 Pesticides (Mnximum Lcvcls in Food) Regulations (1988). 178 pet iinimiils. 27.67.21 I pet roods. w - 2 ~ 33. . 21 I phcnyl iirsonic acid. 1.52 p)pcryinc. 72 pirimiphos-methyl. IS3 populiirion growth. 16 prohiotics. 2 0 1-20? progesterone. 149. 163. 164. 16.5. 167 propriopromazine. 199. 2(N). 201 pyrethrins. 179. 180. 181, 182 pyrimcthaminc. 125. 131. 129. 140. 143 quinoxiiline-2-carhonic acid. IS6 riictopiimine. 172-173 radiolahcllcd compounds. 44.63.78. 135. I10 rcsiducs. see rordar rtur?ied compound rohcnidinc. 125. 131. 139. 140-141. 113 ronidiizolc. S3. 125. 131. 137. 139. 1-11. 142. 1-13 siilhut;imol. 172-173 siilinomycin. 10s. 125. 138. 140. 151. 153. 159. I61 Snlmonclla. 9 . 3 0 . 203-204 selenium. 184. 191 toxicity. I86 spiriimycin. S?. XX. 0-1.96 defection limits. 107 hplc. 113. 153. 1.59 tlc. I09 stilhcncs. 163. 166. 170. 172 stilhocstrol. see dicthylstilhocstrol streptomycin. 84.86. 88.92 dctcction limit. 107 hplc. 113 rcsiducs. I IS tlc. I08 sulphadimidine (sulfamcthazinc). S8. 97. 101. 139. 142. 143. 1 6 1 dctcction limits. 107 hplc. I13 residues. I l l ) . I IS xulphanitriin. 139. 14;.

233

sulphaquinoxalinc. 07. 101. 125. 132. 134. 13s. 139-143 MRL. I16 sulphonamidcs. SJ. 97. 125 methods. 111.5. 109-1 I4 swah tcst. I(H

tcstostcronc. 149. 162. 163. 164. 165. 168 mcrhods. 170 tctr;icyclincs (sce ulso chlortctracyclinc. oxytcrracyclinc). 84.X8. 92. 97. 103. 106 dctcction limit. l(17 hplc. IOY. I I I . 113-1 I4 rcsiducs. I IS tlc. l(l,s-loY tctramisolc. see levamisolc thinhcndiizolc, 67. 72. 74 methods. 76 thiopcptin. 153. 160 thiophanatc. 72 tiamulin. 84.88. 125. 1.51. 153. 1S7. 1.59. 161 TLC. 46-47 antihiotics. 108 hptlc. 47 trace elements. 9. 34. 177. 1x5-193. 202 toxicity. I86-lX7.2I I tranquillizcrs. 35. 177. 197-201. 212 trcnholone. 163. 164. 168 mcthod. 170 residues. 170-17 I trichothccencs, 193. 195. 196. I97 trimethoprin. 89. 97. IWi. 107 tylosin. X?. 89.94.97. 125. 161 detection limits. 107 hplc. I14 tlc. 109 USA tolcranccs for drug rcsiducs. 223 Vancomycin hplc. 114 tlc. 109 Virginiamycin. 84. X9. 94.99. 106. 125. 153. 161 hplc. I I 4 withdrnwiil periods. 124. 214 anthelmintics. 67.7X coccidiostats. see rrrtrler mined conlpolrds xylaxinc. 199. 200. 201 zcranol. 149. 163. 164. 16s. 168 method. 170 rcsiducs. I7I zinc. I86 zinc hacitriicin. s e e hacitriicin