Controlled Release Pesticides

Controlled Release Pesticides In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Soci...

Author: Herbert B. Scher

71 downloads 992 Views 3MB Size Report

This content was uploaded by our users and we assume good faith they have the permission to share this book. If you own the copyright to this book and it is wrongfully on our website, we offer a simple DMCA procedure to remove your content from our site. Start by pressing the button below!

Report copyright / DMCA form

DOWNLOAD PDF

Controlled Release Pesticides

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Controlled Release Pesticides Herbert B. Scher, EDITOR Stauffer Chemical Co.

A symposium sponsored by the Division of Pesticide Chemistry at the 173rd Meeting of the American Chemical Society, New Orleans, La., March 21-22, 1977.

ACS SYMPOSIUM SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D. C. 1977

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

53

Library of Congress CIP Data Controlled release pesticides. (ACS symopsium series; 53 ISSN 0097-6156) Includes bibliographical references and index. 1. Pesticides, controlled release—Congresses. I. Scher, Herbert B., 1937II. American Chemical Society. Division of Pesticide Chemistry. III. Title. IV. Series: American Chemical Society. ACS symposium series; 53. SB951.C648 1977 ISBN 0-8412-0382-2

668'.65

77-22339

Copyright © 1977 American Chemical Society All Rights Reserved. No part of this book may be reproduced or transmitted in any form or by any means—graphic, electronic, including photocopying, recording, taping, or information storage and retrieval systems—without written permission from the American Chemical Society. PRINTED IN T H E UNITED STATES O F A M E R I C A

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

ACS Symposium Series Robert F. Gould, Editor

Advisory

Board

D o n a l d G . Crosby Jeremiah P. Freeman E. Desmond Goddard Robert A . Hofstader J o h n L. Margrave N i n a I. M c C l e l l a n d J o h n B . Pfeiffer Joseph V . R o d r k k s Alan

C. Sartorelli

Raymond B . Seymour R o y L. W h i s t l e r Aaron W o l d

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

FOREWORD The A C S S Y M P O S I U M SERIES was founded i n 1 9 7 4 to provide

a medium for publishing symposia quickly i n book form. The format of the SERIES parallels that of the continuing A D V A N C E S I N C H E M I S T R Y SERIES except that i n order to save time the papers are not typeset but are reproduced as they are submitted b y the authors i n camera-ready form. A s a further means of saving time, the papers are not edited or reviewed except b y the symposium chairman, who becomes editor of the book. Papers published i n the A C S S Y M P O S I U M SERIES are original contributions not published elsewhere i n whole or major part and include reports of research as well as reviews since symposia may embrace both types of presentation.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PREFACE /Controlled release technology was

pioneered by

the

drug industry

^ approximately 25 years ago. The initial goal was to produce controlled release oral drug forms that could maintain an effective level of drug i n the body, thereby eliminating the side effects caused by administrating high doses of conventional drugs. More recently, the drug industry has become even more sophisticated and has introduced controlled release drug forms capable of being implanted at the site of action, which further reduces drug level Applying the same controlled release principles, pesticide scientists are now developing controlled release pesticide formulations capable of maintaining an effective level of pesticide in the soil or on foliage, thereby reducing pesticide application rates and minimizing pesticide levels i n the environment. In addition, controlled release pesticide formulations can reduce pesticide toxicity and extend pesticide residual activity. This volume is a compilation of information dealing with the structural and chemical factors governing the controlled release of pesticides from polymer systems. The first five papers deal w i t h controlled release concepts, controlled release theory, and the environmental and toxicological aspects of controlled release pesticides. The next seven papers describe polymer systems that control the release of pesticides—i.e., elastomers, biodegradable matrices, polymers containing pendant pesticides, and microcapsules. The final four papers include research on microencapsulated insecticides for field use, laminated insecticide tapes for home use, a variety of systems for controlling the release of gypsy moth pheromone, and a microcapsule system for controlling the release of an insect growth regulator. I would like to thank all the authors and J . J . Menn, J . P. Minyard, Jr., and G . G . Still of the Pesticide Division for their full cooperation during all phases of this symposium. Richmond, Calif.

H E R B E R T B. S C H E R

M a r c h 1977

ix

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1 Principles of Controlled Release Pesticides D. H. LEWIS and D. R. COWSAR Southern Research Institute, Birmingham,Ala.35205

The rapidly growing deman entific community with a operations i n both industrial a n d a g r i c u l t u r a l production is paramount. M e t h o d s and processes t h a t a f f o r d higher y i e l d s and b e t t e r q u a l i t y , r e q u i r e less t i m e a n d m o n e y , a n d do n o t pose a t h r e a t t o t h e e n v i r o n m e n t a r e b e i n g sought a t a n u n p a r a l l e l e d p a c e w h i c h undoubtedly w i l l i n t e n s i f y f u r t h e r i n t h e l a s t q u a r t e r o f t h i s c e n t u r y . T h e c o n t r o l o f pests, a b a t t l e fought f o r g e n e r a t i o n s , i s u n q u e s t i o n a b l y a crucial t a s k if our goals f o r t h e f u t u r e c o n c e r n i n g food and e n e r g y a r e t o b e a c h i e v e d . R e c e n t e s t i m a t e s suggest t h a t losses due t o i n e f f i c i e n t p e s t - c o n t r o l t e c h n i q u e s a m o u n t t o b e t w e e n $10 and 30 billion e a c h y e a r (1). Losses o f cotton alone t o i n s e c t s e x c e e d $500 million p e r a n n u m . (2) In India, rodents a r e r e p o r t e d (3) t o destroy a fourth of t h e harvested grain crop annually. The astounding losses due t o pests a r e n o t limited t o food supplies a l o n e . T h e f o u l i n g o f s h i p hulls c o s t s t h e U . S . N a v y a n a d d i t i o n a l $150 m i l l i o n / y e a r i n f u e l (4), $15 m i l l i o n / y e a r i n labor a n d m a t e r i a l s f o r r e p a i n t i n g ships w i t h a n t i f o u l a n t s , and a p p r o x i m a t e l y $200 million e a c h y e a r f o r r e p l a c e m e n t o f b i o l o g i c a l l y d e t e r i o r a t e d m a r i n e p i l i n g s (5). T h e i m p o r t a n c e o f p e s t i c i d e s is e v i d e n c e d by t h e e s t i m a t e d sale o f $2.5 billion o f p e s t i c i d e s e a c h y e a r i n t h e U . S . alone (6). A l t h o u g h t h e reality o f i n c r e a s i n g danger t o m a n from persistent pesticides is recognized, the frightening fact remains that if terrestrial h e r b i c i d e s alone w e r e b a n n e d , s t a r v a t i o n w o u l d b e c o m e m o r e p r e v a l e n t i n t h e w o r l d p o p u l a t i o n i n short o r d e r . Historically, s c i e n t i s t s h a v e d e a l t w i t h t h e p r o b l e m o f pest c o n t r o l by designing new, .more potent a g e n t s . H o w e v e r , use o f these agents t o produce t h e d e s i r e d b i o l o g i c a l response is o f t e n i n e f f i c i e n t , p r i m a r i l y because o f i n a b i l i t i e s t o d e l i v e r t h e agents t o t h e i r t a r g e t s a t t h e p r e c i s e t i m e and i n t h e o p t i m u m q u a n t i t i e s r e q u i r e d . E n o r m o u s a m o u n t s o f funds are r e q u i r e d f o r t h e d e v e l o p m e n t o f a n e w b i o c i d e . R e c e n t e s t i m a t e s p l a c e t h e d e v e l o p m e n t costs f o r a new p e s t i c i d e a t about $8 million (6). R e c o g n i z i n g t h e c o s t a n d limitations i n t h e design o f n e w p e s t i c i d e s , s c i e n t i s t s began t o t u r n i n t h e 1960s t o a n alternative a p p r o a c h , t h a t o f i m p r o v i n g t h e d e l i v e r y o f t h e a g e n t s , b o t h n e w e r agents and o l d . In today's t e r m i n o l o g y , a c o n t r o l l e d - r e l e a s e f o r m u l a t i o n o r d e l i v e r y s y s t e m i s d e f i n e d as a c o m b i n a t i o n o f b i o l o g i c a l l y a c t i v e agent and e x -

1

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

CONTROLLED

RELEASE

PESTICIDES

c i p i e n t , usually a p o l y m e r , a r r a n g e d t o a l l o w d e l i v e r y of t h e agent t o the t a r g e t at c o n t r o l l e d r a t e s o v e r a s p e c i f i e d p e r i o d . The r a p i d e m e r g e n c e of c o n t r o l l e d r e l e a s e as an e s t a b l i s h e d s c i e n t i f i c f i e l d is e v i d e n c e d by the g r o w i n g n u m b e r of r e l a t e d p u b l i c a t i o n s a p p e a r i n g i n t h e l i t e r a t u r e and the i n c r e a s i n g n u m b e r of s y m p o s i a on t h e subject e a c h y e a r . A s r e c e n t as 1973, for e x a m p l e , only one s y m p o s i u m was d e v o t e d t o c o n t r o l l e d r e l e a s e , w h i l e d u r i n g 1976 s e v e r a l major m e e t i n g s addressed t h e subject i n d e p t h . F e w areas of r e s e a r c h have a c t i v a t e d t h e i n t e r e s t and a t t e n t i o n of s u c h a m u l t i d i s c i p l i n a r y group of p r o f e s s i o n a l s . A t t e n d e e s at w o r k s h o p s , c o n f e r e n c e s , and s y m p o s i a on c o n t r o l l e d r e l e a s e t y p i c a l l y i n c l u d e b i o l o g i s t s , chemists, engineers, pharmacologists, agronomists, entomologists, vete r i n a r i a n s , d e n t i s t s , and p h y s i c i a n s . It is now a w e l l r e c o g n i z e d f a c t t h a t t h e t e c h n o l o g y or c o n t r o l l e d r e l e a s e c a n c o n t r i b u t e p o s i t i v e l y t o man's f i g h t against disease and hunger. C o n t r o l l e d release a b e c o m i n g the subject o f e r t i l i z e r s w e r e k n o w n at l e a s t 30 years ago, m o s t of the s i g n i f i c a n t a d v a n c e s have c o m e i n t h e l a s t 10 y e a r s . O b v i o u s l y , i n a f i e l d e x p a n d i n g so r a p i d l y , a c o m p l e t e r e v i e w of t h e l i t e r a t u r e c a n n o t be g i v e n h e r e . H o w e v e r , a n u m b e r of e x c e l l e n t p u b l i c a t i o n s are a v a i l a b l e w h i c h o f f e r m o r e d e t a i l e d t r e a t m e n t s on f u n d a m e n t a l s of c o n t r o l l e d r e l e a s e and discussions of c o n t r o l l e d - r e l e a s e p e s t i c i d e f o r m u l a t i o n s (7-12). C a r d a r e l l i (1), a pioneer i n t h e f i e l d , has a u t h o r e d an e x c e l l e n t c o m p r e h e n s i v e r e v i e w of c o n t r o l l e d - r e l e a s e p e s t i c i d e f o r m u l a t i o n s . T h i s c h a p t e r is i n t e n d e d to i n t r o d u c e the n e w c o m e r t o the f i e l d , and for t h e e x p e r i e n c e d r e s e a r c h e r , t o m a k e t h e papers t h a t f o l l o w m o r e c o h e s i v e . F i r s t , a b r i e f d i s c u s s i o n of t h e s h o r t c o m i n g s of c o n v e n t i o n a l methods of d e l i v e r y w i l l be g i v e n , t h e n an o v e r v i e w of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s , and f i n a l l y a f e w of t h e c u r r e n t a p p l i c a t i o n s of c o n t r o l l e d r e l e a s e . A d v a n t a g e s of C o n t r o l l e d R e l e a s e The p r i n c i p a l a d v a n t a g e of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s is t h a t t h e y a l l o w m u c h less p e s t i c i d e t o be used for the s a m e p e r i o d of a c t i v i t y . M o r e o v e r , w h e n t h e n o r m a l h a l f - l i f e of a potent p e s t i c i d e is s h o r t , the r e l e a s e f o r m u l a t i o n s are e s p e c i a l l y advantageous i n c o m p a r i s o n t o c o n v e n t i o n a l methods of a p p l i c a t i o n . T o f u l l y u n d e r s t a n d t h i s b e n e f i t , one m u s t f i r s t u n d e r s t a n d the m a g n i t u d e of t h e e n v i r o n m e n t a l f o r c e s t h a t a c t t o r e m o v e excesses of p e s t i c i d e s f r o m t h e i r s i t e s of a p p l i c a t i o n . When a p p l i e d by c o n v e n t i o n a l m e t h o d s , p e s t i c i d e s are i n v a r i a b l y subject t o l e a c h i n g , e v a p o r a t i o n , and d e g r a d a t i o n ( p h o t o l y t i c , h y d r o l y t i c , and m i c r o b i a l ) , a l l of w h i c h r e m o v e t h e a c t i v e m a t e r i a l s f r o m t h e i r t a r g e t b e f o r e they c a n p e r f o r m t h e i r f u n c t i o n . In m o s t c a s e s , t h e r a t e of r e m o v a l f o l l o w s f i r s t - o r d e r k i n e t i c s , i . e . , t h e r a t e of r e m o v a l a t any t i m e is d i r e c t l y p r o p o r t i o n a l t o the a m o u n t (or c o n c e n t r a t i o n of t h e p e s t i c i d e present i n t h e e n v i r o n m e n t at t h a t t i m e . A m a t h e m a t i c a l e x p r e s s i o n of t h e f i r s t - o r d e r r a t e l a w is g i v e n by E q u a t i o n 1, (1)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

LEWIS

AND

COWSAR

Principles

of Controlled

Release

Pesticides

3

w h e r e dM/dt is t h e r a t e of r e m o v a l , k is t h e r a t e c o n s t a n t , and M is t h e a m o u n t of p e s t i c i d e present at any f i m e t . The i n t e g r a t e d s o l u t i o n t o E q u a t i o n 1 is M 1 η (

Ί5Γ

)

=

- ν

(2)

00

where M The r a t e expressed order rate œ

is t h e a m o u n t present at t = 0; M is thus t h e a m o u n t a p p l i e d . of r e m o v a l of a p e s t i c i d e f r o m t h e e n v i r o n m e n t is o f t e n as t h e agent's h a l f - l i f e , ty. The h a l f - l i f e is r e l a t e d t o the f i r s t c o n s t a n t f o r r e m o v a l , k , as f o l l o w s : œ

In 2 = - k t r Vz f/

or,

(3)

k

If M is the m i n i m u m e f f e c t i v e l e v e l of p e s t i c i d e and M is t h e a m o u n t
l (__) M e n

=

|< t re

/c\ (5)

F r o m E q . 5 , i t f o l l o w s t h a t t o i n c r e a s e t h e e f f e c t i v e d u r a t i o n of a c t i o n , t , of a c o n v e n t i o n a l l y a p p l i e d p e s t i c i d e , e x p o n e n t i a l l y g r e a t e r q u a n t i t i e s of t h e p e s t i c i d e m u s t be a p p l i e d . O n t h e o t h e r h a n d , i f t h e p e s t i c i d e c o u l d be m a i n t a i n e d at t h e m i n i m u m e f f e c t i v e l e v e l , Μ , by a c o n t i n u o u s supply t o r e s t o r e the f r a c t i o n d i s s i p a t e d , t h e n t h e o p t i m u m p e r f o r m a n c e of a p e s t i c i d e w o u l d be r e a l i z e d when the i n s t a n t a n e o u s r a t e of r e m o v a l equals t h e i n s t a n t a n e o u s r a t e of d e l i v e r y , | = - k M + k .Μ = 0 dt r e d e (6) In E q u a t i o n 6, k^ is the r a t e c o n s t a n t for p e s t i c i d e d e l i v e r y . When a p e s t i c i d e is f o r m u l a t e d for s u s t a i n e d d e l i v e r y , t h e d u r a t i o n of a c t i o n , t , of t h e f o r m u l a t i o n is g i v e n by E q u a t i o n 7. d

e

M

- M M

e

de

F i g u r e 1 shows t h e r e l a t i o n s h i p s b e t w e e n the l e v e l of a p p l i c a t i o n and t h e d u r a t i o n of a c t i o n for c o n v e n t i o n a l f i r s t - o r d e r f o r m u l a t i o n s ( E q u a t i o n 5 is p l o t t e d as C u r v e A ) and f o r c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s ( E q u a t i o n 7 is p l o t t e d as C u r v e B). In p r e p a r i n g F i g u r e 1, we a s s u m e d t h a t t h e h a l f l i f e of t h e p e s t i c i d e was 15 days and t h a t t h e m i n i m u m e f f e c t i v e l e v e l was 1 g/acre. T o a c h i e v e p r o t e c t i o n for 50 days w i t h a c o n v e n t i o n a l

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4

CONTROLLED RELEASE

PESTICIDES

f o r m u l a t i o n ( C u r v e A ) , t h e l e v e l of a p p l i c a t i o n w o u l d have to i n c r e a s e t e n f o l d , but only a t h i r d of t h e p e s t i c i d e w o u l d be used to c o n t r o l the t a r g e t o r g a n i s m . F o r double and t r i p l e t h i s d u r a t i o n of a c t i o n , t h e l e v e l s of p e s t i c i d e a p p l i e d must be m u l t i p l i e d by a hundred and a t h o u s a n d , r e s p e c t i v e l y . F o r an o p t i m i z e d c o n t r o l l e d - r e l e a s e f o r m u l a t i o n ( C u r v e B), the a m o u n t s needed for 50, 100, and 150 days of pest c o n t r o l a r e , r e s p e c t i v e l y , 3.3, 5.6, and 7.9 g of t h e a c t i v e m a t e r i a l . The a r e a b e t w e e n C u r v e s A and Β on the l o g a r i t h m i c s c a l e represents the f r a c t i o n of c o n v e n t i o n a l p e s t i c i d e a p p l i e d w h i c h s e r v e s no useful purpose; h e n c e , i t is wasted. M o r e o v e r , t h e m a g n i t u d e of t h e a m o u n t w a s t e d is i n c r e a s e d s u b s t a n t i a l l y i f t h e h a l f - l i f e of t h e c o n v e n t i o n a l b i o c i d e is s h o r t e r t h a n our a r b i t r a r y 15 d a y s . O b v i o u s l y , t h e p e s t i c i d e s a l r e a d y i n use c a n be i m p r o v e d to m i n i m i z e t h e w a s t e of these c o s t l y and t o x i c c h e m i c a l s , w h i c h m a y l a t e r cause an écologie c a t a s t r o p h y , and t o e x t e n d t h e d u r a t i o n of a c t i o n of s a f e r , l e s s p e r s i s t e n t a n a l o g s . The ke d e l i v e r y d e v i c e s and f o r m u l a t i o n s . The e x t e n t t o w h i c h o p t i m u m r e s u l t s a r e a c h i e v a b l e depends p r i m a r i l y on t h e degree t o w h i c h the f a c t o r s a f f e c t i n g t h e r a t e and d u r a t i o n of r e l e a s e of p e s t i c i d e s f r o m s u s t a i n e d d e l i v e r y s y s t e m s c a n be c o n t r o l l e d p r e c i s e l y . M e c h a n i s m s of C o n t r o l l e d R e l e a s e C o n t r o l l e d r e l e a s e is not synonymous w i t h s u s t a i n e d r e l e a s e , a m u c h o l d e r and w e l l r e c o g n i z e d c o n c e p t f r o m w h i c h the new s c i e n c e is e m e r g i n g , a l t h o u g h the t w o are s i m i l a r i n p r i n c i p l e and s o m e t i m e s o v e r l a p . S u s t a i n e d - r e l e a s e f o r m u l a t i o n s a r e s o - c a l l e d because t h e y c o n t a i n s e v e r a l t i m e s the n o r m a l single a p p l i c a t i o n , and they p r o v i d e for r e p l a c e m e n t of t h e agent a t s o m e r a t e w h i c h gives a m e a s u r a b l e i n c r e a s e i n t h e d u r a t i o n of a c t i v i t y . The r a t e m a y d e c r e a s e due t o g r a d u a l loss of a g e n t , or i n c r e a s e t h r o u g h a m a x i m u m due t o b r e a k d o w n of a p r o t e c t i v e b a r r i e r . A c o n t r o l l e d - r e l e a s e f o r m u l a t i o n , i n c o n t r a s t , m a y e x h i b i t a fast or a s l o w r e l e a s e , or a c o n s t a n t or a c h a n g i n g r e l e a s e , depending on the d e s i g n . The p r i n c i p a l d i f f e r e n c e l i e s not e n t i r e l y i n t h e p r o f i l e s of r e l e a s e but i n t h e m e c h a n i s m of r e l e a s e . The d i s t i n c t i o n is d r a w n m a i n l y by t h e d e g r e e of c o n t r o l of b o t h t h e o p t i m u m l e v e l and t h e o p t i m u m t i m e of a v a i l a b i l i t y of t h e b i o l o g i c a l l y a c t i v e a g e n t . T h e c o n c e p t and p r a c t i c e of c o n t r o l l e d r e l e a s e encompasses many m e c h a n i s m s . A l t h o u g h the e a r l i e s t f o r m u l a t i o n s w e r e based on t h e des o r p t i o n of p e s t i c i d e s f r o m s t r o n g sorbents l i k e s i l i c a g e l , m i c a , and a c t i v a t e d c h a r c o a l (13), m o s t of the c u r r e n t s y s t e m s a r e based on m o r e c o n t r o l l a b l e m e c h a n i s m s such as d i f f u s i o n t h r o u g h r a t e - c o n t r o l l i n g m e d i a , e r o s i o n of b i o d e g r a d a b l e b a r r i e r m a t e r i a l s , and r e t r o g r a d e c h e m i c a l r e a c t i o n s . D e s i g n e r s of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s or d e v i c e s usually s t r i v e f o r z e r o - o r d e r (constant) r a t e s of r e l e a s e , but s y s t e m s w i t h t i m e dependent r e l e a s e k i n e t i c s are p r o v i n g t o be useful for p e s t i c i d e s , e s p e c i a l l y when the r a t e and d u r a t i o n of r e l e a s e are p r e d i c t a b l e and w e l l c o n t r o l l e d . In p r a c t i c e , t h e r a t e of p e s t i c i d e r e l e a s e m a y be c o n t r o l l e d by s e v e r a l s e q u e n t i a l or s i m u l t a n e o u s m e c h a n i s m s w h i c h do not l e n d t h e m s e l v e s t o s i m p l e a n a l y s i s , but i t is u s u a l l y possible to d e t e r m i n e

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

LEWIS

A N D COWSAR

S

ο

Principles

of Controlled

Release

Pesticides

10,000

jo

c

1,000 h

CONVENTIONAL„ PESTICIDE

100

10h CONTROLLED-RELEASE PESTICIDE 0

50

I 100

I 150

200

D U R A T I O N O F P E S T I C I D E E F F E C T I V E N E S S , days

Figure 1. Rehtionships between the level of application and the duration of action for conventional and controlled release formula tions

Figure 2. Reservoir and monolithic diffusion controlled devices

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6

CONTROLLED RELEASE

PESTICIDES

e x p e r i m e n t a l l y an o v e r a l l " a p p a r e n t " order of r e l e a s e for these c o m p l e x systems. M a n y design c o n c e p t s have been s t u d i e d in d e v e l o p m e n t of c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s for p e s t i c i d e s . T h r e e of t h e most p r o m i s i n g ones are the f o l l o w i n g : (1) capsules of p o l y m e r i c m a t e r i a l f i l l e d w i t h a s o l i d or l i q u i d p e s t i c i d e or w i t h a suspension or s o l u t i o n of t h e agent in a f l u i d , i n w h i c h the r e l e a s e of p e s t i c i d e is c o n t r o l l e d by F i c k i a n d i f f u s i o n t h r o u g h the c a p s u l e w a l l s or t h r o u g h m i c r o p o r e s in t h e c a p s u l e w a l l s ; (2) a heterogeneous dispersion of p a r t i c l e s or d r o p l e t s of p e s t i c i d e i n a s o l i d p o l y m e r i c m a t r i x , w h i c h c a n be e i t h e r b i o d e g r a d a b l e or nonbiodegradable and w h i c h c o n t r o l s the r e l e a s e of agent by d i f f u s i o n t h r o u g h the m a t r i x , by e r o s i o n of the m a t r i x , or by a c o m b i n a t i o n of b o t h d i f f u s i o n and e r o s i o n ; and (3) c h e m i c a l bonding of a p e s t i c i d e to a n a t u r a l or s y n t h e t i c p o l y m e r i c m a t e r i a l , as by pendant a n h y d r i d e or e s t e r l i n k a g e s , or f o r m a t i o n of m a c r o m o l e c u l e s of p e s t i c i d e s v i a i o n i c or c o v a l e n t l i n k a g e s , w h i c h c o n t r o l the r e l e a s d i s s o c a t i o n , m i c r o b i a l d e g r a d a t i o n , or s o m e other r e t r o g r a d e c h e m i c a l r e a c t i o n of the l i n k a g e s . R e l e a s e by m e m b r a n e - m o d e r a t e d diffusion. Diffusion-controlled m e m b r a n e d e v i c e s c a n be d i v i d e d i n t o t w o m a i n c a t e g o r i e s : reservoir s y s t e m s i n w h i c h the p e s t i c i d e is t o t a l l y e n c a p s u l a t e d w i t h i n a r a t e - c o n t r o l l i n g m e m b r a n e , and m o n o l i t h i c s s y s t e m s i n w h i c h t h e p e s t i c i d e is dispersed or dissolved i n a r a t e - c o n t r o l l i n g m a t r i x . These s y s t e m s are d e p i c t e d i n F i g u r e 2. It has been d e m o n s t r a t e d t h a t the d i f f u s i o n rates f r o m c o n t r o l l e d - r e l e a s e s y s t e m s f o l l o w F i c k ' s law of d i f f u s i o n , w h i c h s t a t e s t h a t the r a t e of d i f f u s i o n depends on f i v e f a c t o r s . T w o of t h e f a c t o r s i n v o l v e t h e g e o m e t r y or dimensions of the d e v i c e , and t h r e e involve pesticide-polymer interactions. dM dt

£ D(C - K C ) h s e

(8)

In E q u a t i o n 8, the d i m e n s i o n a l f a c t o r s are A , the s u r f a c e a r e a of the m e m b r a n e ; and h , t h e t h i c k n e s s t h r o u g h w h i c h d i f f u s i o n o c c u r s . The d i f f u s i o n a l f a c t o r s are D , the d i f f u s i o n c o e f f i c i e n t of t h e p e s t i c i d e i n the p o l y m e r ; C , the s a t u r a t i o n s o l u b i l i t y of t h e p e s t i c i d e i n t h e p o l y m e r ; and K , t h e p a r t i t i o n c o e f f i c i e n t of t h e p e s t i c i d e b e t w e e n t h e p o l y m e r and the m e d i u m w h i c h surrounds t h e d e v i c e . C i n E q u a t i o n 8 is t h e c o n c e n t r a t i o n of r e l e a s e d p e s t i c i d e i n the e n v i r o n m e n t . The s o l u b i l i t y and the p a r t i t i o n coefficient are s u s c e p t i b l e t o a n a l y s i s and p r e d i c t i o n i n t e r m s of appropriate thermodynamic solution theories. The m o b i l i t y of the p e n e t r a n t p e s t i c i d e m o l e c u l e s , as m e a s u r e d by t h e d i f f u s i o n c o e f f i c i e n t , is a k i n e t i c p a r a m e t e r governed by the s i z e , shape, and p o l a r i t y of t h e p e n e t r a n t and by t h e morphology of t h e d i f f u s i o n m e d i u m . When a p p l i e d to r e s e r v o i r s y s t e m s , F i c k ' s l a w p r e d i c t s t h a t i f a p e s t i c i d e is e n c l o s e d w i t h i n an i n e r t m e m b r a n e , and i f t h e c o n c e n t r a t i o n is m a i n t a i n e d c o n s t a n t w i t h i n the e n c l o s u r e , t h e n a steady s t a t e w i l l be e s t a b l i s h e d d u r i n g w h i c h the r e l e a s e r a t e w i l l be z e r o o r d e r , L e , c o n s t a n t . The various f o r m s of F i c k ' s l a w w h i c h apply to r e s e r v o i r s y s t e m s of s

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

LEWIS

AND

COWSAR

Principles

of Controlled

Release

7

Pesticides

f a m i l i a r g e o m e t r i e s a r e g i v e n i n F i g u r e 3 f o r t h e slab or l a m i n a t e d e v i c e and f o r t h e sphere or m i c r o c a p s u l e . M e m b r a n e - m o d e r a t e d m o n o l i t h i c s y s t e m s i n w h i c h t h e p e s t i c i d e is dispersed or d i s s o l v e d i n a r a t e - c o n t r o l l i n g p o l y m e r m a t r i x a r e s i m p l e t o p r e p a r e , but t h e y do not have t h e z e r o - o r d e r r e l e a s e k i n e t i c s of t h e r e s e r v o i r s y s t e m s . T h e p e s t i c i d e is r e l e a s e d f r o m t h e s u r f a c e l a y e r s of a m o n o l i t h i c d e v i c e f i r s t , and t h e d i s t a n c e t h e p e s t i c i d e must diffuse t o r e a c h t h e s u r f a c e i n c r e a s e s w i t h t i m e . T h u s , these s y s t e m s have s l o w l y d e c l i n i n g r a t e s of r e l e a s e . T h e k i n e t i c s of r e l e a s e c a n f o l l o w t w o p a t t e r n s depending on w h e t h e r t h e p e s t i c i d e is present as a s o l u t i o n or as a d i s p e r sion. F o r d e l i v e r y of p e s t i c i d e w h i c h has been d i s s o l v e d i n a s p h e r i c a l p o l y m e r bead of r a d i u s r , t h e expressions of F i c k ' s l a w w h i c h d e s c r i b e t h e r a t e of r e l e a s e a r e g i v e n % y E q u a t i o n s 9 and 10. d M

~3t

=

6

ΐ77_Γ

dMt/M

Π " ο

(9)

-iT Dt e x p (2

α dt~~

(10)

E q u a t i o n 9 is c a l l e d t h e " e a r l y - t i m e a p p r o x i m a t i o n " a n d is v a l i d f o r M / M < 0 . 5 , and E q u a t i o n 10 is c a l l e d t h e " l a t e - t i m e a p p r o x i m a t i o n " a n d is valid for M /M > 0 . 5 . F r o m these e q u a t i o n s i t is a p p a r e n t t h a t about t h e f i r s t 5 0 % o? t h e p e s t i c i d e is r e l e a s e d at a r a t e w h i c h decreases as t h e square root of t i m e , and t h e r a t e of r e l e a s e of r e m a i n i n g p e s t i c i d e f o l l o w s e x p o n e n t i a l of f i r s t - o r d e r k i n e t i c s . F i g u r e b d e p i c t s these equations g r a p h i c a l l y . E q u a t i o n s f o r t h e slab and c y l i n d r i c a l g e o m e t r i e s have also been d e r i v e d (Ik). If t h e p e s t i c i d e is dispersed i n t h e s p h e r i c a l p o l y m e r m a t r i x r a t h e r t h a n d i s s o l v e d , t h e release k i n e t i c s a r e a l t e r e d , and t h e r a t e of r e l e a s e is d e s c r i b e d by E q u a t i o n 11. t

dM./M t « dt

3C D s r C ο ο 2

(1-M /M ) t

1/3

œ

1/3 1-(1-M./M ) t «

(11)

This e q u a t i o n is v a l i d as l o n g as t h e t o t a l a m o u n t of p e s t i c i d e i n t h e m a t r i x C is m u c h l a r g e r t h a n t h e s a t u r a t i o n s o l u b i l i t y of p e s t i c i d e i n t h e m a t r i x , C ? . F i g u r e 5 shows t h e r e l e a s e p r o f i l e s of m o n o l i t h i c d e v i c e s w i t h d i f f e r e n t i n i t i a l l o a d i n g s . It is not possible i n this c a s e t o express t h e release r a t e as a single f u n c t i o n of t i m e . If, h o w e v e r , E q u a t i o n 11 is i n t e g r a t e d , a n e x p r e s s i o n of t h e t i m e , t , r e q u i r e d f o r t h e s p h e r i c a l beads t o b e c o m e t o t a l l y e x h a u s t e d of d i s p e r s e d p e s t i c i d e c a n be d e r i v e d as shown i n E q u a t i o n 12.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICIDES

Figure 3.

Expressions of Fick's law for reservoir devices

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

LEWIS

A N D COWSAR

0

Principles

of Controlled

0.1

Release

Pesticides

0.2

0.3

TIME

Figure 4.

Fraction of agent desorbed from a monolithic as a function of time

device

TIME

Figure 5.

Release profiles of monolithic devices with different initial loadings of dispersed agent

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10

CONTROLLED RELEASE

r

C ο ο 6 DC

PESTICIDES

2

(12)

S

R e l e a s e by e r o s i o n . When the p o l y m e r c o n t a i n i n g dispersed or d i s s o l v e d p e s t i c i d e is w a t e r s o l u b l e , h y d r o l y t i c a l l y u n s t a b l e , or o t h e r w i s e b i o d e g r a d a b l e , t h e a c t i v e m a t e r i a l c a n be r e l e a s e d by d i f f u s i o n of t h e p e s t i c i d e f r o m the p o l y m e r , by e r o s i o n of the p o l y m e r , or by a c o m b i n a t i o n of b o t h d i f f u s i o n and e r o s i o n . R e l e a s e by e r o s i o n is a s u r f a c e - a r e a - d e p e n d e n t p h e n o m e n o n , and i f t h e s u r f a c e a r e a of a d e v i c e s t a y s c o n s t a n t w h i l e i t is e r o d i n g , t h e r e l e a s e of p e s t i c i d e w i l l be z e r o o r d e r . The g e n e r a l e x p r e s s i o n w h i c h the d e s c r i b e s t h e r a t e of r e l e a s e by a p u r e l y e r o s i o n m e c h a n i s m is g i v e n i n E q u a t i o n 13, dM.

w h e r e k g is the e r o s i o n r a t e c o n s t a n t , A is t h e s u r f a c e a r e a exposed t o the e n v i r o n m e n t , and C is the l o a d i n g of p e s t i c i d e i n t h e e r o d i b l e m a t r i x . F o r t h e f l a t f i i m or slab g e o m e t r y , t h e s u r f a c e a r e a does not c h a n g e as e r o s i o n o c c u r s , and c o n s e q u e n t l y , t h e r e l e a s e of agent is c o n s t a n t u n t i l the f i l m u l t i m a t e l y d i s a p p e a r s . F o r an e r o d i b l e sphere or radius r , t h e r a t e of r e l e a s e of p e s t i c i d e is g i v e n by E q u a t i o n l*f. dM - i f - = at

C k (r - k t ) ο Ε ο Ε p

p

2

(14)

It is a p p a r e n t f r o m t h i s e q u a t i o n t h a t p e s t i c i d e r e l e a s e decreases s l o w l y w i t h t i m e , and t h a t z e r o - o r d e r k i n e t i c s a r e not possible w i t h s p h e r i c a l s y s t e m s of t h i s t y p e . If the p e s t i c i d e is c o n t a i n e d as a s i n g l e r e s e r v o i r w i t h i n a s p h e r i c a l b i o e r o d i b l e m e m b r a n e , as i n s o m e m i c r o c a p s u l e s , t h e m e c h a n i s m of r e l e a s e c a n be t h e e r o s i o n and r u p t u r e of t h e b a r r i e r m e m b r a n e . V a r i o u s d e l i v e r y p a t t e r n s , i n c l u d i n g e s s e n t i a l l y c o n s t a n t r e l e a s e , c a n be a c h i e v e d by b l e n d i n g m i c r o c a p s u l e s of a p p r o p r i a t e w a l l t h i c k n e s s e s . R e l e a s e by r e t r o g r a d e c h e m i c a l r e a c t i o n s . A s opposed t o p h y s i c a l c o m b i n a t i o n s of p e s t i c i d e s d i s s o l v e d or e n t r a p p e d i n p o l y m e r s , c h e m i c a l c o m b i n a t i o n s have t h e p e s t i c i d e f i r m l y a t t a c h e d t o t h e p o l y m e r i c sub s t r a t e by a d e f i n i t e i d e n t i f i a b l e c h e m i c a l b o n d . T h e a c t i v e m a t e r i a l is r e l e a s e d when e n v i r o n m e n t a l r e a c t a n t s s u c h as w a t e r , a i r , s u n l i g h t , or microorganisms act to cleave the specific c h e m i c a l linkages which a t t a c h t h e p e s t i c i d e t o t h e s u b s t r a t e . The g e n e r a l m e c h a n i s m for r e t r o g r a d e c h e m i c a l s y s t e m s is shown i n E q u a t i o n 15. synthesis Polymer + P^stirirte

Λ

* Polvmfirir Pesticide environment

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(15)

1.

LEWIS AND

COWSAR

Principles

of Controlled

Release

11

Pesticides

O b v i o u s l y , o n l y those p e s t i c i d e s w i t h at l e a s t one r e a c t i v e f u n c t i o n a l m o i e t y c a n be u t i l i z e d i n d e l i v e r y s y s t e m s of t h i s t y p e . The most c o m m o n l i n k a g e s a r e e s t e r s , a n h y d r i d e s , and a c e t a l s . The r a t e of r e l e a s e of p e s t i c i d e s v i a r e t r o g r a d e r e a c t i o n s depends on t h e p r o p e r t i e s of t h e m a c r o m o l e c u l e and i t s s u r r o u n d i n g m e d i u m . When w a t e r present i n the e n v i r o n m e n t is used t o a c t i v a t e the r e l e a s e of p e s t i c i d e , t h e r a t e of h y d r o l y s i s depends on t h e s t r e n g t h and c h e m i c a l n a t u r e of t h e p o l y m e r p e s t i c i d e b o n d . F o r e x a m p l e , an a n h y d r i d e l i n k a g e is m o r e s u s c e p t i b l e t h a n an e s t e r or a m i d e l i n k a g e t o h y d r o l y s i s . The r a t e of h y d r o l y s i s of a l i n k a g e is also dependent on the groups s u r r o u n d i n g i t . H y d r o p h o b i c groups thus o f f e r p r o t e c t i o n against r a p i d h y d r o l y s i s . A n u n c r o s s l i n k e d p o l y m e r is m u c h m o r e s u s c e p t i b l e t o h y d r o l y s i s t h a n a h i g h l y c r o s s l i n k e d one, a n d a s t e r e o r e g u l a r or c r y s t a l l i n e p o l y m e r is less s u s c e p t i b l e t o h y d r o l y t i c a t t a c k t h a n an a m o r p h o u s or a t a c t i c p o l y m e r . The k i n e t i c expression cides from retrograde c h e m i c a h y d r o l y s i s r e a c t i o n , f o r e x a m p l e , o c c u r s on t h e s u r f a c e of an i n s o l u b l e p a r t i c l e or i n s o l u t i o n . F o r a h e t e r o g e n e o u s r e a c t i o n on the s u r f a c e of i n s o l u b l e s p h e r i c a l p a r t i c l e s , t h e r a t e of r e l e a s e of p e s t i c i d e is g i v e n by E q u a t i o n 16, dM

(16)

dt

w h e r e h is t h e n u m b e r of p a r t i c l e s of a v e r a g e radius r , k^ is t h e r e a c t i o n r a t e c o n s t a n t for h y d r o l y s i s , and C is t h e c o n c e n t r a t i o n of p e s t i c i d e p o l y m e r l i n k a g e s . F o r w a t e r - s o l u b l e d e l i v e r y s y s t e m s , t h e r a t e of r e l e a s e of pendant p e s t i c i d e groups f o l l o w s c o n v e n t i o n a l f i r s t - o r d e r k i n e t i c s . F i n a l l y , r e t r o g r a d e c h e m i c a l s y s t e m s w h i c h a r e based on d e p o l y m e r i z a t i o n r e a c t i o n s may i n d e e d be z e r o o r d e r i f t h e m e c h a n i s m of r e l e a s e c o m p r i s e s u n z i p p i n g of p o l y m e r c h a i n s . Applications M e m b r a n e - m o d e r a t e d d i f f u s i o n s y s t e m s f o r h o m e use w e r e s o m e of t h e iirjst c o n t o l l e d - r e l e a s e p e s t i c i d e s t o be m a r k e t e d . The H e r e o n L u r e N Kill F l y T a p e and R o a c h - T a p e * are laminated reservoir devices d e v e l o p e d by t h e H e a l t h C h e m C o r p o r a t i o n (15). T h e H e r e o n s t r i p s c o m p r i s e a g e n t - c o n t a i n i n g r e s e r v o i r s s a n d w i c h e d b e t w e e n l a y e r s of p l a s t i c f i l m . The o u t e r p l a s t i c f i l m serves as a m e m b r a n e t o c o n t r o l t h e r e l e a s e of p e s t i c i d e f r o m t h e r e s e r v o i r . The H e r e o n f l y s t r i p is p r o b a b l y t h e f i r s t s u c h p r o d u c t t o c o m b i n e an i n s e c t i c i d e w i t h a n ^ n s e c t a t t r a c t a n t . R e s m e t h r i n , the a c t i v e ingredient in the L u r e N K i l l F l y T a p e , k i l l s by d i r e c t c o n t a c t r a t h e r t h a n by v a p o r s . T h e p r o d u c t is r e p o r t e d t o be e f f e c t i v e f o r at l e a s t t h r e e m o n t h s . T h e S h e l l N o - P e s t Strip® is a n o t h e r w i d e l y used c o n t r o l l e d - r e l e a s e p r o d u c t . S i n c e d i c h l o r v o s , the a c t i v e i n s e c t i c i d e , is c o d i s s o l v e d w i t h a p l a s t i c i z e r i n the P V C m a t r i x , t h e N o P e s t S t r i p is a m o n o l i t h d e v i c e , a n d the r e l e a s e r a t e d e c r e a s e s w i t h t h e square r o o t of t i m e . f

f

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12

CONTROLLED RELEASE

PESTICIDES

NoFoul® R u b b e r d e v e l o p e d and m a r k e t e d by the B . F . G o o d r i c h C o m p a n y has p r o v e n s u c c e s s f u l as an a n t i f o u l i n g c o a t i n g ( 6 - 8). The p r o d u c t releases b i s ( t r i - n - b u t y l t i n ) o x i d e ( T B T O ) w h i c h is d i s s o l v e d at a l e v e l of 2 t o 5% i n N e o p r e n e r u b b e r . A f t e r e x t e n s i v e e v a l u a t i o n s , the N o F o u l p r o d u c t has p r o v e n t o be e f f e c t i v e f o r periods of up t o 92 m o n t h s . C a r d a r e l l i and his c o w o r k e r s (17, 18) have been responsible for m a n y of the a d v a n c e s m a d e i n c o n t r o l l e d - r e l e a s e a n t i f o u l a n t s y s t e m s . B e g i n n i n g around 1968, a n u m b e r of s y s t e m s for d e l i v e r i n g a q u a t i c h e r b i c i d e s w e r e i n v e s t i g a t e d . C a r d a r e l l i (1) i n c o r p o r a t e d the bûtoxyethanol e s t e r of 2,4-D(2,4-D B E E ) i n a v a r i e t y of p o l y m e r s i n c l u d i n g n a t u r a l r u b b e r . The p r i m a r y m e c h a n i s m of r e l e a s e of t h a t h e r b i c i d e f r o m the n a t u r a l rubber m a t r i x was m e m b r a n e - m o d e r a t e d d i f f u s i o n of agent d i s s o l v e d i n the m o n o l i t h s i n c e 2 , 4 - D - B E E is 35 t o 4 0 % s o l u b l e i n n a t u r a l r u b b e r . C a r b o n b l a c k was used t o slow the r e l e a s e of a g e n t . The p a r t i c l e s i z e , s t r u c t u r e , and a m o u n t of c a r b o n b l a c k w e r e shown t o be c r i t i c a l . A v a r i e t y of f o r m u l a t i o n s , t e r m e a l l o w agent to be r e l e a s e d at t h e w a t e r s u r f a c e or at p r e d e t e r m i n e d d e p t h s . F i e l d t e s t s have shown t h e d u r a t i o n of a c t i o n of t h e s y s t e m t o be about t w o y e a r s . Y o u n g and N e l s o n i n c o r p o r a t e d a n u m b e r of 2,4-D d e r i v a t i v e s i n c l u d i n g 2,4-D B E E i n p l a s t i c i z e d P V C (19). The m e c h a n i s m of r e l e a s e f r o m those f o r m u l a t i o n s a p p e a r e d t o be c o d i f f u s i o n of p l a s t i c i z e r s and a g e n t s . H a r r i s (20) has p r e p a r e d a series of d i f f u s i o n - t y p e d e l i v e r y s y s t e m s by d i s p e r s i n g t h e h e r b i c i d e Fenac® (sodium s a l t of 2,3,6t r i c h l o r o p h e n y l a c e t i c acid) i n porous p o l y e t h y l e n e m a t r i x e s . M i c r o e n c a p s u l a t i o n t e c h n i q u e s have been used t o p r e p a r e s p h e r i c a l shaped r e s e r v o i r d e v i c e s for c o n t r o l l e d r e l e a s e of p e s t i c i d e s . T h e most o f t e n - u s e d procedures i n c l u d e phase s e p a r a t i o n , c o a c e r v a t i o n , spray c o a t i n g , s o l v e n t e v a p o r a t i o n f r o m e m u l s i o n s , and i n t e r f a c i a l p o l y m e r i z a t i o n s . The c h o i c e of m e t h o d depends m a i n l y upon t h e c h a r a c t e r i s t i c s of t h e p e s t i c i d e and r e l e a s e - c o n t r o l l i n g m e m b r a n e . C o m m o n p o l y m e r i c w a l l m a t e r i a l s i n c l u d e p o l y a m i d e s , p o l y e s t e r s , p o l y u r e a s , c e l l u l o s e , and g e l a t i n . The most n o t a b l e of t h e c u r r e n t l y m a r k e t e d m i c r o c a p s u l e p r o d u c t s is p r o b a b l y the P e n n c a p - M f o r m u l a t i o n d e v e l o p e d by t h e P e n n w a l t C o r p o r a t i o n (21, 22). The s h o r t - a c t i n g p e s t i c i d e , m e t h y l p a r a t h i o n , is e n c a p s u l a t e d i n a p o l y a m i d e (nylon) w a l l m a t e r i a l . The m i c r o c a p s u l e s are about 30 m i c r o n s i n d i a m e t e r , and they c o n t a i n about 8 0 % of t h e a c t i v e agent by w e i g h t . T h i s p r o d u c t , w h i c h has r e c e i v e d r e g i s t r a t i o n w i t h the E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , e x h i b i t s d e c r e a s e d t o x i c i t y and longer a c t i v i t y when c o m p a r e d w i t h t h e c o n v e n t i o n a l a p p l i c a t i o n of the i n s e c t icide. The 3 M C o m p a n y m a r k e t s a l i n e of f e r t i l i z e r s m i c r o e n c a p s u l a t e d i n p o l y m e r i c m e m b r a n e s . These a r e p r i m a r i l y s p e c i a l i t y p r o d u c t s for h o m e use s u c h as t h e P r e c i s e T i m e d - R e l e a s e P l a n t F o o d , t h e P r e c i s e T i m e d R e l e a s e A f r i c a n V i o l e t F o o d , a m o n g o t h e r s . R e l e a s e of t h e agent o c c u r s by c o n t r o l l e d d i f f u s i o n t h r o u g h the c a p s u l e w a l l s and t h e d u r a t i o n of a c t i o n is 3 t o 6 m o n t h s . In a d d i t i o n t o these d e l i v e r y s y s t e m s w h i c h o p e r a t e by d i f f u s i o n or l e a c h i n g m e c h a n i s m s , o t h e r f o r m u l a t i o n s w h i c h r e l y on e r o s i o n or a c o m b i n a t i o n of e r o s i o n and d i f f u s i o n have been r e p o r t e d .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1.

LEWIS

AND

COWSAR

Principles

of Controlled

Release

Pesticides

13

S i n c l a i r (23) d e m o n s t r a t e d t h a t s o l i d agents c o u l d be m i x e d w i t h a p o l y m e r i c m a t e r i a l and e x t r u d e d or pressed i n t o p e l l e t s w h i c h w o u l d t h e n d e l i v e r t h e agent at a slow r a t e . T h e s o d i u m s a l t of 2,4-D was m i x e d w i t h p u l v e r i z e d polyûactic acid) ( P L A ) , and the r e s u l t i n g m i x t u r e was pressed i n t o p e l l e t s . The s l o w - r e l e a s e c h a r a c t e r i s t i c s of t h e p e l l e t s , d e t e r m i n e d in v i t r o i n m o i s t sandy s o i l , s h o w e d t h a t 7 0 % of t h e agent was r e l e a s e d i n about 20 days, w i t h 2 5 % being d u m p e d on t h e f i r s t d a y . E r o s i o n of t h e P L A and l e a c h i n g of t h e s o l u b i l i z e d agent g o v e r n e d t h e r e l e a s e of t h e herbicide. A series of s o l i d and l i q u i d p e s t i c i d e s was r e c e n t l y m i c r o e n c a p s u l a t e d in s t a r c h x a n t h a t e by Shasha and c o w o r k e r s (24). The m e c h a n i s m of r e l e a s e f r o m the s t a r c h capsules was a c o m b i n a t i o n of d i f f u s i o n and e r o s i o n . I n c o r p o r a t i o n of a s m a l l a m o u n t of l a t e x rubber w i t h the s t a r c h x a n t h a t e s l o w e d t h e r e l e a s e of p e s t i c i d e f r o m t h e s y s t e m , but t h e y d i d not d e t e r m i n e w h e t h e r t h e l a t e x i n h i b i t e d d i f f u s i o n or e r o s i o n . O n e of the f i r s t m i c r o e n c a p s u l a t e Tossits®, a D D T p r o d u c t m a r k e t e d by t h e W y c o I n t e r n a t i o n a l C o m p a n y . The D D T / o i l m i x t u r e i n the c o r e of t h e g e l a t i n - w a l l e d capsules was d u m p e d w h e n t h e w a l l s of the m i c r o c a p s u l e s r u p t u r e d . The W u r s t e r c o a t i n g process (25) has been used t o p r e p a r e a n u m b e r of e r o s i o n c o n t r o l l e d f o r m u l a t i o n s . W a r f i n , c o a t e d i n t h a t m a n n e r , is m o r e e f f e c t i v e as a r o d e n t i c i d e s i n c e the c o a t i n g serves t o m a s k t h e t a s t e of t h e b a i t u n t i l i t is i n j e s t e d . T h e t i m e of r e l e a s e is c o n t r o l l e d s i n c e the r o d e n t i c i d e is r e l e a s e d i n t h e r a t ' s s t o m a c h . A n i n c r e a s i n g l y a t t r a c t i v e a p p r o a c h t o d e s i g n i n g new c o n t r o l l e d r e l e a s e s y s t e m s is t h a t of a t t a c h i n g t h e a g e n t by c o v a l e n t or i o n i c bonds t o a p o l y m e r c h a i n as pendent groups. In m o s t of t h e f o r m u l a t i o n s of t h i s t y p e r e p o r t e d thus f a r , t h e p r i n c i p l e m e c h a n i s m of r e l e a s e is h y d r o l y s i s of a c o v a l e n t l i n k a g e b e t w e e n t h e pendent p e s t i c i d e group and t h e b a c k b o n e of t h e p o l y m e r . A l l a n (26, 27) and c o w o r k e r s w e r e a m o n g t h e f i r s t t o r e p o r t t h e synthesis and e v a l u a t i o n of v a r i o u s p o l y m e r s c o n t a i n i n g pendent h e r b i c i d e moitiés. R e c e n t l y , H a r r i s et a l p r e p a r e d a s e r i e s of h o m o p o l y m e r s and c o p o l y m e r s w i t h pendant h e r b i c i d e s u b s t i t u e n t s (28, 29). The 2a c r y l o y l o x y e t h y l e s t e r s of 2,4-D and S i l v e x w e r e c o p o l y m e r i z e d w i t h c o m o n o m e r s such as t r i m e t h y l a m i n e m e t h a c r y l i m i d e and a c r y l i c a c i d . T h e i r studies showed t h a t t h e r a t e of h y d r o l y s i s of c o n n e c t i n g e s t e r l i n k a g e s c a n be g r e a t l y e n h a n c e d by the i n c o r p o r a t i o n of a m i n i m i d e or c a r b o x y l i c groups a l o n g t h e p o l y m e r c h a i n . In a n o v e l a p p r o a c h , N e o g i a n d A l l a n (30, 31) c o m b i n e d m o n o m e r i c herbicides with bark from the Douglas F i r tree. One herbicide, 2,4-dichlorophenoxy-γ-butyric a c i d , was e s t e r i f i e d w i t h the b a r k t o p r o d u c e about 3 7 % of r e l e a s a b l e a g e n t . T h e h e r b i c i d e was a p p l i e d at s e v e r a l l e v e l s i n a 25-ft d i a m e t e r c i r c l e a r o u n d D o u g l a s F i r s e e d l i n g s . Data o b t a i n e d a f t e r 4 years show t h a t t r e e s t r e a t e d w i t h t h e c o n t r o l l e d - r e l e a s e f o r m u l a t i o n are g r o w i n g 16% f a s t e r per y e a r t h a n the u n t r e a t e d t r e e s . In a d d i t i o n t o the d e v e l o p m e n t s of h e r b i c i d e s r e p o r t e d by A l l a n and H a r r i s , advances have been m a d e w i t h v a r i o u s a n t i f o u l i n g agents i n a s i m i l a r a p p r o a c h . U . S . N a v y r e s e a r c h e r s (4, 32) h a v e s u c c e s s f u l l y i n c o r p o r a t e d o r g a n o t i n units as pendent groups a l o n g t h e b a c k b o n e of a d d i t i o n p o l y m e r s . The most p r o m i s i n g f o r m u l a t i o n s appear t o be those w i t h e s t e r

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14

CONTROLLED

R E L E A S E PESTICIDES

l i n k a g e s b e t w e e n the p e s t i c i d e and t h e p o l y m e r b a c k b o n e . A s w i t h the h e r b i c i d e s , t h e p r i m a r y mode of r e l e a s e is h y d r o l y s i s of the e s t e r group. F i e l d t r i a l s of f o r m u l a t i o n s d e v e l o p e d by t h e N a v y i n d i c a t e up t o 4 years of 1 0 0 % r e s i s t a n c e t o a l l f o r m s of f o u l i n g (4)· The i d e a l c o n t r o l l e d - r e l e a s e p e s t i c i d e s y s t e m w o u l d p r o b a b l y be one in w h i c h the a c t i v e agent was g e n e r a t e d as needed f r o m a m a c r o m o l e c u l a r s t r u c t u r e of the agent i t s e l f . In o t h e r w o r d s , t h e m o n o m e r i c p e s t i c i d e w o u l d be h o m o p o l y m e r i z e d t o a h i g h - m o l e c u l a r - w e i g h t s u b s t a n c e w h i c h upon h y d r o l y s i s , t h e r m o d y n a m i c d i s s o c i a t i o n , or m i c r o b i a l d e g r a d a t i o n w o u l d y i e l d a c t i v e a g e n t . O r perhaps a c o m o n o m e r c o u l d be used w h i c h w o u l d not be d e t r i m e n t a l i f r e l e a s e d t o t h e e n v i r o n m e n t . Very l i t t l e r e s e a r c h and d e v e l o p m e n t has been r e p o r t e d i n t h i s a r e a . N e o g i i n 1970 (33) p r e p a r e d a n u m b e r of c o n d e n s a t i o n p o l y m e r s w h i c h c o n t a i n e d p e s t i c i d e s i n the p o l y m e r c h a i n . We are a w a r e of no o t h e r s u c c e s s f u l a t t e m p t s t o f o r m u l a t e a p e s t i c i d e - r e l e a s i n g s y s t e m of t h i s t y p e . Other controlled-releas d i f f e r e n t f r o m those p r e v i o u s l y d i s c u s s e d . H o l l o w f i b e r s have been used t o d e l i v e r b i o l o g i c a l l y a c t i v e agents for e x t e n d e d p e r i o d s . The F R L C o r p o r a t i o n d e v e l o p e d the C o n r e f Hollow-Fiber Controlled-Release S t r i p s (34, 35). The a c t i v e agent is c o n t a i n e d w i t h i n t h e l u m e n of a s m a l l d i a m e t e r h o l l o w f i b e r usually m a d e of p o l y e s t e r . The r e l e a s e of agent is a t h r e e - s t e p m e c h a n i s m : e v a p o r a t i o n at the l i q u i d - v a p o r i n t e r f a c e , d i f f u sion t o the open end of t h e f i b e r , and c o n v e c t i o n away f r o m t h e open e n d . T h e Conrel® s y s t e m has been t e s t e d f o r d e l i v e r y of b e h a v i o r a l c h e m i c a l s s u c h as e n d o - and e x o - b r e v i c o m i n f o r c o n t r o l of t h e S o u t h e r n P i n e B e t t l e . The agents w e r e r e l e a s e d at n e a r l y c o n s t a n t r a t e s of 3.0 mg/day o v e r a 30-day p e r i o d . The h o l l o w - f i b e r dispenser has p r o v e n useful i n the mass t r a p p i n g of a n u m b e r of o t h e r i n s e c t s w i t h phenomones. S t e w a r d and c o w o r k e r s (36) r e c e n t l y r e p o r t e d f i e l d t r i a l s w i t h a w a t e r - i n - o i l emulsion which delivers the aquatic herbicide, D i q u a t , over prolonged periods. The m o s t p r o m i s i n g s y s t e m s w e r e f o r m u l a t e d w i t h d i e s e l o i l s as the o r g a n i c phase; t h e y c o n t a i n e d a number of e m u i s i f i e r s and s t a b i l i z e r s . The a d d i t i o n of t r i e t h a n o l a m i n e / c o p p e r c o m p l e x e s i n c r e a s e d the e f f i c a c y of t h e D i q u a t f o r m u l a t i o n s . O n e s h o u l d r e c o g n i z e t h a t m a n y p e s t i c i d e s a r e not a m e n a b l e to a d m i n i s t r a t i o n by c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s or d e v i c e s , and o t h e r s c a n be d e l i v e r e d e q u a l l y e f f e c t i v e l y by s i m p l e a l t e r n a t i v e m e a n s . It must also be e m p h a s i z e d t h a t e a c h agent usually r e q u i r e s a d e l i v e r y s y s t e m designed s p e c i f i c a l l y for t h e agent and the i n t e n d e d a p p l i c a t i o n . U n f o r t u n a t e l y , c o n s i d e r a b l e a m o u n t s of t i m e and funds have o f t e n been expended in u n s u c c e s s f u l a t t e m p t s t o f o r m u l a t e a c c e p t a b l e d e l i v e r y s y s t e m s f r o m s o - c a l l e d g e n e r a l or u n i v e r s a l p r o c e d u r e s . If the numerous p o t e n t i a l a d v a n t a g e s of c o n t r o l l e d r e l e a s e are t o be f u l l y r e a l i z e d , the r e s e a r c h e r m u s t s e l e c t and f o r m u l a t e t h e best s y s t e m possible for the p a r t i c u l a r end use.

Literature C i t e d 1.

C a r d a r e l l i , N. F., "Controlled R e l e a s e P e s t i c i d e s F o r m u l a t i o n s " , CRC P r e s s , Inc., C l e v e l a n d , O h i o , 1976.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

I. 2. 3. 4.

5.

6. 7. 8. 9. 10. 11.

12. 13. 14.

15.

16. 17. 18. 19.

20. 21.

22.

23. 24.

LEWIS

AND

COWSAR

Principles

of Controlled

Release

Pesticides

15

M a r x , J. L . , S c i e n c e , (1977), 195, 860. A n o n . , W i l d l i f e R e s e a r c h L a b o r a t o r y R e p o r t , U . S . D e p t . of the In terior, D e n v e r , 1969. C a s t e l l i , V . J. and Y e a g e r , W. L . , i n "Controlled R e l e a s e P o l y m e r i c F o r m u l a t i o n s " , D . R . P a u l and F . W. H a r r i s , eds., p p . 2 3 9 - 2 4 7 , A C S S y m p o s i u m Series 3 3 , A m e r i c a n C h e m i c a l S o c i e t y , W a s h i n g t o n , D . C . , 1976. F i s c h e r , E . C., i n " P r o c e e d i n g s 1976 I n t e r n a t i o n a l C o n t r o l l e d R e l e a s e Pesticide Symposium", N . F . Cardarelli, e d . , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. O v e l l e t e , R . P . and King, J., C h e m i c a l W e e k , J u n e 2 3 , 1976, p. 2 7 . T a n q u a r y , A . C. and L a c e y , R . E . , eds., "Controlled R e l e a s e of Bio logically Active A g e n t s " , P l e n u m P r e s s , N e w Y o r k , 1974. Cardarelli, N . F., ed., "Proceedings Controlled Release Pesticide S y m p o s i u m " , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1974. H a r r i s , F . W., e d . , " P r o c e e d i n g p o s i u m " , W r i g h t S t a t e U n i v e r s i t y , D a y t o n , O h i o , 1975. Cardarelli, N. F . , e d . , " P r o c e e d i n g s 1976 C o n t r o l l e d R e l e a s e P e s t i c i d e S y m p o s i u m " , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. P a u l , D . R . and H a r r i s , F . W., eds., "Controlled Release Polymeric F o r m u l a t i o n s " , A C S S y m p o s i u m Series 3 3 , A m e r i c a n C h e m i c a l So ciety, W a s h i n g t o n , D.C., 1976. B a k e r , R . W. and L o n s d a l e , H. K., C h e m t e c h , (1975), 5, 668. C a p r i o , A . F . and H o r b a c k , W., U . S . P a t e n t 2,460,376, F e b r u a r y 1, 1949. B a k e r , R . W . and L o n s d a l e , H . K . , i n "Controlled R e l e a s e of Biolo gically Active A g e n t s " , A . C. T a n q u a r y and R . E . L a c e y , eds., pp. 156 1 , P l e n u m P r e s s , N e w Y o r k , 1974. Q u i s u m b i n g , A. R . , K y d o n i e u s , A . F . , Calsett, D . R . , and H a u s , J. B . , i n " P r o c e e d i n g s 1976 C o n t r o l l e d R e l e a s e P e s t i c i d e S y m p o s i u m " , N . F . Cardarelli, e d . , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. P h i l l i p , A . T . , P r o g . O r g . Coat., (1973), 2, 159. Cardarelli, N . F . and N e f f , H. F . , F r e n c h P a t e n t 1, 506,704 (1966). Cardarelli, N. F . and N e f f , H. F., U . S . P a t e n t 3,639,583, (1972). Y o u n g , W. W. and N e l s o n , L . L . , " E v a l u a t i o n of c o n t r o l l e d r e l e a s e h e r b i c i d e f o r m u l a t i o n s for a q u a t i c w e e d s " , S p e c i a l Study N o . 31-00469/70. D e p t . of the A r m y , U . S . A r m y E n v i r o n m e n t a l H y g i e n e A g e n c y , E d g e w o o d A r s e n a l , Md., 1969. H a r r i s , F . W., N o r r i s , S. V . , and P o s t , L . K . , W e e d Sci., (1973), 21., 318. K o e s l t e r , R . C . and Ivy, Ε. E . i n " P r o c e e d i n g s C o n t r o l l e d R e l e a s e Pesticide Symposium", N . F . Cardarelli, e d . , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1974. K o e s l t e r , R . C . , i n " P r o c e e d i n g s 1976 C o n t r o l l e d R e l e a s e P e s t i c i d e S y m p o s i u m " , N . F . Cardarelli, e d . , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. S i n c l a i r , R . G., E n v i r o n m e n t a l S c i e n c e and T e c h n o l o g y , (1973), 7, 9 5 5 . Shasha, B . S., D o a n e , W . M., and R u s s e l l , C. R . , J. P o l y . Sci., P o l y m e r L e t t e r s E d i t i o n , (1976), 14, 4 1 7 .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16 25.

26. 27.

28. 29.

30.

31.

32. 33. 34.

35.

36.

CONTROLLED RELEASE

PESTICIDES

A n o n . , " T h e W u r s t e r A i r Suspension P r o c e s s for E n c a p s u l a t i o n " , Wisconsin A l u m n i Research Foundation, C o a t i n g Laboratory Report, M i d d l e t o n , W i s c o n s i n , 1974. A l l a n , G. G., C h o p r a , C. S., N e o g i , A. N., and W i l k i n s , R . M., T a p p i , (1971), 54, 1293. A l l a n , G. G., C h o p r a , C. S., F r i e d l o f f , J. F . , G a r a , R . I., M a g g i , M . W., N e o g i , A . N . , R o b e r t s , S. C., and W i l k i n s , R . W., C h e m . T e c h . , (1973), M a r c h , 171. H a r r i s , F . W. and P o s t , L . K . , J. P o l y . Sci., P o l y m e r L e t t e r s E d i t i o n , (1975), 13, 2 2 5 . H a r r i s , F. W., A u l a b a u g h , A. E., C a s e , R . D . , D y k e s , M. K., and Field, W. Α . , i n "Controlled R e l e a s e P o l y m e r i c F o r m u l a t i o n s " , D . R . P a u l and F . W. H a r r i s , eds., ACS S y m p o s i u m Series N u m b e r 3 3 , pp. 2 2 2 230, A m e r i c a n C h e m i c a l Society, Washington, D . C . N e o g i , A. N . and Allan, C. G., i n "Controlled R e l e a s e of B i o l o g i c a l l y Active A g e n t s " , A . C. P l e n u m P r e s s , N e w Y o r k , 1974. A l l a n , G . G . , C o u s i n , M . J., M c C o n n e l l , W. J., P o w e l l , J. C . , and Y a h i a o u i , Α., i n " P r o c e e d i n g s 1976 C o n t r o l l e d R e l e a s e P e s t i c i d e S y m p o s i u m " , N . F . Cardarelli, e d . , U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. D y c k m a n , E . J., M o n t e m a r a n o , J. Α., and F i s c h e r , E . C., N a v . E n g . J., (1973), 85, 3 3 . N e o g i , A . N . , " P o l y m e r Selection for C o n t r o l l e d Release Pesticides", P h . D . T h e s i s , U n i v e r s i t y of W a s h i n g t o n , 1970. A s h a r e , E . , B r o o k s , T . W., and Swenson, D . W . , i n " P r o c e e d i n g s Con trolled R e l e a s e P e s t i c i d e S y m p o s i u m " , F . W. H a r r i s , e d . , W r i g h t S t a t e University. P a y n e , T . L . , C o s t e r , J. E . , Johnson, P . C . , i n " P r o c e e d i n g s 1976 Controlled Release Pesticide Symposium", N . F. Cardarelli, ed., U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976. S t e w a r d , Κ. K . , J o n e s , A . O . , and H a y l , C. J., i n P r o c e e d i n g s 1976 Controlled Release Pesticide Symposium", N . F . Cardarelli, ed., U n i v e r s i t y of A k r o n , A k r o n , O h i o , 1976.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2 Structural and Chemical Factors Controlling the Permeability of Organic Molecules through a Polymer Matrix C. E. ROGERS Department of Macromolecular Science, Case Western Reserve University, Cleveland, Ohio 44106 The use o f polymeri cation systems almost alway bility and diffusivity of the active agent in the polymer m a t r i x . The c o n f i g u r a t i o n of the r e l e a s e system, be it r e s e r v o i r - t y p e o r a simple d i s p e r s a l o f d i s s o l v e d agent (we exclude any specific d i s c u s s i o n of polymer degradation r e l e a s e systems), is of little s i g n i f i c a n c e in this c o n t e x t . In certain systems there may be a rate-controlling step r e l a t e d t o interfacial processes which a f f e c t the attainment o f e q u i l i b r i u m across a reservoir-membrane phase boundary apart from normal boundary l a y e r phenomena. Except f o r such uncommon situations, the r e l e a s e r a t e characteristics of the system will reflect the diffusion r a t e s , s o l u t i o n levels, and r e s u l t a n t g r a d i e n t s o f d i s s o l v e d and diffusing agent w i t h i n the controlling polymer membrane. The inherent nature of t r a n s p o r t processes in polymeric media can be e x p l a i n e d and p r e d i c t e d in terms o f e s t a b l i s h e d models, t h e o r i e s , and phenomenological o b s e r v a t i o n s . There is an e x t e n s i v e literature which d e a l s w i t h the solution, diffusion, and permeation o f low molecular weight gases, vapors, liquids, and i o n s in polymer f i l m s (1-6). U n f o r t u n a t e l y , there a r e relatively few s t u d i e s i n v o l v i n g the t r a n s p o r t characteristics of l a r g e r o r g a n i c molecules in polymers. T h i s , in l a r g e p a r t , is due t o the experimental difficulties i n v o l v e d in such i n v e s t i g a t i o n s . P e r t i n e n t data relating t o the solubility and m i g r a t i o n of l a r g e r molecules in polymers can be gleaned from t h e literature d e a l i n g w i t h c o n t r o l l e d r e l e a s e systems (7-16), encapsulation (17-23), and plasticizer technology. The nature o f s o l u t i o n , diffusion, and permeation behavior in all membrane systems is common i n s o f a r as those processes and other p r o p e r t i e s of the m a t e r i a l s a r e governed by the p h y s i o chemical composition and s t r u c t u r e of the components under g i v e n environmental c o n d i t i o n s . The phenomena o f c o n t r o l l e d r e l e a s e are s i m i l a r ( o f t e n identical) t o those i n v o l v e d i n plasticizer technology, c o a t i n g s technology, environmental r e s i s t a n c e of polymers, and r e l a t e d areas of polymer technology. The e x t e n s i v e 17

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

18

C O N T R O L L E D R E L E A S E PESTICIDES

i n v e s t i g a t i o n s i n those areas can serve as both t h e o r e t i c a l and p r a c t i c a l guides i n the development of c o n t r o l l e d r e l e a s e systems. An important c o n s i d e r a t i o n l e a d i n g to an e l u c i d a t i o n of s o l u t i o n and d i f f u s i o n behavior i n many c o n t r o l l e d r e l e a s e a p p l i c a t i o n s i s that the polymeric m a t r i x o f t e n i s m o d i f i e d upon exposure to the a p p l i c a t i o n environment. Examples of common m o d i f i c a t i o n s are changes i n polymer s t r u c t u r e and morphology due to changes i n temperature or pH and changes i n polymer d e n s i t y and homogeniety of s t r u c t u r a l packing due to s w e l l i n g caused by an imbided e n v i ronmental s p e c i e s such as water. Other major c o m p l i c a t i o n s a f f e c t i n g c o n t r o l l e d r e l e a s e systems, such as boundary l a y e r phenomena and/or membrane f o u l i n g , are w e l l recognized. Consequently, i t i s a c h a l l e n g e to e i t h e r a l l e v i a t e the seriousness of these e f f e c t s o r , perhaps even b e t t e r to t u r n them to some advantage In any case, an understandin f u s i o n processes and t h e i environmental f a c t o r s i s a key element i n the design of v i a b l e polymer membrane c o n t r o l l e d r e l e a s e systems. With these concepts i n mind, we w i l l d i s c u s s aspects of the g e n e r a l dependence of d i f f u s i o n and s o l u t i o n processes on c e r t a i n s t r u c t u r a l f a c t o r s . We wish to emphasize a few u n d e r l y i n g p r i n c i p l e s and phenomena common to many types of a p p l i c a t i o n and to suggest avenues to approach the s o l u t i o n of remaining problem areas. In p a r t i c u l a r , we want to c a l l a t t e n t i o n to aspects of the g e n e r a l c o n c e n t r a t i o n dependence of s o l u t i o n / d i f f u s i o n p r o cesses which seem to be both neglected (or misunderstood) and promising f o r the development of e f f e c t i v e c o n t r o l l e d r e l e a s e systems. F a c t o r s A f f e c t i n g Membrane P e r m e a b i l i t y The mechanism of t r a n s p o r t of a penetrant agent w i t h i n a polymeric m a t e r i a l can be c l a s s i f i e d i n terms of the presence or absence of a) a gross porous (or h i g h l y swollen) s t r u c t u r e and b) f i x e d i o n i c charges. In the f i r s t case, the t r a n s p o r t behavior i s c l o s e l y governed by the r e l a t i v e molecular dimensions of the penetrant as compared to the pore diameter and c o n n e c t i v i t y . T h i s mechanism i s dominant i n d i a l y s i s and u l t r a f i l t r a t i o n membrane systems. The e l e c t r o s t a t i c i n t e r a c t i o n s between the penetrant molecule and the polymer-fixed i o n i c groups, as modif i e d by the a c t i o n of other sorbed s p e c i e s , i s a dominant f a c t o r i n i o n exchange and some b i o l o g i c a l membrane systems. In the absence of the above o v e r r i d i n g f a c t o r s , the most common mechanism of t r a n s p o r t i s the s o l u t i o n - d i f f u s i o n model. In t h i s case, the o v e r a l l t r a n s p o r t process depends on a m u l t i tude of f a c t o r s r e l a t i n g to such aspects as the s i z e , shape, composition, and c o n c e n t r a t i o n of the penetrant and the polymer composition, s t r u c t u r e , and morphology. Although the number of f a c t o r s , and i n t e r a c t i o n s between f a c t o r s , may l e a d to complex r e l a t i o n s h i p s to d e s c r i b e the s o l u t i o n - d i f f u s i o n behavior, i t i s

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

ROGERS

Permeability

through

a Polymer

19

Matrix

t h i s complexity which can a l l o w us to d e s i g n and develop unique and u s e f u l membrane systems. Regardless of the s t a t e of aggregation of the m i x t u r e , the d i f f u s i o n f l o w or f l u x , J , of a substance i n a mixture w i t h other substances can be d e f i n e d as the amount passing d u r i n g u n i t time through a s u r f a c e of u n i t area normal t o the d i r e c t i o n of f l o w . I n many cases of i n t e r e s t f o r r e l e a s e a p p l i c a t i o n s , i t i s neces sary t o r e a l i z e t h a t the t o t a l f l u x may be a combination of a pure d i f f u s i v e f l u x and other f l u x e s due to mass f l o w , f l o w through d e f e c t s , or f l o w due t o e x t e r n a l l y imposed s t r e s s or other d r i v i n g f o r c e . S u i t a b l e c o r r e c t i o n s to account f o r the frame of r e f e r e n c e f o r such systems have been d i s c u s s e d (2,3,5). The concepts and procedures of i r r e v e r s i b l e thermodynamics are g e n e r a l l y a p p l i c a b l e . These c o r r e c t i o n s seldom have been made i n p r a c t i c e so t h a t the i n t e r p r e t a t i o s u b j e c t to r e a p p r a i s a l i on the b a s i s of concepts and t h e o r i e s f o r d i f f u s i v e mechanisms of transport. The f l u x i n the s t e a d y - s t a t e (or pseudo-steady-state over r e l a t i v e l y short time p e r i o d s ) f o r c o r r e c t e d pure d i f f u s i v e f l u x can be expressed as: J - -DK(dc/dx) = -D*(dlna/dlnc)(dc/dc)(dc/dx)

(1)

where DK = J?, the p e r m e a b i l i t y constant. The d i f f u s i o n c o e f f i c i e n t D* i s a measure of the average m o b i l i t y of penetrant mole c u l e s w i t h i n the d i f f u s i o n medium. The d i s t r i b u t i o n f a c t o r (solubility coefficient) Κ = (dc/dc)

(2)

i s a measure of the p a r t i t i o n i n g of penetrant between a polymer s o l u t i o n phase, "c, and an ambient penetrant phase, c. The l a t t e r phase may be the phase e x t e r n a l to the membrane, the enclosed penetrant r e s e r v o i r , or d i s p e r s e d phase-separated penetrant " m i c r o - r e s e r v o i r s " w i t h i n the polymeric m a t r i x . The Nernst-type d i s t r i b u t i o n f u n c t i o n i s a thermodynamic parameter c h a r a c t e r i z i n g the ρenetrant-polymer system which can be a f u n c t i o n of pressure or c o n c e n t r a t i o n as w e l l as temperature. The apparent F i c k ' s Law d i f f u s i o n c o e f f i c i e n t , D, i s the product of the non-negative m o b i l i t y f a c t o r and a thermodynamic f a c t o r r e l a t e d to the i d e a l i t y of the penetrant-polymer m i x t u r e : D = D*(dlna/dlnc)

(3)

where a i s the a c t i v i t y and "c i s the c o n c e n t r a t i o n of penetrant i n s o l u t i o n i n the polymer phase. When the mixture i s a thermodynamically i d e a l s o l u t i o n , dlna/dlric i s u n i t y . However, most mixtures e x h i b i t d e v i a t i o n s from i d e a l behavior of a magnitude

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

20

C O N T R O L L E D R E L E A S E PESTICTOES

p r o p o r t i o n a l t o the c o n c e n t r a t i o n . The thermodynamic term a l s o can be expressed as d l n a / d l n c - 1 + (dlny/dlnc)

(4)

where γ i s the a c t i v i t y c o e f f i c i e n t . I f , f o r any reason, the thermodynamic term becomes negative i n s i g n , d i f f u s i o n occurs a g a i n s t t h e c o n c e n t r a t i o n g r a d i e n t . The presence o f u n s t a b l e phase r e g i o n s w i t h i n the d i f f u s i o n medium, due, f o r example, t o sudden l o c a l changes i n a p p l i e d s t r e s s o r temperature, w i l l l e a d to t h i s " u p h i l l " d i f f u s i o n behavior which i s phenomenologically s i m i l a r t o " a c t i v a t e d " t r a n s p o r t i n b i o l o g i c a l systems. The c o n c e n t r a t i o n dependence o f D i s seen t o a r i s e from two sources: the c o n c e n t r a t i o n dependence of the m o b i l i t y , u s u a l l y the dominant f a c t o r , an the n o n - i d e a l nature o i n t e r p r e t e d and assessed i n terms of t h e o r i e s o r models concerned w i t h polymer s o l u t i o n behavior, the mode of s o r p t i o n , molecular f r i c t i o n f a c t o r s , c h a i n segmental m o b i l i t y , f r e e volume concepts, etc. C e r t a i n of these aspects w i l l be d e s c r i b e d i n a l a t e r section. I t i s w e l l t o note t h a t the d e f i n i t i o n s of Κ and D do n o t impose any r e s t r i c t i o n s as t o t h e f u n c t i o n a l dependence of t h e parameters on experimental c o n d i t i o n s . I n t e r p r e t a t i o n o f t h e s i g n i f i c a n c e o f the parameters must be made i n l i g h t o f r e f i n e d and r e a l i s t i c t h e o r i e s o r models which account f o r the nature of the system t o i n c l u d e the dominant t r a n s p o r t mechanism, frame of reference c o r r e c t i o n s , boundary l a y e r e f f e c t s , and other r e l e v a n t concepts. For engineering design purposes, the parameters can serve as phenomenological c o e f f i c i e n t s which d e s c r i b e the system under the g i v e n c o n d i t i o n s without need f o r c o r r e c t i o n o r i n t e r pretation. A g e n e r a l mechanism t o d e s c r i b e the m i g r a t i o n o f a penetrant molecule through a medium v i s u a l i z e s the process as a sequence of u n i t d i f f u s i o n steps or jumps under the i n f l u e n c e of a chemical p o t e n t i a l (concentration) g r a d i e n t by a cooperative a c t i o n o f the surrounding complex of molecules d u r i n g which the penetrant molecule passes over a p o t e n t i a l b a r r i e r s e p a r a t i n g one s i t e from the next. The magnitude o f the d i f f u s i o n c o e f f i c i e n t i s equated as a product o f a constant times the p r o b a b i l i t y o f a s u c c e s s f u l jump. That p r o b a b i l i t y can be r e l a t e d t o the ease o f h o l e forma t i o n which depends on t h e r e l a t i v e m o b i l i t i e s of penetrant mole c u l e s and polymeric c h a i n segments as they are a f f e c t e d by changes i n s i z e , shape, c o n c e n t r a t i o n , and i n t e r a c t i o n between components. Another major f a c t o r a f f e c t i n g t r a n s p o r t i s the number, s i z e , and d i s t r i b u t i o n of d e f e c t s t r u c t u r e s , such as v o i d s , c a p i l l a r i e s , and domain boundaries, w i t h i n the polymer m a t r i x . The inherent morphological nature of the polymer, coupled w i t h the p a r t i c u l a r sample f a b r i c a t i o n and p r o c e s s i n g c o n d i t i o n s , determine the de t a i l e d defect structure.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

ROGERS

Permeability

through

a Polymer

21

Matrix

I n r e l a t i v e l y homogeneous polymers the dependence of permea b i l i t y on the a n t i c i p a t e d c o n t r o l l i n g f a c t o r s can be s t a t e d q u i t e g e n e r a l l y . For example, the temperature dependence of d i f f u s i o n and s o l u b i l i t y over reasonable temperature ranges can be represented by the Arhennius-type equations D • D exp(-E /RT)

(5)

S - S exp(-AH /RT)

(6)

Q

Q

D

s

where Eq i s the apparent a c t i v a t i o n energy f o r d i f f u s i o n and AH i s the heat of s o l u t i o n . Consequently, any f a c t o r which a c t s to reduce the ease of h o l e f o r m a t i o n f o r d i f f u s i o n can be expected to decrease the o v e r a l quite noticeable i n studie t r a n t s of i n c r e a s i n g molecular s i z e and shape s i n c e the o v e r a l l t r a n s p o r t process i s extremely s e n s i t i v e to the magnitude and s i z e d i s t r i b u t i o n of " h o l e s " a v a i l a b l e per u n i t time and volume f o r d i f f u s i v e jumps as determined by the i n h e r e n t o r m o d i f i e d polymer c h a i n segmental m o b i l i t i e s . The l o c a l segmental m o b i l i t y or c h a i n s t i f f n e s s may be a f f e c t e d by c h a i n i n t e r a c t i o n s a r i s i n g from hydrogen bonding, p o l a r group i n t e r a c t i o n s , or simple van der Waal's a t t r a c t i o n s . As the number of these groupings per u n i t c h a i n segment l e n g t h i n c r e a s e s , the degree of i n t e r a c t i o n i n c r e a s e s , the segmental m o b i l i t y decreases, and t h e r e f o r e the permeation r a t e a l s o decreases. These e f f e c t s a r e e s p e c i a l l y pronounced f o r the case of symmetrical s u b s t i t u t i o n of p o l a r groups s i n c e the packing of adjacent c h a i n segments i s somewhat f a c i l i t a t e d l e a d i n g to more efficient interactions. Other m o d i f i c a t i o n s ( 1 - 2 ) which serve to decrease c h a i n segmental m o b i l i t y , and t h e r e f o r e decrease permeation, are s u f f i c i e n t l y h i g h degrees of c r o s s l i n k i n g , the presence of s o l i d a d d i t i v e s ( f i l l e r s ) onto which the polymer i s s t r o n g l y adsorbed, and the occurrence of c r y s t a l l i n e domains w i t h i n the polymer i t s e l f . An i n c r e a s e i n d e n s i t y and c r y s t a l l i n e content r e s u l t s m a i n l y i n a corresponding decrease i n s o l u b i l i t y s i n c e c r y s t a l l i n e r e g i o n s are not g e n e r a l l y a c c e s s i b l e f o r s o r p t i o n . However, the conc u r r e n t p e r m e a b i l i t y decrease i s s u b s t a n t i a l l y g r e a t e r , i n d i c a t i n g that the d i f f u s i o n c o e f f i c i e n t a l s o i s decreased, p r e s u mably because of the r e s t r a i n i n g e f f e c t s of c r y s t a l l i n e r e g i o n s on l o c a l c h a i n segmental motion i n a d j o i n i n g n o n - c r y s t a l l i n e r e g i o n s and a more t o r t u o u s path through the m i x t u r e of amorphous and c r y s t a l l i n e domains. The l o c a l c h a i n segmental m o b i l i t y of a polymer i s enhanced by the presence of an added p l a s t i c i z e r , r e s u l t i n g i n a l o w e r i n g of the g l a s s t r a n s i t i o n temperature of the polymer. The permeat i o n of s o l v e n t s i n a polymer i s s i m i l a r i n t h a t the sorbed and d i f f u s i n g s o l v e n t a c t s to " p l a s t i c i z e " the polymeric system. S

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

22

C O N T R O L L E D R E L E A S E PESTICIDES

The net r e s u l t of the much higher sorbed c o n c e n t r a t i o n s of good s o l v e n t s i n a polymer (a h i g h Κ value) times the attendant p l a s t i c i z i n g a c t i o n which i n c r e a s e s the corresponding d i f f u s i o n c o e f f i c i e n t i s a marked i n c r e a s e i n the o v e r a l l permeation r a t e . T y p i c a l l y , f o r low c o n c e n t r a t i o n s (up to about 10 percent by weight) of a sorbed penetrant, where Henry's Law i s reasonably v a l i d , the d i f f u s i o n c o e f f i c i e n t v a r i e s w i t h c o n c e n t r a t i o n as: D = D(c=o)exp(ac)

(7)

where D(c=o) i s the e x t r a p o l a t e d v a l u e of D a t zero c o n c e n t r a t i o n and α i s a c h a r a c t e r i s t i c parameter which can be r e l a t e d , f o r example, to the Flory-Huggins i n t e r a c t i o n parameter. For wider ranges of sorbed c o n c e n t r a t i o n s , b e t t e r r e p r e s e n t a t i o n s are ob t a i n e d i n terms of s o l v e n D = D(c=o)exp(a a)

(8)

T h i s i n c l u d e s the r e g i o n s of sorbed c o n c e n t r a t i o n where Henry's Law i s no longer obeyed, but r a t h e r the s o r p t i o n f o l l o w s the Flory-Huggins equation or the r e l a t e d e x p r e s s i o n ( 2 , 3 ) : Κ = K(c=o)exp(orc)

(9)

Combination of Equations (8) and (9) f o r the case when σ ap proaches zero leads to Equation ( 7 ) . D e t a i l e d t h e o r i e s have been proposed to r a t i o n a l i z e the observed c o n c e n t r a t i o n depen dence of d i f f u s i o n , mainly i n terms of f r e e volume concepts, and to account f o r the phenomena of penetrant c l u s t e r formation w i t h i n the polymeric m a t r i x . We w i l l consider some of these aspects i n a l a t e r s e c t i o n . I n most i n v e s t i g a t i o n s of d i f f u s i o n and s o l u t i o n i n p o l y mers, the t a c i t assumption has been made t h a t the a c c e s s i b l e r e g i o n s are s t r u c t u r a l l y homogeneous so that d i f f u s i o n can be considered to occur by a s i n g l e a c t i v a t e d mechanism w i t h i n the continuum. R e c e n t l y , however, evidence has been presented f o r the presence of a microporous s t r u c t u r e i n c e r t a i n amorphous polymers below or near t h e i r g l a s s temperature, and i n semic r y s t a l l i n e polymers above t h e i r g l a s s temperature. The d i s t r i b u t i o n of v o i d s i z e and shape, dependent on the manner of membrane p r e p a r a t i o n and f a b r i c a t i o n , may range from submicrovoids of the order of u n i t - c e l l dimensions to p o r o s i t i e s and cleavages of much g r e a t e r dimensions w i t h non-random c o n f i g u r a t i o n s . These v o i d s are to be d i s t i n g u i s h e d from the f r e e volume a s s o c i a t e d w i t h l i q u i d s or amorphous s o l i d s and t h e i r magnitude i s not a thermodynamic q u a n t i t y . I n g l a s s y amorphous polymers as the temperature i s lowered below the g l a s s tempera t u r e , the a c t u a l t o t a l volume occupied by a polymer becomes pro g r e s s i v e l y g r e a t e r than the e q u i l i b r i u m volume of an e q u i v a l e n t l i q u i d . Since segmental m o b i l i t y i s low, t h i s volume d i f f e r e n c e

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

ROGERS

Permeability

through

a Polymer

Matrix

23

must r e s u l t i n the formation of d i f f e r e n t d e n s i t y regions on the m i c r o s c a l e . The l e s s densely packed r e g i o n s then correspond i n e f f e c t to v o i d s w i t h i n the surrounding more densely packed m a t r i x . This phenomenon may be even more pronounced f o r c e l l u l o s i c polymers which e x h i b i t v e r y low r a t e s of conformational rearrangement due to t h e i r inherent low segmental c h a i n m o b i l i t y . The c o n d i t i o n s of p r o c e s s i n g , such as c a s t i n g temperature, s o l u t i o n composition, and subsequent annealing treatments, w i l l have a marked e f f e c t on the m i c r o s t r u c t u r e of the membrane. In many cases, the r e s u l t a n t s t r u c t u r a l h e t e r o g e n e i t i e s can be cons i d e r e d as v o i d s w i t h i n the terms of the above d i s c u s s i o n . The v o i d content w i l l be c h a r a c t e r i z e d by a magnitude and s i z e d i s t r i b u t i o n which w i l l then change w i t h time as the membrane i s subjected to more extreme environmental c o n d i t i o n s during i t s use. The v o i d d i s t r i b u t i o c h a i n conformation s t a t i s t i c s The e f f e c t of a microporous s t r u c t u r e on the s o l u b i l i t y and t r a n s p o r t p r o p e r t i e s depends on the c o n t i n u i t y of path a f f o r d e d by the d i s t r i b u t i o n of microvoids and on the nature of the penet r a n t contained w i t h i n such v o i d s . The presence of i n t e r c o n nected micropores, s m a l l channels, c r a c k s , or other flaws i n polymer s t r u c t u r e permits convection of penetrant to occur through the medium i n a d d i t i o n to a c t i v a t e d d i f f u s i o n . Such c a p i l l a r y f l o w does not show v e r y pronounced d i f f e r e n c e s f o r v a r i o u s penetrants unless the d i f f u s i n g molecule i s of a dimens i o n comparable w i t h that of the c a p i l l a r y . For the case of a homogeneous d i s t r i b u t i o n of n o n - i n t e r c o n nected microvoids the o v e r a l l r a t e of t r a n s p o r t would be expected to i n c r e a s e somewhat owing to the smaller s t r u c t u r a l packing d e n s i t y a f f o r d e d by the presence of the lower d e n s i t y v o i d r e g i o n s . However, when the cohesive f o r c e s between penetrant molecules are g r e a t e r than the a t t r a c t i v e f o r c e s between penet r a n t and polymer, the incoming penetrant tends to c l u s t e r w i t h i n the polymer. With reference to the o v e r a l l d i f f u s i o n f l u x , a molecule w i t h i n a c l u s t e r g e n e r a l l y w i l l be l e s s mobile than an i s o l a t e d f r e e molecule owing to the a d d i t i o n a l energy r e q u i r e d to break f r e e from the c l u s t e r . A d e t a i l e d d i s c u s s i o n of the dependence of the d i f f u s i o n f l u x on c l u s t e r formation as i t v a r i e s w i t h penetrant c o n c e n t r a t i o n , v o i d content, time, and other f a c t o r s has been presented (2,3). A more fundamental and comprehensive approach to the general problem of d i f f u s i o n i n multicomponent systems i s a f f o r d e d by the theory of i r r e v e r s i b l e thermodynamics. The r a t e of f l o w of a substance i n such a system i s dependent not o n l y on i t s own g r a d i e n t of chemical p o t e n t i a l ( i . e . , c o n c e n t r a t i o n g r a d i e n t ) but a l s o on the g r a d i e n t s of chemical p o t e n t i a l of the other components as w e l l as e x t e r n a l f o r c e g r a d i e n t s ( s t r e s s , e l e c t r i c f i e l d s , temperature, e t c . ) . For systems not f a r removed from e q u i l i b r i u m , t h i s interdependence may be assumed to be l i n e a r .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

24

C O N T R O L L E D R E L E A S E PESTICIDES

The r e s u l t a n t c r o s s terms have been neglected o r considered n e g l i g i b l e i n almost a l l past i n v e s t i g a t i o n s of d i f f u s i o n . However, these terms c e r t a i n l y are s i g n i f i c a n t i n many cases, such as i n s o - c a l l e d " a c t i v e " b i o l o g i c a l t r a n s p o r t , and t h e r e f o r e should be i n c l u d e d to o b t a i n a more complete understanding of d i f f u s i o n phenomena. C o n c e n t r a t i o n Dependence of D i f f u s i o n A major f a c t o r which may a f f e c t the performance of con t r o l l e d r e l e a s e systems i s the p r o g r e s s i v e enhancement of d i f f u s i o n r a t e s by the d i s r u p t i o n of the polymer m a t r i x due to s w e l l i n g f o r one cause or another. Related e f f e c t s , to e i t h e r i n c r e a s e or d i m i n i s h the r a t e of t r a n s p o r t are due to changes i n the inherent m o b i l i t v a r i a t i o n s i n the mod s i d e r e d under the g e n e r a l concept of c o n c e n t r a t i o n dependence of d i f f u s i o n . As mentioned p r e v i o u s l y , the thermodynamic term ( d l n a / d l n c ) i n equations ( 1 ) , ( 3 ) , and (4) can be assessed d i r e c t l y from the s o l u t i o n theory equation which best r e p r e s e n t s the s o r p t i o n i s o therm f o r the p a r t i c u l a r system. I n most cases, t h i s term i s of r e l a t i v e l y minor s i g n i f i c a n c e as compared to the e f f e c t s on the m o b i l i t y parameter. The m o b i l i t y term, D*, i n equations (1) and (3) can be f u r t h e r d e f i n e d i n terms of two concepts: a) i m m o b i l i z a t i o n of penetrant molecules, and b) the segmental m o b i l i t y of polymer c h a i n s . The f i r s t concept i n v o l v e s c o n s i d e r a t i o n s of the e f f e c t s of d i f f e r i n g modes of s o r p t i o n , such as s p e c i f i c s i t e s o l v a t i o n , chemisorρtion, or c l u s t e r f o r m a t i o n , on the a c t u a l m o b i l i t y of the i n d i v i d u a l penetrant molecules. The other con cept c o n s i d e r s p l a s t i c i z a t i o n and other e f f e c t s of s w e l l i n g , u s u a l l y i n terms of f r e e volume treatments. An understanding of the nature of polymer s o l u t i o n s sug gests t h a t one should a n t i c i p a t e a spectrum of penetrant mole c u l a r m o b i l i t i e s , D t ( c i ) , r e l a t e d to a spectrum of modes of s o r p t i o n determined by the experimental time s c a l e and the i n t e r a c t i o n e n e r g e t i c s of v a r i o u s s o r p t i o n s i t e s i n the system. Penetrant molecules i n v o l v e d i n s p e c i f i c s i t e s o r p t i o n or i n p h y s i c a l c l u s t e r s ( p e n e t r a n t - r i c h domains below l i q u i d n u c l e a t i o n s i z e ) can be considered as l o c a l i z e d i f the r a t e of ex change of molecules between those modes of s o r p t i o n and f r e e l y d i f f u s i n g s p e c i e s i s slower than the r a t e of the u n i t d i f f u s i o n process. I n the s i m p l e s t case, we can consider the d u a l s o r p t i o n mode approximation which d e f i n e s the t o t a l sorbed c o n c e n t r a t i o n , "c, as composed of f r e e l y d i f f u s i n g s p e c i e s of c o n c e n t r a t i o n , "c-, and bound s p e c i e s of c o n c e n t r a t i o n c" . With the assumption that the bound s p e c i e s i s t o t a l l y immobilized (D^ 0 ) , equaβ

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

Permeability

ROGERS

through

a Polymer

25

Matrix

t i o n (1) may be r e w r i t t e n as: J = -D (dlna /dlnc )(dc /dc)(dc/dc)(dc/dx) f

f

f

f

The e x p e r i m e n t a l l y determined

d i f f u s i o n c o e f f i c i e n t i s then:

D = D (dlna /dlnc )(dc /dc) f

f

(10)

f

(11)

f

The context of the assumption i s such t h a t the f r e e l y d i f f u s i n g species can be considered t o form an i d e a l s o l u t i o n mixture so that equation (11) can be s t a t e d as simply: D = D (c /ïï) f

(12)

f

Thus any process whic w i t h i n the d i f f u s i o n medium w i l l cause t o be l e s s than c" and the e x p e r i m e n t a l l y determined v a l u e of D w i l l be l e s s than the " t r u e " v a l u e Df. T h i s phenomenon has been e x t e n s i v e l y confirmed and the model treatments extended (4)· There have been s e v e r a l model r e l a t i o n s h i p s proposed t o account f o r the e f f e c t s of sorbed low molecular weight m a t e r i a l to p l a s t i c i z e the polymer and so i n c r e a s e the r a t e of d i f f u s i o n . The general method has been t o estimate the p r o b a b i l i t y of a s u c c e s s f u l d i f f u s i o n jump i n terms of e i t h e r the energy r e q u i r e d f o r a c r i t i c a l volume d i s t u r b a n c e o r f r e e volume e f f e c t s (3,5). Those based on f r e e volume concepts have gained the widest acceptance but the energy c o n s i d e r a t i o n s show g r e a t e r promise f o r extended treatments to e l u c i d a t e the nature of the d i f f u s i o n mechanism. In the f r e e volume model proposed by F u j i t a and Kishimoto (24-26), the p r o b a b i l i t y of h o l e formation i s r e l a t e d to the p r o b a b i l i t y of o b t a i n i n g a f r e e volume domain of a s i z e s u f f i c i e n t to a l l o w a d i f f u s i o n jump (as d e f i n e d f o r other processes by Cohen and T u r n b u l l and by D o o l i t t l e ) . The d i f f u s i o n c o e f f i c i e n t i s s t a t e d as D* = D(dlricYdlna) = Aoexp(-Bo/f)

(13)

where Arj i s a constant a t a g i v e n temperature, f i s the f r e e volume f r a c t i o n , and i s a parameter, c h a r a c t e r i s t i c of the system, which g i v e s a measure of the e f f i c i e n c y of use of a v a i l a b l e f r e e volume by the d i f f u s i o n process. According to the WLF equation, the temperature dependence of f r e e volume i n u n d i l u t e d polymer a t Τ > Tg i s f(o,T) = f ( o , T ) + a ( T - T ) g

where T

g

2

g

(14)

i s the g l a s s temperature of pure (dry) polymer and a

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2

26

CONTROLLED

R E L E A S E PESTICIDES

i s the d i f f e r e n c e between the thermal expansion c o e f f i c i e n t s above and below Tg. Provided the c o n c e n t r a t i o n o f d i l u e n t i s not too h i g h , the c o n c e n t r a t i o n dependence a t a g i v e n sorbed volume f r a c t i o n , φ-^, o f penetrant a t a g i v e n temperature Τ may be g i v e n as f(φ ,Τ) - f(o,T) + 3φ = fο + βφχ χ

χ

(15)

where β i s a parameter r e p r e s e n t i n g the c o n t r i b u t i o n of the d i l u e n t toward i n c r e a s i n g the f r e e volume. Β i s a f u n c t i o n o f Τ but, t o a f i r s t approximation, i s independent o f φ·^. The con c e n t r a t i o n dependence o f d i f f u s i o n a t a g i v e n temperature i s then ln[D*/D(o) where D(o) i s the v a l u e of D* a t φ^ = 0 . Under c o n d i t i o n s such t h a t ΒΦ]/£ « I t t h i s equation reduces t o 0

ln[D*/D(o)] - B B ^ j / f g

(17)

and lnD*(and InD) i s approximately l i n e a r w i t h φ^ (correspon d i n g t o equation ( 7 ) ) . These r e l a t i o n s h i p s can represent data over ranges of c o n c e n t r a t i o n and s w e l l i n g corresponding t o those found i n a p p l i c a t i o n s o f p r a c t i c a l membrane systems. They a l l o w u s e f u l p r e d i c t i o n s t o be made of a n t i c i p a t e d behavior based on a v a i l a b l e m a t e r i a l parameters. The f r e e volume approach t o d i f f u s i o n behavior a l s o i s of i n t e r e s t i n t h a t i t b r i n g s t o the f o r e f r o n t the correspondence between mass t r a n s f e r and momentum t r a n s f e r i n polymeric s y s tems (27-29). R h e o l o g i c a l and mechanical p r o p e r t i e s of p o l y mers, such as v i s c o s i t y , creep, s t r e s s - r e l a x a t i o n , and dynamicmechanical b e h a v i o r , a r e l i k e w i s e determined by the nature of the c h a i n segmental motion processes i n polymers, both i n the absence and presence of a d i l u e n t . Many s u c c e s s f u l model treatments t o e x p l a i n and p r e d i c t v a r i o u s r e l a x a t i o n processes a r e based on f r e e volume concepts. The correspondence between d i f f u s i o n processes and s t r e s s r e l a x a t i o n processes i n a s e r i e s o f random copolymers o f i s o prene and methylmethacrylate has been measured u s i n g the d e r i v e d r e l a t i o n s h i p , i n terms o f f r e e volume as above, i n the form: ln[D*/D(o)] = ( B / B ) l n ( a ) o D

where:

n

c

(18)

( a ) « π Φ2/η(Φΐ) η = v i s c o s i t y ( o r modulus) a t φ^ = ο η(φ^) = v i s c o s i t y a t φ^ = φ^ c

0

0

0

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

ROGERS

Permeability

through

a Polymer

27

Matrix

The parameters Bip and Β η c h a r a c t e r i z e the e f f i c i e n c i e s by which the processes of penetrant d i f f u s i o n and s t r e s s r e l a x a t i o n u t i l i z e the a v a i l a b l e f r e e volume i n the system. I t i s found that the r a t i o ( Β β / Β η ) tends to u n i t y as the s i z e of the penetrant molecule i n c r e a s e s . T h i s i s i n accord w i t h the r e a l i z a t i o n t h a t f o r s u f f i c i e n t l y h i g h molecular weight pene t r a n t s , the d i f f u s i o n process corresponds w i t h t h a t f o r s e l f d i f f u s i o n of polymer segments and c h a i n s . Since many agents i n c o n t r o l l e d r e l e a s e a p p l i c a t i o n s are of moderately h i g h molecular weight, i t seems a p p r o p r i a t e to assess t h e i r t r a n s p o r t behavior i n analogy to the v i s c o u s f l o w behavior of the polymeric m a t r i x . Thus, an a p p r a i s a l of the log modulus versus time-temperature-concentrâtion master curve g i v e s a t l e a s t q u a l i t a t i v e i n d i c a t i o n of the behavior to be expected i n a system w i t time, temperature, or of d i f f u s i o n ( i n v e r s e l y r e l a t e d to v i s c o s i t y ) should i n c r e a s e i n accord w i t h the decrease i n modulus. The decrease i n modulus w i t h added p l a s t i c i z e r i s w e l l known and w e l l represented by model treatments. A c o m p l i c a t i o n i n p r e d i c t i o n by the above c o r r e l a t i o n method i s due to the p o s s i b i l i t y of non-uniform s w e l l i n g of a polymer by a d i l u e n t . I n such a case, the unswollen domains d i s t r i b u t e d through an otherwise s w o l l e n m a t r i x would c o r r e spond i n e f f e c t to a d i s p e r s e d impermeable f i l l e r . I f the degree of s w e l l i n g i s e x t e n s i v e , the system would resemble a porous d i f f u s i o n medium. C o r r e c t i o n f o r these e f f e c t s can be made on the b a s i s of model treatments d e r i v e d f o r those cases as i n d i c a t e d e a r l i e r . The permeation of l a r g e molecules i n r e l a t i v e l y non-swollen media can be t r e a t e d by the r e a l i z a t i o n t h a t the d i f f e r e n c e s i n d i f f u s i o n c o e f f i c i e n t s w i l l be r e l a t i v e l y s m a l l between homologous members due to the r e l a t i v e l y s m a l l number of s u i t a b l e h o l e s or f r e e volume domains of a p p r o p r i a t e s i z e f o r d i f f u s i o n jumps. Therefore, the net f l u x w i l l be determined more by the s o l u b i l i t y l e v e l d i f f e r e n c e s between penetrant s p e c i e s than by m o b i l i t y , per se. The s o l u b i l i t y can be estimated by use of t y p i c a l polymer s o l u t i o n theory expressions such as the s i m p l i f i e d form of the Flory-Huggins equation * lna

x

- 1ηφ

+ φ

χ

The c h a r a c t e r i s t i c parameter the Hildebrand equation X l

- v /RT(6 1

£

+

Χ ι

φ|

(19)

can be estimated, i n t u r n , by

1

-

δ )

2

2

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

(20)

28

C O N T R O L L E D R E L E A S E PESTICIDES

The s o l u b i l i t y parameters, δ, can be estimated by group c o n t r i b u t i o n methods, heat of v a p o r i z a t i o n data, o r other methods. T h i s general approach has been used and extended t o p r e d i c t the r e l e a s e r a t e c h a r a c t e r i s t i c s of s t e r o i d s from polymers w i t h c o n s i d e r a b l e success (30). Conclusion The d i f f u s i o n - s o l u t i o n model f o r understanding and p r e d i c t i n g c o n t r o l l e d r e l e a s e r a t e s can be extended t o i n c l u d e many other aspects and f a c t o r s . Of p a r t i c u l a r i n t e r e s t i s t h e strong dependence o f t r a n s p o r t behavior on polymer composition, s t r u c t u r e , and morphology. M o d i f i c a t i o n s of these system v a r i a b l e s can be achieved by c a r e f u l s e l e c t i o n , f a b r i c a t i o n , and p o s t - f a b r i c a t i o n chemica use of multicomponent hanced and b e t t e r c o n t r o l l e d f l u x behavior. The development of s p e c i f i c polymeric f o r m u l a t i o n s f o r p a r t i c u l a r agents and a p p l i c a t i o n c o n d i t i o n s i s not only d e s i r a b l e but a l s o p o s s i b l e . The b a s i s f o r t h a t development r e s t s , i n p a r t , on o b t a i n i n g and ex tending our knowledge of the dependence o f t r a n s p o r t processes on the nature of the system components and t h e i r i n t e r a c t i o n w i t h the a p p l i c a t i o n environment.

Literature

Cited

1.

Crank, J. and Park, G. S., eds. "Diffusion in Polymers", Academic Press, New York, 1968. 2. Rogers, C. Ε., in "Physics and Chemistry of the Organic Solid State", D. Fox, M. Labes, and A. Weissberger, eds., Vol. II, Wiley-Interscience, New York, 1965, Chap. 6. 3. Rogers, C. E. and Machin, D., CRC Critical Reviews of Macromolecular Science, (1972), 1, 245. 4. Hopfenberg, H. B., ed., "Permeability of Plastic Films and Coatings to Gases, Vapors, and Liquids", Vol. 6 of Polymer Science and Technology, Plenum Press, New York, 1974. 5. Crank, J., "The Mathematics of Diffusion", 2nd Ed., Claren don Press, Oxford, 1975. 6. Flynn, G. L., Yalkowsky, S. Η., and Roseman, T. J., J . Pharmaceutical Sci., (1974), 63, 479. 7. Tanquary, A. C. and Lacey, R. Ε., Eds., "Controlled Release of Biologically Active Agents", Vol. 47 of Advances in Experimental Medicine and Biology, Plenum Press, New York, 1974. 8. Cardarelli, N. F., Ed., "Controlled Release Pesticide Sym posium", The University of Akron, 1974. 9. Harris, F. W., Ed., "Proceedings 1975 International Con trolled Release Pesticide Symposium", Wright State University, Dayton, Ohio, 1975. 10. Williams, Α., "Sustained Release Pharmaceuticals", Noyes Development Corp., Parkridge, N. J., 1969.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

2.

ROGERS

Permeability

through

a Polymer

Matrix

29

11. Allan, G. G., Chopra, C. S., Friedhoff, J. F., Gara, R. I., Maggi, M. W., Neogi, Α. Ν., Roberts, S. C., and Wilkens, R. Μ., "Pesticides, Pollution, and Polymers", Chemtech., (1973), 3, 171. 12. Colbert, J. C., "Controlled Action Drug Forms", Noyes Data Corp., Park Ridge, N.J.,1974. 13. Cardarelli, N. F., "Concepts in Controlled Release-Emerging Pest Control Technology", Chemtech., (1975), 5, 482. 14. Baker, R. W. and Lonsdale, Η. Κ., "Controlled Delivery-An Emerging use for Membranes", Chemtech., (1975), 5, 668. 15. Cardarelli, N. F., "Controlled Release Pesticides Formula tions", CRC Press, Cleveland, Ohio, 1976. 16. Paul, D. R. and Harris, F. W., eds., "Controlled Release Polymeric Formulations", ACS Symposium Series 33, Am. Chem. Soc., Washington 1976 17. Chang, T. M. S., Ill., 1972. 18. Gutcho, Μ., "Capsule Technology and Microencapsulation", Noyes Data Corp., Park Ridge, N.J.,1972. 19. Vandegaer, J. E., Ed., "Microencapsulation-Processes and Applications", Plenum Press, New York, 1974. 20. Fanger, G. O., "What Good are Microcapsules", Chemtech., (1974), 4, 397. 21. Goodwin, J. T. and Somerville, G. R., Microencapsulation by Physical Methods", Chemtech., (1974), 4, 623. 22. Chang, T. M. S., "Artificial Cells", Chemtech., (1975), 5, 80. 23. Thies, C., "Physicochemical Aspects of Microencapsulation", Polymer-Plast. Technol. Eng., (1975), 5(1), 1. 24. Fujita, H., Fortschr. Hochpolym. Forsen., (1961), 3, 1. 25. Fujita, H. and Kishimoto, Α., J. Chem. Phys., (1961), 34, 393. 26. Fujita, H. and Kishimoto, Α., J. Polym.Sci.,(1958), 28, 547, 569. 27. Machin, D. and Rogers, C. E.,J.Polym.Sci.A2, (1972), 10, 887. 28. Machin, D. and Rogers, C. E.,J.Polym.Sci.,Phys., (1973) 11, 1535, 1555. 29. Rogers, C. Ε., Semancik, J. R., and Kapur, S., Polym. Sci. Tech., (1973), 1, 297. 30. Michaels, A. S., Wong, P. S. L., Prather, R. and Gale, R. M., AlChE J., (1975), 21, 1073.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3 A Challenge for Controlled Release Pesticide Technology PHILIP C. KEARNEY Agricultural Environmental Quality Institute, U.S. Department of Agriculture, Beltsville, Md. 20705

Controlled releas f o r improving the efficacy i n g the environmental problems a s s o c i a t e d w i t h others. Previous c o n t r o l l e d r e l e a s e d technology has been concerned w i t h f i n d i n g the c o r r e c t m a t r i x f o r combining the pesticide in a form t h a t will alter its availability t o the t a r g e t organism. C o n t r o l l e d - r e l e a s e f o r m u l a t i o n s , which improve p e s t i c i d e performance are now under i n v e s t i g a t i o n . Some o f the g r e a t e s t challenges t o the new field o f technology, however, may be in altering the environmental beh a v i o r of pesticides. Several environmental parameters, i n c l u d ing volatility, photodecomposition, l e a c h i n g , m i c r o b i a l metabolism, b i n d i n g , and accumulation, determine the p e r s i s t e n c e , distribution, and indirectly t h e efficacy of pesticides. Laboratory and field techniques have been developed, which allow f o r the measurement o f some o f these environmental parameters affecting pesticides. These techniques o f f e r o p p o r t u n i t i e s o f studying t h e effects o f formulation on p e r s i s t e n c e and movement o f p e s t i c i d e s . The purpose o f this paper is t o challenge scientists engaged in c o n t r o l l e d - r e l e a s e technology t o consider some o f t h e broader o p p o r t u n i t i e s o f f e r e d f o r improving p e s t i c i d e efficacy and s a f e t y . The ability t o manipulate t h e c o n c e n t r a t i o n o f the t o x i n presented t o the pest and t h e environment may make some o l d e r compounds more attractive commercially and may overcome some problems a s s o c i a t e d w i t h potentially u s e f u l new compounds t h a t otherwise might not be r e g i s t e r e d . The f o l l o w i n g d i s c u s s i o n will center p r i m a r i l y on the organic h e r b i c i d e s , s i n c e t h e author's e x p e r t i s e is more e x t e n s i v e in this branch o f pesticide chemistry. Persistence The o p p o r t u n i t y o f a l t e r i n g the p e r s i s t e n c e o f c e r t a i n herb i c i d e s seems t o be one o f the primary advantages o f c o n t r o l l e d r e l e a s e technology. There i s a group o f extremely usef u l herbicides that unfor30

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Controlled

KEARNEY

5

10

Release

15

Technology

20

25

30

35

40

Days

Figure 1. Persistence of seven herbicides in soil. The length of each bar represents the time required for 90% loss of the herbicide from the site of application.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

32

C O N T R O L L E D R E L E A S E PESTICIDES

t u n a t e l y do not p e r s i s t long enough under a c t u a l f i e l d usage t o a f f o r d f u l l - s e a s o n weed c o n t r o l . Some o f these l e a s t - p e r s i s t e n t compounds are shown i n Figure 1, where the length o f the bar rep resents the time f o r 90% l o s s . From an environmental standpoint, these commpounds have been s t u d i e d e x t e n s i v e l y and seem to o f f e r no major problems. The r o l e t h a t c o n t r o l l e d - r e l e a s e technology can b r i n g t o im proved weed c o n t r o l can be represented i n a diagram r e c e n t l y sug gested by Dawson (1976) ( F i g 2 ) . One o f the f a c t o r s governing h e r b i c i d e s e l e c t i v i t y i s the maximum amount o f h e r b i c i d e t o l e r a t e d by the crop p l a n t and the minimum amount that c o n t r o l s the weed. Herbicides are g e n e r a l l y a p p l i e d at some economic r a t e between these two l i m i t s . I f the h e r b i c i d e degrades according to a f i r s t order r e a c t i o n r a t e , then an excess amount must be a p p l i e d t o achieve a reasonably lon the short-term h e r b i c i d e l e v e l i s achieved. In t h i s i d e a l i z e d scheme ( F i g . 2 ) , the c o n t r o l led r e l e a s e (CR) formation provides j u s t enough h e r b i c i d e f o r weed c o n t r o l at any one time, and the p e r i o d of a c t i v i t y i s s i g n i f i c a n t l y extended. Figure 2 i s s i m i l a r i n concept to one proposed by Cowan (1973) f o r responses from a s i n g l e i n j e c t i o n of a drug. Microencapsulation o f chlorpropham, one of the s h o r t - l i v e d h e r b i c i d e s ( F i g 1 ) , extended h e r b i c i d a l e f f e c t i v e n e s s f o r a s i g n i f i c a n t l y longer p e r i o d o f time than the commercial f o r m u l a t i o n (Gentner and Danielson, 1976). A 4.5 kg/ha a p p l i c a t i o n o f micro encapsulated chlorpropham at concentrations o f 17, 22, and 26 per cent were h e r b i c i d a l l y e f f e c t i v e f o r longer than 66 days, w h i l e a s i m i l a r a p p l i c a t i o n o f the commercial f o r m u l a t i o n was completely i n a c t i v e a f t e r 41 days, and i t s e f f i c a c y was questionable a f t e r 31 days. V o l a t i l i z a t i o n i s one o f the mechanisms by which c h l o r p r o pham i s l o s t from the s i t e o f a p p l i c a t i o n . Turner et a l . (1977) compared the vapor losses o f chlorpropham i n a microencapsulated f o r m u l a t i o n w i t h those i n an e m u l s i f i a b l e concentrate under f i e l d c o n d i t i o n s . In the f i r s t 4 hours a f t e r a p p l i c a t i o n , 86 g/ha of the . e m u l s i f i a b l e and 5.3 g/ha microencapsulated chlorpropham were v o l a t i l i z e d from the t a r g e t area. S o i l a n a l y s i s confirmed that a f t e r 7 days, 26% of the a p p l i e d e m u l s i f i a b l e concentrate and 51% of the microencapsulated chlorpropham remained i n the t a r g e t area. A major b e n e f i t that c o n t r o l l e d r e l e a s e technology can b r i n g t o weed c o n t r o l i s t o expand h e r b i c i d e s e l e c t i v i t y t o a d d i t i o n a l crops. As i l l u s t r a t e d i n Figure 3, based on a suggestion by Dawson (1976), the amount o f h e r b i c i d e r e q u i r e d t o c o n t r o l weeds i n crop A may i n j u r e crop B. U n f o r t u n a t e l y , the amount o f h e r b i cide t o l e r a t e d by crop Β i s too low t o p r o v i d e a s u f f i c i e n t p e r i o d of weed c o n t r o l . The c o n t r o l l e d - r e l e a s e f o r m u l a t i o n provides a continuous amount of h e r b i c i d e at a l e v e l s u f f i c i e n t to c o n t r o l weeds but not i n j u r e e i t h e r crop. Several experimental techniques are now a v a i l a b l e f o r measur ing the e f f e c t o f c o n t r o l l e d - r e l e a s e formulations on the mechanism

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

Controlled

KEARNEY

Release

Technology

33 Max τ

Formulated

y

tolerated crop

herbicide

J CR

herbicide

niHIINIIIIIIHI

Illlll

IIIIIMtMNHIIIIlH,,,^

Min

β*··».-. '•••••••«t

I 1

1 2

I 3

I 4

5

6

Weeks

7

8

after

9

teiiB

that

cp n t r ο I s

10

11

weeds

12

13

14

Application

Figure 2. Degradation of formulated and controlled release (CR) herbicide as a function of time in a single-crop system

high

Max

\

\

5=5 £ •σ φ. Φ

> c a ο Φ a

.ϊ

Ο

by

tolerated

crop

Max by

w %

\

\ \

Formulated

\

tolerated

crop

Β

herbicide

d

\

A

CR

herbicide

Si U

φ "·····««»...,

controls

*

none

Π

1

2

3

4

5

Weeks

6

weeds

I

-···'— I

I

7

8

after

Γ

9

10

11

12

13

14

Application

Figure 3. Degradation of formulated and controlled release (CR) herbicide as a function of time in a two-crop system

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

34

C O N T R O L L E D R E L E A S E PESTICIDES

and r a t e o f h e r b i c i d e l o s s . Turner and G l o t f e l t y (1977) measured v o l a t i l i t y l o s s e s under f i e l d c o n d i t i o n s by many polyurethane foam plugs. A simple m o d i f i c a t i o n o f the polyurethane foam p l u g technique has been adopted by Kearney and Kontson (1976) to measure both v o l a t i l i z a t i o n and metabolic metabolism under l a b o r a t o r y cond i t i o n s . The development o f the agroecosystem by B e a l l e_t a l . (1976) o f f e r s another, more e l a b o r a t e , technique f o r a n a l y z i n g v a r i o u s environmental components t h a t e f f e c t a p e s t i c i d e molecule i n a c l o s e d system. Agroecosysterns are inexpensive to c o n s t r u c t and operate, and o f f e r many advantages over conventional growth chambers f o r balance s t u d i e s on p e s t i c i d e s . A l l o f these systems o f f e r s c i e n t i s t s engaged i n c o n t r o l l e d - r e l e a s e technology s e v e r a l methods f o r measuring v o l a t i l i t y , degradation, and p e r s i s t e n c e under both l a b o r a t o r y and f i e l d c o n d i t i o n s . The most c h a l l e n g i n tence has been to shorten the e f f e c t i v e l i f e o f some of the more s t a b l e compounds. To date, there i s l i m i t e d experimental evidence that some compounds can be rendered l e s s p e r s i s t e n t . E a r l y work w i t h the phenoxy h e r b i c i d e s (Audus, 1960) showed that s o i l induced to metabolize MCPA would a l s o metabolize s e v e r a l phenoxyacetic a c i d s s u p p l i e d t o i t f a s t e r than would uninduced s o i l . This suggested that s o i l m i c r o b i a l populations would be induced t o metabol i z e a p a r t i c u l a r c l a s s o f h e r b i c i d e s , and more s p e c i f i c a l l y a l i n k a g e i n the molecule common t o members of t h a t c l a s s . In f i e l d s t u d i e s , MCPA was found t o degrade s i g n i f i c a n t l y f a s t e r i n s o i l s p r e v i o u s l y r e c e i v i n g f i v e annual a p p l i c a t i o n s o f the h e r b i c i d e than i n untreated s o i l (Fryer and K i r k l a n d , 1970). Therefore, i t may be f e a s i b l e t o a l t e r the s o i l m i c r o b i a l p o p u l a t i o n near a s o i l a p p l i e d h e r b i c i d e t o a c c e l e r a t e i t s metabolism. Loos and Kearney (1977) have attempted t o a l t e r the s o i l mic r o b i a l environment by p r o v i d i n g degradable substrates which s t r u c t u r a l l y resemble a t r a z i n e . Previous research on a t r a z i n e degradat i o n r e v e a l s that there are two major types o f cleavage: chemical replacement o f the c h l o r i n e i n the 2 - p o s i t i o n w i t h a hydroxyl group and m i c r o b i a l d e a l k y l a t i o n o f the e t h y l group (Esser ejt a l . , 1976). In the experiments o f Loos and Kearney (1977), s e v e r a l compounds c o n t a i n i n g carbon n i t r o g e n bonds were a p p l i e d to s o i l s t o a c c e l e r ate d e a l k y l a t i o n . These compounds i n c l u d e d ammelide, ammeline, cyanuric a c i d , N-ethylammelide, N^ethylammeline, urea, b i u r e t , and quanidine. To date, these experiments have o n l y met w i t h l i m i t e d success. Whether c o n t r o l l e d - r e l e a s e technology could provide a v e h i c l e f o r combining the h e r b i c i d e and a c c e l e r a t o r compound remains t o be t e s t e d . The goal o f being able t o p r e d i c t and modify the time of e f f e c t i v e n e s s o f p e r s i s t e n t h e r b i c i d e s i s an e x c i t i n g challenge that may yet be p o s s i b l e t o achieve. Movement As discussed i n the previous s e c t i o n , microencapsulation r e tarded the v o l a t i l i z a t i o n o f CIPC and, thereby, extended i t s e f f e c -

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3.

KEARNEY

Controlled

Release

Technology

35

t i v e n e s s under f i e l d c o n d i t i o n s . Another form o f movement that can reduce a h e r b i c i d e ' s e f f e c t i v e n e s s i s v e r t i c a l l e a c h i n g i n t o the s o i l p r o f i l e . For many preemergence h e r b i c i d e s , the compound must remain i n the germination zone o f the weed s e e d l i n g t o be e f f e c t i v e . M e t r i b u z i n i s a promising h e r b i c i d e f o r weed c o n t r o l i n soybeans and s e v e r a l other crops. The compound i s somewhat water s o l u b l e and, under c e r t a i n c o n d i t i o n s , extensive v e r t i c a l movement has been observed. I f t h i s movement can be c o n t r o l l e d , then much b e t t e r weed c o n t r o l i s obtained. Recently, Savage and McCormick (1977) combined m e t r i b u z i n i n a polymer system, which r e s t r i c t e d l e a c h i n g and s i g n i f i c a n t l y improved weed c o n t r o l . Several simple and s o p h i s t i c a t e d techniques are a v a i l a b l e t o r measuring l e a c h i n g o f h e r b i c i d e s i n s o i l s . H e l l i n g (1971) devised a s o i l t h i n - l a y e r system, which allows f o r a r a p i d , simple method o f measuring l e a c h i n g . H e r b i c i d 14C-labeled compounds, p l a t e s ; thus, nonlabeled p e s t i c i d e s have been v i s u a l i z e d u s i n g b i o assay organisms. Savage and McCormick (1977) used s o i l t h i n - l a y e r m o b i l i t y s t u d i e s t o demonstrate the slow r e l e a s e o f m e t r i b u z i n . More complex column procedures are a l s o a v a i l a b l e f o r determining the l e a c h a b i l i t y o f p a r t i c u l a r h e r b i c i d e s . New

Challenges While the most promising challenges f o r c o n t r o l l e d r e l e a s e technology i s a l t e r i n g p e s t i c i d e p e r s i s t e n c e and movement, there may be other environmental parameters t h a t can be m o d i f i e d or a l t e r e d by f o r m u l a t i o n . P e s t i c i d e b i n d i n g t o p h y s i c a l and b i o l o g i c a l surfaces may be i n f l u e n c e d by f o r m u l a t i o n . The f u l l s i g n i f i c a n c e o f b i n d i n g i s not completely understood at t h i s time, although Kearney (1976) has discussed two aspects of p e s t i c i d e b i n d i n g to soils. Bound residues may be b e n e f i c i a l as a decontamination mechanism f o r i n a c t i v a t i n g p e s t i c i d e s i n s o i l s or u n d e s i r a b l e as potent i a l storage s i t e s f o r subsequent r e l e a s e o f the p e s t i c i d e s back i n t o the environment. When the f u l l i m p l i c a t i o n o f the b e n e f i c i a l or adverse e f f e c t s o f p e s t i c i d e b i n d i n g are understood, c o n t r o l l e d r e l e a s e technology may provide f o r m u l a t i o n s that enhance or deter b i n d i n g . The c a r r i e r could p r e f e r e n t i a l l y i n t e r a c t w i t h the b i n d ing s u r f a c e to modify the nature o f attachment o f the p e s t i c i d e . Several methods are a v a i l a b l e f o r measuring bound residues (Kaufman ot a l . , 1976) and these may provide i n f o r m a t i o n on the e f f e c t o f v a r i o u s f o r m u l a t i o n s on the extent and s t r e n g t h o f b i n d i n g . As c o n t r o l l e d r e l e a s e p e s t i c i d e technology continues t o expand i n the f i e l d o f p e s t i c i d e chemistry, new o p p o r t u n i t i e s w i l l a r i s e f o r s o l v i n g some o f the environmental problems a s s o c i a t e d w i t h expanded p e s t i c i d e usage. One o f the g r e a t e s t challenges t o improving c o n t r o l l e d r e l e a s e technology i s t o develop and u t i l i z e reasonable model systems f o r measuring v o l a t i l i t y , photodecomposition, metabolism, and other parameters. These simple systems o f f e r the most reasonable approach t o r a p i d l y a c h i e v i n g new advances i n cont r o l l e d - r e l e a s e technology.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

36

C O N T R O L L E D R E L E A S E PESTICIDES

Literature Cited 1. 2. 3.

4. 5.

6. 7. 8. 9.

10.

11. 12. 13. 14.

Andus, L. J. in H e r b i c i d e s and the Soil (Ε. Κ. Woodford and G. R. Sager, eds.), B l a c k w e l l , Oxford pp 1-19 (1960). B e a l l , M. L., Jr., Nash, R. G., Kearney, P. C., Proc. Conf. Environ. Modeling S i m u l a t i o n EPA 600/9-76-016 (1976). Cowan, D. R., I n t r o d u c t i o n t o C o n t r o l l e d Release o f Biolog ically A c t i v e Agents, E d i t e d by A. C. Tanquary 2nd; R. E. Lacy, Plenum Press pp 1-13 (1973). Dawson, J. Η., Personal Communication (1976). Esser, H. O., Dupuis, G., E b e r t , Ε., Vogel, C., Marco, G. J., s - T r i a z i n e s in H e r b i c i d e s : Chemistry, Degradation and Mode o f A c t i o n (P. C. Kearney and D. D. Kaufman, eds.) V o l . 1, pp 129-208, 2 ed., Marcel Dekker, Inc., New York (1975). F r y e r , J. D., K i r k l a n d Κ. Weed Res 10 133 (1970) Gentner, W. Α., Danielson lease P e s t i c . Symp H e l l i n g , C. S., Soil Sci. Soc. Am. Proc. 35, 737 (1971). Kaufman, D. D., Still, G. G., Paulson, G. D., Bandai, S. Κ., Bound and Conjugated P e s t i c i d e Residues. ACS Symp. Ser. 29, 396 pp. (1976). Kearney, P. C., Summary o f Soil Bound Residue D i s c u s s i o n Ses s i o n in Bound and Conjugated P e s t i c i d e Residues (D. D. Kauf man, G. G. Still, G. D. Paulson and S. K. Bandal, eds.). ACS Symp. Ser. 29, 378-382 (1976). Kearney, P. C., Kontson, Α., J. A g r i c . Food Chem. 24, 424 (1976). Savage, Κ. Ε., McCormick, C. L., Proc. Southern Weed Sci. Soc., D a l l a s , Texas (1977). Turner, B. C., Glotfelty, D. Ε., A n a l . Chem. 49, 7 (1977). Turner, B. C., Glotfelty, D. Ε., T a y l o r , A. W. and Watson, D. R., 173rd N a t l . Mtg. Amer. Chem. Soc. (Abstr.) #8, New Orleans, La. (1977).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4 Environmental Aspects of Controlled Release Pesticide Formulations GUNTER ZWEIG Environmental Protection Agency, Office of Pesticide Programs, Washington, D.C. 20460

During the past 10 chlorinated hydrocarbons mental and toxicological problems. In their place, less persistent, but sometimes more acutely toxic pesticides have been substituted and created other problems: (a) greater chances for accidental, high exposure to operators and farm workers; and (b) a need for multiple applications because of lower persistence. Controlled-release (CR) formulations of these pesticides appear to offer an ideal solution to these problems. To cite another consideration, the insect growth regulator methoprene, for example, is so unstable in the aquatic environment that its practical application could only be effected as a controlled release formulation. Newly developed pesticides may never reach the market unless they can be stablized long enough to effect control through controlled-release formulations. Economic and environmental advantages might also be gained by the release of constant but lower concentrations of toxicants than may be possible with conventional type formulations. The technology of microencapsulation and other controlled release systems, as will be discussed during this Symposium, have been developed to the point of making controlled release pesticide formulations a r e a l i t y . Yet, there appears to be no satisfactory explanation why this f i e l d has not advanced more rapidly. One popular explanation might be that Government regulations for toxicological and environmental testing have become so cumbersome that they discourage further development of these formulations. In this paper, some personal reflections may help to alleviate these concerns, and i t may become apparent that the proposed tests are probably no more stringent than those required for conventional pesticide formulations. Asterisked terms throughout this paper indicate trademark products. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Environmental Protection Agency. 37

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

38

PESTICIDES

F e a s i b l e CR P e s t i c i d e Formulations Although the number o f commercial c o n t r o l l e d - r e l e a s e p e s t i c i d e products on the market may be few compared to the more than 3 0 , 0 0 0 other r e g i s t e r e d products, i t appears f e a s i b l e that a l l c l a s s e s of p e s t i c i d e chemicals are amenable to formulation as c o n t r o l l e d - r e l e a s e products. In a number o f cases, as i n the case o f methoprene, the CR formulation i s the method o f choice and e n hances the e f f i c a c y o f the p e s t i c i d e , a l b e i t , makes i t f e a s i b l e to be used as an e f f e c t i v e pest c o n t r o l agent. Table I i s a l i s t of these p e s t i c i d e c l a s s e s followed by a few words o f e x p l a n a t i o n . TABLE I CLASSES OF PESTICIDES FORMULATED AS CONTROLLED-RELEAS Anti-Foulants Molluscicides Insecticides Herbicides Fungicides

Rodenticides Nematicides Algicides Predator Control Repellents

Devices

Anti-foulants. A n t i - f o u l i n g paints are composed o f a t o x i c a n t , f o r example, cuprous oxide which i s held w i t h i n a polymeric v e h i c l e such as p o l y a c r y l a t e , polyamide, p o l y e s t e r , c h l o r i n a t e d p o l y i s o p r e n e , polyurethane, e t c . Other t o x i c a n t s that have been s u c c e s s f u l l y incorporated i n t o a n t i - f o u l a n t paints include organot i n compounds ( e . g . , t r i butyl t i n ) and organoleads ( e . g . , t r i phenyl l e a d ) . These a n t i - f o u l i n g coatings have been shown to be b i o l o g i c a l l y e f f i c a c i o u s and long l a s t i n g (up to 9 years) (1_). The unresolved environmental problems with these products are (a) the p o s s i b l e long-term e f f e c t on aquatic organisms of low concentrations of t o x i c a n t s , and (b) the c h a r a c t e r i z a t i o n o f the released material which may have undergone chemical o r b i o l o g i c a l changes during i t s r e l e a s e . Molluscicides. M o l l u s c i c i d e s are used to c o n t r o l s n a i l s and slugs and are extremely important i n t r o p i c a l areas where a major d i s e a s e , S c h i s t o s o m i a s i s , i s transmitted by members o f the Schistosoma s n a i l family i n h a b i t i n g r i v e r s , streams and l a k e s . N.F. C a r d a r e l l i , Professor o f Chemistry, U n i v e r s i t y o f Akron, Ohio, has been a pioneer i n the development o f CR m o l l u s c i c i d e s . T r i butyl t i n oxide (TBTO) and t r i butyl t i n f l u o r i d e , niclosamide (ethanolamine s a l t o f 2 , 5 - d i c h l o r o - 4 ' - n i t r o s a l i c y l a n i l i d e ) , and copper s u l f a t e have been incorporated i n t o various elastomeric materials. The toxicants are released over a p e r i o d of many months f o l l o w i n g immersion i n t o i n f e c t e d waters. Although the t i n compounds are t o x i c to f i s h , when used as CR f o r m u l a t i o n s , however, the adverse e f f e c t on f i s h appears minimal. Most v a s c u l a r species o f plants are unaffected by t r i butyl t i n o x i d e ,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

Environmental

ZWEIG

Aspects

39

although some adverse e f f e c t s on algae have been observed. Other nontarget aquatic organisms appear to be t o l e r a n t to TBTO at the concentration of the CR f o r m u l a t i o n s . The environmental fate of organotins i s not f u l l y understood, but t i n does not seem to bioaccumulate i n higher organisms and, as a matter of f a c t , i s an e s s e n t i a l trace element i n mammalian n u t r i t i o n . Another CR technique f o r s n a i l c o n t r o l i s the use of CR baits. In t h i s technique, the t o x i c a n t [niclosamide or t r i f e n morph ( N - t r i t y l m o r p h o l i n e ) ] and an a t t r a c t a n t are incorporated i n t o an i n s o l u b l e binding matrix ( e . g . , p o l y a c r y l a t e s c r o s s - l i n k e d with Z n or C a ) . S n a i l s are a t t r a c t e d by a g e n u s - s p e c i f i c a t t r a c t a n t and i n g e s t the polymers c o n t a i n i n g the t o x i c a n t . The use of CR m o l l u s c i c i d e s , although of minor importance i n the United S t a t e s , i l l u s t r a t e s that a t o x i c a n t can be used at lower concentrations than those required by d i r e c t a p p l i c a t i o n and provides greater environmenta + +

+ +

Insecticides. In t h i s category are included (a) conventional t a r g e t i n s e c t i c i d e s and i n s e c t growth r e g u l a t o r s which are formul a t e d to produce c o n t r o l l e d r e l e a s e , and (b) pheromones and other a t t r a c t a n t s which are incorporated i n t o b a i t s c o n t a i n i n g convent i o n a l i n s e c t i c i d e s f o r the k i l l . One of the f i r s t types of a commercial CR formulation i s Penncap-M*, microencapsulated methyl parathion. The microencapsulation process i s based on forming a polycondensation polymer s h e l l ( c r o s s - l i n k e d polyamide) around the material to be encapsulated. The i n s e c t growth r e g u l a t o r methoprene i s incorporated i n t o a polyurethane foam providing some degree of p r o t e c t i o n from e n v i ronmental degradation. This product i s s o l d commercially as A l t s o s i d SR-10*. C h l o r p y r i f o s (TA) has been incorporated i n t o p o l y v i n y l c h l o r i d e , polyurethane foam, and polyamide and provides e x c e l l e n t c o n t r o l of mosquito larvae over a 2 2 to 24-week p e r i o d , as compared with 1 to 2 weeks using c h l o r p y r i f o s emulsion ( 2 ) . Even longer c o n t r o l was e f f e c t e d with polyethylene or p o l y v i n y l c h l o r i d e CR pellets ( 3 ) . Encapsulated Rabon* [(Gardona* - - 2 - c h l o r o - l - ( 2 , 4 , 5 - t r i c h l o r o p h e n y l ) v i n y l dimethyl phosphate] has been shown to provide l a r v a l feed-through c o n t r o l i n the manure of p o u l t r y and c a t t l e

(4, 5 ) . The second category of CR i n s e c t c o n t r o l agents are pheromones and a t t r a c t a n t s which have been reviewed r e c e n t l y (6). For example, d i s p a r l u r e has been formulated i n t o g e l a t i n capsules {7) or laminated p l a s t i c dispensers (8, £ ) ; grandiure has been formulated i n t o laminated p l a s t i c s (10); and encapsulated t r i m e d l u r e has been combined with methyl parathion or malathion (11). A l l of these formulations have the advantage of prolonging the l i f e of the environmentally l a b i l e and v o l a t i l e pheromones.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

40

C O N T R O L L E D R E L E A S E PESTICIDES

At t h i s time, pheromones have been i d e n t i f i e d f o r at l e a s t 40 economically important i n s e c t species (8), and a l a r g e r number of pheromone/toxicant or pheromone/trap systems may be expected to be developed on a commercial s c a l e i n the f u t u r e . Another type of CR i n s e c t i c i d e formulation i s represented by an a n t i - c o c k r o a c h p a i n t c o n t a i n i n g c h l o r p y r i f o s (12) and the Hereon* p l a s t i c i n s e c t i c i d e dispenser i n c o r p o r a t i n g c h l o r p y r i f o s , Baygon* ( o-isopropoxypheny1 N-methyl carbamate), or d i a z i n o n [ 0 , 0 - d i e t h y l 0 - ( 2 - i s o p r o p y l - 6 - m e t h y l - 4 - p y r i m i d i n y l ) phosphorot h i o a t e ] i n a 3 - l a y e r laminated p o l y v i n y l c o n s t r u c t i o n (13). DDVP ( d i c h l o r v o s - - 2 , 2 - d i c h l o r o v i n y l dimethylphosphate), widely used as a CR formulation under the trade name of No-Pest* s t r i p , i s i n corporated i n t o p o l y v i n y l c h l o r i d e and montan wax. The c h i t i n s y n t h e s i s i n h i b i t o r d i m i l i n [1 - ( 4 - c h l o r o p h e n y 1 ) - 3 - ( 2 , 6 - d i f 1 u o r o benzoyl)urea] has been experimentally incorporated i n t o c a s t o r wax and a s i l i c a t e to produc hydrolyzes to r i c i n o l e i c a c i d and g l y c e r o l with no apparent e n v i ronmental consequences. Herbicides. CR formulations o f h e r b i c i d e s may be c l a s s i f i e d as a q u a t i c / p l a s t i c , a q u a t i c / e l a s t o m e r i c , and a g r i c u l t u r a l . Aquatic h e r b i c i d e s (phenoxy e s t e r s , e n d o t h a l l , d i c h l o b e n i l ) have been incorporated i n t o polyamide, p o l y v i n y l (15, 16), and p o l y ethylene r e s i n matrices (17) to provide long-term c o n t r o l of Eurasian w a t e r m i l f o i l (18"]7 Long-term aquatic weed c o n t r o l i s c l e a r l y p o s s i b l e by h e r b i c i d e r e l e a s e from p l a s t i c matrices (19). Another experimental approach has been to incorporate hydrol y z a b l e phenoxy h e r b i c i d e moieties i n t o a polymerized v i n y l p o l y mer (20, 2 χ ) . Other CR m a t e r i a l s which have been tested i n c l u d e rubber-based compounds as s i n k i n g p e l l e t s slowly r e l e a s i n g the h e r b i c i d e (22, 23) with no detectable f i s h t o x i c i t y (18). During t h i s work the phenomenon of c h r o n i c i t y was d i s c o v e r e d , which w i l l be discussed i n greater d e t a i l l a t e r i n the paper. Although the use of aquatic h e r b i c i d e s as c o n t r o l l e d r e l e a s e formulations may r e c e i v e wider acceptance, there are r e l a t i v e l y few CR formulated commercial a g r i c u l t u r a l h e r b i c i d e s . Fungicides. F u n g i c i d a l r e s i n s f o r paints can be made by the polycondensation of g l y c o l , chlorophenol e s t e r , and benzene carboxylic acid. Seed p r o t e c t i o n can be afforded by the use o f CR formulations o f fungicides added to rubber l a t e x or as an encapsu l a t e d m a t e r i a l , e . g . , B e n l a t e * , for use on onion seeds. Rodenticides. Encapsulation of anticoagulants appears to e n hance b a i t acceptance (24), presumably masking the b i t t e r t a s t e o f , f o r example, norbormide (25). However, although encapsulation improves rodent i n g e s t i o n o f the a n t i c o a g u l a n t , i t does not im prove the e f f i c a c y (26) p o s s i b l y because of the competition between d e t o x i c a t i o n and slower r e l e a s e .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

Aspects

41

Nematicides. Ethoprop (0-ethyl S , S - d i p r o p y l phosphorodithi o a t e ) , incorporated i n t o natural rubber and an e t h y l e n e - p r o p y l enediene terpolymer (27), has been shown to have an e f f e c t i v e r e l e a s e of three months. Dibromodichloropropane (DBCP) has been encapsulated with a w a t e r - s e n s i t i v e , biodegradable wall material (27A); t h i s formulation may p e r s i s t during dry periods u n t i l s u f f i c i e n t s o i l moisture ruptures the capsule membrane. The basic problem of processing nematicides by press cures of elastomers or hot melt e x t r u s i o n of p l a s t i c s i s the low b o i l i n g p o i n t of most fumigant-nematicides. Algicides. Most copper s a l t s have a short l i f e i n water and must be a p p l i e d p e r i o d i c a l l y to c o n t r o l the growth of a l g a e . Thus, CR formulations of C u ions would be h i g h l y d e s i r a b l e . Copper s u l f a t e has been incorporated i n t o a microporous polymer (Envirocap*). Another C has been shown e f f e c t i v e against blue-green algae f o r as long a period as 54 days a f t e r a p p l i c a t i o n . No published information on the composition of these CR matrices i s a v a i l a b l e (28). Experimental copper r e l e a s i n g thermoplastic m a t e r i a l s have been shown to r e l e a s e the metal ion f o r several months (29, 30, 31). Inc r e a s i n g e f f o r t i n t h i s f i e l d should y i e l d p r a c t i c a l a l g a l control methods by CR technology. + +

Predator Control Devices. A method that might be included i n t h i s b r i e f survey of CR p e s t i c i d e formulation i s the cyanide c o l l a r attached to a s a c r i f i c i a l lamb, which, upon attack by a coyote, i s punctured and releases the deadly poison. Many o b j e c t i o n s have been r a i s e d by c o n s e r v a t i o n i s t s and members of humane s o c i e t i e s that t h i s type of predatory c o n t r o l c o n s t i t u t e s a s i n g u l a r l y c r u e l method, and EPA has made no d e c i s i o n at t h i s time to allow the use of these d e v i c e s . Repellents. Diethyl-m-toiuamide (DEET) can be incorporated i n t o sprayable polymeric m a t e r i a l s (32) l i k e p o l y a c r y l i c s and polyurethane (unpublished data by N.F. C a r d a r e l l i ) . These formulations have been shown to r e l e a s e DEET on window screens f o r several months, while DEET alone i s r a p i d l y degraded i n sunlight. Specific

Products

Table II 1 i s t s some of the CR p e s t i c i d e formulations which have been r e g i s t e r e d by the EPA and are commercially a v a i l a b l e . In the study funded by EPA and r e c e n t l y completed (EPA Contract No. 68-01-1922), C a r d a r e l l i and Walker found references i n the open, patent, and company l i t e r a t u r e of 141 p e s t i c i d e chemicals which are p r a c t i c a l or have been t r i e d as CR f o r m u l a t i o n s . Thus, t h i s 1 i s t i n Table II seems 1 i m i t e d , and i t i s expected that a d d i t i o n a l CR products w i l l be on the market i n the f u t u r e .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

42

CONTROLLED RELEASE

TABLE

PESTICIDES

II

CONTROLLED RELEASE PESTICIDES Product Altosid* Biomet* CAP-CYC* CBL-9B Herbicide 14 ACE-B1 Hereon* roach tape Incracide*

E-51

Killmaster* Nofoul* No-Pest* S t r i p Penncap-M* Staph-Chek*

Pesticide Action J u v e n i l e Hormone Mimic Molluscicide Plant Growth Regulator Molluscide Herbicide Insecticide Molluscide Algicide Herbicide Anti-foulant Insecticide Insecticide Bacteriostat

A l t o s i d * i s the CR formulation of the i n s e c t growth methoprene.

regulator

Biomet* i s an organotin m o l l u s c i c i d e . CAP-CYC* i s 3M*s encapsulated chlormequat ( 2 - c h l o r o e t h y l t r i me thy 1 ammo ni urn c h l o r i d e ) , a p l a n t growth r e g u l a t o r . The composit i o n of the encapsulant and a d d i t i v e s are not p u b l i c information. CBL-9B i s a natural rubber matrix c o n t a i n i n g t r i butyl t i n f l u o r i d e as a c t i v e m o l l u s c i c i d e . Herbicide 14 ACE-B1 i s the 2,4-D butoxyethanol e s t e r formul a t e d with natural rubber; t h i s has been prepared as f l o a t i n g or s i n k i n g p e l l e t s and suspending s t r a n d s , depending on the nature of the v u l c a n i z e d elastomers. Hereon* roach tape u t i l i z e s the Hereon dispenser constructed from laminar s t r i p s c o n t a i n i n g an i n s e c t i c i d e i n a p l a s t i c r e s e r voir. Hereon* roach tape containing Baygon* i s e f f e c t i v e as a s t a t i o n a r y i n s e c t i c i d e dispenser e s p e c i a l l y useful against cockroaches around human h a b i t a t i o n . I n c r a c i d e * E-51 i s a terpolymer CR formulation of copper s u l f a t e intended as a m o l l u s c i c i d e , a l g i c i d e , and s e l e c t i v e herbicide. K i l l m a s t e r * i s a p a i n t a b l e or sprayable taining chlorpyrifos.

CR formulation c o n -

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

43

Aspects

Nofoul* i s an a n t i - f o u l i n g rubber, the p r i n c i p l e of which r e s t s on d i f f u s i o n - d i s s o l u t i o n . The i n g r e d i e n t s are p r o p r i e t a r y information. No-Pest* S t r i p i s probably the best known CR formulation and i s composed of d i c h l o r v o s i n a s t a b i l i z e d p o l y v i n y l c h l o r i d e base. Penncap-M* i s a widely used CR i n s e c t i c i d e and i s polyamideencapsulated methyl p a r a t h i o n . At 25%-cross linkage of the polymer w a l l , the e f f i c a c y of Penncap-M* against the bollworm and b o l l w e e v i l was extended from one day to about 10 days when compared with conventional e m u l s i f i a b l e concentrate (EC) formulations (33). Comparative t o x i c i t y data i n d i c a t e that Penncap-M* i s approximately 50 times l e s s t o x i c to r a b b i t s by s k i n a b s o r p t i o n , 8 to 10 times l e s s t o x i c to white mice, and 4 to 7 times l e s s t o x i c to rats by i n g e s t i o An unexpected hazard of Penncap-M* to the bee population has been discovered r e c e n t l y (34). The microcapsules, which are a p p r o x i mately the same s i z e as p o l l e n g r a i n s , adhere to the bee as i t f l i e s from sprayed flowers and returns the " p o l l e n " to the hive where i t contaminates the whole colony. Staph-Chek* i s a b a c t e r i o s t a t i c f a b r i c used i n h o s p i t a l s . Organotin or another b a c t e r i o c i d e ( s t a t ) i s incorporated i n t o PVC f i l m which i s laminated on a f a b r i c base. Other CR p e s t i c i d e products and commercial r e l e a s e systems are shown i n Table III. TABLE

III

CONTROLLED RELEASE PRODUCTS Polyethylene/chlorpyrifos Conrel* Hereon* Dispenser Microcapsule Dispenser Poroplastic* Sustrelle*

Blend 3714

Polyethylene - c h l o r p y r i f o s i s a CR mosquito l a r v i c i d e d e v e l oped by the U.S. Army Environmental Hygiene Agency; r e g i s t r a t i o n by the EPA has been a p p l i e d f o r . C o n r e l * i s a trademark f o r a wide range of f i b e r systems, e s p e c i a l l y s u i t a b l e f o r v o l a t i l e pheromones. C o n t r o l l e d vapor r e l e a s e rates can t a i l o r i n g the f i b e r s to s p e c i f i c diameters and The Hereon* Dispenser has been described

p r e c i s i o n hollow p e s t i c i d e s and be achieved by lengths.

previously.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

44

PESTICIDES

Microcapsule Dispenser. No information i s a v a i l a b l e about the composition o f the Microcapsule Dispenser produced by Cont r o l l e d Release Chemical C o r p o r a t i o n , Santa Fe, N. Mex. The dispenser i s useful for r e l e a s i n g pheromones and i n s e c t i c i d e s . P o r o p l a s t i c * (sheets) and S u s t r e l l e * are trade names f o r gelled cellulose triacetate. The c o s t of these m a t e r i a l s i s r e l a t i v e l y high to make them p r a c t i c a l for use at t h i s time, but i n p r i n c i p l e , they should f u n c t i o n as a sustained and c o n t r o l l e d r e l e a s e system.

Environmental

Impact of

Polymers

Before c o n s i d e r i n g the environmental impact of CR p e s t i c i d e f o r m u l a t i o n s , i t i s importan m a t e r i a l s , or the s o - c a l l e d " i n e r t s , " which make up the bulk of these types of f o r m u l a t i o n s . Table IV i s a l i s t of s i g n i f i c a n t polymers that were chosen f o r c l o s e r i n v e s t i g a t i o n . TABLE IV CONTROLLED RELEASE MATERIALS Rubber Natural Synthetic Ethylene - Propylene Polymer C e l l u l o s i c Materials P o l y i s o b u t y l e n e - Butyl Rubber Styrene - Butadiene Copolymer P o l y a c r y l o n i t r i 1 es Polyacrylates Polyesters Polyamides

Polyethylene Polyvinyl Chloride Chloroprene Polymer Polyurethanes Ci s Polybutadiene Acetal Copolymer Others: S i l i c o n Rubber Polyacrylamides Hydrin Rubber Microporous P l a s t i c

Sheet

A d i r e c t quotation by C a r d a r e l l i and Walker i n t h e i r f i n a l r e p o r t to the EPA on the Development of R e g i s t r a t i o n C r i t e r i a f o r CR P e s t i c i d e Formulations, sums up t h e i r views on the e n v i r o n mental impact from the use of CR p e s t i c i d e products : " I t should be recognized that the polymeric material must degrade i n some fashion before there can be any environmental impact i n the c h e m i c a l , biochemical or b i o l o g i c a l sense. With reference to s o i l or the beds of watercourses, i t i s c o n c e i v a b l e , though b a r e l y , that the a d d i t i o n of a polymer to the ambient environment w i l l r e s u l t i n p h y s i c a l changes. It i s well known that the a p p l i c a t i o n of an i n e r t m a t e r i a l to s o i l a i d s i n a e r a t i o n . Thus, a non-

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

45

Aspects

degraded polymer plowed i n t o s o i l w i l l enhance soil aeration. Since the authors cannot v i s u a l i z e more than a few hundred pounds per acre of a given polymer being a p p l i e d annually (a few pounds per acre being much more 1 i k e l y ) , and s i n c e the weight of an a c r e - f o o t of s o i l i s i n excess of a m i l l i o n pounds, the environmental impact a f t e r d i l u t i o n would appear to be n i l . I f polymers f o r use i n c o n t r o l l e d r e l e a s e were completely i n e r t or t h e i r degradation r a t e was measured i n geologic time - as occurs with g l a s s , the cumulative aspect would be a matter of concern. However, al 1 organic polymers degrade upon exposure to outdoor e n v i r o n ment, and with few exceptions t h e i r nature i s comp l e t e l y o b l i t e r a t e d a f t e r a number o f decades." Degradation of polymers occurs by one or a l l mechanisms: 1. 2. 3. 4. 5.

Solar radiation (especially Heat Hydrolysis Oxidation (oxygen or ozone) B i o l o g i c a l degradation

of the

following

ultraviolet)

In conventional polymer technology, i t i s u s u a l l y the i n t e n t to prevent environmental degradation by modifying the polymeric s t r u c t u r e or to add s t a b i l i z e r s . There appears ample l i t e r a t u r e on the degradation o f polymers i n order to improve the f i n a l product. A number of p l a s t i c s and polymers appear as food-contact m a t e r i a l s i n packaging or c l o s u r e s and have been exempted from a t o l e r a n c e by the EPA under s e c t i o n 40 CFR 180.1001. Yet i t i s prudent to r a i s e questions on the environmental impact, e s p e c i a l l y i n 1ight of the c u r r e n t i n t e r e s t on the s o - c a l l e d " i n e r t s " i n p e s t i c i d e products. Natural Rubber degrades r a p i d l y upon environmental exposure through m i c r o b i a l , o x i d a t i v e , and photochemical a c t i o n . Normally, a n t i - o x i d a n t s and p r e s e r v a t i v e s are added to rubber to extend i t s 1 i f e , but rubber formulations can be t a i l o r e d to increase degradat i o n , i f this is desired. C h l o r i n a t e d natural rubber, now i n use i n a n t i - f o u l i n g c o a t i n g s , i s h i g h l y r e s i s t a n t to b i o l o g i c a l attack but may be t o x i c to microorganisms (Unpublished o b s e r v a t i o n s , N.F. C a r d a r e l l i ) . Ethylene-Propy1ene Polymers show r e l a t i v e l y l i t t l e degradat i o n caused by heat, humidity or u v - r a d i a t i o n , ozone a t t a c k , and oxidation. C e l l u l o s i c M a t e r i a l s g e n e r a l l y degrade under environmental c o n d i t i o n s when exposed to the atmosphere and s u n l i g h t . Bacterial

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

46

C O N T R O L L E D R E L E A S E PESTICIDES

decay i n l o o s e , moist s o i l i s extremely r a p i d . Cellulose t r i a c e t a t e has been c l e a r e d f o r food contact usage. Carboxymethylc e l l u l o s e s are used i n foods as gel 1 ants and thickeners and are e s s e n t i a l l y nontoxic to man. P o l y i s o b u t y l e n e and Butyl Rubber. Compounded butyl rubber m a t e r i a l s are h i g h l y r e s i s t a n t to moisture and f a i r l y r e s i s t a n t to o x i d a t i o n . A d d i t i o n o f peroxides, however, w i l l a c c e l e r a t e t h e i r breakdown. The degree of environmental impact depends on the c u r i n g agent ( e . g . , s u l f u r or lead p e r o x i d e ) . Generally speaking, butyl rubber degradation by environmental f a c t o r s appears to proceed very s l o w l y . No information has been found on environmental breakdown products. Styrene - Butadien tack by oxygen, ozone, an rubber, these compounds e x h i b i t a g r e a t e r r e s i s t a n c e to b a c t e r i a l attack. I d e n t i f i c a t i o n o f metabolism or breakdown products has not been found i n the l i t e r a t u r e surveyed. P o l y a c r y l o n i t r i 1 es tend to be r e s i s t a n t to m i c r o b i a l degradation, but ozone degrades these m a t e r i a l s r a p i d l y . P o l y a c r y l a t e s . Carboxylated a c r y l i c systems such as Carboset* are r e a d i l y degraded by microorganisms, e s p e c i a l l y f u n g i . Carbos e t * polymers are ingested by m o l l u s c s , i n s e c t s , and probably nematodes (personal o b s e r v a t i o n , N.F. C a r d a r e l l i ) . Carboset* 514 has been exempted by EPA from the requirements o f a tolerance when used i n a g r i c u l t u r e (CFR 40 S e c t . 180.1001). No information i s a v a i l a b l e on the t o x i c i t y o f Carboset* to f i s h or plants or any other segment o f the b i o t a ; no environmental f a t e studies have been conducted by the manufacturer. P o l y e s t e r s are known f o r t h e i r r e s i s t a n c e to chemical and r a d i a t i o n - i n d u c e d degradation. Breakdown products a t elevated temperatures i n c l u d e a l l y l a l c o h o l , acetaldehyde, carbon d i o x i d e , water, formic and a c e t i c a c i d s . No information on p o s s i b l e b i o degradation was found. Polyamides degrade under the i n f l u e n c e o f heat and r a d i a t i o n to simple hydrocarbons and cyclopentanone. Under ambient e n v i r o n mental c o n d i t i o n s , however, the degradation o f Nylon microcapsules i s expected to be very slow. No environmental s t u d i e s were found i n t h i s survey. Exemption has been granted by the EPA under CFR 40 S e c t . 180.1001. Polyethylene (PE). P o l y e t h y l e n e , c h l o r i n a t e d - and c h l o r o sulfonated PE*s have been used f o r CR matrices ( e . g . , c h l o r p y r i fos/PE, Table III) and are g e n e r a l l y r e s i s t a n t to environmental degradation and m i c r o b i a l a t t a c k .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

47

Aspects

P o l y v i n y l C h l o r i d e i s degraded a t d i f f e r e n t rates depending on the p l a s t i c i z e r used: phthalate and phosphate p l a s t i c i z e r s s t a b l e ; a d i p a t e , a z e l a t e , and sebacate p l a s t i c i z e r s - - suscept i b l e to degradation. The p o s s i b i l i t y o f v i n y l c h l o r i d e monomer present i n the p l a s t i c or as a degradation product must be investigated. Chloroprene polymers are h i g h l y r e s i s t a n t to m i c r o b i a l attack (35, 36). Polyurethanes are e s p e c i a l l y prone to fungal and b a c t e r i a l attack (35) but are r e s i s t a n t to chemical degradation. C i s Polybutadiene i s thermally s t a b l e , ronmental studies were no t h a t these polymers behav

and although e n v i -

Acetal Copolymers, used i n the C o n r e l * d e l i v e r y system (Table I I I ) , may degrade to formaldehyde and ethylene oxide i n s o i l and water, although no hard data could be found to v e r i f y t h i s hypothesis. Other M a t e r i a l s . Although s i l i c o n e rubber i s not p r e s e n t l y used i n CR p e s t i c i d e f o r m u l a t i o n s , i t has found usage i n CR drug d e l i v e r y , systems and thus may f i n d future a p p l i c a t i o n s i n p e s t i cide products. S i l i c o n e s are recognized as nontoxic and extremely i n e r t to b i o l o g i c a l a t t a c k . Polyacrylamides are not p r e s e n t l y used f o r p e s t i c i d e formulat i o n s ; these m a t e r i a l s degrade slowly under the i n f l u e n c e o f heat, and i t i s a n t i c i p a t e d that they w i l l g r a d u a l l y depolymerize to ammonia or ammonium ions depending on pH. Hydrin rubber r e p r e sents another CR matrix f o r p e s t i c i d e s ; i t i s the homopolymer o f epichlorohydrin. Hydrin rubber i s s t a b l e to heat and ozone but might be s u s c e p t i b l e to m i c r o b i a l a t t a c k . The Microporous P l a s t i c Sheet* i s made o f s i l i c a modified PVC or v i n y l c h l o r i d e v i n y l acetate copolymers. It i s a l i k e l y candidate f o r CR formul a t i o n s , but l i t t l e i s known about i t s environmental behavior. Polymer - A d d i t i v e s Space does not permit extensive d i s c u s s i o n o f the nature and environmental impact o f polymer a d d i t i v e s . These a d d i t i v e s are a variety of p l a s t i c i z e r s , antioxidants, release regulators, e t c . Many o f these compounds are exempt from tolerance (CFR 40, Sect. 180.1001), although some, l i k e the p h t h a l a t e s , have been shown to e x h i b i t t o x i c o l o g i c a l and environmental problems. However, one would have to assess t h e i r escape from the CR system to evaluate p o s s i b l e environmental and human exposure. For a more complete d e s c r i p t i o n o f these a d d i t i v e s and t o x i c o l o g i c a l e v a l u a t i o n , the reader i s r e f e r r e d to the EPA Report on CR P e s t i c i d e Formulations (EPA Contract No. 68-01-1922). American Chemical Society Library 1155 16th St., N.W. Washington. D £Release 2003S Pesticides; Scher, H.; In Controlled

ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

48

PESTICIDES

T o x i c o l o g i c a l and Environmental Testing Generally speaking, CR formulations of p e s t i c i d e s and the conventional e m u l s i f i a b l e concentrate or wettable powder formulat i o n s are not considered d i f f e r e n t e n t i t i e s under present p e s t i c i d e laws and r e g u l a t i o n s . The p e s t i c i d e law (FIFRA as amended i n 1972 and 1975) addresses i t s e l f to " p e s t i c i d e s " and i t s i n t e n t i s to r e g u l a t e each of the approximately 30,000 p e s t i c i d e products. The Gui d e l i n e s f o r R e g i s t e r i n g P e s t i c i d e s i n the United S t a t e s , which are p r e s e n t l y undergoing f i n a l r e v i s i o n s before p u b l i c a t i o n , c l e a r l y d i s t i n g u i s h between the " t e c h n i c a l c h e m i c a l , " which p e s t i c i d e s c i e n t i s t s have always considered to be synonomous with " p e s t i c i d e , " and " p e s t i c i d e f o r m u l a t i o n s , " which the l e g i s l a t o r s have termed " p e s t i c i d e s " . It i s doubtful that any regul a t i o n s now or i n the future w i l l r e q u i r e d e t a i l e d t o x i c o l o g i c a l and environmental t e s t i n D e t a i l e d t o x i c o l o g i c a l and environmental t e s t s w i l l have to be performed on the t e c h n i c a l material (or s o - c a l l e d " a c t i v e i n g r e d i e n t " ) , although some a t t e n t i o n w i l l be d i r e c t e d towards the s o - c a l l e d " i n e r t " i n g r e d i e n t s , which have been discussed i n d e t a i l above f o r c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s . It appears t h a t most matrices so f a r u t i l i z e d for CR p e s t i c i d e formulations may be covered by CFR 40 Section 180.1001 (exempt c a t e g o r y ) , although t h i s d e c i s i o n must be made on each i n d i v i d u a l b a s i s . The crux of the unresolved question might be phrased l i k e this: Does the a c t i v e i n g r e d i e n t placed i n t o a p l a s t i c capsule behave d i f f e r e n t l y t o x i c o l o g i c a l l y than i f i t were formulated more c o n v e n t i o n a l l y as an e m u l s i f i a b l e concentrate or a dust? Toxicological Testing. D e t a i l e d d i s c u s s i o n s on t h i s t o p i c w i l l be covered i n the chapter by J . D o u l l . The best example o f lower t o x i c i t y , which one would g e n e r a l l y expect from a c o n t r o l l e d - or s l o w - r e l e a s e f o r m u l a t i o n , i s the case of Penncap-M* compared to methyl parathion e m u l s i f i a b l e c o n c e n t r a t e . As d i s cussed above, the dermal and oral t o x i c i t y of the CR formulation was c o n s i d e r a b l y lower than that of the e m u l s i f i a b l e concentrate (33). Table V i s a l i s t i n g o f the major t o x i c o l o g i c a l t e s t s now r e q u i r e d by the EPA f o r r e g i s t r a t i o n purposes. TABLE V MAJOR TOXICOLOGICAL TESTS FOR REGISTRATION OF PESTICIDES Acute Oral Subacute Oral Chronic ( i n c l . cancer) Eye I r r i t a t i o n Dermal I r r i t a t i o n

Acute Dermal Subacute Dermal Acute Inhalation Teratogenicity Mutagenicity

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

49

Aspects

If the complete t e s t s have been performed on the p e s t i c i d e chemical i t s e l f , i t appears reasonable that only the acute t e s t s may be required f o r the CR product. Environmental T e s t i n g . As has been discussed before, the lack of knowledge about the environmental f a t e of CR matrices makes i t d i f f i c u l t to reach a d e c i s i o n on which environmental t e s t s should be r e q u i r e d . Furthermore, the mechanism of c o n t r o l l e d r e l e a s e of smal1 concentrations o f a t o x i c a n t over an extended period of time may present environmental problems t h a t cannot be p r e d i c t e d . Two problems, those of " c h r o n i c i t y " and " r e s i s t a n c e " have been i d e n t i f i e d and w i l l be discussed below. Therefore, i t i s only p o s s i b l e to summarize environmental t e s t requirements and f o r each t e s t to pose the q u e s t i o n : "Is i t reasonable to assume that the CR formulation behaves d i f f e r e n t l y than, f o r example, an E the required environmental t e s t s proposed i n the EPA Gui d e l i n e s f o r R e g i s t e r i n g P e s t i c i d e s soon to be p u b l i s h e d . TABLE VI ENVIRONMENTAL TESTS Hydrolysis Photolysis

Field dissipation Terrestrial Aquatic Forest

Metabolism Aerobic s o i l Anaerobic s o i l Aerobic aquatic Anaerobic aquatic Microbial on p e s t i c i d e s on microbes a c t i v a t e d sludge Mobility Leaching Volatility Adsorption/desorption Water d i s p e r s a l

Accumulation Rotational crops F i s h accumulation Aquatic noncrop uses Reentry Dislodgeable residues Volatility Photodegradation Procedures storage

for d i s p o s a l

and

" C h r o n i c i t y " Phenomenon. Chronic i n t o x i c a t i o n requires much l e s s of the c o n t r o l agent than that necessary to produce acute e f fects. As the c o n c e n t r a t i o n of the agent i s decreased, the time to e f f e c t l e t h a l i t y does not increase l i n e a r l y . This phenomenon has been termed " c h r o n i c i t y " by C a r d a r e l l i (37) and has been demonstrated with a number of CR formulations of phenoxy h e r b i c i d e s , d i q u a t , and d i c h l o b e n i l to c o n t r o l aquatic weeds l i k e water l e t t u c e , Eurasian w a t e r m i l f o i l , El odea, Southern n a i a d , and water

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

50

C O N T R O L L E D R E L E A S E PESTICIDES

hyacynth. " C h r o n i c i t y " has a l s o been demonstrated with a n t i f o u l ing agents, incorporated i n t o c e r t a i n rubbery m a t e r i a l s , and molluscicides. The butoxyethanol e s t e r o f 2 , 4 - D , compounded i n t o natural rubber, has been shown to y i e l d e f f e c t i v e c o n t r o l concent r a t i o n s f o r over 18 months. From the p o i n t of view o f e f f i c a c y , the " c h r o n i c i t y " phenomenon may be advantageous. On the other hand, whether the phenomenon poses an environmental hazard, f o r example to f i s h , remains to be r e s o l v e d . An example of " c h r o n i c i t y " i s i l l u s t r a t e d i n Table V I I , which shows the extended c o n t r o l o f w a t e r m i l f o i l by diquat over a 32-day period a t d i f f e r ent concentrations o f diquat tested (38). TABLE VII THE CONTROL OF EURASIAN WATERMILFOIL BY DIFFEREN CONCN. OF DIQUAT

a

LT 99

9

L l

(PPM)

(Days)

1.0 0.1 0.01 0.001

11 19 16 32

Time which 99% c o n t r o l i s

effected

The Resistance Problem. The use o f c o n t r o l 1ed-release p e s t i c i d e s ( l a r v i c i d e s ) may well enhance the r e s i s t a n c e problem. Subl e t h a l dosages o f i n s e c t i c i d e s tend to lead to the development of more r e s i s t a n t p o p u l a t i o n s . Since c o n t r o l l e d r e l e a s e l a r v i c i d e s w i l l be c o n c e p t u a l l y used i n very low c o n c e n t r a t i o n s , and l o n g term r e l e a s e w i l l be achieved f o r c o s t e f f e c t i v e n e s s , c o n s i d e r a b l e s u b l e t h a l dosing can be expected. This e f f e c t r e s u l t s i n many generations o f the same species i n the same l o c a l e exposed to the a c t i o n of the l a r v i c i d e . The problem o f enhanced t o l e r a n c e (or r e s i s t a n c e ) through the use o f c o n t r o l l e d methods has y e t to be investigated. Summary A survey o f the types o f c o n t r o l l e d - r e l e a s e formulations of d i f f e r e n t c l a s s e s of p e s t i c i d e s has been presented. Some CR p e s t i c i d e formulations have become commercial products, while others are s t i l l experimental and f e a s i b l e but have not been t e s t e d . A d i s c u s s i o n o f the various CR matrices has shown that the environmental f a t e o f many i n e r t s i s unknown and should be s t u d i e d before they are introduced i n t o the environment. At the

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

Aspects

51

present s t a t e o f knowledge there do not seem to be serious e n v i ronmental problems except f o r p o s s i b l e r e s i s t a n c e and t o x i c i t y to nontarget populations o f b e n e f i c i a l i n s e c t s . Acknowledgements This paper i s l a r g e l y based on a study funded by EPA, Contract No. 68-01-1922, Development of R e g i s t r a t i o n C r i t e r i a f o r C o n t r o l l e d Release P e s t i c i d e s , and s p e c i a l thanks are due to the authors o f t h i s r e p o r t , N.F. C a r d a r e l l i , K . E . Walker, and M. Beroza. General

References

C a r d a r e l l i , N.F. C o n t r o l l e d Release P e s t i c i d e Formulations. CRC Press, C l e v e l a n d , Ohio Proc. C o n t r o l l e d Release P e s t i c i d e Symposium, Univ. o f Akron, Ohio. (1974, 1976). Proc. C o n t r o l l e d Release P e s t i c i d e Symposium, Wright State U n i v . , Dayton, 0. (1975).

Literature Cited 1. 1A. 2. 3. 4. 5.

6.

7. 8.

9. 10.

Wuerzer, D.R., Senderling, R . L . , and Cardarelli, N.F. Rubber World, (Nov. 1967) 157 (2), 77. Nelson, L.L., Barnes, W.W., Harris, F.W. and Lawson, M.A., J . Econ. Entomol. (1970) 63, 1870. M i l l e r , T . A . , Nelson, L.L., Young, W.W., Roberts, L.W., Roberts, D.R. and Wilkinson, R . N . , Mosq. News, (1973) 33 148. Nelson, L.L., M i l l e r , T . A . , Whitlaw, J.T., Young, W.W., and Lawson, M.A., Mosq. News, (1973) 33, 403. Wasti, S.S., Shaw, F.R. and Smith, C . T . , J. Econ. Entomol. (1970) 63, 1355. M i l l e r , R.W., Drazek, P . Α . , Martin, M.S. and Gordon, C.H., Rep. No. 169, Ann. Mtng. Amer. Dairy S c i . Assoc., Gainesville, Fla. DCRB 70-8, (June 1970). Inscoe, M.N. and Beroza, M. in Pest Management with Insect Sex Attractants, (pp. 145-181), M. Beroza, e d . , ACS Symposium Series 23, Amer., Chem. Soc., Wash., D.C. (1976). Cameron, E . A . , Schwalbe, C.P., Stevens, L.J. and Beroza, M . , J . Econ. Entomol., (1975) 68, 158. B i e r l , B.A. and DeVilbiss, D . , Proc. Controlled Release Pesticide Symp., 230, Wright State University, Dayton, OH, (September 8-10, 1975). Beroza, M . , Paszek, E . C . , DeVilbiss, D . , B i e r l , B.A. and Tardif, J . G . R . , Environ. Entomol., (1975) 4, 712. Hardee, D.C., McKibben, G.H. and Huddleston, P . M . , J. Econ. Entomol., (1975) 68, 477.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

52 11.

12. 13.

14. 15.

16.

17.

18.

19. 20.

21.

22.

23. 24. 25. 26.

C O N T R O L L E D R E L E A S E PESTICIDES

Keiser, I., Kobayashi, R.M. and Harris, E.J., Proc. Controlled Release Pesticide Symp., 264, Wright State University, Dayton, OH, (September 8-10, 1975). Olton, G . S . , Proc. Controlled Release Pesticide Symp., 258, Wright State University, Dayton, OH (September 8-10, 1975). Quisumbing, A . R . , Lawatsch, D.J. and Kydonieus, A.F., Proc. Controlled Release Pesticide Symp., 247, Wright State University, Dayton, OH (September 8-10, 1975). Sjogren, R.D., Proc. Controlled Release Pesticide Symp. 217, Wright State University, Dayton, OH (September 8-10, 1975). Barnes, W.W. and Whitlaw, J.T., Preliminary Evaluation of Controlled Release Herbicide Formulations for Aquatic Weeds, Rep. U.S. Army Environ. Hygiene Agency, Edgewood, MD (Proj. 31-004-69/70) (1970). Young, W.W. and Nelson Release Herbicid Spec. Study No. 31-004-69/71, U.S. Army Environment Hygiene Edgewood, MD (July 1969 - July 1970). Harris, F.W., Norris, S.O. and Post, L . K . , Investigation of Factors Influencing Release of Herbicides from Polymer Matrices: The Polyethylene Matrix, Quart. Rep. II, Contract No. DACW 73-71-C-0053, U.S. Army Corps Engineers, (Oct. 1971-Dec. 1971). Steward, K . K . , Weed Investigations - Aquatic and Noncrop Areas Annual Rep., Agricultural Research Service, Ft. Lauderdale Fla., (July 1970 - June 1971). Harris, F.W., Norris, S.O. and Post, L . K . , Weed Sci., (1973) 21 (4), 318. Harris, F.W., Feld, W.A. and Post, L . K . , Investigation of Factors Influencing Release of Herbicides from Polymers Containing Herbicides as Pendent Side Chains. Annual Rep. Contract No. DACW 73-74-C-0001, U.S. Army Office Chief Engineer, Washington, D . C . , (July 1973-June 1974). Harris, F.W. and Post, L . K . , Rep. No. 17, Proc. Controlled Release Pesticide Symp., University of Akron, Akron, OH, (September 16-18, 1974). B i l l e , S., Mansdorf, S.F. and Cardarelli, N . F . , Development of Slow Release Herbicide Materials for Controlling Aquatic Plants, Annual Rep. II to Dept. Army Office Chief Engineer, Contract No. DACW 73-70-C0030, (Nov. 1969 - July 1971) University of Akron, Product Development Lab., (July 1971). Mansdorf, S . F . , Rep. No. 12, Proc. Controlled Release Pesticide Symp., University of Akron, Akron, OH (September 1618, 1974). Abrams, J. and Hinkes, T . M . , Pest Control, (May 1974) 14. Jackson, W.M., Rep. No. 6, Controlled Release Pesticide Symp., University of Akron, Akron, OH (September 16-18, 1974). Cornwall, P . B . , International Pest Control (1970) 12 (4), 35.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

4.

ZWEIG

Environmental

Aspects

27.

53

Cardarelli, N.F. and Feldmesser, J., Proc. Controlled Release Pesticide Symp., 386, Wright State University, Dayton, OH (September 8-10, 1975). 27A. Feldmesser, J . Progress Report on Controlled Release of a Nematicide. Rep. No. 32, Proc. Controlled Release Pest. Symp. Akron, OH (Sept. 16-18, 1974). 28. Cardarelli, N . F . , Evaluation of Incracide E-51 Against Select Aquatic Weeds and Algae, Rep. Creative Biology Lab., Proj. 104 to International Copper Research Assoc., New York, N.Y. (April 5, 1975). 29. Cardarelli, N.F. and B i l l e , S.M., Evaluation of Environ mental Chemicals, Inc. Controlled Release Copper Sulfate, Rep. 1, Proj. 121, Creative Biology Lab., Barberton, OH, (March 1, 1976). 30. Hesketh, Β . , McKechni spondence to Cardarelli OH (13 February 1976). 31. Anon., Envirocap C . , Chem. Eng. News (1972) 50 (23), 68. 32. Cardarelli, N . F . , Dermal Protective Films, U.S. Patent 3,749,772 (1973). 33. Ivy, E.E., J. Econ. Entomol., (1972) 65, 473. 34. Selkirk, J., Envir. Action Bulletin, 3 (Oct. 2, 1976). 35. Hep, W.M. and Morrell, S . H . , J. Appl. Chem., (1968) 18 (7), 189. 36. MacLachlin, J., Heap, W.M. and P a c i t t i , J., Monograph, Soc. Chemistry Industry, (1966) 23, 185. 37. Cardarelli, N . F . , Weeds, Trees & Turf, (1972) 11 (5), 16 38. Janes, G . A . , B i l l e , S.M. and Cardarelli, N . F . , Development and Evaluation of Controlled Release Herbicides, Quart. Rep. U.S. Army Corps Engineers Contract No. DACW 39-76-C-0029 (Oct. 1 - Dec. 31, 1975).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5 Clinical Toxicology Aspects of Controlled Release Pesticide Formulations JOHN DOULL University of Kansas Medical Center, Kansas City, Kans. 66103

We are scheduled a some of the clinical toxicologi - r e l e a s e or microencapsulated p e s t i c i d e s . At the present t i m e , however, there are no reported human cases of poisoning w i t h microencapsulated p e s t i c i d e s , to my knowledge, and there i s relatively little acute and c h r o n i c toxicity data a v a i l a b l e f o r these agents in a n i m a l s . It i s e v i d e n t , t h e r e f o r e , that all we can do at t h i s point in time i s to speculate on how the use of these agents might a f f e c t the incidence and s e v e r i t y of p e s t i c i d e poisoning in t h i s country and to t r y to i d e n t i f y some of the problems that the emergency room p h y s i c i a n may have to deal w i t h in the event that these agents r e c e i v e widespread commercial usage. In looking back over the l a s t 40 years at the incidence and causes of p e s t i c i d e poisoning in t h i s c o u n t r y , i t seems to me that we have witnessed three more or l e s s distinct phases in the epidemiology of p e s t i c i d e poisoning and that we are now e n t e r i n g i n t o what may be a f o u r t h phase of t h i s problem. Pre-DDT Phase o f P e s t i c i d e P o i s o n i n g The f i r s t p h a s e , w h i c h I d e s i g n a t e a s t h e pre-DDT e r a , was c h a r a c t e r i z e d by t h e heavy m e t a l s a s t h e c h i e f c a u s e o f p e s t i c i d e p o i son i n g w i t h a r s e n i c a s t h e number o n e o f f e n d e r . Almost a l l o f t h e a g e n t s w h i c h were used a s p e s t i c i d e s d u r i n g t h i s p e r i o d were h i g h l y t o x i c and t h i s was t r u e f o r t h e b o t a n i c a l s , s u c h a s s t r y c h n i ne and η i c o t i n e , a s w e l l a s f o r t h e heavy m e t a l s , s u c h as a r s e n i c and l e a d . A l t h o u g h t h e u s e o f t h e s e a g e n t s was m o d e r a t e by t o d a y ' s s t a n d a r d s , t h e t o x i c i t y o f t h e s e a g e n t s made p e s t i c i d e p o i son i n g a s i g n i f i c a n t p r o b l e m i n p o i s o n control. Even i n t h o s e d a y s , h o w e v e r , i t was a r e l a t i v e l y m i n o r ρrobI em when compared w i t h o t h e r a g e n t s t h a t were r e s p o n s i b l e f o r p o i s o n ing c a s e s . I t has been e s t i m a t e d ( J j t h a t p e s t i c i d e s were r e s p o n s i b l e f o r between 5 and 101 o f t h e c a s e s

54

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

DOULL

Clinical

Toxicology

55

Aspects

o f human p o i s o n i n g d u r i n g t h i s pre-DDT phase and t h a t r a t e was a b o u t 1 p e r m i l l i o n p o p u l a t i o n . DDT P h a s e o f

Pesticide

the

death

Poisoning

The s e c o n d phase o f p e s t i c i d e p o i s o n i n g e p i d e m i o l o g y began w i t h t h e i n t r o d u c t i o n o f DDT i n t h e 1 9 ^ 0 s and t h e s u b s e q u e n t a d d i t i o n of other c h l o r i n a t e d hydrocarbon i n s e c t i c i d e s in the 1950's. D u r i n g t h i s p e r i o d t h e r e was a g r e a t i n c r e a s e i n t h e use o f p e s t i c i d e s i n t h i s c o u n t r y , b u t t h e r e was no c o r r e s p o n d i n g i n c r e a s e i n t h e number o f human c a s e s o f p e s t i c i d e p o i s o n i n g (2). In f a c t , t h e r e were d e c r e a s i n g t r e n d s i n b o t h t h e a b s o l u t e m o r t a l i t y and i n t h e p e r c e n t i n c i d e n c e o f p o i s o n i n g d u r i n g many p o r t i o n s o f what I r e f e r t o a s t h e DDT phase o f p e s t i c i d e poisoning epidemiology. Although the poison c o n t r o l s t a t i s t i c s f o r t h i s p e r i o d were e n c o u r a g i n g s i n c e we had a n t i c i p a t e d t h a t t h e r e p l a c e m e n t o f h i g h l y t o x i c p e s t i c i d e s l i k e a r s e n i c and s t r y c h n i n e w i t h a g e n t s l i k e DDT, which is comparatively n o n - t o x i c f o l l o w i n g acute i n g e s t i o n , w o u l d d e c r e a s e t h e emergency room p r o b l e m from p e s t i c i d e p o i s o n ing. I t was f u r t h e r a n t i c i p a t e d t h a t t h e m o r t a l i t y and m o r b i d i t y a s s o c i a t e d w i t h t h e o l d e r a g e n t s w o u l d d e c r e a s e a s t h e y were r e p l a c e d , and t h i s a l s o t u r n e d o u t t o be t r u e f o r b o t h a r s e n i c and s t r y c h n i n e ( 2 ) . These t r e n d s were somewhat c o u n t e r a c t e d , h o w e v e r , by t h e g r o w i n g p r o b l e m o f human p o i s o n i n g w i t h t h e o r g a n i c p h o s p h a t e i n s e c t i c i d e s and t o a much l e s s e r e x t e n t w i t h the carbamate i n s e c t i c i d e s . I t was a p p a r e n t d u r i n g t h e e a r l y I 9 6 0 s , f o r example, t h a t the o r g a n i c phosphate i n s e c t i c i d e s were c a u s i n g more o c c u p a t i o n a l p e s t i c i d e f a t a l i t i e s t h a n any o t h e r c l a s s o f a g r i c u l t u r a l c h e m i c a l s and t h a t i n heavy use a r e a s , l i k e F l o r i d a and C a l i f o r n i a , t h e o r g a n i c p h o s p h a t e i n s e c t i c i d e s were r e s p o n s i b l e f o r o v e r h a l f o f t h e s u i c i d e deaths. In one y e a r , f o r e x a m p l e , t h e y c a u s e d more d e a t h s i n Dade C o u n t y , F l o r i d a , t h a n a s p i r i n , w h i c h i s t r a d i t i o n a l l y o u r number one c a u s e o f p o i s o n i n g i n a l l a r e a s (J_). 1

1

P o s t - D D T Phase o f

Pesticide

Poisoning

W i t h t h e b a n n i n g o f DDT i n t h e l a t e s i x t i e s and t h e s u b s e q u e n t removal o f o t h e r c h l o r i n a t e d h y d r o c a r b o n i n s e c t i c i d e s i n t h e e a r l y s e v e n t i e s , we have e n t e r e d i n t o what I c a l l t h e p o s t DDT o r t h i r d phase o f p e s t i c i d e e p i d e m i o l o g y . I t i s now a l m o s t 10 y e a r s s i n c e t h e a p p e a r a n c e o f t h e Mrak r e p o r t i n w h i c h t h e DDT ban was recommended. One o f t h e t h i n g s w h i c h was o f r e a l c o n c e r n t o s e v e r a l o f us who p a r t i c i p a t e d i n t h e p r e p a r a t i o n o f t h i s r e p o r t was t h e l i k e l i h o o d t h a t by e l i m i n a t i n g DDT, f a r m e r s and o t h e r u s e r s w o u l d be f o r c e d t o t u r n t o s u b s t i t u t e s w h i c h were f a r more t o x i c a c u t e l y and t h a t , i n e f f e c t , from t h e p o i s o n c o n t r o l v i e w p o i n t , we m i g h t have a s i t u a t i o n where t h e c u r e was w o r s e t h a n t h e d i s e a s e . Most emergency room p h y s i c i a n s

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

56

CONTROLLED

RELEASE

PESTICIDES

t h a t t h i s i s e x a c t l y what has o c c u r r e d ( 3 ) . P e s t i c i d e s a r e v e r y much l i k e a n t i b i o t i c s i n t h a t t h e b e s t a g e n t o r d r u g o f c h o i c e i s u s u a l l y t h e one w h i c h e x h i b i t s a h i g h l y s e l e c t i v e t o x i c i t y to the i n v a d i n g p a r a s i t e or p e s t , yet i s r e l a t i v e l y n o n - t o x i c to the host or n o n - t a r g e t s p e c i e s . When t h e p h y s i c i a n i s d e n i e d t h e u s e o f a f i r s t - l i n e a n t i b i o t i c s u c h as pen i c i 11 i n b e c a u s e o f a l l e r g y o r some o t h e r r e a s o n and f o r c e d t o t u r n t o a s e c o n d - 1 i n e d r u g s u c h as v a n c o m y c i n o r even e r y t h r o m y c i n , he e x p e c t s t o e n c o u n t e r more t o x i c i t y p r o b l e m s . S i m i l a r l y , i n r e p l a c i n g f i r s t - l i n e p e s t i c i d e s l i k e DDT o r 2 , 4 - D , w h i c h c a u s e few a c u t e t o x i c i t y p r o b l e m s w i t h a g e n t s l i k e p a r a t h i o n o r p a r a q u a t , which p r e s e n t major treatment problems to t h e emergency room p h y s i c i a n , i t i s u n r e a l i s t i c t o e x p e c t t h a t we can e s c a p e t h e c o n s e q u e n c e s e i t h e r i n t e r m s o f t h e i n c i d e n c e o f p o i s o n i n g o r i n t h e s e v e r i t y o f t h e c a s e s w h i c h we see i n t h e emergency room o b t a i n e d from t h e N a t i o n a l C l e a r i n g House f o r P o i s o n C o n t r o l C e n t e r s suggests t h a t i n s e c t i c i d e s a r e r e s p o n s i b l e f o r about h a l f o f a l l c a s e s o f p e s t i c i d e p o i s o n i n g , but t h e r e i s no breakdown o f t h i s d a t a i n t o t y p e o f i n s e c t i c i d e . In o u r own emergency room, i n s e c t i c i d e s a c c o u n t e d f o r a b o u t 7\% o f t h e p e s t i c i d e c o n t a c t s , but almost a l l o f the p e s t i c i d e p o i s o n i n g c a s e s w h i c h we t r e a t e d were o r g a n i c p h o s p h a t e i n t o x i c a t i o n s . We have had o n l y one c a s e o f c h l o r i n a t e d h y d r o c a r b o n i n s e c t i c i d e p o i son i n g w h i c h r e q u i r e d t r e a t m e n t i n t h e p a s t s e v e r a l m o n t h s , and t h a t was a 2 - y e a r - o l d g i r l who i n g e s t e d L i n d a n e . feel

E l d o n Savage and h i s a s s o c i a t e s a t t h e Un i v e r s i t y o f Iowa, t h e Med i c a l Un i v e r s i t y o f S o u t h C a r o l i n a , and C o l o r a d o S t a t e Un i v e r s i t y have r e c e n t 1 y p u b l i s h e d t h e r e s u l t s o f t h e i r s u r v e y o f h o s p i t a l i z e d a c u t e p e s t i c i d e p o i son i n g i n t h e U n i t e d S t a t e s d u r i n g t h e y e a r s o f 1 9 7 1 , 1 9 7 2 , and 1973 W . In t h i s s t u d y , i n v e s t i g a t i v e teams w e r e s e n t o u t t o h o s p i t a l s i n b o t h h i g h and low p e s t i c i d e u s e a r e a s t o c o l l e c t d e m o g r a p h i c and h o s p i t a l r e c o r d i n f o r m a t i o n on b o t h o c c u p a t i o n a l and n o n - o c c u p a t i o n a l cases of p e s t i c i d e p o i s o n i n g . Organophosphate i n s e c t i c i d e s were t h e 1ead i n g c a u s e o f h o s p i t a l i z e d p e s t i c i d e p o i son i n g i n each of the three years surveyed f o r the o c c u p a t i o n a l exposure g r o u p , b u t i n t h e n o n - o c c u p a t i o n a l l y e x p o s e d g r o u p , w h i c h was m o s t l y c h i l d r e n u n d e r 5 , t h e o r g a n o p h o s p h a t e i n s e c t i c i d e s were r e s p o n s i b l e f o r l e s s t h a n 20% o f t h e p o i son i n g c a s e s . In i n t e r p r e t i n g t h i s t y p e o f d a t a , i t s h o u I d be k e p t i n mind t h a t p a t i e n t s who a r e h o s p i t a l i z e d f o r symptoms o f p e s t i c i d e p o i s o n i n g a r e more t h a n t w i c e a s l i k e l y t o d i e as t h o s e h o s p i t a l i z e d f o r symptoms o f o t h e r t y p e s o f p o i son i n g , and t h e d i f f e r e n c e is even more s t r i k i n g when one compares t h e outcome o f different c l a s s e s o f p e s t i c i d e s o r even d i f f e r e n t t y p e s o f i n s e c t i c i d e s . Prevention of

Pesticide

Poisoning

To r e t u r n t o t h e q u e s t i o n o f

how m i c r o e n c a p s u l a t i o n may

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

DOULL

Clinical

Toxicology

Aspects

57

a f f e c t p e s t i c i d e p o i s o n i n g i n t h e f u t u r e , we need t o c o n s i d e r some o f t h e c u r r e n t a p p r o a c h e s t o t h e p r o b l e m o f p r e v e n t i n g pesticide poisoning. One a p p r o a c h w o u l d be t o d e v e l o p new p e s t i c i d e s w h i c h e x h i b i t a much g r e a t e r s e l e c t i v e t o x i c i t y t h a n the c u r r e n t l y a v a i l a b l e p e s t i c i d e s . T h i s p r i n c i p l e has been used i n d e v e l o p i n g a n t i b i o t i c s s u c h as pen i c i 11 i n w h i c h k i 1 1 t h e p a r a s i t e by a mechan i sm wh i c h does n o t ex i s t i n t h e h o s t o r n o n - t a r g e t o r g a n i s m and t h e r e b y p r o v i d e s a t h e r a p e u t i c i n d e x o r s a f e t y m a r g i n o f o v e r 1000. I n s e c t g r o w t h r e g u l a t o r s and j u v e n i l e hormones a r e e x a m p l e s o f a g e n t s i n w h i c h an a t t e m p t i s made t o u t i l i z e a u n i q u e b i o l o g i c a l p r o p e r t y o f t h e i n s e c t t o p r o d u c e l e t h a l i t y and f o r w h i c h t h e r e may be no s t r i c t mammalian equivalent. Most p r e v i o u s a t t e m p t s t o d e v e l o p t h i s k i n d o f a b s o l u t e s e l e c t i v e t o x i c i t y i n p e s t i c i d e s have n o t been p r o d u c t i v e , b u t a t l e a s t one o a p p e a r s t o be r e m a r k a b l A n o t h e r r e l a t e d a p p r o a c h i s t o u s e i n s e c t s e x pheromones and kairmones w i t h a t r a p p i n g system to reduce i n s e c t p o p u l a t i o n s . S i n c e i t t a k e s o n l y a few m o l e c u l e s o f t h e s e a g e n t s t o p r o d u c e t h e i r e f f e c t , i t does n o t a p p e a r l i k e l y t h a t t h e i r u s e w i l l create serious acute poisoning problems. I t has a l s o been p r o p o s e d t o use c h e m o s t e r i l a n t s , s u c h as t h e a l k y l a t i n g a g e n t s , o r g a n o t i n and f o r m a m i d i n e s , f o r i n s e c t c o n t r o l , b u t s i n c e some of these agents produce s e r i o u s t o x i c e f f e c t s , t h e r e are at l e a s t p o t e n t i a l poison c o n t r o l problems a s s o c i a t e d w i t h t h e i r use. There i s a l s o a g r e a t deal of c u r r e n t i n t e r e s t i n the use o f i n t e g r a t e d p e s t management p r a c t i c e s a s a p o s s i b l e s o l u t i o n t o t h e p e s t i c i d e p o i son i n g p r o b l e m and i n t h e d e v e l o p m e n t o f n a t u r a l l y o c c u r r i n g i n s e c t i c i d e s and new d e r i v a t i v e s o f o l d e r c l a s s e s of i n s e c t i c i d e s , such as the p y r e t h r o i d s (5). Although some o f t h e s e a p p r o a c h e s c o u l d have a s i g n i f i c a n t impact on t h e p r o b l e m o f p e s t i c i d e p o i son i n g as seen i n t h e emergency room, i t l o o k s l i k e i t i s g o i n g t o be q u i t e some t i m e b e f o r e t h e s e a p p r o a c h e s p r o d u c e any s i g n i f i c a n t change i n e i t h e r t h e i n c i d e n c e o r t y p e o f p o i son i n g t h a t we a r e e x p e r i e n c i n g t o d a y . T h e r e a r e , h o w e v e r , some o t h e r a p p r o a c h e s wh i c h c o u l d have a more immediate i m p a c t . One o f t h e s e w h i c h has been used abroad i s to r e s t r i c t the use o f h i g h l y t o x i c p e s t i c i d e s such a s p a r a t h i o n and m e t h y l p a r a t h i o n , w h i c h c a u s e more c a s e s o f o r g a n i c p h o s p h a t e i n s e c t i c i d e p o i son i n g t h a n a l l o f t h e r e s t o f the agents i n t h i s c l a s s . T h i s c o u l d be a c c o m p l i s h e d by s i m p l y b a n n i n g s e l e c t e d a g e n t s a s was done i n J a p a n o r by r e s t r i c t i n g the use o f such agents to 1icensed pest c o n t r o l o p e r a t o r s as p r o p o s e d by t h e EPA. E l i m i n a t i n g a l l o f t h e h i g h l y t o x i c a g e n t s , however, w i l l not e l i m i n a t e the problem of p e s t i c i d e p o i son i ng s i n c e p o i s o n i ng c a n a l s o o c c u r w i t h t h e l e s s t o x i c agents provided the exposure i s s u f f i c i e n t l y g r e a t . As s t a t e d by P a r a c e l s u s , t h e f a t h e r o f t o x i c o l o g y , " A l l s u b s t a n c e s a r e p o i s o n s , t h u s d o s a g e a l o n e d e t e r m i n e s p o i son i n g " ( 0 . As a f i r s t s t e p , h o w e v e r , we c a n s o l v e t h e p r o b l e m o f p e s t i c i d e

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

58

CONTROLLED RELEASE

PESTICIDES

p o i s o n i n g i n t h e u s e r by i n s u r i n g t h a t a l l p e s t i c i d e s a r e f o r m u l a t e d i n s u c h a way t h a t i t becomes i m p o s s i b l e o r ν i r t u a l l y i m p o s s i b l e f o r t h e u s e r t o be e x p o s e d t o a t o x i c d o s e . We a r e a l r e a d y d o i n g t h i s t o some e x t e n t i n t h e d r u g a r e a by t h e use o f s a f e t y c l o s u r e s and l i m i t i n g t h e q u a n t i t y o f a g e n t i n e a c h c o n t a i n e r , and i t has made a d i f f e r e n c e i n t h e c a s e o f a s p i r i n poisoning. We a r e a l r e a d y moving i n t h i s d i r e c t i o n i n t h e p e s t i c i d e a r e a by u s i n g g r a n u l a r formulât i o n s , low volume s p r a y t e c h n i q u e s , and s y n e r g i z e r s wh i c h r e d u c e t h e amount o f p e s t i c i d e needed i n t h e formulât i o n . I t seems t o me t h a t m i c r o e n c a p s u l a t i o n o f p e s t i c i d e s o f f e r s an i n t e r e s t i n g and p o t e n t i a l method f o r a c h i e v i n g t h e same g o a l . As an emergency room phys i c i a n , I am a p p a l l e d when I w a l k i n t o my l o c a l h a r d w a r e s t o r e and f i n d t h a t I can p u r c h a s e b o t t l e s o f p e s t i c i d e s f o r m u l a t e d so t h a t a s i n g l e m o u t h f u l c o n s t i t u t e s a l e t h a l dose the f a c t t h a t each of these b o t t l e s c o n t a i n s a warning l a b e l d e s c r i b i n g the hazards a s s o c i a t e d w i t h exposure to the p e s t i c i d e , s i n c e most o f o u r p o i s o n i n g c a s e s o c c u r i n c h i l d r e n under f i v e who c a n ' t r e a d , o r a r e i n t e n d e d s u i c i d e s who u s e t h e l a b e l warn i n g a s a b a s i s f o r t h e i r s u i c i d e a t t e m p t . Changes i n o u r f o r m u l a t i o n p r a c t i c e s may n o t p r e v e n t p e s t i c i d e p o i s o n i n g i n t h e w o r k e r s engaged i n t h e m a n u f a c t u r e and f o r m u l a t i o n o f p e s t i c i d e s , and i t may n o t be p r a c t i c a l as a s o l u t i o n t o t h e problem o f o c c u p a t i o n a l p e s t i c i d e p o i s o n i n g i n a g r i c u l t u r e , but i t w o u l d c e r t a i n l y r e d u c e t h e p r o b l e m i n o u r emergency room and t h a t of o t h e r urban medical c e n t e r s . P o s s i b l e Tox i co1og i c P r o b l e m s w i t h M i c r o e n c a p s u l a t e d

Pesticides

I f we l o o k a t o u r p r e v i o u s e x p e r i e n c e w i t h g r a n u l a r f o r m u l a t i o n s o f p e s t i c i d e s , i t would appear t h a t the m i c r o e n c a p s u l a t e d p e s t i c i d e s s h o u l d be more e f f e c t i v e i n r e d u c i n g t h e i n c i d e n c e o f p e s t i c i d e p o i s o n i n g f o l l o w i n g dermal and i n h a l â t i o n e x p o s u r e than w i t h i n g e s t i o n . H o w e v e r , i n p a t i e n t s who i n g e s t g r a n u l a r f o r m u l a t i o n s o f p e s t i c i d e s , t h e symptoms g e n e r a l l y d e v e l o p more s l o w l y and a r e l e s s s e v e r e t h a n t h o s e seen i n p a t i e n t s who ingest p e s t i c i d e concentrates. G a s t r i c l a v a g e and a n t i d o t a l t r e a t m e n t a r e u s u a l l y more e f f i c a c i o u s i n s u c h c a s e s i n r e d u c i n g t h e amount o f p e s t i c i d e a b s o r b e d and i n p r e v e n t i n g t h e s u b s e q u e n t symptoms. Removal o f t h e g r a n u l a r m a t e r i a l by l a v a g e o r ernes i s sometimes p r e s e n t s p r o b l e m s b e c a u s e o f t h e t e n d e n c y o f t h e g r a n u l e s to form c o n c r e t ions i n the stomach. 11 i s a l s o p o s s i b l e t h a t the use o f the m i c r o e n c a p s u l a t e d p e s t i c i d e formul â t i o n i n an e n c l o s e d a r e a c o u l d , o v e r a l o n g per i o d o f t i m e , p r o d u c e an i n h a l â t i o n h a z a r d t o o c c u p a n t s o f t h e a r e a . I would a l s o be c o n c e r n e d a b o u t t h e p o s s i b i 1 i t y o f an i n d i v i d u a l ingesting the m i c r o e n c a p s u l a t e d p e s t i c i d e t o g e t h e r w i t h a s o l v e n t or emuls i f i e r w h i c h m i g h t f a c i l i t a t e t h e r e l e a s e o f t h e p e s t i c i d e . A l t h o u g h t h e m i c r o e n c a p s u l a t i o n p r o c e s s w o u l d n o t be e x p e c t e d

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

5.

DOULL

Clinical

Toxicology

Aspects

59

to i n t e r f e r e w i t h the a n t i d o t a l e f f i c a c y of the c u r r e n t l y a v a i l a b l e p e s t i c i d e a n t i d o t e s o r w i t h the usual t h e r a p e u t i c r e g i m e s used i n t h e management o f p o i s o n i n g , t h i s p o s s i b i 1 i t y s h o u l d be i n v e s t i g a t e d p r i o r t o t h e i r c o m m e r c i a l u s e . In a v e r y r e a l s e n s e , t h e emergency room phys i c i a n i s a t t h e end o f a l o n g d e v e l o p m e n t a l p r o c e s s , and by t h e t i m e he has to deal w i t h t h e p r o b l e m , t h e t o x i c o l o g y i s a c l o s e d book, t h e t o l e r a n c e s have been s e t , and t h e c h e m i s t s a r e a l l o f f l o o k i n g f o r a new a g e n t . I t seems t o me t h a t we need a more e n l i g h t e n e d a p p r o a c h t o t h e d e v e l o p m e n t o f new p e s t c o n t r o l measures w h i c h w o u l d r e c o g n i z e t h a t b o t h a c c i d e n t a l and i n t e n t i o n a l e x p o s u r e t o t h e a g e n t w i l l o c c u r and i n c l u d e s , t h e r e f o r e , a s p e c i f i c e f f o r t a l o n g t h e way t o f i g u r i n g o u t how s u c h p a t i e n t s s h o u l d be h a n d l e d . i t i s a l o t e a s i e r t o t r e a t a p o i s o n i n g when t h e management i s p r e p l a n n e d and t e s t e d t h a n when i t i s d i c t a t e d by a c r i s i s s î tuat ion invol învi t i n g me t o p a r t i c i p a t e a t t h i s e a r l y s t a g e .

Literature Cited 1.

Murphy, S. D., "Pesticides" In: Toxicology, the Basic Science of Poisons, Eds. L. J. Casarett and J. Doull, Macmillan Publishing Co., New York, Ν. Y . , 1975. 2. Hayes, W. J., "Recognized and Possible Effects of Pesticides in Man" In: Toxicology of Pesticides, Ed. W. J. Hayes, Williams and Wilkins, Baltimore, Md., 1975. 3. Doull, J., "The Treatment of Insecticide Poisoning" In: Insecticide Biochemistry and Physiology, Ed. C. F. Wilkinson, Plenum Publishing Co., New York, Ν. Y . , 1976. 4. Savage, Ε. P., "A Study of Hospitalized Acute Pesticide Poisoning in the United States", 1971 to 1973" EPA Contract 68-02-1271 and 68-01-3138, 1975. 5. Woods, J. S., Ed., Conference on Human Health Effects of New Approaches to Insect Pest Control, Environmental Health Perspectives (1976) 14: 1-193.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6 Matrix Factors Affecting the Controlled Release of Pesticides from Elastomers N. F. CARDARELLI and S. V. KANAKKANATT Environmental Management Laboratory, University of Akron, Akron, Ohio 44325

I t i s w e l l known t h a t v a r i o u s o r g a n i c m a t e r i a l s u t i l i z e d as pest c o n t r o l agents a r es o l u b l ei n elastomers. I f t h es o l u t i o n l i m i t i s n o t exceeded, s o l u t e molecules a r euniformly dispersed throughout the m a t r i x i naccordance w i t h t h e p r i n c i p l e s governing s o l u t i o n e q u i l i b r i u m . During environmental exposure agent molecules adsorbed on t h eelastomer s u r f a c e o r absorbed j u s t below t h a t s u r f a c e w i l l pass v i a d i s s o l u t i o n processes into t h esurrounding a i r , s o i l , o r water. This action e f f e c t i v e l y creates a condition o f l o c a l i z e d d i s e q u i l i b r i u m and s o l u t e molecules, d r i v e n by s o l u t i o n p r e s s u r e , m i g r a t e t o w a r d s t h e d e p l e t i n g surface. Thus a c o n t i n u o u s l o s s p r o c e s s i s e s t a b lished. The mechanism h a s been t r e a t e d a t l e n g t h by v a r i o u s authors^-"^. B i o l o g i c a l l y e f f i c a c i o u s longevi t y o f s u c h s y s t e m s h a s b e e n known t o e x c e e d n i n e years.2 Present commercial a p p l i c a t i o n s a r ei n t h e areas o f a n t i f o u l i n g coatings and long l a s t i n g m o l l u s c i c i d e s . ^""7 In g e n e r a l , work w i t h c o n t r o l l e d r e l e a s e m a t e r i a l s has been keyed t o p r a c t i c a l a p p l i c a t i o n s a n d b a s e d upon an e m p i r i c a l a p p r o a c h . The d i f f u s i o n - d i s s o l u t i o n mechanism h a s been e l u c i d a t e d b u t v e r y l i t t l e p a s t e f f o r t has been devoted t o t h e development o f a fundam e n t a l u n d e r s t a n d i n g r e g a r d i n g t h e i n f l u e n c e o f compounding v a r i a b l e s andm a t r i x s e l e c t i o n on t h e loss mechanism. Such knowledge would be o f c o n s i d e r a b l e value t o the design o f controlled release pesticide formulations and theo p t i m i z a t i o n o f favorable o r d e s i r a b l e p r o p e r t i e s . The work r e p o r t e d h e r e i n i s a step i nthat d i r e c t i o n .

60

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

CARDARELLI AND

General

KANAKKANATT

Matrix

Factors

61

Considerations

P r o p e r compounding o f t h e c o n t r o l l e d release formulation i s e s s e n t i a l t o develop various desirable properties - long h a l f - l i f e , a p p r o p r i a t e agent loss r a t e , i n t e g r i t y o f t h e p r o c e s s e d geometry and t h e like. E x p e r i e n c e h a s shown t h a t t h e n a t u r e o f t h e m a t r i x , degree o f c r o s s l i n k i n g and t h e use o f a d d i t i v e s such as c u r a t i v e s , a c c e l e r a t o r s , reinforcing agents, a n t i o x i d a n t s , e t c . g r e a t l y i n f l u e n c e agent s o l u b i l i t y and l o s s r a t e . The c u r e s y s t e m u s e d a f f e c t s both t h e r a t e o f c r o s s l i n k i n g and t h e u l t i m a t e crosslink density. Carbon b l a c k and p o s s i b l y o t h e r r e i n f o r c i n g additives tend t o decreas the p e s t i c i d e by i n c r e a s i n I t may a p p e a r t h a t t h e p a r t i c l e s i z e o f c a r b o n b l a c k u t i l i z e d i s a s c r i t i c a l a s t h e amount. But fine b l a c k s do n o t r e t a r d o r p r e v e n t d i f f u s i o n t o any g r e a t e r degree than coarse carbon b l a c k s w i t h i n t h e l i m i t s studied. In general, increasing the overall m o l e c u l a r weight and/or d e c r e a s i n g t h e m o l e c u l a r w e i g h t between c r o s s l i n k s w i l l lower t h e d i f f u s i o n c o e f f i c i e n t thus slowing loss r a t e . The s e g m e n t a l m o t i o n o f a p o l y m e r c h a i n i n c r e a s e s as t h e t e m p e r a t u r e r i s e s o r when t h e a m b i e n t t e m p e r a t u r e i s v e r y f a r removed from t h e g l a s s - t r a n s i t i o n t e m p e r a t u r e s (Tg) a n d t h e t e s t t e m p e r a t u r e w o u l d b e much a b o v e i t . V a r i a t i o n i n t h e e n v i r o n m e n t a l t e m p e r a t u r e s (T) a l t e r s t h e m a g n i t u d e o f t h e d i f f e r e n c e , Τ - Tg. Two d i s t i n c t v o l u m e f r a c t i o n s m u s t b e c o n s i d e r e d i n a thorough study. One c o n s i s t s o f t h e v o l u m e f r a c t i o n o f t h e rubber i n t h e s w o l l e n s t a t e , a r i s i n g from pesticide incorporation. T h i s volume f r a c t i o n reflects the o r i g i n a l concentration of the pesticide. The o t h e r f r a c t i o n c o n s i s t s o f t h a t v o l u m e o f r u b b e r containing the carbon black a d d i t i v e . The v a r i a t i o n o f t h e a b o v e p a r a m e t e r s i s n o t entirely linear. However, f o r s i m p l i c i t y and t h e narrow l i m i t s o f v a r i a t i o n e n v i s i o n e d , the assumption o f l i n e a r i t y appears t o be j u s t i f i a b l e . Serious departures from l i n e a r i t y a r e covered i n t h i s t r e a t ment by a p p r o x i m a t e c o r r e c t i o n factors. P r o p e r t i e s such as c r y s t a l l i n i t y , diffusant geometry, m o l e c u l a r weight o f t h e s t a r t i n g elastomer, and i n t e r a c t i o n s b e t w e e n a d d i t i v e s a r e n o t c o n s i d e r e d at t h i s time. Thus i t i s n e c e s s a r y t o h a v e a r e f e r ence f o r m u l a t i o n . B a s e d upon d i f f u s i o n d a t a o b t a i n e d w i t h t h e r e f e r e n c e m a t e r i a l , new f o r m u l a t i o n s c a n b e 8

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

62

CONTROLLED RELEASE PESTICIDES

designed

t o provide a predicted release rate.

Theoretical

Treatment

The f o l l o w i n g e q u a t i o n s , u s e d previously derived:

h e r e i n , have been

8

(1)

D

F

= (2/3-V ) £ D r

[<X-d

(V -V )] s

s

(2)

D

F

= D

Q

where:

2

+rt(T -T ) 2

g

g

- ( T - T )] X

-

U

( Τ χ - Τ )]

-

K+

(bc

1

D

c

c

l

(dc -dc ) 2

2

(d -d

s

s

2

+ri(T -T )

q

= final diffusion coefficient. Subscripts 1 a n d 2 r e p r e s e n t t h e e q u a t i o n number. D = original diffusion coefficient V = volume f r a c t i o n o f rubber i n t h e carbon black f i l l e d formulation. V , V = two d i f f e r e n t volume f r a c t i o n s o f ^ t h e p e s t i c i d e - polymer composite. 1' 2 d i f f e r e n t environmental temperatures. Τ , Τ = g l a s s t r a n s i t i o n temperatures o f 1 Ζ t h e two polymers. o( = c r o s s - l i n k i n g d e n s i t y c o e f f i c i e n t . = carbon b l a c k content c o e f f i c i e n t . y = temperature c o e f f i c i e n t . tf = s l o p e o f t h e c u r v e oCversus V . F

Q

r

s

Τ

g o

T

=

t

w

o

g

Experimental

Models

In order t o v a l i d a t e t h e t h e o r e t i c a l equations t h r e e groups o f m a t e r i a l s were examined. Three standard controlled release molluscicides i n a chlorop r e n e m a t r i x a r e shown i n t a b l e I , a l o n g w i t h a c o n t r o l ? s e r i e s AA c o m p o u n d s c o n s i s t i n g o n l y o f a n e l a s t o m e r a n d a p e r o x i d e c u r a t i v e ; a n d s e r i e s EB n a t u r a l r u b b e r compounds w h e r e i n t h e t y p e a n d q u a l i t y o f carbon b l a c k were s t u d i e d .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

CARDARELLI AND KANAKKANATT

Matrix

63

Factors

TABLE I STANDARD M O L L U S C I C I D E FORMULATIONS ( C u r e d a t 300°F f o r 60 m i n u t e s ) Recipe (by p a r t s p e r h u n d r e d p a r t s e l a s t o m e r ) Ingredient CBL-49A CBL-3A CBL-4 PDL-1 Chloroprene"** Zinc Oxide Magnesium o x i d e FEF B l a c k HAF B l a c k PBNA MBT Laurie Acid TBTO TBTF DS649 2

100 5 4 14

100 5 4 14

100 5 4 14

1

1 1

1

100 5 4 15 1

3

4

5

6

δ

—

7

.

8

10

———

TABLE I I S E R I E S AA COMPOUNDS ( C u r e d a t 300°F f o r 50 m i n u t e s ) Recipe (by p a r t s p e r h u n d r e d p a r t s r u b b e r ) Ingredient AA-002 AA-003 AA-- 0 0 1 9 Polybutadiene N a t u r a l Rubber Butyl Rubber Styrene-butadiene Copolymer C h l o r o p r e n e 12 N i t r i l e R u b b e r 13

100 100

———

100

,

1 0

1 1

ί

AA-004

Polybutadiene^ N a t u r a l Rubber Butyl Rubber Styrene-butadiene Copolymer Chloroprene N i t r i l e R u b b e r 13

AA-005

AA-006

1 0

100

1 1

1 2

100

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

100

64

CONTROLLED RELEASE

TABLE I I I S E R I E S EB COMPOUNDS ( C u r e d a t 300°F f o r 5 m i n u t e s ) Recipe Ingredient (by p a r t s p e r h u n d r e d p a r t s CB-001 EB-001 Natural DICUP HCCB 15 FEF MT ^

Rubber

100

1 4

1.6

PESTICIDES

rubber) EB-002

100 1.6

100 1.6

EB-004

EB-005

1

EB-003 N a t u r a l Rubber DICUP HCCB 5 FEF MT 1 4

10 1.6

1

1.6 14

1.6

14

1 6

14

Notes 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

N e o p r e n e WRT C a r b o n b l a c k , 79 mMaverage particle size C a r b o n b l a c k 40 t o 45 mMaverage particle size Pheny1-B-naphthylamine Mercaptobenzothiazole bis(tri-n-butyltin) oxide Tributyltin fluoride 3,3,4,4, t e t r a c h l o r o t e t r a h y d r o t h i o p h e n e p y r i d i n e 1,1-dioxide Polybutadiene Butyl rubber S t y r e n e - b u t a d i e n e c o p o l y m e r (SBR P l i o f l e x ) N e o p r e n e WRT N i t r i l e rubber Dicumyl peroxide C a r b o n b l a c k , 15 i t j ^ i . a v e r a g e p a r t i c l e s i z e C a r b o n b l a c k , 256 n u * c a v e r a g e p a r t i c l e s i z e

Release Rate

Study

S p e c i m e n s o f t h e s t a n d a r d m o l l u s c i c i d e compounds w e r e c u t f r o m c u r e d s h e e t s a t 2.5 χ 2.5 χ 0.15 cm, w a s h e d i n d i s t i l l e d w a t e r a n d s u s p e n d e d i n 400 m l o f water. Samples were m e c h a n i c a l l y shaken a t a c o n s t a n t rate throughout the experiment. I m m e r s i o n w a t e r was e v a p o r a t e d t o c o n c e n t r a t e t h e a g e n t and t h e amount o f p e s t i c i d e released determined a n a l y t i c a l l y .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

CARDARELLI AND KANAKKANATT

Matrix

Factors

65

Diffusion Coefficient Determination The d i f f u s i o n c o e f f i c i e n t s f o r t h e AA a n d EB S e r i e s were d e t e r m i n e d by b o t h s o r p t i o n and d e s o r p t i o n techniques. I n t h e former method the sample i s immersed i n t h e s o r p t i n g l i q u i d and w e i g h t g a i n n o t e d at regular time i n t e r v a l s . The l a t t e r t e c h n i q u e c o n s i s t e d of p r e s w e l l i n g the specimen t o e q u i l i b r i u m , r e m o v i n g f r o m t h e l i q u i d medium and p e r i o d i c a l l y n o t i n g w e i g h t l o s s a s a c o n t i n u o u s a i r s t r e a m was passed over the surface. In a c o r r e l a r y study swollen t e s t specimens were exposed a t v a r y i n g t e m p e r a t u r e s i n a l o w vacuum oven and w e i g h t l o s s d e t e r m i n e d . R e s u l t s and

Discussio

I t i s a p p a r e n t f r o m t h e r e s u l t s shown i n T a b l e t h a t the presence of extremely hydrophobic agents (TBTO a n d TBTF) r e d u c e w a t e r a b s o r p t i o n w h e r e a s C B L - 4 9 A c o n t a i n i n g a h y d r o p h i l l i c a g e n t (DS649) r e s u l t e d i n an i n c r e a s e d w a t e r a b s o r p t i o n r a t e .

IV

9

TABLE I V D I F F U S I O N C O E F F I C I E N T DETERMINATION BY WATER ABSORPTION

Material

Molluscicide

Type

Diffusion Coefficient

cmVsec CBL-49A PDL-1 CBL-4 CBL-3A

DS-649 None TBTO TBTF

hydrophillic hydrophobic hydrophobic

2. 5. 0 χ 9. 4 χ 4.0 χ

-8 -9 10 -10 10 10 -10

In the study of the e f f e c t of the glass t r a n s i t i o n t e m p e r a t u r e (Tg) o n t h e d i f f u s i o n c o e f f i c i e n t , ( s e e T a b l e V ) , n - d e c a n e was u s e d a s t h e d e s o r b i n g liquid. The d e c r e a s e i n d i f f u s i o n c o e f f i c i e n t w i t h i n c r e a s i n g Tg i s c o n s i s t e n t w i t h t h e known t h e o r i e s o f diffusion. The d e p e n d e n c e o f D o n Tg c a n b e g e n e r a l l y r e p r e s e n t e d by use o f t h e d i f f e r e n c e between Τ ( t e s t t e m p e r a t u r e ) and Tg. Thus t h e e f f e c t o f e n v i r o n m e n t a l temperature v a r i a t i o n i s incorporated i n the governing e q u a t i o n s b y u s e o f t h e T-Tg parameter.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

66

C O N T R O L L E D R E L E A S E PESTICIDES

TABLE V E F F E C T OF GLASS T R A N S I T I O N TEMPERATURE ON D I F F U S I O N C O E F F I C I E N T

Material

Matrix

Diffusion Coefficient 2/

Tg(°C)

c

AA- 0 0 1 AA- 002 AA- 0 0 3 AA- 004 AA- 005 AA- 006

s

e

c

7

6.6 χ 1 0 " 2.99 χ 1 0 " 1.3 χ 1 0 ~ 1.27 χ 10""" 0.5 χ 1 0 " 0.1 χ 10

-109 -70 -65 -61 -49 -24

Polybutadiene N a t u r a l Rubber B u t y l Rubber Styrene-butadiene Chloroprene Nitrile

m

7

7

7

7

7

The e f f e c t s o f c o n t e n t a r e d e p i c t e d i n T a b l e V I . Two t r e n d s a r e apparent: (1) D i f f u s i o n c o e f f i c i e n t i n c r e a s e s w i t h r i s i n g t e m p e r a t u r e , a n d (2) i n c r e a s i n g c a r b o n b l a c k c o n t e n t d e c r e a s e s D. Carbon b l a c k p a r t i c l e s i z e i s seemingly unimportant t o n-decane d i f f u s i o n . 9

TABLE V I E F F E C T OF TEST TEMPERATURE AND CARBON BLACK CONTENT ON D I F F U S I O N C O E F F I C I E N T I N NATURAL RUBBER Carbon Black Content (pphr)

Material

CB-001 EB-001 EB-002 EB-003 EB-004 EB-005

0 4 8 14 14 14

Particle S i z e , nm —

79 79 79 15 256

Diffusion Coefficient (10~6 c m / s e c ) 26°C 46°C 70°C 90°C 2

3.08 2.20 1.91 1.82 1.86 1.70

4.02 3.10 2.70 2.31 2.25 2.10

5.42 4.35 3.80 3.11 2.99 2.81

7.00 5.90 4.96 3.98 3.66 3.33

The m o l e c u l a r w e i g h t s o f t h e c h a i n s e g m e n t s between c r o s s l i n k s , M , have been d e t e r m i n e d by t h e e q u i l i b r i u m s w e l l i n g method. Figure 1 depicts the dependence o f t h e d i f f u s i o n c o e f f i c i e n t on t e m p e r a t u r e and M . D i s p l o t t e d a g a i n s t T-Tg f o r m a t r i c e s o f varying M . The d i f f u s i o n c o e f f i c i e n t i n c r e a s e s a s T-Tg a n d Mc i n c r e a s e . c

c

c

Computer

Analysis

A computer a s s i s t e d

analysis

o f equations

(1) a n d

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

CARDARELLI AND ΚΑΝΑΚΚΑΝΑΤΓ

Matrix

FactOTS

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

67

68

C O N T R O L L E D R E L E A S E PESTICIDES

( 2 ) was u n d e r t a k e n . C o m p l e t e t r e a t m e n t o f a l l 13 v a r i a b l e s was n o t p o s s i b l e ; s o s e v e r a l w e r e h e l d constant. They were: Do

=

Ï

- c2

ck = ci

=

s$

=

C

3

C

4

C

5

The f o l l o w i n g s i n g l e were h a n d l e d as shown V

r

=

X

l -• (T (Tl-

< 2" T g ) T

2

2

- Vs

dc

2

- dc^ = X

bc

2

- bc^ = X

Y

(4)

Y

±

2

= 2/3-Χχ = C

X

=

x2

(1) a n d ( 2 ) r e d u c e t o (3) a n d ( 4 )

Thus e q u a t i o n s respectively: (3)

)

= X

Vs

x

T g i

(C

x

+ C X ) - (C + C X )

+ C X - (C 2

2

3

2

+

3

C4X3)

X

4

4

3

- C X 5

X

4

5

where Y r e p r e s e n t s Df A c o m p l e t e p r o g r a m was c o m p o s e d t o p l o t c u r v e s f o r e q u a t i o n s (3) a n d ( 4 ) w h e r e i n Χ χ , X , X 3 , X a n d X 5 were v a r i e d one a t a t i m e . A few o f t h e hundreds of completed p l o t s a r e presented. The e f f e c t s o f d i f f u s a n t c o n c e n t r a t i o n , temper a t u r e and carbon b l a c k content a r e i l l u s t r a t e d i n f i g u r e s 2 a n d 3. I n f i g u r e 2 , i t i s e v i d e n t t h a t t h e d i f f u s i o n c o e f f i c i e n t , Υ χ, i n c r e a s e s a s t h e d i f f u s a n t concentration, r e f l e c t e d b y X-j, i n c r e a s e s . Also Υχ r i s e s as X , which r e f l e c t s h i g h e r ambient temperature, a lower Tg, o r both, i n c r e a s e s . A s i m i l a r trend i s n o t e d i n f i g u r e 3. By c o m p a r i n g f i g u r e s 2 a n d 3 i t i s evident that increasing the carbon black content reduces the d i f f u s i o n c o e f f i c i e n t ; i . e . , i n f i g u r e 3 2

4

1 0

2

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CARDARELLI AND

KANAKKANATT

Matrix

Factors

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICIDES

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CARDARELLI AND

KANAKKANATT

Matrix

Factors

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

72

C O N T R O L L E D R E L E A S E PESTICIDES

Χχ = 1 i n d i c a t e s n o c a r b o n b l a c k a n d i n f i g u r e 2, Χχ = 0.2 means a n 8 0 % b l a c k c o n t e n t . The e f f e c t o f c r o s s l i n k d e n s i t y i s c l e a r l y s e e n b y c o m p a r i n g f i g u r e s 2 a n d 4. N o t e t h a t t h e s u p p r e s s i o n o f D i s more p r o n o u n c e d a t l o w e r t e m p e r a t u r e and lower d i f f u s a n t concentrations. At higher values o f these v a r i a b l e s , D i s r e l a t i v e l y unaffected—even with a fourfold increase i n crosslink density. Conclusions B o t h e x p e r i m e n t a l and computer methods o f t e s t i n g the v a l i d i t y o f equations (1) a n d (2) i n d i c a t e t h a t they a r e adequate f o r p r e d i c t i o n o f t h e d i f f u s i o n c o e f f i c i e n t and r e l e a s Although several variable d e r i v e d e q u a t i o n s have a d e f i n i t e e f f e c t on r e l e a s e r a t e , t h e e q u a t i o n s and computer drawn c u r v e s c a n be used as guides t o d e s i g n f o r m u l a t i o n s w i t h t h e appropriate release rates f o ra particular applica tion.

Abstract D i f f u s i o n c o n t r o l l e d r e l e a s e of the a c t i v e agent is effectively used t o deliver a p e s t i c i d e from elastomeric matrices t o the i n s e c t h a b i t a t . The r a t e of r e l e a s e is i n f l u e n c e d by the nature of the elastomer as w e l l as the c o n d i t i o n s of the environ ment. Some o f these i n f l u e n c i n g f a c t o r s are consid ered and equations t o estimate the diffusion coeffi cient are derived. A computer e v a l u a t i o n o f these equations is attempted. Literature Cited 1. 2. 3. 4. 5. 6.

P a u l , D. R., and H a r r i s , F. W., eds, C o n t r o l l e d Release Polymeric Formulations, ACS Symp. Ser. 33, ACS, Wash., D.C., 1976. C a r d a r e l l i , N. F., " C o n t r o l l e d Release P e s t i c i d e s Formulations," CRC Press, Cleveland, OH, 1976. H i g a c h i , I . , Mechanisms of Sustained A c t i o n Medication, J . Pharm. Sci. 52, 1145, 1963. C o l l i n s , R. L., A T h e o r e t i c a l Foundation For Slow Release, Proc. C o n t r o l l e d Release P e s t i c i d e Symp., Rep. 9, Univ. Akron, Akron, OH, Sept. 16-18, 1974. C a r d a r e l l i , N. F. and Caprette, S. J., A n t i f o u l i n g Covering, U.S. Patent 3,426,473, 1969. C a r d a r e l l i , N. F. and Neff, H. F., Biocidal Elastomeric Compositions, U.S. Patent 3,639,583,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6.

C A R D A R E L L I AND

KANAKKANATT

Matrix

Factors

73

1972. C a r d a r e l l i , N. F., B i o c i d a l Elastomeric Composit i o n and Method f o r D i s p e r s i n g P e s t i c i d e s Therew i t h , U.S. Patent 3,851,053, 1974. 8. Kanakkanatt, S. V., The E f f e c t of Matrix P r o p e r t i e s on the D i f f u s i o n C o e f f i c i e n t of L i q u i d s Through Rubber, Macromol. Reprint, 1, 614, 1971. 9. Kanakkanatt, S. V., Schistosomiasis C o n t r o l By Slow Release M o l l u s c i c i d e s , Product Development Lab., Univ. Akron, Report to World Health Organization (Unpub.), Sept. 15, 1972. 10. Kanakkanatt, S. V., Influence of Formulation P r o p e r t i e s on the D i f f u s i o n - D i s s o l u t i o n Mechanism, Proc. C o n t r o l l e d Release P e s t i c i d e Symp. 8.42, Univ. Akron, Akron 7.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7 Encapsulation of Pesticides within a Starch Matrix W. M. DOANE, B. S. SHASHA, and C. R. RUSSELL Northern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Peoria, Ill. 61604

At the Northern Regional Research Center, a research program i s directed towards developing agriculturally based raw materials as renewable resources for chemicals to replace in part those derived from petroleum. Starch, a polysaccharide produced i n great abundance i n nature, i s a prime candidate as a raw material because ofitsavailability and relatively low cost and because it can be converted readily into a variety of useful monomeric and polymeric products by chemical and biochemical means. A low-cost derivative, starch xanthate, is usefulinpapermaking applications (1), for reinforcement of rubber (2),inmaking powdered rubber (3), and for removing heavy metals from polluted water (4). Because of the ease with which starch xanthate can be insolubilized from an aqueous solution by crosslinking under mild oxidation conditions or with metal cations, and because of the film-forming nature of certain crosslinked products, we explored the possibility of using this material as an encapsulating matrix for pesticides. We envisioned that release of a lipophilic pesticidal chemical from a hydrophilic but water-insolublestarch matrix would be slow and could be controlled to a considerable degree by simple modifications. Such a matrix would have an added advantage of being biodegradable and thus would leave no residue in the environment. A preliminary report (5) described our f i r s t attempts to u t i l i z e oxidatively coupled starch xanthate (xanthide) as a slow-release matrix for pesticides and suggested that such a system was worthy of further research i n attempts to optimize release characteristics. We now wish to report the results of our further studies and data from preliminary f i e l d tests with selected formulations.

74 In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DOANE ET

AL.

Encapsulation

within

a Starch

Matrix

75

The procedure based on starch xanthate consists of dispersing the active agent i n an aqueous starch xanthate solution and subsequently crosslinking the starch xanthate either oxidatively, or with multivalent metal ions, or with difunctional reagents such as epichlorohydrin. Cereal f l o u r s , which contain about 101 protein along with starch, also can be xanthated and used as an encapsulating matrix. Upon crosslinking, which i s effected w i t h i n a few seconds under ambient conditions, the entire mass becomes g e l l i k e and, on continued mixing f o r an additional few seconds, becomes a particulate s o l i d which can be dried to low moisture content with only minimal or no loss of the entrapped chemical. That only a single phase i s produced on crosslinking with no supernatant i s important i assurin essentiall complete entrapment of bot p e s t i c i d a l chemicals. Other polymers can be incorporated readily into the products as a means to modify release properties. Polymers l i k e polystyrene, polyethylene, and poly(vinyl chloride) are j u s t dissolved i n a small amount of an appropriate solvent such as benzene or acetone then added to the xanthate solution. Poly (styrene-butadiene), comnercially provided as a latex, i s conveniently added i n t h i s form. li>on crosslinking the xanthate, the other polymers are entrapped along with the active agents. Another modification e a s i l y made which can modify release properties provides products which are doubly encapsulated. This i s achieved on addition of more starch xanthate, either alone or containing another polymer, after the i n i t i a l crosslinking reaction has been effected and then adding additional crosslinking agent. The starch xanthate used f o r encapsulation i s prepared under ambient conditions by treating a water suspension of starch with carbon d i s u l f i d e and an a l k a l i metal hydroxide. Typically about 701 of the carbon d i s u l f i d e i s converted to xanthate within 30 minutes with l i t t l e or no additional conversion occurring on prolonged standing. Although the theoretical number of xanthate groups possible for each anhydroglucose repeating u n i t of starch i s 3 [degree of substitution (DS) of 3 ] , we f i n d that a DS of 0 . 1 to 0 . 3 5 i s s u f f i c i e n t . V i s c o s i t y of xanthate solutions increases proportionally with DS and starch xanthate concentration. When whole unmodified starch (regular pearl starch) i s used as the starting material, a starch xanthate concentration of near 151 i s about the maximum that can be handled for the encapsulation process. Higher concentrations, usable i n t h i s process, of up to nearly 601 can be achieved, i f the starting starch i s reduced i n molecular size by hydrolysis of some of the glucopyranosyl linkages with acids or enzymes.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

76

C O N T R O L L E D R E L E A S E PESTICIDES

Such modifications are conventional commercial procedures designed to provide degraded starch products for a variety of i n d u s t r i a l uses. Use of the more concentrated starch xanthate solutions has an obvious advantage i n cost for drying the particulate encapsulated product. However, there are c e r t a i n l i m i t a t i o n s on using the highly concentrated solutions. The amount of active agent that can be e f f e c t i v e l y encapsulated within the crosslinked starch xanthate matrix i s inversely proportional to starch xanthate concentration. For example, when starch xanthate of 1 4 1 concentration i s used, a f i n a l product i s obtained which contains a maximum of 471 of a l i q u i d thiocarbamate. When 501 xanthate i s employed the maximum i s reduced to 1 3 1 . The values conceivabl might with th natur f the chemical to be encapsulated the active agent was butylate (S-ethy diisobutylthiocarbamate) At the highest l e v e l , where the particulate product consists of nearly 501 of the highly v o l a t i l e l i q u i d butylate, the p a r t i c l e s have a wetted appearance and are not completely free flowing. At about 401 or l e s s , they appear dry and give a free-flowing product. Although various methods have been employed for crosslinking the xanthate with apparently s i m i l a r r e s u l t s , we have worked mostly with the oxidative method and have used either nitrous acid or hydrogen peroxide as the selected oxidant. Both oxidants e f f e c t i v e l y crosslink the xanthate S S to xanthide (starch-O-C-S-S-C-0-starch) at a pH of 4 to 5. Since the xanthate i s made under a l k a l i n e conditions, the pH must be lowered to allow crosslinking. For pesticides, which are l a b i l e to a l k a l i , the pH can be adjusted to near n e u t r a l i t y before addition of the active agent. For the nitrous acid system, sodium n i t r i t e i s added to the alkaline xanthate solution and becomes the active oxidant when the pH i s lowered to 4-5. When peroxide i s used, i t i s added to a neutralized xanthate and then pH i s lowered further. Only s l i g h t l y more than stoichiometric amounts of oxidant are required, and since the oxidation proceeds to completion rapidly, even active agents which are susceptible to oxidation are not l i k e l y to be oxidized during encapsulation. Although * This paper reports the r e s u l t s of research only. Mention of a pesticide i n t h i s paper does not constitute a reconmendation for use by the U.S. Department of Agriculture nor does i t imply r e g i s t r a t i o n under FIFRA as amended. Also, mention of f i r m names does not constitute an endorsement by the U.S. Department of Agriculture over other firms not mentioned.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DO A N E E T A L .

Encapsulation

within a Starch

Matrix

77

both oxidants appear to work equally w e l l i n crosslinking the xanthate, encapsulated products are quite different i n appearance and i n release properties of the active agent. Nitrous acid crosslinked products contain numerous microscopic openings i n the matrix, due apparently to small amounts of nitrous oxide gas generated during the reaction. These openings result i n a r e l a t i v e l y rapid rate o f release as w i l l be described l a t e r . The peroxide-coupled products are without v i s i b l e openings and provide much slower release of active agent. Shelf l i f e of the starch-encapsulated pesticides i s good, and there i s no appreciable loss on storage i n closed containers during 1 year. When placed i n open containers for several days, loss of v o l a t i l e agent i s n e g l i g i b l e However, when products ar active agent i s then release simple laboratory screening test for comparing release properties of thiocarbamate- containing products to assist i n selection of formulations f o r subsequent bioassay. The test consists of placing several 1-gram portions of a product i n watch glasses placed i n a hood and applying to each 2-ml of water. The water slowly evaporates during a 24-hour period i n the hood. Then water i s again added and the wetted product again allowed to stand f o r 24 hours. This repeated wetting and drying i s continued for the duration o f the test with entire 1-gram samples being removed p e r i o d i c a l l y and analyzed f o r t o t a l nitrogen content i n those instances where the active agent contains nitrogen. Table I shows the release characteristics f o r four different formulations containing butylate. Table I Release Properties of Butylate Formulations Loss of butylate, % Xanthate b a s e

1 day

a

A c i d - m o d i f i e d flour* Acid-modified flours t a r c h mixture Starch S t a r c h + 201 l a t e x None ( c o n t r o l )

3

2 days

8 days

29

58

68

20 0 0 68

36 0 0 98

48 8 37 100

^ Xanthate DS was 0.35 and double encapsulation was used f o r each. NalC^ used f o r oxidation. E,0~ used f o r oxidation.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICrDES

78

I t would appear that either the protein component i n the f l o u r or the lower molecular weight of the starch component of the f l o u r contributes to a faster release of butylate; however, t h i s remains to be confirmed. Other preliminary tests indicate that DS of xanthate, e.g., crosslink density of the matrix, may play a s i g n i f i c a n t role i n controlling release of active agent, and studies to confirm t h i s are underway. Depending on the amount of shear placed on the p a r t i c u l a t e product before drying, a range of p a r t i c l e sizes can r e s u l t . With simple hand mixing, a p a r t i c l e size of 14 mesh or larger i s t y p i c a l l y obtained. For small laboratory preparations, we shear the wet product i n a Waring Blendor for a few seconds to produce smaller p a r t i c l e sizes. We have not as ye enough to pass 100 mesh products can y i e l d f i n e powders but considerable amounts of pesticide are l o s t , especially i f they are highly v o l a t i l e ones. Whereas shearing of the wet product results mostly i n breaking up the agglomerates composed of several smaller p a r t i c l e s , grinding or m i l l i n g of dry products disrupts the matrix encapsulating the pesticide. A product prepared from starch xanthate of DS 0.175 and crosslinked with r^C^ i n the presence of EPTC (S-ethyl dipropyl thiocarbamate) was dried and separated into four fractions by sieving. The four fractions were analyzed for active agent content and loss of agent a f t e r treatment with water for 2 days. Results are shown i n Table I I . Table I I Properties of Starch Xanthide-EPTC Formulations as Related to P a r t i c l e Size

Mesh size

ξ of Total

>60 30-60 14-30 <14

5 10 70 15

EPTC, % 14.0 21.7 21.7 21.7

Loss of EPTC a f t e r water treatment, % of t o t a l 14 17 5 5

Except f o r the 51 f r a c t i o n which passed 60 mesh, there was no difference i n the amount of pesticide contained i n the p a r t i c l e s of various sizes. I t does appear that smaller size p a r t i c l e s release EPTC at a faster rate.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DO A N E

ET AL.

Encapsulation

within

a Starch

Matrix

79

Some of the formulations we have prepared have been evaluated by others i n various laboratory bioassay tests and, i n one instance, i n replicated f i e l d p l o t s . Although the data obtained are encouraging and indicate considerable promise for the starch technology, i t should be understood that the data are preliminary and that the formulations tested are by no means the optimum formulations that can be developed. That the release properties of various pesticides from the crosslinked starch or f l o u r xanthate matrix can be considerably improved through minor modifications i n the encapsulation process i s strongly supported by our continuing research. Feldmesser et a l . (6) reported on laboratory evaluations of starch xanthide formulations of DBCP (l,2-dibromo-3chloropropane), a nematicide (2-isopropyl-6-methyl-4-pyrimidinyl insecticide-nematicide f o r nematicidal a c t i v i t y . Two DBCP formulations containing 35.61 and 42.01 active agent and two diazinon ones containing 42.0 and 43.61 active were studied. To determine retention o f active agent under various conditions, the products were aerated both wet and dry i n open dishes for several days and then amount retained was determined by bioassays against nematodes i n a standard i n v i t r o test. During 10 days aeration of wet DBCP formulations, most of the active agent was l o s t and t h e i r subsequent effectiveness for k i l l i n g nematodes was minimal. Retention of diazinon was considerably greater, perhaps due to i t s much lower vapor pressure than DBCP. During the 10-day aeration tests and an additional 34 days o f aeration i n the dry, the two diazinon formulations l o s t only about 20-331 o f t h e i r active ingredient. The mortality o f Panagrellus rediviuus, a saprophagous nematode, after 48 hours exposure to 200 ppm diazinon i n the form of the two starch xanthide formulations a f t e r various periods of aeration i s shown i n Table I I I . Cooperative work i s continuing between Feldmesser's and our Laboratories i n attempts to develop formulations capable of e f f e c t i v e l y k i l l i n g nematodes over an extended period. Whereas many herbicides must be incorporated i n the s o i l soon a f t e r application to the surface to prevent extensive losses due to v o l a t i l i z a t i o n or decomposition by sunlight, i t i s hoped that controlled release formulations may prolong the time before incorporation i s needed, or i d e a l l y , to provide control without being incorporated. Four formulations containing butylate prepared by us were evaluated i n the laboratory by Stauffer Chemical Company for the a b i l i t y to delay time before incorporation. Butylate as an emulsifiable concentrate (EC) was applied as a control. Rates of active agent (ai) o f 3 and 4 lb/A were applied. Formulations were placed on the surface o f wet s o i l and incorporated immediately and a f t e r 24 hours. Results are shown i n Tables IV and V.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

80

PESTICIDES

Table I I I Release Properties of Starch Xanthide-Diazinon Formulation Percent k i l l 42.01

43.61

10 days

44 days

10 days

69.4 66.2 74.6

63.0 63.1 76.0

76.3 75.4 78.1

81. 76.6 89.0

0 0

77.4 95.1

44 days

Starch-diazinon Wet Dry Uhaerated h

52.5 70.0 74.3

Technical diazinon a

Wet Dry Unaerated h

0 0

Second aeration period o f 34 days following 10 day wet and dry aeration and 48 hours exposure was dry f o r a l l granules. Granules not aerated f o r f i r s t 10 days. Aerated dry f o r 34 days.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DO AN E

ET AL.

Encapsulation

within

a Starch

Matrix

81

Table IV Percent Weed Control by Delayed Incorporation of Butylate Formulations Incorporation Formulation SX-butylateJ? SX-butylate Butylate (EC) c

Rate

0 Hours

3 l b ai/A 3 l b ai/A 3 l b ai/A

80 85 87

24-Hour delay 75 67 10

a Average control of barley f o x t a i l wil k crabgrass, annual ryegrass Starch xanthate of DS 0.3; NaNO was used for crosslinking; about 251 butylate. Same as b except containing 351 butylate. ?

Table V Percent Weed Control by Delayed Incorporation of Butylate Formulations Incorporation Formulation SX-butylate? SX-butylate Butylate (EC)

Rate 4 l b ai/A 4 l b ai/A 4 l b ai/A

0 Hours

24-Hour delay

77 79 82

68 69 28

Starch xanthate of DS 0.3; NaNCL used f o r crosslinking; 25.51 k butylate. Same as a except larger p a r t i c l e s i z e . Although the results are preliminary, a benefit i s seen for the encapsulated products i n allowing a longer time on the s o i l surface before incorporation. Schreiber (7), at Purdue university, recently reported results of greenEbuse and f i e l d tests of two starch xanthideEPTC products. The formulations were made from starch xanthates of DS 0.35, and sodium n i t r i t e was used f o r crosslinking. One formulation contained 141 EPTC and the other was a double-encapsulated product containing 201 latex polymer and 221 EPTC. In the greenhouse, the double-encapsulated product was compared with EPTC applied as the emulsifiable concentrate. The materials were applied to s o i l s at a rate o f 3 lb/A and were incorporated into s o i l s seeded with robust purple foxtail.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

82

C O N T R O L L E D R E L E A S E PESTICIDES

At 31 days after seeding, the plants were removed and weighed and the pots reseeded. This procedure was repeated at 52 and 87 days and the f i n a l harvest was at 120 days. Results are shown i n Table VI. Table VI Weed Control by Starch Xanthide-EPTC Formulation Y i e l d , g/pot Treatment

31 Days

Untreated EPTC (EC) Starch xanthide-EPTC

1.6 0 0

52 Days

87 Days

2.0 0.1 0.01

2.8 2.7 0.4

120 Days 2.2 2.8 3.9

At 31 and 52 days, both the EC and the starch xanthide formulations gave excellent control of f o x t a i l . However, between 52 and 87 days, the EC completely l o s t i t s effectiveness while the starch product s t i l l gave good control. Between 87 and 120 days, the starch product l o s t i t s effectiveness. The greater weight of plant material i n both treated pots over the control i s due to the greater f e r t i l i t y l e v e l remaining i n the s o i l of these pots. In the f i e l d , the EC, single-encapsulated and doubleencapsulated products were applied at active ingredient levels o f 3 and 6 l b ai/A, incorporated, and over seeded with yellow, giant, and giant green f o x t a i l . Natural populations of pigweed, lambsquarter, smartweed, jimson, and velvetleaf were the dominant broadleaf weeds. Forty-seven days after application, weed stand counts and weed weights by species were made on each plot. Results are shown i n Table VII. Table VII Weed Control by Single and Double Encapsulated EPTC Formulations Treatment

a

Untreated EC-EPTC Starch-EPTC (single) Starch-EPTC (double)

Total weed Count

Weight, g

95.3 48.0

924.8 247.8

33.7

186.0

33.0

31.0

A p p l i e d a t a r a t e o f EPTC o f 3 lb/A.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

7.

DOANE E T A L .

Encapsulation

within

a Starch

Matrix

When applied at the 6 l b ai/A l e v e l , excellent control of a l l vegetation was obtained 105 days after treatment with the double-encapsulated formulations. Cooperative work between Schreiber's Laboratory and ours i s continuing with plans made f o r extensive f i e l d testing during 1977. Literature Cited 1. 2. 3. 4. 5. 6. 7.

Hamerstrand, G. E., Carr, M. E., Hofreiter, B. T., and Russell, C. R. Staerke (1976) 28(7):240-243. Buchanan, R. Α., Seckinger, Η. L., Kwolek, W. F., Doane, W. M., and Russell, C. R. J . Elast. Plast. (1976) 8(1):82-95. Abbott, T. P., James C. R. J . Elast. Plast Wing, R. E., Doane, W. Μ., and Russell, C. R. J . Appl. Polym. S c i . (1975) 19(3):847-854. Shasha, B. S., Doane, W. Μ., and Russell, C. R. J . Polym. S c i . , Polym. Lett. Ed. (1976) 14(7):417-420. Feldmesser, J u l i u s , Shasha, B. S., and Doane, W. M. Proceedings 1976 Controlled Release Pesticide Symposium, Akron, Ohio, September 13-15, 1976, pp. 6.18-6.29. Schreiber, Marvin. Efficacy and Persistence o f Starch Encapsulated EPTC. Presented at the Northcentral Weed Control Conference, Omaha, Nebraska, December 7-9, 1976.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8 Controlled Release of Pesticides from Kraft Lignin Carriers H. T. DELLICOLLI Polychemicals Department, Westvaco Corp., N. Charleston, S. C. 29406

C o n s t i t u t i n g par land p l a n t s , lignin is abundant aromatic polymer. In fact, lignin which is exceeded only by cellulose i n abundance, is the pri mary non-petroleum source of the aromatic nucleus in nature. Native lignin, o r lignin as it exists in the living t r e e f o r example, imparts s t r u c t u r a l rigidity to stems of the plant by a c t i n g as a bonding agent between cells. I t a l s o plays a role in decreasing the permeation of water across cell w a l l s i n the vascular system of the tree and imparts r e s i s t a n c e to attack by c e r t a i n microorganisms, presumably because of its phenolic nature. This m a t e r i a l is produced i n nature from the glucosides o f coniferyl and s i n a p y l a l c o h o l s .

The a c t u a l polymerization is proceeded by an en zymatic dehydrogeneration which leads t o a f r e e radical w i t h e l e c t r o n density d e l o c a l i z e d to the phenolic oxygen and carbons 5, 1, and β. According 84

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

D E L L i COLLI

Controlled

Release from Kraft Lignin

Carriers

85

to Nimz (1) random coupling through each of these r e a c t i v e s i t e s leads to a n a t u r a l m a t e r i a l with a s t a t i s t i c a l d i s t r i b u t i o n of at l e a s t ten d i f f e r e n t types of bonds. Kraft Lignin The form of k r a f t l i g n i n to be discussed i n the f o l l o w i n g pages however, i s not the n a t i v e l i g n i n described above, but a product of the k r a f t pulping process. Here, the l i g n i n i n the wood i s s o l u b i l i z e d during the pulping process by p a r t i c l e depolymerizat i o n and i n c o r p o r a t i o n of a s o l u b i l i z i n g group to allow separation of l i g n i n and hemicellulose from the cellulose fibers. Technical k r a f which i s s o l u b l e i n very a l k a l i n e aqueous s o l u t i o n s such as k r a f t pulping l i q u o r s , but h i g h l y i n s o l u b l e i n n e u t r a l or a c i d i c media. This i s i n contrast to the l i g n o s u l f o n a t e s i s o l a t e d as by-products of the s u l f i t e pulping process which are s o l u b l e under n e u t r a l and moderately a c i d i c c o n d i t i o n s . Both s u l f i t e l i g n i n s and sulfonated k r a f t l i g n i n s are used e x t e n s i v e l y i n the a g r i c u l t u r a l chemical indus t r y as a n i o n i c dispersants. They, j u s t to name a few, have the f a m i l i a r Marasperse, Maracarb, (American Can - s u l f i t e ) , REAX and POLYFON (Westvacosulfonated k r a f t ) tradenames. The p h y s i c a l chemistry of k r a f t l i g n i n i s to say the l e a s t , a nebulous area, a s i t u a t i o n due i n part to the random and not yet f u l l y understood mode of i n v i v o synthesis of the parent n a t i v e l i g n i n , the s t a t i s t i c a l d i s t r i b u t i o n of i t s f u n c t i o n a l i t y and the changes i n i t s s t r u c t u r e and composition which take place during the pulping process. C u r r e n t l y a v a i l a b l e data (2,3,4) i n d i c a t e that aside from s o l u b i l i t y i n a l k a l i n e s o l u t i o n s as w e l l as many p o l a r organic s o l v e n t s , t e c h n i c a l k r a f t l i g n i n has an i n t r i n s i c v i s c o s i t y {η}= 6 ml/g. Other hydrodynamic data such as d i f f u s i o n and sedimentation c o e f f i c i e n t s suggest a roughly s p h e r i c a l shape f o r the d i s s o l v e d macromolecule. Number average molec u l a r weights are 1600 and 1050 f o r pine and hardwood l i g n i n r e s p e c t i v e l y . This m a t e r i a l i s moderately polydisperse, Mw/Mn = 2.2 f o r pine and 2.8 f o r hard wood ( 5 ).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICIDES

86

K r a f t L i g n i n as a C a r r i e r Pesticide

f o r C o n t r o l l e d Release

K r a f t l i g n i n appears t o have s e v e r a l advantages over p e t r o c h e m i c a l based polymers as a p o t e n t i a l c a r r i e r system f o r p e s t i c i d e s . The a r o m a t i c n a t u r e of l i g n i n makes i t an e x c e l l e n t p r o t e c t i v e m a t r i x for b i o l o g i c a l l y active materials s e n s i t i v e t o d e g r a d a t i v e p r o c e s s e s i n i t i a t e d by u l t r a v i o l e t r a d i a t i o n from s u n l i g h t . Secondly, the a n t i o x i d a n t p r o p e r t i e s o f l i g n i n would add f u r t h e r s t a b i l i t y t o the c h e m i c a l l y unstable p e s t i c i d e s , a c h a r a c t e r i s t i c o f many o f t h e n o n - p e r s i s t a n t a g e n t s i n u s e t o d a y or b e i n g developed f o r f u t u r e u s e . L i g n i n i s b i o degradable, a f a c t o and u n d o u b t e d l y f u t u r t r o l makes t h i s n a t u r a l p o l y m e r h i g h l y d e s i r a b l e a s a carrier. In the s o i l , l i g n i n i s m i c r o b i a l l y deg r a d e d by s e v e r a l m i c r o o r g a n i s m s s u c h a s t h e w h i t e rot f u n g i belonging t o t h e f a m i l y Basidomycetes t o p r e c u r s o r s o f humus, o n e o f t h e f e w n a t u r a l s u b s t a n c e s c o n s i d e r e d more u b i q u i t o u s t h a n l i g n i n i t s e l f . S e v e r a l o f t h e pathways o f t h e d e g r a d a t i o n o f l i g n i n b y m i c r o f l o r a i n t o humus w e r e r e v i e w e d a n d d e s c r i b e d by C h r i s t m a n a n d O g l e s b y ( 6 ) . a f t e r a l l has been s a i d and done about t h e p e r formance o f c o n t r o l l e d r e l e a s e systems i n the l a b o r a t o r y o r i n t h e greenhouse, t h e d e l i v e r y system itself must be c a p a b l e o f b e i n g e c o n o m i c a l l y c o n v e r t e d t o a s t a b l e and u s a b l e f o r m u l a t i o n w h i c h c a n be u t i l i z e d by i t s i n t e n d e d u s e r , t h e f a r m e r . I f these forms or f o r m u l a t i o n s a r e s i m i l a r t o t h e c u r r e n t l y used systems such as e m u l s i f i a b l e c o n c e n t r a t e s , w e t t a b l e powders, o r g r a n u l e s , t h e c o n t r o l l e d r e l e a s e f o r m u l a t i o n w i l l a p p e a r l e s s a l i e n t o t h e f a r m e r and a c c e p t ance by t h e u s e r w i l l o c c u r sooner t h a n i f t h e system r e q u i r e d a major change i n a p p l i c a t i o n p r a c t i c e . In l i g h t of the reeducation necessary f o r c o n t r o l l e d r e l e a s e s y s t e m s t o g a i n g e n e r a l a c c e p t a n c e , any f a c t o r w h i c h w i l l make t h i s c o n c e p t a p p e a r l e s s a l i e n w i l l h a s t e n t h e a p p e a r a n c e o f t h e t i m e when t h e d e l i v e r y s y s t e m w i l l f i n d common u s e . To t h i s e n d , many l i g n i n / p e s t i c i d e s y s t e m s h a v e the c a p a b i l i t y of being converted t o f o r m u l a t i o n s s u c h a s t h o s e d e s c r i b e d a b o v e i n t h e same e q u i p m e n t now u s e d t o p r o d u c e c o n v e n t i o n a l f o r m u l a t i o n s o f t h e t h e s e p e s t i c i d e s . F o r example, w e t t a b l e powders have been p r e p a r e d from s i m i z i n e , p e n t a c h l o r o n i t r o b e n z e n e , hexachlorophene, methyl p a r a t h i o n c o n t r o l l e d r e l e a s e c o m p o s i t e s a n d 2,4-D w h i l e g r a n u l e s i n c o r p o r a t i n g f f

f f

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

D E L L i COLLI

Controlled

Release from

Kraft Lignin

Carriers

87

several phenoxyacetics, s u b s t i t u t e d benzoic acids and c a r b a m a t e s have been p r o d u c e d i n t h e l a b o r a t o r y . A l l o f t h e above u t i l i z e d c a r r i e r systems a r e based upon t e c h n i c a l k r a f t l i g n i n . I t became a p p a r e n t , h o w e v e r , when s e v e r a l comp o s i t e s o f t e c h n i c a l k r a f t l i g n i n and organophosphates such as I t h o p r o p ( M o b i l C h e m i c a l ) and carbamates such a s B u x ( C h e v r o n ) t o o k t h e f o r m o f v i s c o u s gums o r d e f o r m a b l e s o l i d s w h i c h c o u l d o n l y be g r o u n d c y r o g e n i c a l l y t h a t t h e l i g n i n was n o t u n i v e r s a l l y a c c e p t able as a c a r r i e r . Even a f t e r t h e low t e m p e r a t u r e g r i n d , t h e f o r m u l a t i o n s h a d a b s o l u t e l y no s h e l f stability. Both s m a l l p a r t i c l e f o r m u l a t i o n s and granules e i t h e r s i n t e r e d w i t h i n hours at temperatures a s l o w a s 30°C o r i w i t h i n days a t s l i g h t l T h e s e o b s e r v a t i o n s l e d t o t h e d e v e l o p m e n t o f a chemi c a l l y m o d i f i e d l i g n i n c a r r i e r p r e p a r e d by m o d i f y i n g the parent t e c h n i c a l k r a f t t o produce a r e v e r s a b l y s w e l l a b l e porous matrix. W i t h few e x c e p t i o n s , t h i s c a r r i e r made p o s s i b l e t h e p r e p a r a t i o n o f s t a b l e formulations of those a g r i c u l t u r a l chemicals which p l a s t i c i z e d the parent lignin. I n a n o t h e r i n s t a n c e , t h e l i g n i n was c o n v e r t e d t o a s e c o n d m o d i f i c a t i o n . The c a r r i e r s y s t e m p r o d u c e d was a g a i n s w e l l a b l e , b u t u n d e r w e n t 1 1 - f o l d v o l u m e i n c r e a s e upon h y d r a t i o n as compared t o a t w o - f o l d change d i s p l a y e d by t h e p r e v i o u s c a r r i e r . This c a r r i e r was f o u n d u s e f u l f o r w a t e r s o l u b l e p e s t i c i d e s s u c h a s t h e a m i n e s a l t s o f 2,4-D, e t c . The a b o v e m o d i f i c a t i o n s w e r e made p o s s i b l e because o f one o f t h e major advantages o f k r a f t lignin. T h i s f a c t o r i s i t s a b i l i t y t o be c h e m i c a l l y modified. Work t o b e d i s c u s s e d i n t h e e n s u i n g paragraphs d e s c r i b e f i e l d r e s u l t s o f these composites each o f w h i c h employs one o f t h e b a s i c c a r r i e r s d e s c r i b e d above. These e x p e r i m e n t a l systems a r e k r a f t l i g n i n / T e r r a c l o r (PCNB), m o d i f i e d lignin/Mocap ( e t h o p r o p ) , and m o d i f i e d l i g n i n / 2 , 4 - D ( d i m e t h y l amine s a l t ) . Carrier Selections. W h i l e t h e c h o i c e o f c a r r i e r systems f o r any given t e c h n i c a l p e s t i c i d e i s s t i l l largely emperical, some i n s i g h t i n t o t h e e x t e n t w h i c h t h e c a r r i e r a n d a c t i v e i n g r e d i e n t i n t e r a c t and p l a s t i c i z e k r a f t lignin c a n be g a i n e d by c a l c u l a t i n g t h e s o l u b i l i t y parameter o f the p e s t i c i d e . Generally, e s t i m a t i o n of t h i s parameter w i t h t h e s t r u c t u r a l group c o n s i d e r -

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

88

C O N T R O L L E D R E L E A S E PESTICIDES

ation of Small (7) w i l l s u f f i c e . E x p e r i e n c e h a s shown w h e r e β f o r t h e p e s t i c i d e f a l l s b e t w e e n 1 0 . 5 a n d 12 (cal/cm ) V the l i k e l i h o o d of p l a s t i c i z a t i o n i s high. A v a l u e o f 6=11.5 i s u s e d f o r t e c h n i c a l k r a f t l i g n i n . 3

2

T e s t r e s u l t s - L i g n i n - 2,4-D. The f i r s t s y s t e m t e s t e d c o n s i s t e d o f a g r a n u l a r composite o f chemically modified l i g n i n with a loading o f 1 0 % b y w e i g h t 2,4-D ( a s t h e d i m e t h y l a m i n e s a l t ) . C o m p o s i t e s were p r e p a r e d by p l a c i n g t h e d r y l i g n i n b a s e d c a r r i e r i s a s o l u t i o n o f t h e 2,4-D s a l t , a l l o w ing i t t o s w e l l and absorb a l l o f t h e s o l u t i o n (500 grams o f s o l u t i o n p e r 50 grams o f l i g n i n ) , d r y i n g and g r a n u l a t i n g the composite A series of soi 1 f t . compartments were p l a c e d on t h e windward s i d e o f a d i t c h b a n k i m m e d i a t e l y a d j a c e n t t o a l a r g e weed covered f i e l d . I t was i n t e n d e d t h a t t h e s e t r a y s c a t c h w i n d b o r n e s e e d a n d a l l o w i t t o g e r m i n a t e w h e r e no c h e m i c a l was u s e d o r p r e v e n t g e r m i n a t i o n w h e r e h e r b i c i d e was e m p l o y e d . C o n t r o l l e d r e l e a s e c o m p o s i t e was a p p l i e d t o t e n t r a y s as g r a n u l e s and c o n v e n t i o n a l 2,4-D a m i n e s a l t f o r m u l a t i o n s a s a q u e o u s s p r a y . Ten t r a y s were l e f t as c o n t r o l s ( u n t r e a t e d ) . Herbicide was a p p l i e d a t t h e r a t e o f è l b . / a c r e f o r b o t h c o n t r o l l e d r e l e a s e and c o n v e n t i o n a l formulations. The t e s t p l o t s w e r e e x a m i n e d m o n t h l y a n d a l l g r o w i n g p l a n t s were removed. As a f u r t h e r check, 5 bean seeds were p l a n t e d i n each compartment and t h e t o t a l number o f b e a n p l a n t s r e c o r d e d a t e a c h e v a l u a t i o n , removed and t h e n r e p l a n t e d . Observations are recorded i n the following table. Table I F i e l d r e s u l t s o f l i g n i n / 2 , 4 - D (amine s a l t ) c o n t r o l l e d release granules Controlled Release Weeds Beans

Date A p r i l 1974 May 1974 June 1974 J u l y 1974 August 1974 September 1974 October 1974

27 20 18 27 94 86 226

0 0 0 0 0 26 50

Conventional Formulation Weeds Beans 24 31 115 241 296 251 341

0 0 31 50 48 50 50

Check Weeds Beans 74 96 133 237 304 276 300

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

48 45 50 50 49 49 50

8.

DELLi

COLLI

Controlled

Release from Kraft Lignin

Carriers

89

These d a t a i n d i c a t e t h a t the c o n t r o l l e d r e l e a s e form o f 2,4-D d i d provide e f f e c t i v e c o n t r o l of susceptable s p e c i e s f o r f i v e months b e f o r e l o s i n g a c t i v i t y w h i l e t h e c o n v e n t i o n a l f o r m o f t h e same h e r b i c i d e a p p l i e d a t t h e same r a t e l a s t e d two m o n t h s . A system s u c h as t h i s w o u l d f i n d use p e r h a p s as a preemergent b r o a d l e a f herbicide f o r winter grain crops. Lignin

-

ethoprop.

A second f i e l d e x e r c i s e i n v o l v e d the e v a l u a t i o n o f l i g n i n - e t h o p r o p (Mocap) c o m p o s i t e s i n the c o n t r o l o f t h e r o o t k n o t nematode. Because of i t s extreme s e n s i t i v i t y t o b o t h s o i l p e s t s and p h y t o t o x i c c h e m i c a l s , t h e cucumbe The c o m p o s i t e l i g n i n , PC-402, d e v e l o p e d f o r use w i t h organophosphates. Incorporation of the a c t i v e m a t e r i a l i n t o t h e c a r r i e r was a m a t t e r o f s p r a y i n g t h e p r e h e a t e d c a r r i e r (80°C) w i t h a s o l u t i o n o f e t h o p r o p i n 95/5 ( v / v ) m e t h y l e n e c h l o r i d e , e v a p o r a t i n g t h e methanol s o l v e n t and f o r m u l a t i n g as a m i c r o g r a n u l e (80-100 mesh). C a r r i e r P C - 4 0 2 was s e l e c t e d b e c a u s e e a r l i e r attempts to formulate with t e c h n i c a l k r a f t l i g n i n r e s u l t e d i n a s y s t e m w h i c h c o u l d n o t be crushed because of i t s p l a s t i c c o n s i s t e n c y . F i e l d e v a l u a t i o n o f t h e c o m p o s i t e s was carried out at the Clemson U n i v e r s i t y T r u c k Experiment S t a t i o n i n C h a r l e s t o n , S. C. I n i t i a l d a t a became a v a i l a b l e d u r i n g t h e f a l l o f 1974 a n d i s p r e s e n t e d i n T a b l e I I . Table I I E f f e c t o f nematocide f o r m u l a t i o n s on the y i e l d and on c o n t r o l o f root-knot nematodes o f cucumbers. ( F a l l 1974) Method o f Yield Root-Knot Treatment A p p l i c a t i o n Rate/Acre (bu/acre) Index 1/

Control Mocap Mocap-lignin composite Fumazone

Broadcast

5.0 l b s .

210 180

3.0 2.8

Broadcast Row

5.0 l b s . 0.5 g a l .

210 247

1.6 0.1

1/ Root-knot index = 0.0 decayed r o o t s , e t c .

(no r o o t damage) - 5.0

(mass g a l l s ,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

90

C O N T R O L L E D R E L E A S E PESTICIDES

T h i s d a t a i n d i c a t e s t h a t the c o n t r o l l e d r e l e a s e formul a t i o n a p p l i e d a t t h e same r a t e a s t h e c o n v e n t i o n a l f o r m u l a t i o n was m o r e e f f e c t i v e i n c o n t r o l l i n g t h e t a r g e t o r g a n i s m as i n d i c a t e d by a l o w e r r o o t - k n o t index. O n l y F u m a z o n e was m o r e e f f e c t i v e t h a n t h e c o n t r o l l e d r e l e a s e system. An a d d i t i o n a l b e n e f i t d e r i v e d f r o m t h e c o n t r o l l e d r e l e a s e f o r m u l a t i o n was a y i e l d increase a t t r i b u t e d to a reduced p h y t o t o x i c e f f e c t o f t h e c h e m i c a l p r e s u m a b l y due t o i t s l o w e r i n i t i a l a v a i l a b i l i t y to the plant. S p r i n g 1975 saw t h e i n s t a l l a t i o n o f a s e c o n d test. T h i s e v a l u a t i o n was d e s i g n e d t o d e t e r m i n e t h e l o n g - r a n g e e f f e c t s o f two c o n t r o l l e d r e l e a s e f o r m u l a t i o n s o f M o c a p , 10 a n d 2 5 % m i c r o g r a n u l e s . The p e s t i c i d e was a p p l i e d o n immediately overplanted May. A s e c o n d c r o p was p l a n t e d i n A u g u s t w i t h h a r v e s t i n mid-September. No r e a p p l i c a t i o n o f n e m a t o c i d e was made b e t w e e n t h e s p r i n g a n d f a l l seasons. The d a t a i n T a b l e I I I show t h a t b o t h t h e 10 a n d 2 5 % f o r m u l a t i o n s w e r e e f f e c t i v e i n c o n t r o l l i n g the t a r g e t o r g a n i s m s e v e n m o n t h s a s i n d i c a t e d by the root knot i n d i c e s . Y i e l d s w e r e r e d u c e d by t h e 25% composite during the s p r i n g season again because of t h e p h y t o t o x i c i t y o f t h e c h e m i c a l . Table I I I Long range e f f e c t o f c o n t r o l l e d r e l e a s e nematocides on t h e y i e l d and on c o n t r o l o f root-knot nematocides o f cucumbers. Rate Yield Root-Knot Y i e l d Root-Knot Treatment ( l b s . A I / a c r e ) (bu/acre) Index (bu/acre) Index 10% AI l i g n i n composite 25% AI l i g n i n composite Check

4

487

0

112

1

4 0

390 432

0 0

135 125

0 3.5

A p p l i c a t i o n date - March 15, 1975 F i r s t harvest - May 30, 1975 Replant date - August 2, 1975 Second harvest - September 12, 1975 F a l l data reveal that the "higher loading" composite was m o r e e f f e c t i v e d u r i n g t h e s e c o n d h a l f o f t h e t e s t b o t h from a c o n t r o l and y i e l d s t a n d p o i n t . A s i d e from c o n t r o l of nematodes w h i c h account f o r m i l l i o n s o f d o l l a r s i n l o s s e s a n n u a l l y (8) t o g r o w e r s o f f i e l d c r o p s , f r u i t and n u t s , and v e g e t a b l e crops, p r o t e c t i o n of crops from the e f f e c t of the very

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

DELLi

COLLI

Controlled

Release from Kraft Lignin

Carriers

91

c h e m i c a l d e s i g n e d t o p r o t e c t them from t h e m i c r o s c o p i c worms has been shown t o be a v e r y d e s i r a b l e s i d e e f f e c t o f c o n t r o l l e d r e l e a s e f o r m u l a t i o n s . F a l l 1976 p r o v i d e d an a d d i t i o n a l o p p o r t u n i t y t o s t u d y t h i s phenomenon. A v e r y wet and c o o l g r o w i n g season e l i m i n a t e d nematode a c t i v i t y so a t e s t was r u n s i m p l y t o study y i e l d e f f e c t s . T a b l e IV c o n t a i n s t h e d a t a w h i c h is self-explanatory. T a b l e IV Effect of controlled release and conventional nematocides on the y i e l d of cucumbers. F a l l 1976. Treatment

Rate (lbs.AI/acre)

25% EI Mocap/lignin 10% AI Mocap/lignin Mocap 10G Fumazone 86E Control

4 lbs. 4 lbs. i gal. 0

Yield

(bu/acre)

263 205 187 305

L i g n i n - PCNB. The t h i r d system t o be s t u d i e d was a t e c h n i c a l k r a f t l i g n i n - T e r r a c l o r (PCNB) system p r e p a r e d by c o p r e c i p i t a t i n g t h e f u n g i c i d e w i t h t h e l i g n i n from an aqueous s o l u t i o n . F i e l d work was done a t t h e D e l t a Experiment S t a t i o n i n S t o n e v i l l e , M i s s i s s i p p i under t h e d i r e c t i o n o f C. P. Hegwood. The t e s t o r g a n i s m was t h e s o i l fungus R h i z o c t o n i a S o l a n i r e s p o n s i b l e f o r " f r u i t r o t o f cucumbers, tomatoes, and p e a n u t s . This p a r t i c u l a r organism i s r e s p o n s i b l e f o r e x c e s s i v e c r o p l o s s e s i n a r e a s where i t i n f e c t s t h e s o i l . For example, d u r i n g 1976, o v e r 50% o f t h e cucumbers grown on t h e M i s s i s s i p p i D e l t a , f o r p r o c e s s i n g i n t o p i c k l e s were d i s c a r d e d (9) i n f l i c t i n g economic l o s s e s t o growers. P r o c e s s o r tomatoes cannot be grown i n t h e same a r e a because o f problems a s s o c i a t e d w i t h R. s o l a n i d e s p i t e n e a r p e r f e c t c l i m a t i c c o n d i t i o n s . ( 1 0 ) F o l l o w i n g a s p r i n g 1976 f i e l d t e s t where t h e l i g n i n / P C N B c o m p o s i t e , a 50% w e t t a b l e powder, was i d e n t i f i e d along with several conventional formulat i o n s , as b e i n g e f f e c t i v e i n c o n t r o l l i n g t h e m i c r o o r g a n i s m s , a s e r i e s of greenhouse t e s t s were i n s t i tuted. S o i l samples from t h e same f i e l d used i n t h e s p r i n g t e s t s were s t e r i l i z e d and p l a c e d i n aluminum pans. R. s o l a n i i n o c u l u m was p l a c e d on a l l o f t h e s o i l samples and a l l o w e d t o i n c u b a t e . F u n g i c i d e s were t h e n a p p l i e d t o t h e pans a t r a t e s recommended by t h e i r 1 1

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

92

C O N T R O L L E D R E L E A S E PESTICIDES

respective manufacturers. Subsequently, fresh c u c u m b e r s w e r e p l a c e d on t h e s o i l s , c o v e r e d w i t h a p o l y e t h y l e n e s h e e t , and a l l o w e d t o r e m a i n undisturbed for f i v e days. F o l l o w i n g t h i s , t h e f r u i t was r e m o v e d f r o m t h e p a n s and e x a m i n e d f o r f r u i t r o t l e s i o n s . Date i n Table V d e s c r i b e s the r e s u l t s of the work. Table V F u n g i c i d e Screening Data - S i n g l e A p p l i c a t i o n Percentage o f I n f e c t e d F r u i t Days A f t e r A p p l i c a t i o n 49 24 17 Treatment 11 PC-474* PC-460** Terraclor T e r r a c l o r (Tech. ) Nabac Nabac (Tech) Difolatan Lignin Check

8 58 100 100 92 100 100

0 25 92 100 100 100 100

42 67 100 100 83 100 100

45 83 83 92 75 100 100

* 60% wettable powder c o n t a i n i n g 19% o f i t s a c t i v e content as f r e e un-incorporated PCNB. ** 50% w e t t a b l e powder c o n t a i n i n g 100% of i t s a c t i v e cont e n t as i n c o r p o r a t e d PCNB. S e v e n w e e k s a f t e r a p p l i c a t i o n , t h e two lignin based f o r m u l a t i o n s were s t i l l e f f e c t i v e i n k e e p i n g t h e m i c r o o r g a n i s m s u n d e r c o n t r o l . T h i s i s somewhat significant since current practive involves fungicide a p p l i c a t i o n s h o r t l y a f t e r p l a n t i n g with repeated a p p l i c a t i o n at weekly i n t e r v a l s . Such c o s t l y p r o c e dures continue u n t i l the plants reach a layby stage. H e r e t h e p l a n t s f o r m a d e n s e c a n o p y and s h i e l d t h e ground w i t h t h e i r f o l i a g e . At t h i s t i m e c o n v e n t i o n a l f u n g i c i d e s c a n n o t be s u c c e s s f u l l y a p p l i e d t o t h e g r o u n d o r t h e f r u i t and f o l i a g e o f t h e p l a n t s . From t h i s p o i n t on, t h e r i p e n i n g f r u i t must depend upon residual fungicide for protection. The t i m e e l a p s e d b e t w e e n p l a n t i n g and h a r v e s t f o r p r o c e s s o r t y p e cucumbers i s 45-50 d a y s . A s y s t e m s u c h as PC-460 o r PC-474 w h i c h r e m a i n s e f f e c t i v e f o r s i x o r s e v e n w e e k s w o u l d make i t p o s s i b l e f o r t h e g r o w e r t o r e l y on a s i n g l e a p p l i c a t i o n o f f u n g i c i d e a t t h e t i m e o f p l a n t i n g a n d a t t h e same t i m e r e a l i z e y i e l d s , i f not unmarked, at l e a s t l e s s s e v e r e l y s c a r r e d by l o s s e s due t o f r u i t r o t .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

8.

B E L L I COLLI

Controlled

Release from Kraft Lignin

Carriers

93

Conclusions The t h r e e s y s t e m s e v a l u a t e d t h u s f a r d e m o n s t r a t e the f e a s i b i l i t y o f t h e u s e o f k r a f t l i g n i n as a con t r o l l e d r e l e a s e c a r r i e r system. Modifications of k r a f t l i g n i n c a n a l s o be used as c a r r i e r s t o e x t e n d the p e r i o d o f b i o l o g i c a l a c t i v i t y o f p e s t i c i d e s , reduce t h e i r a p p l i c a t i o n r a t e s , and reduce t h e f r e q u e n c y o f a p p l i c a t i o n i n c a s e s where t h e p a r e n t l i g n i n c a n n o t be used. Acknowledgement The a u t h o r w i s h e D r . Wayne S i t t e r l y o E x p e r i m e n t S t a t i o n , C h a r l e s t o n , S. C. a n d D r . C. P. Hegwood o f t h e D e l t a E x p e r i m e n t S t a t i o n , S t o n e v i l l e , M i s s i s s i p p i f o rt h e f i e l d e v a l u a t i o n o f t h e nematocide a n d f u n g i c i d e c o m p o s i t e s a n d t o D r . S. I . F a l k e h a g a n d Mr. H. H. M o o r e r o f t h e W e s t v a c o C o r p o r a t i o n f o r t h e i r encouragement and g u i d a n c e o f t h i s work.

Literature Cited (1)

Nimz, H., Angew Chem. Internat, Ed., 13 313 (1974). (2) Lindberg, J . J., Tylli, Η., and Magani, C., Paperi Puu, 46, 521 (1964). (3) Rezanowich, Α., Yean, W. Q., and Goring, D. A. I., Svensk Papperstidn., 66, 141 (1963). (4) Gupta, P. R., and Goring, D. A. I . , Can. J. Chem., 38, 270 (1960). (5) Marton, J . , and Marton, T., Tappi, 47, 471 (1964). (6) Christman, R. F., and Oglesby, R. T. in L i g n i n , Occurrances and S t r u c t u r e s , Sarkanen and Ludwig, E d i t o r s Wiley New York (1971). (7) Small, P. Α., J. Appl. Chem., 3, (Feb., 1953). (8) Feldmeser, J . , USDA-ARS Beltsville, Md., P r i v a t e Communication. (9) Hegwood, C. P., D e l t a Experiment S t a t i o n , P r i v a t e Communication. (10) Batson, W. Ε., Mississippi State U n i v e r s i t y , P r i v a t e Communication.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9 Controlled Release of Herbicides from Biodegradable Substrates G. G. ALLAN,* J. W. BEER, and N. J. COUSIN College of Forest Resources, University of Washington, Seattle, Wash. 98195

The controlled releas firm foothold in pesticid plethora of symposia which have been organized around the U.S. in recent years (1-3). Although many different controlled release techniques have been presented at these gatherings actually few have progressed beyond laboratory evaluation. Among those which have i s a con t r o l l e d release herbicide primarily intended as a reforestation aid (4). This is based on the chemical linkage of a herbicide to a biodegradable substrate by means of a hydrolyzable bond. After t h i s chemical combination is placed on the forest f l o o r , herbicide is slowly released to suppress the growth of competitive vegetation in the vicinity of the seedling for a period of time, measured in months or years. However, if this type of controlled release herbicide which has been successful in forestry is to be used in agriculture shorter periods of release w i l l be more appropriate. The design of such systems is now underway and t h i s paper describes an assessment of the effect of the degree of substitu tion on the rate of hydro l y t i c degradation of α-cellulose 2,4dichlorophenoxyacetate both in v i t r o and in νivo. Results and Discussion The α-ce I Iulose 2,4-d ichlorophenoxyacetates studied in t h i s project contained 4.1, 4.9 or 21.5$ by weight of combined herbi cide. The rates of hydrolysi s for these biocides in water at varying pH values are quite d i fferent. The data in Figure I shows that the release is dependent on both the degree of substitution and the acid ity or a l k a l i n i t y of the hydrolysis medium. Moreover, since the hydro Iysi s samples contained the same quantity of com bined active ingredient i t is clear that a faster release of *Address inquiries to Professor G. G. A l l a n , University of Wash ington, AR-10, Seattle, WA 98195. 94

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

ALLAN ET AL.

Herbicide

Release from

Riodegradables

95

h e r b i c i d e was o b t a i n e d w i t h t h e α-cellulose e s t e r h a v i n g t h e lower d e g r e e o f s u b s t i t u t i o n . T h i s p a t t e r n o f h e r b i c i d e r e l e a s e c a n be e x p l a i n e d i n t e r m s o f t h e m i c r o - s t r u c t u r e o f t h e α-cellulose f i b e r w h i c h c o n t a i n s d i s p e r s e d c r y s t a l l i n e (60%) and amorphous (40%) regions. In n o n p o l a r n o n s w e l I i n g r e a c t i o n media t h e l a t t e r p r o v i d e s e s s e n t i a l l y a l l o f t h e r e a d i l y a v a i l a b l e r e a c t i v e hydroxy groups. I η u n s w o l I en n a t i v e e e l lu l o s e t h o s e amount t o on I y 0.4% o f t h e t o t a l f i b e r m a t e r i a l ( 5 ) . T h i s v a l u e i s i n c r e a s e d t o 0.54% as a r e s u l t o f t h e i s o I a t i o n p r o c e d u r e s wh i c h g e n e r a t e a b o u t o n e t h i r d more s u r f a c e a r e a (j3). T h u s , i t c a n be a n t i c i p a t e d t h a t e s t e r i f i c a t i o n r e a c t i o n s w i l l b e g i n r a n d o m l y on a c c e s s i b l e amor phous s u r f a c e s and s u b s e q u e n t l y s p r e a d a l o n g t h e p o l y s a c c h a r i d e chains. As a r e s u l t , t h e d e n s i t y and p a t t e r n o f s u b s t i t u e n t s w i l l v a r y t h r o u g h o u t t h e α-cellulose s u b s t r a t e ( I ) . T h i s v a r i a n c e i s compounded by t h e unequa reacti i t i e each a n h y d r o g l u c o s e u n i t o s y I a t i o n e x p e r i m e n t s have shown t h a t t h e C O , groups a r e e s t e r i f i e d i n t h e r a t i o of 2 1 5 : 3 3 : 1 F u r t h e r m o r e , a k i net i c s t u d y d e m o n s t r a t e d t h a t group r e a c t s f i f t y - e i g h t t i m e s f a s t e r than i t s

C 2 and C 3 h y d r o x y respectively (1). t h e p r i m a r y hydroxy secondary neighbors

(8).

As a r e s u l t o f a l l t h e s e f a c t s , i t c a n be c o n c l u d e d t h a t e s t e r i f i c a t i o n r e a c t i o n s o f α-cellulose a t low d e g r e e s o f s u b s t i t u t i o n wt I I random I y o c c u r a I most e x e l u s i v e l y on t h e f i b e r s u r f a c e s a s s o c i a t e d w i t h t h e amorphous r e g i o n a t t h e p r i m a r y h y d r o x y g r o u p s o f t h e C§ c a r b o n atom o f e a c h g l u c o s e u n i t . It therefore f o l l o w s t h a t i n t h e α-ce I I u l o s e d e r i v a t i v e t h e r e w i l l be g r o u p s o f more o r l e s s c l o s e l y l o c a t e d e s t e r u n i t s s e p a r a t e d by a r e a s h a v i n g on I y an o c c a s i o n a I e s t e r s u b s t i t u e n t and hence a h y d r o p h i I i c c h a r a c t e r c o m p a r a b l e t o t h e o r i g i n a l amorphous r e g i o n o f t h e α-cellu lose. Of c o u r s e , a s t h e d e g r e e o f s u b s t i t u t i o n i s i n c r e a s e d , t h e s i z e o f t h e s e h y d r o p h i I i c a r e a s must d e c r e a s e . Ultimately, the h y d r o p h i I i c i t y c a n become s o s m a l l t h a t w a t e r c a n n o t p e r m e a t e t h e poIymer m a t r i x ( 9 ) t o e f f e c t h y d r o l y t i c r e I e a s e o f t h e h e r b i c i de (10, II). T h i s s t r u c t u r a I p i c t u r e t h e r e f o r e p r o v i des a s a t i s f y i n g expIanation f o r h y d r o l y t i c r e l e a s e data i n Figure I s i n c e t h e more h y d r o p h i I i c α-cellulose e s t e r c a n be e x p e c t e d t o h y d r o l y z e a t a f a s t e r r a t e t h a n t h e more h y d r o p h o b i c p o I y m e r i c e s t e r . Ob v i o u s l y a def i η i ng mi η imum l i m i t must e x i s t where f u r t h e r d e c r e a s e s i n t h e amount o f p e n d a n t e s t e r l i n k a g e s w i l l n o t l e a d t o a f a s t e r r a t e o f h y d r o l y s i s . T h i s l e v e l r e m a i n s t o be e s t a b I i s h e d . In s p i t e o f t h e c l a r i t y o f t h e s e h y d r o l y t i c e x p e r i m e n t s , t h e a c t u a l b e h a v i o r o f t h e α-cellulose e s t e r i n s o i l w i l l be somewhat more c o m p l e x . C e r t a i n l y h y d r o l y t i c c l e a v a g e o f t h e p e n d a n t e s t e r w i l l o c c u r i n t h e s o i I b u t t h i s s c i s s i o n w i I I be s u p p I e m e n t e d by m i c r o b i a l and e n z y m i c a t t a c k on t h e α-cellulose d e r i v a t i v e . I t i s we I I known ([2) t h a t rap î d d e t e r i o r a t i o n o f e e l I u l o s e o c c u r s i n s o i l and t h a t t h e t e n s i l e p r o p e r t i e s o f r e g e n e r a t e d r a y o n , f o r example, a r e compIeteI y l o s t a f t e r f o u r t e e n days o f s o i l b u r i a l .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

HO

PESTICIDES

μ

10

*

IS

TIME

2C

25

JO

35

IN DAYS

Figure 1. The cumulative release of 2,4-D from its α-cellulose esters where A, B, and C are the 4.1% w/w combinations exposed to solutions of pH 4, 7, and 10, respectively, and D, E, and F are the corre sponding treatments of the 21.5% w/w combinations subjected to the same treatments

I

I 0.5

I 1.0

I 1.5

LOG (APPLICATION LEVEL) Figure 2. The duration of herbicidal effectiveness provided by various application levels of a-cellulose 2,4-dichlorophenoxyacetate (D.S. 0.05)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

ALLAN ET AL.

Herbicide

Release from

Biodégradables

97

However, t h e α-cellulose r e l e a s e m a t r i x need n o t be d e s t r o y e d w i t h i n t h i s s h o r t p e r i o d o f t i m e because o f t h e p r o t e c t i v e e f f e c t o f t h e e s t e r i f y i ng h e r b i c i de a c i d . T h u s , i n c o n t r a s t t o t h e une s t e r i f i e d c e l l u l o s e f i b e r s , t h e physicaI properties of t h e i r m o n o a c e t y l a t e d c o u n t e r p a r t s were n o t a d v e r s e l y a f f e c t e d by e x p o s u r e t o s o i I b u r i a I f o r s i x months ( 1 3 ) . T h e s e e n z y m i c and m i c r o b i a I p a r a m e t e r s c a n b e s t be e x p l o r e d u n d e r a c t u a I u s e cond i t i o n s , t h a t i s , by e x p e r i m e n t s us i ng s o i l . However, t o o b t a i n r e p r o d u c i b I e r e s u l t s i n a b i o a s s a y i t i s n e c e s s a r y t o c a r e f u I I y c o n t r o I t h e cond i t i o n s . Under s u c h precî s e cond i t i o n s t h e r a t e o f s u r f a c e h y d r o Iys i s f o r an e s t e r o f a w a t e r i n s o I u b I e poIymer i n a moi s t u r e î n u n d a t e d s o i I c a n be w r i t t e n a s
C = C e" ο

K +

(25

A t t h e c r i t i c a I t i m e t wh i c h marks t h e end o f t h e p e r i o d o f h e r b i c i d a l e f f e c t i v e n e s s o f t h e α-cellulose e s t e r t h e r a t e o f r e l e a s e R f o r an a p p I i c a t i o n o f w e i g h t W f o l lows f r o m e q u a t i o n so t h a t c

}

(2)

K t

R = WKC e " c (3) ο Since t h e time t o reach t h i s c r i t i c a l p o i n t i s actuaI I y t h e dura t i o n o f h e r b i c i d a l e f f e c t i v e n e s s (D ) t h e n pr D = M log W - Ν (4) pr y

where M = 2.3/K and Ν = ( 2 . 3 / K ) l o g ( R / C K ) . T h e r e f o r e , a p l o t o f t h e d u r a t i o n o f h e r b i c i da I e f f e c t i v e n e s s v e r s u s t h e l o g a r i t h m o f t h e w e i g h t o f α-cellulose 2 , 4 - d i c h l o r o p h e n o x y a c e t a t e a p p l i e d should give a s t r a i g h t l i n e (10). Although t h e data i n F i g . 2 v a l i d a t e s e q u a t i o n 4 i t must be remembered t h a t t h e s e s o i l e x p e r i ments a r e v e r y w e l l c o n t r o I I e d . Under t h e u n c o n t r o l l e d c o n d i t i o n s o f a c t u a l u s e t h e p a t t e r n o f r e l e a s e w i l l be much more c o m p l e x . A s an i I I u s t r a t i o n , F i g u r e 3 shows t h e c o m p l e x c I i m a t o l o g i c a I d a t a f o r a f i e l d s i t e i n t h e S e d r o Wool l e y a r e a o f W a s h i n g t o n where a c o n t r o l Ied r e l e a s e h e r b i c i d e t e s t was c a r r i e d o u t . Q

O b v i o u s I y , t h e h i g h t e m p e r a t u r e s o f m i d y e a r wouId be e x pected t o k i n e t i c a I I y a c c e l e r a t e t h e r a t e o f h y d r o l y s i s o f ac e l l u l o s e e s t e r s . However, i n a c t u a l f a c t , t h e l a c k o f w a t e r a t t h i s t i m e probabI y means t h a t t h e r a t e o f h y d r o l y s i s w i l l be mi ni m a l . C o n v e r s e I y, t h e a b u n d a n t m o i s t u r e a v a i l a b l e a t t h e b e g i n n i n g and end o f t h e y e a r , w h i c h would f a c i I i t a t e h y d r o l y s i s , i s

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

98

C O N T R O L L E D R E L E A S E PESTICIDES

counterbalanced by t h e f r e e z i n g t e m p e r a t u r e s w h i c h w i l l s l o w t h e r a t e o f h y d r o l y s i s . T h i s t y p e o f c l imate-mod i f i e d r a t e o f r e l e a s e i s un i que t o chemi caI I y bonded s y s t e m s and c o n s t i t u t e s a s t r o n g r a t i o n a I e f o r t h e i n i t i a l s e l e c t i o n o f t h i s t y p e o f c o n t r o I Ied r e l e a s e system. In c o n t r a s t , e n c a p s u l a t i o n o r o t h e r d i f f u s i o n c o n t r o l Ied p r o c e s s e s w i l l n o t t u r n t h e m s e l v e s o f f when t e m p e r a t u r e r i s e and m o i s t u r e l e v e l s f a l l . Indeed, r e l e a s e from such dev i c e s a c t u a I I y w i I I speed up u n d e r cond i t i o n s wh i c h a r e a l r e a d y g e n e r a I I y u n f a v o r a b I e f o r t h e germi n a t i o n o f t h e weeds t o be c o n trolled. CI e a r I y, t h i s i s i n t r i ns i c a I I y w a s t e f u I and i n e f f i c i e n t . T h e r e f o r e , a I t h o u g h b i o a s s a y s a r e more i n f o r m a t i v e t h a n hy d r o I ys i s, a c t u a l f i e l d p e r f o r m a n c e i s t h e f i n a l and s u p e r i o r arbiter. However, c o n t r o l l e d I a b o r a t o r y b i o a s s a y s i n s o i l c a n p r o v i d e u s e f u I ρre I i m i n a r y gu i dance i n t h e d e s i g n o f c o n t r o I Ied r e l e a s e h e r b i c i d e s and i t h i typ f t e s t th f r e herb i c i d i nh i b i t e d germi nat i o n The c o n t r o l Ied r e l e a s e same amount o f h e r b i c i d e as was a p p l i e d i n t h e f r e e s t a t e l a s t e d 30% and 100% l o n g e r . The r e I a t î veI y smaI I d î f f e r e n c e s i n t h e l e n g t h o f t h e p e r i o d o f e f f e c t i v e n e s s i s due t o t h e f a c t t h a t t h e α-cellulose e s t e r s c o n t a i η no f r e e h e r b i c i de. That i s , the h e r b i c i d e r e l e a s e d by h y d r o Iys i s i s n o t f u n c t i o n i n g o n l y t o r e p l a c e t h e l o s s e s from a p r e - e s t a b l i s h e d e f f e c t i v e l e v e l of f r e e h e r b i cide. I n s t e a d , i n t h i s demand i n g b i o a s s a y , t h e α-cellulose e s t e r must f i r s t r e l e a s e enough h e r b i c i d e t o a t t a i n t h e mi η imum e f f e c t i v e I eve I and s u b s e q u e n t I y ma î n t a i n t h î s by add i t i o n a I h y d r o l y s i s . O b v i o u s I y t h i s s t r i n g e n t demand r e d u c e s t h e d u r a t i o n o f t h e p e r i o d of e f f e c t i v e n e s s . T h i s e x p l a i n s the s h o r t e r period of e f f e c t i v e n e s s wh i ch i s provî ded by t h e α-ce I I u l o s e e s t e r w i t h t h e h i g h e r degree o f s u b s t i t u t i o n . That i s , the lower r a t e o f r e l e a s e of t h i s d e r i v a t i v e cannot m a i n t a i n f o r long the r e q u i r e d level of f r e e h e r b i c i d e f o r e f f e c t i v e p e r f o r m a n c e . Under f i e l d c o n d i t i o n s t h i s s i t u a t i o n wouId be a v o i d e d by coadmî η i s t r a t i o n o f t h e c o n t r o I l e d r e l e a s e h e r b i c i de t o g e t h e r w i t h t h e s m a l l amount o f f r e e h e r b i c i d e n e c e s s a r y t o i m m e d i a t e l y a t t a i n î η t h e s o i I t h e mi η imum e f f e c t i v e I eve I r e q u i red t o i n h i b i t germi n a t i o n . Of c o u r s e , a p r a c t i c a l c o n t r o l Ied r e l e a s e h e r b i c i d e s y s t e m s h o u I d n o t be d e s i g n e d i n a vacuum. Among t h e many d e s i g n f a c t o r s w h i c h have t o be t a k e n i n a c c o u n t , t h e d u r a t i o n o f t h e p e r i o d o f e f f e c t i v e n e s s i s one o f t h e most i m p o r t a n t . The a t t a î nment o f t h i s s p e c i f i c a t i o n can be man i p u l a t e d most r e a d i I y by v a r i a t i o n o f t h e I eve I o f esterîfication. T h i s i s g e n e r a l l y t h e c a s e i r r e s p e c t i v e of the s u b s t r a t e . A l t h o u g h t h e r e l e a s e r a t e does c e r t a i n l y depend on t h e c h e m i c a l s t r u c t u r e o f t h e s u b s t r a t e ([4) the e f f e c t o f c h a n g i ng s u b s t r a t e s i s mi n o r r e l a t i v e t o t h e i n f I u e n c e o f t h e l e v e l s o f h e r b i c i d e combined w i t h t h e p o l y m e r . T h a t i s , f o r a g i v e n s u b s t r a t e ^ a s t h e degree of s u b s t i t u t i o n i s increased the r a t e of r e l e a s e of h e r b i c i d e i s sharply decreased. This conc e p t c a n n o t be e x t e n d e d i ndef i n i t e l y b e c a u s e a t h i g h e r d e g r e e s o f s u b s t i t u t i o n t h e hydrophob i c i t y w i l l become so g r e a t t h a t t h e

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Herbicide

ALLAN ET AL.

70

ι

,

Figure 3.

,

,

Release from ,

,

Biodégradables

,

,

,

,

ρ

Monthly average plantation site near Sedro Woolley, Wash.

4,9%

21,5%

W/W COMBINATION

W/W COMBINATION

2,*»-D

I

I

I

I

I

I

4

8

12

16

20

GERMINATION INHIBITION IN DAYS

Figure 4. A comparison of the persistence of germination inhi bition by bioassay between two different w/w-controiled release combinations of a-celluhse 2,4-dichlorophenoxyacetate and the active herbicide at 0.68 mg A.l ./cm 2

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

100

C O N T R O L L E D R E L E A S E PESTICIDES

p o l y m e r i c e s t e r w i l l become e s s e n t i a l l y n o n h y d r o I y z a b l e . On t h e o t h e r hand, t h e s u p e r m o l e c u l a r s t r u c t u r e i s r e l a t i v e l y un i m p o r t a n t a s l o n g a s t h e r e a r e s u t f i c i e n t amorphous r e g i o n s t o a t t a i n a r e a s o n a b l e l e v e l o f a c t i v e h e r b i c i d e i n t h e α-cellulose e s t e r . In p r a c t i c e , formuI a t i o n s c o n t a i n î ng 10 o r 20% a c t i v e i n g r e d i e n t a r e t h e most compat i b I e wi t h e x i s t i ng a p p I i c a t i o n equ i pment and t e c h n i q u e s . The e x i s t e n c e o f a l l t h e s e r e l e a s e p a r a m e t e r s p r o v i d e s s u c h a f1 ex i b i I i t y o f des i g n t h a t i t c a n be c o n f îdentI y a n t i c i p a t e d t h a t c o n t r o l l e d r e l e a s e h e r b i c i d e s based on c h e m i c a I linka g e s t o b i o d e g r a d a b l e s u b s t r a t e s w i l l be an i m p o r t a n t p a r t o f t h i s emergent a r e a o f p e s t i c i d e t e c h n o l o g y . Expérimenta 1 Esteri fication of a c i d. A s u s p e n s i o n of o v e n - d r i e (50g) i n a n h y d r o u s benzene (200ml) a t 22 was t r e a t e d p o r t i o n - w i s e (2ml) w i t h a s o l u t i o n o f 2,4-d i c h l o r o p h e n o x y a c e t y I c h l o r i d e (8.7 o r 24.Og) i n a n h y d r o u s b e n z e n e (50ml) and r e f I u x e d . A f t e r 3 h t h e r e a c t i o n m i x t u r e was e v a p o r a t e d t o n e a r d r y n e s s and f i l t e r e d . The r e s i d u e was exhaustî veI y e x t r a c t e d ( S o x h l e t ) w i t h b e n z e n e , washed w i t h w a t e r , a i r and o v e n - d r i e d b e f o r e baI I-mi I I i ng t o a f f o r d α-cellulose 2 , 4 - d i c h l o r o p h e n o x y a c e t a t e a s a f i n e powder. The e x t e n t o f e s t e r i f i c a t i o n ( 4 . 1 , 4.9 and 21.5% w/w) was c a l c u l a t e d from c h l o r i ne ana I y s i s o f t h e p r o d u c t s us i ng t h e n e u t r o n a c t i v a t i o n t e c h n i q u e o f i r r a d i a t i ng samp I es i n a n e u t r o n f I u x ( I . 4 χ I 0 ' ' n e u t r o n / c m 2 s e c ) f o r 10 mi n. A f t e r a p p r o p r i a t e coo I î ng, t h e samp I es were c o u n t e d by î n t e g r a t i ng t h e I.33 MeV p h o t o peak o f C I w i t h 2.27 KeV (FWHM) u s i n g a G e ( L i ) c r y s t a l and a m u I t i c h a n n e l ana I y z e r . The Ge(Lî) c r y s t a I ( P r i n c e t o n Gamma-Tech) had an e f f i c i e n c y r a t i n g o f 10.6% r e l a t i v e t o a N a l ( T i l ) 3 x3 i n . c r y s t a l and was l o c a t e d 25 cm f r o m t h e s o u r c e . 3 8

H y d r o l y t i c r e l e a s e o f 2 , 4 - d i c h I o r o p h e n o x y a c e t i c a c i d from a ce1 l u i o s e 2 , 4 - d i c h I o r o p h e n o x y a c e t a t e . T r i p l i c a t e s a m p l e s o f exc e l l u l o s e 2 , 4 - d i c h l o r o p h e n o x y a c e t a t e (DS 0.03 and 0.16) s i z e d t o c o n t a i n I25mg o f r e l e a s a b l e 2 , 4 - d i c h I o r o p h e n o x y a c e t i c a c i d , were enveloped i n f o u r l a y e r s o f porous teabag paper ("Flo-ThruR, Thomas J . L i p t o n , I n c . , Englewood CI i f f s , NJ) wh i c h when s e a l e d had an o u t e r s u r f a c e a r e a o f 50cm2. T h e s e bags were t h e n s u s pended i n unstî r r e d d i s t i I l e d w a t e r ( 5 0 0 m l ) , a d j u s t e d t o pH v a Iues o f 4, 7 and 10 u s i ng NaOH o r H C I , and ma i n t a i ned a t a t e m p e r a t u r e o f 22°. T h e r e a f t e r , a t v a r i o u s e l a p s e d t i m e s t h e bags were r e moved and r e s u s p e n d e d i n f r e s h I y p r e p a r e d so I u t i o n s w h i l e t h e r e s i d u a l s o l u t i o n s were a n a l y z e d f o r t h e i r c o n t e n t o f 2,4-d i c h l o r o p h e n o x y a c e t i c a c i d u s i n g a Dohrmann E n v i r o n t e c h DC-50 T o t a l O r g a n i c Carbon A n a l y z e r . B i o a s s a y o f t h e durât i o n o f herb i c i da I e f f e c t i v e n e s s o f a c e l l u l o s e 2,4-dichlorophenoxyacetate. Quadruplicate mixtures (Ig) o f α-cellulose 2 , 4 - d i c h l o r o p h e n o x y a c e t a t e ( c o n t a î η i ng 3 l . l m g o f comb î ned 2 , 4 - d i c h l o r o p h e n o x y a c e t i c a c i d ) and o v e n - d r i e d (105°)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

9.

ALLAN

ET AL.

Herbicide

Release from

Biodégradables

101

s i z e d (40-60 mesh, U.S. S t a n d a r d S i e v e S e r i e s ) s o i l were e v e n l y s p r e a d o v e r t h e s u r f a c e o f n o n s t e r i l e c o m p o s t e d s o i l (7x7x5cm) c o n t a i ned i n r e c t a n g u I a r ρ I a s t i c p o t s . C o n t r o l s c o n t a i η i ng z e r c o r f r e e h e r b i c i d e were s i m i I a r I y p r e p a r e d . Ten cucumber s e e d s ( P e t o s e e d SMR 18, V a r i e t y 0 5 1 , t h i ram t r e a t e d , P e t o s e e d C o . , I n c . , S a t u o y , C A ) were p r e s o a k e d i n w a t e r f o r 2h and random I y ρ Iaced on t h e s o i l s u r f a c e o f e a c h p o t w h i c h was t h e n c o v e r e d w i t h a c l e a r ρIastic p e t r i d i s h . A l l t r e a t m e n t r e p l i c a t e s were p l a c e d t o g e t h e r i n s e p a r a t e w a t e r - f i l l e d a l u m i n u m t r a y s (26.7x39.4x2.5cm) i n a c o n t r o l l e d env i ronment room ( c o n s t a n t l i g h t a t 21° and 65% r e I a t i v e humi d i t y ) . T h e r e a f t e r e a c h 3 d a y s t h e g e r m i n a t e d r o o t s t r u c t u r e s were compared t o t h o s e o f t h e c o n t r o l s (I -1.5cm r o o t l e n g t h ; m y c o r h t z a p r e s e n t ) . The s e e d l i n g s and t h e u n g e r m i n a t e d s e e d s were t h e n removed and r e p l a c e d w i t h f r e s h l y p r e s o a k e d s e e d s . The s t a n d ing w a t e r i n t h e a Iumi nu d thi time T h i s e n t i r e p r o c e d u r e wa a t i n g seeds i n t h e pots g 2,4-dichloro p h e n o x y a c e t a t e were s t a t i s t i c a I I y equ i va I e n t t o t h o s e in the c o n t r o I.

Literature

Cited

1. Allan, G.G. and Neogi, A.N., in Controlled Release of Bio logically Active Agents, Eds., A.C. Tanquary and R.E. Lacey, Plenum Press, NY, 1974, 195 2. Harris, F.W., Proceedings International Controlled Release Pesticide Symposium, College of Science and Engineering, Wright State University, Dayton, Ohio, 1975. 3. C a r d a r e l l i , N.F., Controlled Release Pesticide Symposium, Eng ineering and Science Division, Community and Technical College, The University of Akron, Akron, Ohio, 1976. 4. Allan, G.G., Friedhoff, J.F. and Powell, J.C., Intern. Pest Control, 1974, 12 (2), 4. 5. Timell, T., Ph.D. Thesis, Royal Institute of Technology, Stockholm, Sweden, 1960. 6. Jorgensen, L. and R i b i , Ε., Nature, 1950, 166, 148. 7. Gardner, T.S. and Purves, C.B., J. Am. Chem. Soc., 1942, 64, 1539. 8. Honeyman, J., J. Chem. Soc., 1947, 168. 9. Higuchi, T. and Aguar, A., J. Pharm. S c i . , 1959, 45, 578. 10. Neogi, A.N., Ph.D. Thesis, University of Washington, Seattle, Washington, 1970. 11. Wilkins, R.M., M.S. Thesis, University of Washington, Seattle, Washington, 1970. 12. Allan, F.J., Allan, G.G., Crank, G. and Thomson, J.B., J. Appl. Chem., 1962, 12, 46. 13. Buras, J r . , E.M., Cooper, A.S., Keating, E.J., and Goldthwait, C.F., Amer. Dyestuff Rep., 1954, 43, 203. 14. Allan, G.G., Belgian Patent 706,509 (1966); Australian Patent 423,990 (1967); Italian Patent 820,813 (1967); French Patent 1,544,406 (1968); Japanese Patent 558,788 (1969); U.K. Patent 1,212,842 (1970); Canadian Patents 855,181 (1970), 863,310 (1971); U.S. Patent 3,813,236 (1974).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10 Polymers Containing Pendant Herbicide Substituents: Hydrolysis Studies II FRANK W. HARRIS, MARY R. DYKES, JIM A. BAKER, and ANN E. AULABAUGH Department of Chemistry, Wright State University, Dayton, Ohio 45431

The objective of this research has been the development of controlled-release herbicide of aquatic weeds (1,2). One approach to these materials has been the synthesis of polymers that contain herbicides as pendent substituents (3-5). For example, homopolymers have been prepared that consist of over 80% 2,4-dichlorophenoxyacetic acid (2,4-D) or 2-(2,4,5-trichlorophenoxy)propionic acid (Silvex) as pendent side chains. It was postulated that the herbicide would be released from these systems by the slow, sequential hydrolysis of the herbicide-polymer bonds. Hydrolysis studies, however, showed that the homopolymers will not undergo hydrolysis under mildly alkaline conditions at 30° (6).

102

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

HARRIS E T A L .

Polymers

with Pendant

Herbicides

103

The reactivity of substituents attached to the backbone of a polymer chain is known to be substantially increased by the presence of suitable neighboring groups (7). For example, the hydrolysis of pendent ester groups is enhanced by the incorporation of carboxyl groups along the backbone (8-11). In an attempt to similarly facilitate the hydrolysis of herbicide-polymer bonds, copolymers were prepared that contained pendent herbicide esters and carboxyl groups. Copolymers containing herbicides and hydrophilic aminimide residues were also prepared. Thus, the copolymer!zation of the 2-acryloyloxyethyl esters of 2,4-D (la) and Si 1 vex (lb) with methacrylic acid (II) and trimethyl ami ne methacrylimide (IV) afforded the polymers III and V. A preliminary hydrolysis study of polymer Ilia containing 20 mole percent methacrylic acid indicated that the copolymer undergoes relatively rapid hydrolysis at pH 8 and 30°. (A 1-g sample of the copolymer released 11 the study.) Copolymers containing the aminimide residue, however, hydrolyzed slowly under these conditions. (A 1-g sample of Va containing 35 mole percent IV released 18 mg of 2,4-D in 32 days.) Decreasing the percentage of IV in Copolymer Va resulted in a decrease in the rate of hydrolysis (6). This communication describes the preparation and subsequent hydrolyses of samples of copolymer Ilia which contain reduced amounts of methacrylic acid. The final results of the study of the hydrolysis of copolymer Va are also presented. In addition, a copolymer of 2-methacryloyloxyethyl 2,4-dichlorophenoxyacetate and methacrylic acid has been prepared and subjected to mild hydrolysis conditions. Results and Discussion Copolymers of 2-Acryloyloxyethyl 2,4-Dichlorophenoxyacetate and Methacrylic Aci
In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C/3

M

Figure 1. Hydrolysis of methacrylic acid copolymers. (Ο) 90:10 copolymer of 2-acryloyloxyethyl 2,4-dichlorophenoxy acetate and methacrylic acid. (Φ) 95:5 copolymer of 2-acryloyloxy ethyl 2,4-dichlorophenoxy acetate and methacrylic acid. Β

w

*Ϋ

w

>

w w r w

r< m ο

r

Ο

Ο ο ζ

Ο

10.

HARRIS E T A L .

Polymers

with Pendant

Herbicides

105

p a r t i c l e s , which e v e n t u a l l y prevented f u r t h e r s p e c t r o s c o p i c a n a l y s i s o f the s o l u t i o n s . In f a c t , the l a s t p o i n t on the h y d r o l y s i s curve o f the 90:10 2-acryoyloxyethyl 2 , 4 - d i c h l o r o phenoxyacetate: m e t h a c r y l i c a c i d copolymer may be high due to the c l o u d i n e s s o f the a n a l y t i c a l samples. One o f the r e p l i c a t e s o f t h i s copolymer was a c i d i f i e d and e x t r a c t e d with ether a f t e r 296 days. Approximately 290 mg o f pure 2 , 4 - D , which represents 87% o f the 2,4-D o r i g i n a l l y contained i n the polymer, was recovered. As can be seen i n Figure 1, the r a t e o f h y d r o l y s i s o f both copolymers increased with time. This i s s i m i l a r to the a u t o a c c e l e r a t i o n i n r a t e observed i n the h y d r o l y s i s o f polyacrylamides (12) and p o l y ( v i n y l acetate) (13). In these c a s e s , the a c c e l e r a t i o n has been a s c r i b e d to i n t r a m o l e c u l a r i n t e r a c t i o n s o f n e i g h boring groups generated durin h y d r o l y s i s o f e s t e r group chain has a l s o been a t t r i b u t e d to a neighboring group e f f e c t (8). The enhanced h y d r o l y s i s i s thought to be due to an i n t e r n a l n u c l e o p h i l i c attack o f a neighboring carboxylate ion on the carbonyl carbon o f the e s t e r group, with the formation o f a

S%H "& C

^"Φ-

six-membered a c i d anhydride intermediate being r a t e determining. Considerable subsequent work has s u b s t a n t i a t e d t h a t i n t e r m o l e c u l a r r e a c t i o n s are p r a c t i c a l l y n e g l i g i b l e i n comparison to the i n t r a molecular f u n c t i o n a l i n t e r a c t i o n s between an e s t e r group and a d i r e c t l y v i c i n a l a c i d or carboxylate group. S t e r i c hindrance, however, can reduce or prevent the neighboring group e f f e c t (14). In the present s t u d y , the i n t e r a c t i o n o f a neighboring carboxyl group should r e s u l t i n the generation o f 2-hydroxyethyl 2,4-dichlororophenoxyacetate (VI). Nearly q u a n t i t a t i v e amounts o f

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

106

CONTROLLED RELEASE

PESTICIDES

pure 2 , 4 - D , however have been e x t r a c t e d from the h y d r o l y s i s solutions. I t i s p o s s i b l e t h a t compound VI undergoes subsequent h y d r o l y s i s to a f f o r d 2,4-D and ethylene g l y c o l . Preliminary analyses o f the sample s o l u t i o n s f o r ethylene g l y c o l i n d i c a t e t h a t only 20 to 40% o f the t h e o r e t i c a l amount i s present. The h y d r o l y s i s o f compound VI a t pH 8 i s c u r r e n t l y being i n v e s t i g a t e d . Another p o s s i b l e explanation f o r the a c c e l e r a t i o n i n r a t e i n v o l v e s i n t r a m o l e c u l a r i n t e r a c t i o n s o f carboxyl and e s t e r groups t h a t are not l o c a t e d on neighboring residues i n the polymer chain. In t h i s c a s e , the r a t e o f h y d r o l y s i s r e f l e c t s the p r o b a b i l i t y o f chain conformations t h a t b r i n g the two i n t e r a c t i n g groups i n t o j u x t a p o s i t i o n and, hence, i s r e l a t e d to chain f l e x i b i l i t y and m o b i l i t y . The enhanced h y d r o l y s i s o f acrylamide terpolymers c o n t a i n i n g pendent e s t e r and c a t a l y t i c s u b s t i t u e n t s has been shown to be due to such i n t e r a c t i o n s (15). It has a l s o been demonstrated t h a t i e s t e r group must not be s t e r i c a l l y hindered. Thus, e s t e r groups t h a t are l o c a t e d several atoms away from the terpolymer backbone hydrolyze r a p i d l y while those attached d i r e c t l y to the backbone hydrolyze a t the normal i n t e r m o l e c u l a r r a t e . The polymers i n the present study underwent considerable s w e l l i n g and gradual d i s s o l u t i o n as the h y d r o l y s i s proceeded. Hence, the p r o b a b i l i t y o f i n t r a m o l e c u l a r i n t e r a c t i o n s between d i s t a n t e s t e r and carboxyl groups was i n c r e a s e d . Due to s t e r i c e f f e c t s , the carboxyl groups should only attack the 2,4-D e s t e r

c a r b o n y l s , which would r e s u l t i n the r e l e a s e o f pure 2,4-D. The presence o f more 2,4-D than ethylene g l y c o l i n the h y d r o l y s i s mixtures i n d i c a t e s t h a t considerable h y d r o l y s i s d i d occur at the 2,4-D-polymer e s t e r bond. It i s postulated t h a t the i n i t i a l h y d r o l y s i s o f the copolymers i s due to neighboring group i n t e r a c t i o n s with subsequent h y d r o l y s i s r e s u l t i n g from the i n t e r a c t i o n s o f d i s t a n t groups. Copolymer o f 2-Methacry1oyloxyethyl 2,4-Dichlorophenoxyacetate and M e t h a c r y l i c A c i d . The 2-methacryloyloxyethyl e s t e r

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

HARRIS E T A L .

Polymers

with Pendant

Herbicides

107

o f 2,4-D (VII) was prepared from 2,4-dichlorophenoxyacetyl c h l o r i d e and 2-hydroxyethyl methacrylate by the p r e v i o u s l y described procedure (2). The copolymer!zation o f t h i s monomer with 10 mole percent m e t h a c r y l i c a c i d by the procedure described f o r the a c r y l i c e s t e r afforded a 65% y i e l d o f V I I I . The white copolymer was s o l u b l e i n c h l o r i n a t e d hydrocarbons and had an inherent v i s c o s i t y o f 0.14 (0.5 g/dl i n 2-butanone at 3 0 ° ) .

Samples o f VIII were a l s o irnnersed i n a pH 8 buffer maintained at 3 0 ° . The copolymer, however, d i d not undergo h y d r o l y s i s under these m i l d c o n d i t i o n s . T h i s decrease i n r e a c t i v i t y may be due to increased s t e r i c hindrance i n the formation o f the proposed c y c l i c - a n h y d r i d e i n t e r m e d i a t e . In the m e t h a c r y l i c copolymers, the six-membered r i n g i s t e t r a s u b s t i t u t e d i n the 1,1' and 3 , 3 ' p o s i t i o n s which r e s u l t s i n considerable

IsotactJc

Syndiotactic

s t e r i c hindrance between the two a x i a l s u b s t i t u e n t s . This argument has been used to e x p l a i n the f a c t that m e t h a c r y l i c a c i d methyl methacrylate copolymers hydrolyze about 10-12 times more slowly a t 110° than a c r y l i c acid-methyl a c r y l a t e copolymers with the same molar composition (16). Copolymer o f 2 - A c r y l o y l o x y e t h y l 2,4-Dichlorophenoxyacetate and Trimethylamine Methacrylimide. The p r e v i o u s l y described study o f the h y d r o l y s i s o f copolymer Va c o n t a i n i n g 35 mole percent trimethylamine methacrylimide was completed ( 6 ) . The data shown i n Figure 2 were obtained by employing the procedures used with the m e t h a c r y l i c a c i d copolymers. The study was terminated a f t e r 394 days at which time the copolymer had released 250 mg o f 2,4-D per 0 . 5 - g sample, which corresponds to

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

108

CONTROLLED RELEASE PESTICIDES

I

SS to

*c

SX ο

„o

·*: .ο

oC *3>

*»

to 35 Η

.3 3s *3> V.

to S to 35^

a:i to 35

si • ^ to *C to

ε

C

gI 35 35

ο

ι

to **>

Is

5

to 35

κ ο to 3>

•s to «•Λ

"δCO

1 35

it! 3

S

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

Polymers

HARRIS E T A L .

with Pendant

Herbicides

109

90% o f the amount o r i g i n a l l y present. As can be seen from the F i g u r e , the r a t e o f h y d r o l y s i s increased during the f i r s t few days o f the study and then remained r e l a t i v e l y c o n s t a n t . Since the c o n c e n t r a t i o n o f e s t e r linkages decreases as the polymer i s h y d r o l y z e d , the r a t e constant f o r the h y d r o l y s i s must c o n t i n u a l l y increase. T h i s behavior, i n e f f e c t , provides a z e r o - o r d e r r a t e o f r e l e a s e , which i s i d e a l l y s u i t e d f o r c o n t r o l l e d - r e l e a s e applications. The increase i n the r a t e constant as the h y d r o l y s i s p r o ceeds may a l s o be due to i n t r a m o l e c u l a r c a t a l y s i s . Infrared data i n d i c a t e s t h a t amine acylimides have a reasonance s t a b i l i z e d s t r u c t u r e as shown (17). Hence, i t i s p o s s i b l e that the

R'

R

R

aminimide group acts as a c a t a l y s t i n the same manner as d e s c r i b e d f o r the carboxyl group. The mechanism by which c o polymer Va undergoes h y d r o l y s i s i s c u r r e n t l y being i n v e s t i g a t e d . Experimental U l t r a v i o l e t s p e c t r a were obtained with a Gary Model 14 spectrophotometer. Infrared spectra were obtained on t h i n f i l m s with a Perkin-Elmer Model 457 spectrophotometer. Viscosities were determined with a Cannon Number 75 viscometer. The aminimide monomer was furnished by Ashland Chemicals, Columbus, Ohio. General S o l u t i o n Copolymerization Procedure. Herbicide monomer, comonomer, 2-butanone (4 ml/g o f monomers), and 0.05% AIBN were thoroughly mixed and slowly heated under n i t r o g e n to 75°. A f t e r heating at 75° f o r 3 h r , the mixture was c o o l e d , d i l u t e d with 2-butanone, and p r e c i p i t a t e d i n hexane. The copolymer was c o l l e c t e d by f i l t r a t i o n and d r i e d under vacuum at 60° f o r 3 h r . Hydrolysis Studies. The copolymers were e x t r a c t e d with ether f o r 18 hr to remove unreacted monomer, d r i e d under vacuum, and then ground and sieved to a p a r t i c l e s i z e o f 125-400y. Three 0 . 5 - g samples o f each copolymer were placed i n 500-ml erlenmeyer f l a s k s c o n t a i n i n g 300 ml o f a b o r i c acid-sodium hydroxide buffer (pH = 8 . 0 8 ) . The f l a s k s were maintained a t 30 + 0.1° i n a constant temperature bath. The amount o f h e r b i c i d e r e l e a s e d from each copolymer was determined p e r i o d i c a l l y by spectrophotometric a n a l y s i s at 198 nm.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

110

CONTROLLED RELEASE

PESTICIDES

Acknowledgement Support o f t h i s research by the Department o f the Army, U.S. Army Engineer Waterways Experiment S t a t i o n under Contract DACW39-86-C-0016 (Neg.) i s g r a t e f u l l y acknowledged. Appreciation i s a l s o expressed to AmChem Products, Inc. f o r f u r n i s h i n g the h e r b i c i d e s and to Ashland Chemicals Company f o r f u r n i s h i n g the aminimides used i n t h i s study.

Literature Cited 1. 2.

3. 4. 5.

6.

7. 8. 9. 10. 11. 12. 13. 14.

Harris, Frank W., Norris, Steve O., and Post, Larry Κ., Weed Science, (1973), 21 (4), 318. Harris, Frank W. and Post, Larry K. in "Proceedings 1974 International Controlled Release Pesticide Symposium," Cardarelli, Nate F. 1974. Harris, Frank W., and Post, Larry Κ., Am. Chem. Soc., Polym. Div., Preprints, (1975), 16 (2), 622. Harris, Frank W. and Post, Larry K., J. Polym. Sci., Polymer Letters Ed., (1975), 13, 225. Harris, Frank W., Feld, William Α., and Bowen, Bonnie, in "Proceedings 1975 International Controlled Release Pesticide Symposium," p. 334 Harris, F.W., Ed., Wright State University, Dayton, Ohio, 1975. Harris, Frank W., Aulabaugh, Ann Ε., Case, Robert D., Dykes, Mary Κ., and Feld, William Α., "ACS Symposium Series, No. 33, Controlled-Release Polymeric Formulations," p. 222, Paul, D.R. and Harris, F.W., Ed., American Chemical Society, Washington, D.C., 1976. Morawetz, Η., "Macromolecules in Solution," pp. 422-426, Wiley, New York, 1965. Morawetz, H., and Zimmering, P.E., J. Phys. Chem., (1954), 58, 753. Gaetjens, E. and Morawetz, J. Amer. Chem. Soc., (1961), 83, 1738. Morawetz, Η., and Westhead, E.W., J . Polym. S c i . , (1955), 16, 273. VanBeylen, M.M. in "Stereochemistry of Macromolecules," Vol. 3, p. 335, Ketley, A.D., Ed., Marcel Dekker, New York, 1968. Smets, G. and Hesbain, A.M., J. Polym. S c i . , (1959), 40, 217. Sakurada, I. and Sakaguchi, Y., Kobunshi Kagaku, (1956), 13, 441; Chem. Abst., (1957), 51, 17365 g. Smets, G. and VanHumbeeck, W., J . Polym. S c i . , (1963), 1, 1227.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10.

HARRIS ET A L .

Polymers

with Pendant

Herbicides

15. Goodman, N. and Morawetz, H., J . Polym. S c i . , Part C, (1970), 31, 177. 16. Smets, G., and DeLoecker, W., J . Polym. S c i . , (1960), 45, 461. 17. McKillip, W.J., Sedor, E.A., Culbertson, B.M., and Wawzonek, S., Chem. Rev., (1973), 73, 255.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

111

11 Synthesis, Characterization, and Release Mechanisms of Polymers Containing Pendant Herbicides CHARLES L. McCORMICK and MICHAEL FOOLADI Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Miss. 39401

As the w o r l d ' s populatio faced with the demand f o r enhanced production u t i l i z i n g chemicals with l i t t l e or no detrimental e f f e c t on the surrounding e n v i r o n ment. P e s t i c i d e leaching i n t o drainage waters and subsequent t r a n s p o r t i n t o non-target areas i s o f growing e c o l o g i c a l concern. The immensity o f the problem i s apparent when c o n s i d e r i n g the t o t a l a g r i c u l t u r a l p e s t i c i d e a p p l i c a t i o n and the annual r u n - o f f f o r drainage a r e a s . The M i s s i s s i p p i Watershed area alone covers 1,244,000 square miles i n c l u d i n g vast s t r e t c h e s o f c e n t r a l U.S. farmland. The annual water discharge a t the mouth o f the M i s s i s s i p p i has been estimated to 7.8 χ 1 0 y d s and 2,000,000 tons o f sediment are c a r r i e d i n t o the sea per day. The average annual r a i n f a l l over t h i s area i s about 30 i n c h e s , o f which about one-fourth t r a v e l s to the G u l f o f Mexico by way o f the M i s s i s s i p p i River ( 1 , 2 ) . In 1974, nearly 1.4 b i l l i o n pounds o f organic p e s t i c i d e s were s o l d by U.S. companies, representing a growth o f 12% over 1973. I n s e c t i c i d e s accounted f o r 50.4% o f the t o t a l volume with the balance c o n s i s t i n g o f h e r b i c i d e s , f u n g i c i d e s , and p l a n t hormones (3). With some p e s t i c i d e systems, 70 - 80% of the useful chemical a c t i v i t y i s l o s t by various mechanisms i n c l u d i n g i n t e r a c t i o n with non-target organisms. S c i e n t i s t s have measured the rates o f loss o f a c t i v i t y o f various chemicals i n terms o f "persistence" levels. P e r s i s t e n t p e s t i c i d e s have been attacked i n environmental studies due t o t h e i r usual migration to nont a r g e t areas. However, i t should be pointed out that some degree o f persistence i s necessary t o y i e l d weed, i n s e c t or fungus c o n t r o l f o r a reasonable period o f time i n the t a r g e t area. Often the most p e r s i s t e n t chemicals are a l s o the most effective. Several f a c t o r s are known t o determine p e r s i s t e n c e i n the soil. These include (a) uptake and degradation by microorgan isms, (b) l o s s through p h y s i c a l processes o f v o l a t i l i z a t i o n and l e a c h i n g , and (c) chemical changes such as photo-decomposition and chemical reactions (4). 11

3

112

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

MCCORMICK

A N D FOOLADI

Polymers with Pendant

Herbicides

113

The Environmental P r o t e c t i o n Agency i s imposing s t r i n g e n t requirements on several e f f e c t i v e and p r e v i o u s l y widely used pesticides. The t y p e , amount a p p l i e d , s p e c i f i c i t y , and p e r s i s t e n c e o f each p e s t i c i d e w i l l be under continuing s c r u t i n y . The pest c o n t r o l agents must not merely c o n t r o l t a r g e t organisms but must be harmless to humans, l i v e s t o c k , c r o p s , f i s h , w i l d l i f e , b e n e f i c i a l i n s e c t s , s o i l microorganisms, e t c . Dramatic improvements i n a n a l y t i c a l instrumentation have allowed claims o f d e t e c t i o n o f t r a c e amounts of organic chemicals i n non-target areas i n the parts per b i l l i o n range. T h i s a d vance, i n conjunction with the controversy generated by adverse p u b l i c i t y on i n s e c t i c i d e s such as DDT and Mi rex, has led to a f l u r r y o f experiments on n e a r l y every chemical manufactured i n the U.S. P a r t i c u l a r emphasis has been placed on chemicals having p o t e n t i a l impact on the aquatic environment. For example, B u t l e r ( 5 - 1 2 ) has reporte use of p e s t i c i d e chemicals i s producing environmental changes or residues i n the food web that may cause reproductive f a i l u r e . . " Some organisms have been shown to accumulate or concentrate c e r t a i n p e r s i s t e n t p e s t i c i d e s at alarming r a t e s . The o y s t e r , f o r example, when continuously exposed to 0.1 ppb o f DDT, was r e ported to concentrate i n i t s t i s s u e s up to 7.0 ppm i n a month. It may be p r e d i c t e d that c h l o r i n a t e d h e r b i c i d e s w i l l soon come under attack ( 1 3 , 2 8 - 3 0 ) . S t r i n g e n t r u l e s and r e g u l a t i o n s (apparently subject to frequent m o d i f i c a t i o n ) have been imposed on a g r i c u l t u r a l chemical producers and consumers as a r e s u l t of environmental s t u d i e s . Many knowledgeable sources p r e d i c t an impending d i s a s t e r f o r the whole a g r i c u l t u r a l i n d u s t r y from the high costs o f l i c e n s i n g , r e g i s t r a t i o n , and production of new p e s t i c i d e s . In 1976, new p e s t i c i d e commercialization required an average of 2 . 5 years of research and development at a cost o f over $10,000,000.00. The a g r i c u l t u r a l i n d u s t r y has, i n g e n e r a l , responded to the e n v i r o n mental r e g u l a t i o n s by producing l e s s p e r s i s t a n t but often l e s s e f f e c t i v e p e s t i c i d e s , r e q u i r i n g more frequent a p p l i c a t i o n over an extended growing season. A more l o g i c a l and c e r t a i n l y more f r u i t f u l approach i s to attack the undesired " l e a c h i n g " or t r a n s p o r t of a given p e s t i c i d e r a t h e r than i t s " p e r s i s t e n c e . " A g r i c u l t u r a l chemical leaching and subsequent p e s t i c i d e t r a n s p o r t to non-target environments can be g r e a t l y reduced, p o s s i b l y e l i m i n a t e d , by c o n t r o l l e d - r e l e a s e systems based on macromolecules. Polymers can be synthesized which contain r e a c t i v e chemical bonds to common p e s t i c i d e s ; these bonds are subject to enzymatic or h y d r o l y t i c break-down at a c o n t r o l l a b l e rate. The macromolecular nature of these systems w i l l prevent d i s s o l u t i o n , leaching and t r a n s p o r t to non-target areas. Cont r o l l e d - r e l e a s e can a l s o reduce the number of a p p l i c a t i o n s and the q u a n t i t y of chemical required f o r pest c o n t r o l . A number of n a t u r a l l y o c c u r r i n g polymers ( 2 5 - 2 7 ) o f f e r e x c e l l e n t p o t e n t i a l as raw m a t e r i a l s f o r substrate preparation o f c o n t r o l l e d r e l e a s e systems. In a d d i t i o n , c e r t a i n polysaccharides decompose y i e l d i n g

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

114

CONTROLLED RELEASE

PESTICIDES

products b e n e f i c i a l to the s o i l . Development of a commercial h e r b i c i d e system must combine e f f e c t i v e n e s s , favorable economics, with l i t t l e adverse e n v i r o n mental impact. The chemical must: (1) c o n t r o l weeds at reason able dosages, (2) s e l e c t i v e l y c o n t r o l target organisms o n l y , l e a v i n g b e n e f i c i a l i n s e c t s , p l a n t s , and humans unharmed, (3) p e r s i s t f o r a reasonable time, (4) be inexpensive f o r l a r g e s c a l e usage, and (5) and be e a s i l y a p p l i e d , (preferably with conventional equipment). Provided the above c r i t e r i a are met, p o t e n t i a l b e n e f i t s d e r i v e d from properly formulated c o n t r o l l e d - r e l e a s e systems include: (1) enhanced a g r i c u l t u r a l p r o d u c t i o n , (2) fewer a p p l i c a t i o n s , (3) l e s s environmental p o l l u t i o n and (4) reduced production costs to the farmer. Macromolecular

Design

Polymeric systems f o r c o n t r o l l e d - r e l e a s e of p e s t i c i d e s may be assigned to two broad c a t e g o r i e s . In the f i r s t , the p e s t i c i d e i s p h y s i c a l l y d i s s o l v e d , entrapped, or dispersed i n a polymer matrix. Chemical release i s g e n e r a l l y based on d i f f u s i o n phenomena (14-19, 34-39); however, chemical or b i o l o g i c a l e r o s i o n of the polymer matrix i s a l s o p o s s i b l e . In the second category, the p e s t i c i d e i s chemically bound (pendant) to the macromolecular backbone. Release i s then dependent on the r a t e o f chemical or b i o l o g i c a l break-down of the p o l y m e r - t o - p e s t i c i de (20-24, 31-39). Polymers c o n t a i n i n g pendant p e s t i c i d e s can be prepared by two s y n t h e t i c methods. The f i r s t involves bonding (via covalent o r i o n i c chemical bonds) of a p e s t i c i d e to a ρre-formed polymer. T h i s approach requires macromolecules with pendant f u n c t i o n a l groups capable of r e a c t i o n with p e s t i c i d e s or t h e i r d e r i v a t i v e s . The nature of the chemical bond may be v a r i e d to y i e l d bonds with q u i t e d i f f e r e n t rates of cleavage i n the environment. Ad vantages of t h i s method i n c l u d e : (a) a v a i l a b i l i t y of r e l a t i v e l y inexpensive polymers with b i o d e g r a d a b i l i t y such as c h i t i n , c e l l u l o s e , e t c . , and (b) use of commercially a v a i l a b l e p e s t i c i d e s as s t a r t i n g m a t e r i a l s i n polymer s y n t h e s i s . The second approach involves polymerization of monomeric pesticides. The major advantages of t h i s method l i e i n the a b i l i t y to c o n t r o l the molecular design of the polymer and the pesticide/polymer weight r a t i o . b

o

n

d

s

Experimental Preformed, hydroxy-containing polymers were s e l e c t e d f o r i n i t i a l study. Three polymers - p o l y v i n y l a l c o h o l , c h i t i n , and c e l l u l o s e were chose on the basis o f : (a) p o t e n t i a l biode g r a d a b i l i t y , (b) commercial a v a i l a b i l i t y , and (c) h y d r o p h i l i c i t y i n a d d i t i o n to having proper pendant f u n c t i o n a l i t y . The r e s u l t s o f the experiments on p o l y v i n y l alcohol are reported i n t h i s work

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

MCCORMICK

AND

FOOLADi

Polymers with Pendant

Herbicides

115

Metribuzin was chosen as a model p e s t i c i d e based on: (a) a v a i l a b l e amine f u n c t i o n a l i t y , (b) high a c t i v i t y at r e l a t i v e l y low c o n c e n t r a t i o n s , (c) s e l e c t i v i t y , (d) lack o f p e r s i s t e n c e i n the environment, and (e) high m o b i l i t y . A s e r i e s of laboratory and commercial polymers o f p o l y v i n y l a l c o h o l (with varying r e s i d u a l amounts of unhydrolyzed v i n y l acetate) were c a r e f u l l y c h a r a c t e r i z e d . Isocyanate adducts of metribuzin were prepared and reacted with the pendant hydroxy! f u n c t i o n a l i t y o f the pre-formed polymers (Figure 1). It was p o s s i b l e to prepare copolymers with varying degrees o f s u b s t i t u t i o n on l i n e a r and h i g h l y c r o s s - l i n k e d c h a i n s . The isocyanate to hydroxy1 r a t i o s were v a r i e d over a wide range to prepare solvent s w o l l e n , c r o s s - l i n k e d g e l s . These were converted to microporous s o l i d s by a g i t a t i o n of the product i n the presence of a non-solvent ( s e l e c t e d from s o l u b i l i t y parameter data). Rates o f Release of Metribuzin Polymers with pendant metribuzin (0.100 g) were placed i n an Erlenmeyer f l a s k . 500 ml o f d i s t i l l e d water was added. At designated i n t e r v a l s , samples were taken to determine the c o n c e n t r a t i o n o f released m e t r i b u z i n . U l t r a v i o l e t Spectroscopic Method. A Gary 1756 Spectrophoto meter was used to determine released metribuzin l e v e l s i n water. A standard p l o t of absorbance v s . concentration was obtained using l e a s t squares a n a l y s i s . 3 ml samples were taken at d e s i g nated i n t e r v a l s and placed i n standard quartz c e l l s . The ab sorbance at 293.5 nm was monitored i n two types o f t e s t s . The f i r s t measured t o t a l concentration of released metribuzin over a time p e r i o d . The second t e s t was conducted as f o l l o w s : (a) 0.100 g samples were placed i n 500 ml o f d i s t i l l e d water f o r a predetermined time; (b) the samples were f i l t e r e d , d r i e d and again placed i n a second Erlenmeyer f l a s k c o n t a i n i n g 500 ml o f d i s t i l l e d water; (c) concentrations were measured d i r e c t l y from the f i l t r a t e . Gas Chromatographic Method. 2yl of aqueous s o l u t i o n were removed and e x t r a c t e d with 5.0 ml o f benzene. 1 μΐ o f the benzene phase was then i n j e c t e d i n t o the gas chromatograph (Micro-Tek 220 with e l e c t r o n capture d e t e c t o r ) . S o i l M o b i l i t y Studies T h i n - l a y e r p l a t e s were prepared by spreading a s o i l s l u r r y onto 20 X 20 cm glass p l a t e s to a thickness of 1.0 mm. Plates were d i v i d e d i n t o three equal s e c t i o n s by s c r i b i n g the s o i l layer. Metribuzin was a p p l i e d to one p l a t e by s t r e a k i n g 500 λ o f a 100 g/ml s o l u t i o n onto each s e c t i o n o f the p l a t e 2 cm from the bottom. Polymers c o n t a i n i n g pendant metribuzin were embedded i n

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

3

) C-

3

Ν

i-S-CH.

^Ν-ΝΗ2

Ν-ψ-Ç-N-R Η Ο Η

-S-CHΗ

- f C H ^ C H ^ C H ^ Ç H ^ -

3

(CH ) C3

Η

CH -S-i

Η Ο Η OCNR-N-C-N-N*

î Ν

Figure 1. Synthetic method for preparation of PVA copolymer containing pendant metribuzin

-R-NCO

Ο

11.

M C C O R M I C K

AND

FOOLADi

Polymers with Pendant

Herbicides

117

the s o i l l a y e r on other p l a t e s which were a l s o d i v i d e d i n t o three sections. The p l a t e s were e l u t e d to 10 cm with water, a i r d r i e d , and 1-cm zones were removed from one of the three s e c t i o n s of each p l a t e . The p l a t e s were returned to the chamber and again e l u t e d with 10 cm of water, and the second zone was removed i n 1-cm s e c t i o n s . T h i s procedure was repeated with the t h i r d s e c t i o n of s o i l . The s o i l removed i n t h i s manner was e x t r a c t e d with 5 ml of hexane: acetone (3:1) by shaking. E x t r a c t was analyzed by gas chromatography. Residual P h y t o t o x i c i t y Of Metribuzin From Polymers The polymers c o n t a i n i n g pendant metribuzin were added to the surface of a Bosket sandy loam s o i l contained i n 4" p l a s t i c pots i n a c o n t r o l 1ed-environment chamber. The a p p l i c a t i o n rates were 0, 0 . 1 , 0 . 2 , and 0.3 g l a t i o n of metribuzin was a p p l i e d to other pots at 0.5 and 1.0 ppmw, and thoroughly mixed i n t o the s o i l . The s o i l s were b i o a s sayed over a period of 112 days with a mixture of weeds which are normally s u s c e p t i b l e to the h e r b i c i d e ; a f t e r growing two weeks, the weeds were harvested and f i r s t weights recorded. Results And Discussion Five polymers c o n t a i n i n g pendant metribuzin were chosen f o r study: 22-S, 23-S, 41-S, 45-S, and 50-S. 23-S, 4 5 - S , and 50-S were e s s e n t i a l l y l i n e a r polymers prepared from 99% hydrolyzed polyvinyl alcohol. 22-S and 41-S were h i g h l y c r o s s - l i n k e d m i c r o porous s o l i d s . These system r e q u i r e both h y d r o l y s i s of the urea bond and d i f f u s i o n from a water s w o l l e n , c r o s s - l i n k e d matrix f o r metribuzin r e l e a s e . P l o t s of s o l u t i o n concentration vs. time (Figures 2, 3) i n d i c a t e d that the l i n e a r polymers (23-S, 4 5 - S , and 50-S) r e leased h e r b i c i d e much more r a p i d l y than the c r o s s - l i n k e d systems. The 23-S, 45-S, and 50-S were c h a r a c t e r i z e d by a r a p i d i n i t i a l r e l e a s e i n the f i r s t few hours followed by a more gradual r a t e l a s t i n g several days. The c r o s s - l i n k e d systems 22-S and 41-S (Figure 4) had much lower r e l e a s e rates with l i t t l e i n i t i a l r e lease. T h i s could be p r e d i c t e d by the time required f o r s w e l l i n g o f the h y d r o p h i l i c polymer so that h y d r o l y s i s and d i f f u s i o n could occur. A f t e r s w e l l i n g , s l i g h t concentration increases were noted. The u.v. s p e c t r o s c o p i c data and the gas chromatographic data were i n t e r n a l l y c o n s i s t e n t . It should be noted that the u l t r a v i o l e t technique requires no e x t r a c t i o n and, t h e r e f o r e , o f f e r s less chance f o r e r r o r at small concentrations of metribuzin. S o i l t h i n - l a y e r chromatographic techniques showed metribuzin (Figure 5) moved as a normal chromatogram peak with each s u c c e s s i v e e l u t i o n moving the peak nearer the 10-cm zone. The chromatograms from 23-S (Figure 6) and 45-S (Figure 7) showed " s t r e a k i n g " continuously along the p l a t e i n d i c a t i n g a sustained r e l e a s e mechanism.· The c r o s s - l i n k e d f o r m u l a t i o n s , 22-S and 45-S,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

w

C/3

ο

a Figure 2. Metribuzin release from polymers in water (ultraviolet spectroscopy)

V)

W

*U

W

1

ο r r w α w w r w •

ζ

H-* h-»

00

ο ο

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

MCCORMICK

20

40 TIME

0.5

Polymers

A N D FOOLADi

with Pendant

Herbicides

119

Figure 3. Metribuzin re lease from linear (23S) and cross-linked (22S) polymers

60 (hours)

L

0.4

0.3

0.2

0.1

V

40 TIME

60 (hours)

—ι Figure 4. Metribuzin release 80 from linear (45S) and crosslinked (41S) polymers

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

120

CONTROLLED

DISTANCE

Figure 5.

0

(cm)

Soil thin layer chromatography (TLC) of metribuzin

I 0

RELEASE

! 2

£

£

*

*_

4

6

8

10

DISTANCE

Figure 6.

(cm)

Soil TLC of metribuzin released from 2SS

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PESTICIDES

11.

MCCORMICK

0

A N D FOOLADi

2

Polymers

with Pendant

4

6

DISTANCE

121

Herbicides

8

(cm)

Figure 7. Soil TLC of metribuzin released from 45S

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

10

g

en

η

W

Figure 8. Phytotoxicity of metribuzin from polymer formulations as a function of time

W

>

M

C/3

s

r

5 ο r f w α

to ta

H-*

Ο ο ζ

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

M C c o R M i C K A N D FOOLADi

Polymers with Pendant

Herbicides

123

did not r e l e a s e enough metribuzin f o r a measurable rate i n these studies. Residual p h o t o t o x i c i t y of the four polymeric systems i s i l l u s t r a t e d i n Figure 8. Metribuzin at 1.0 ppmw had d i s s i p a t e d to a l e v e l which was e s s e n t i a l l y n o n - t o x i c a f t e r 78 days. Likew i s e , p h y t o t o x i c i t y from 41-S had diminished to a large extent by t h i s time. A r e l a t i v e l y low l e v e l of p h y t o x i c i t y was observed f o r 22-S i n i t i a l l y ; however, t h i s same l e v e l was maintained f o r over 78 days, then r a p i d l y decreased. The highest l e v e l of p h y t o t o x i c i t y was observed with 23-S and 45-S. These m a t e r i a l s were s t i l l showing p h y t o t o x i c i t y at our l a s t t e s t date of 112 days. It must be noted that p h y t o t o x i c i t y comparison t e s t s of polymeric c o n t r o l l e d - r e l e a s e formulations and commercially formulated h e r b i c i d e s must be i n t e r p r e t e d with c a r e . In the pendant polymeric systems bond cleavage has occurred. For t h i s reason the t o t a l h e r b i c i d e e v e n t u a l l y a v a i l a b l e i n the polymer cannot be compared to t h a t immediately a v a i l a b l e i n a commercial f o r m u l a t i o n . Conclusions Polymeric systems f o r c o n t r o l l e d release of metribuzin have been prepared using biodegradable s u b s t r a t e s . Properly s e l e c t e d macromolecular substrates were reacted with p e s t i c i d e adducts to y i e l d systems with l a b i l e p e s t i c i de-to-polymer bonds s u s c e p t i b l e to chemical or enzymatic h y d r o l y s i s . The metribuzin/polyviny1 alcohol system i n t h i s work i s adaptable f o r formation of a range of products with d i f f e r e n t degrees of c r o s s - l i n k i n g and, t h e r e f o r e , d i f f e r e n t rates of herbicide release. P h y t o t o x i c i t y , s o i l t h i n - l a y e r chromatography, u l t r a v i o l e t spectroscopy, and gas chromatography t e s t s showed sustained r e l e a s e c a p a b i l i t i e s of the polymeric systems. The p r e l i m i n a r y r e s u l t s of t h i s research p o i n t to the immense p o t e n t i a l of polymeric systems f o r c o n t r o l l e d - r e l e a s e of s e l e c t i v e h e r b i c i d e s which can: (1) reduce environmental p o l l u t i o n i n non-target areas by reducing p e s t i c i d e m o b i l i t y , (2) r e q u i r e fewer a p p l i c a t i o n s during the growing season, and (3) r e s u l t i n enhanced a g r i c u l t u r a l production a t , perhaps, lower c o s t to the farmer. Acknowledgements The authors would l i k e to express t h e i r thanks f o r the generous support of research conducted at the U n i v e r s i t y of Southern M i s s i s s i p p i Polymer Science Laboratories provided by Hopkins A g r i c u l t u r a l Chemical Company of Madison, Wisconsin. Research support was a l s o obtained from the USDA Weed Science Laboratories at S t o n e v i l l e , M i s s i s s i p p i , and from the M i s s i s s i p p i Alabama Sea Grant Program. The s o i l studies were conducted by

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

124

CONTROLLED RELEASE

PESTICIDES

Κ. E. Savage, Southern Weed Science L a b . , ARS, USDA, S t o n e v i l l e , MS, 38776.

Abstract Recently, there has been a growing interest in developing pesticide controlled release technology. Much of the impetus has resulted from demands for enhanced agricultural production at lower levels of environmental risk. Most of the activity has been directed toward formulations in which the pesticide is physically dissolved or dispersed in a polymer matrix. Polymers have been prepared in our laboratories which contain labile polymer to pesticide covalent bonds. These linkages are susceptible to aqueous and/or bacterial break-down, resulting in long-term release. Theoretically, the rate of herbicide release can be controlled by changin by altering the cross-link density of the polymer. The synthe sized systems have been characterized by IR, NMR, U.V., GPC, etc. Release studies have been conducted in aqueous media using U.V. and gas chromatography. In addition, soil mobility and phyto toxicity studies are in progress. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Barrett, Β. Β., Louisiana Wildlife and Fisheries Commission Report, Cooperative Gulf of Mexico Estuarine Inventory and Study, Hydrology, p. 115, 1971. Christmas, J.Y., Ed., Cooperative Gulf of Mexico Estuarine Inventory and Study, Mississippi, Publishers: Gulf Coast Research Laboratory, p. 12, 1973. Chemical and Engineering News, July 28, 1975, pp. 18-31. Kearney, R.C. and Kaufman, D.D., Herbicides, Chemistry, Degradation, and Mode of Action, 2nd Edition, Marcel Dekker, Inc., 1975. Butler, P.A., Pesticide Monitoring Journal, Vol. 6(4) 238, 1973. Butler, P.Α., "Pesticides in the Estuary," Proc. of Marsh and Estuary Management Symposium (July 1967), Baton Rouge, LA, pp. 120-124, 1968. Butler, P.A., Proc. of National Symposium on Estuarine Pollution, (August, 1967) Stanford University, p. 107, 1968. Butler, P.Α., "Significance of DDT Residue in Estuarine Fauna," Chemical Fallout, Chapter 9, pp. 205-220, 1969. "Pesticides in the Marine Environment," Journal Appl. Ecology 3, (Supplement) pp. 253-259, 1966. "Problems of Pesticides in Estuaries," American Fish Soc., SPE Public No. 3, pp. 110-115, 1966. Firth, F.E., Ed., "Pesticides in the Sea," Encyclopedia of Marine Resources, pp. 513-516. Butler, P.Α., "Pesticides," U.S. Bureau of Commercial Fisheries Report: Contract No. 85, 1967.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

11.

MCCORMICK

A N D FOOLADi

Polymers with Pendant Herbicides

125

13. Andus, L.J., Ed., The Physiology and Biochemistry of Herbicides, Academic Press, New York, 1964. 14. U.S. Patent #3,074,845. 15. U.S. Patent #3,318,769. 16. U.S. Patent #3,737,521. 17. U.S. Patent #3,127,752. 18. U.S. Patent #3,400,093. 19. U.S. Patent #3,343,941. 20. Allan, G.C., et al. Nature, 234, 349 (1971). 21. Neogi, A.N., Ph.D., Thesis University of Washington, Seattle, Washington, (1970). 22. Jakube, H.D., Busch, E., F. Chem, 13 (3), p. 105 (1973). 23. Allan, G.C., et al. Int. Pest Control, 14 (2), p. 15 (1972). 24. Harris, F.W. and Post, L.K., Polymer Preprints, 16 (1), pp. 622-627, (1975). 25. Pariser, E.R. and Block, S., Chitin and Chitin Derivatives, Report No. MITSG 73-2, October 15, 1972, (A bibliography with 593 references). 26. Davidson, R.L. and Sittig, Marshall, Eds., Water-Soluble Resins, Van Nonstrand Reinhold Co., New York, 1968. 27. Bikales, N.M., Water-Soluble Polymers, Plenum Press, New York, 1973. 28. O'Brien, R.D., Insecticides, Action and Metabolism, Academic Press, New York, 1967. 29. White-Stevens, R., Pesticides in the Environment, Marcel Dekker, 1973. 30. Chemical Engineering, January 19, 1976. 31. Allan, G.C., Canadian Patent #846785. 32. Allan, G.C., Canadian Patent #863310. 33. Allan, G.C., Canadian Patent #855181. 34. Chemical and Engineering News, June 28, 1976. 35. Controlled Release Pesticide Symposium, The University of Akron, September, 1974. 36. Proceedings 1975 International Controlled Release Pesticide Symposium, Wright State University, September, 1975. 37. Proceedings 1976 Controlled Release Pesticide Symposium, The University of Akron, September, 1976. 38. Cardarelli, N., Controlled Release Pesticides Formulations, CRC Press, Cleveland, Ohio, 1976. 39. Paul, D.R. and Harris, F.W., Eds., Controlled Release Polymeric Formulations, ACS Symposium Series; 33, 1976.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12 Microencapsulated Pesticides HERBERT B. SCHER Formulations Section, Chemical Research Department, Stauffer Chemical Co., 1200 So. 47th St., Richmond, Calif. 94804

Microcapsules are 1 or l i q u i d core surrounde polymeric i n nature (Figure 1) and c o n s t i t u t e s 5-25 percent o f the microcapsule by weight. The wall i s o l a t e s and protects the core material i n storage but i s designed to r e l e a s e the core m a t e r i a l i n a c o n t r o l l e d fashion when the microcapsules are e x posed t o the environment. The core material can be released from the microcapsules by crushing the w a l l , breaking the wall by pressure from w i t h i n , d i s s o l v i n g the w a l l , hydrolyzing the wall o r by d i f f u s i n g through the w a l l . Controlled release of pesticides ( i n s e c t i c i d e s , herbicides, f u n g i c i d e s , fumigants, j u v e n i l e hormone mimics, i n s e c t sex a t t r a c t a n t s and animal health compounds) can be achieved by microencapsulation. P e s t i c i d e microcapsule systems can be designed t o : 1. Reduce mammalian t o x i c i t y and extend a c t i v i t y . 2. Reduce evaporative l o s s e s . 3. Reduce p h y t o t o x i c i t y . 4. Protect p e s t i c i d e s from environmental degradation. 5. Reduce l e a c h i n g . 6. Reduce p e s t i c i d e l e v e l s i n the environment. An aqueous d i s p e r s i o n o f p e s t i c i d e microcapsules i s a p a r t i c u l a r l y useful c o n t r o l l e d r e l e a s e p e s t i c i d e formulation because: 1. It i s composed o f d i s c r e t e microcapsules as opposed to aggregates. 2. I t can be d i l u t e d with water or l i q u i d f e r t i l i z e r s and sprayed using conventional equipment. Uniform f i e l d coverage o f p e s t i c i d e i s p o s s i b l e . 3. I t requires l e s s polymeric component per pound o f p e s t i c i d e than m o n o l i t h i c d e v i c e s . 4. I t i s capable o f e s t a b l i s h i n g a constant p e s t i c i d e r e l e a s e rate (See Figures 2 and 3 ) .

126

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

SCHER

Microencapsulated

127

Pesticides

Gelatin

Polyethers

Gum A r a b i c

Polyesters

Starch

Polyamides

Sugar Ethyl

Polybutadiene

Cellulose

Carboxymethyl

Cellulose

Polysiloxanes

Paraffin Polyvinyl

Polyisoprene

alcohol

Polyurethanes

Polyethylene

Epoxy r e s i n s

Polypropylene

inorganic

silicates

Polystyrene Polyacrylamide Encyclopedia of Polymer Science and Technology

Figure 1. Common microcapsule wall materials

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

128

C O N T R O L L E D R E L E A S E PESTICIDES

0 * Diffusion Coefficient Κ » Distribution Coefficient DK * Permeability AC

s

Concentration Difference Across Wall

I n i t i a l high release due to migration of p e s t i c i d e

approaches exhaustion

Time Chemical Technology Figure 2.

Pesticide release rate from microcapsule (2)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Microencapsulated

SCHER

Pesticides

129

(SLAB GEOMETRY)

Dissolved P e s t i c i d e dM dt

dM dt

2M„

Dispersed P e s t i c i d e 1/2

M

dM dt

π l t 2

f o r 0.4 <

8DM00 ^—exp

2

vço^y

M < 1.0 Moo

where D - D i f f u s i o n c o e f f i c i e n t

C

t - time M^

Moo/ÎDCs^

· t o t a l concentration of agent i n matrix s o l u b i l i t y of agent i n matrix

- Total mass of p e s t i c i d e dM dt

release rate

Release -Dissolved

Rate /mass. time'

•Dispersed

l

TIME Chemical Technology Figure 3.

Pesticide release rate from monolithic device (2)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

130

C O N T R O L L E D R E L E A S E PESTICIDES

The p e s t i c i d e r e l e a s e rate can be v a r i e d over wide limits by varying the microcapsule p a r t i c l e s i z e d i s t r i b u t i o n , the microcapsule wall thickness and the m i c r o capsule wall p e r m e a b i l i t y . Mixtures o f d i f f e r e n t microcapsules can a l s o be used to adjust the p e s t i c i d e release rate. 6. A d d i t i v e s such as f i l m forming agents can be added d i r e c t l y to the f o r m u l a t i o n . These agents can improve the adhesion of microcapsules to f o l i a g e . Microencapsulation processes can be d i v i d e d i n t o three c a t egories (3)(4)· In the Phase Separation category, microcapsules are formed by emulsifying or d i s p e r s i n g the core material i n an immiscible continuous phase i n which the wall material i s d i s solved and then the wall material i s caused to p h y s i c a l l y seperate from the continuous phase and deposit around the core particles. In the I n t e r f a c i a are formed by emulsifying or d i s p e r s i n g the core material i n an immiscible continuous phase and then an i n t e r f a c i a l polymerization r e a c t i o n i s caused to take place at the surface of the core particles. In the Physical Methods category, wall material and core p a r t i c l e s are p h y s i c a l l y brought together and the wall flows around the core p a r t i c l e to form the microcapsule. Microencapsulation processes are l i s t e d below according to these three c a t e g o r i e s . 5.

I.

Phase Separation Methods a. b. c. d. e.

II.

Interfacial a. b. c.

III.

Aqueous Phase Separation (complex coacervation) National Cash Register Company. Organic Phase Separation - I.B.M. Meltable D i s p e r i o n - National Cash R e g i s t e r Company. Spray Drying - Moore Business Forms, National Starch and Chemical C o r p o r a t i o n . F l u i d i z e d - B e d Spray Coating - Smith, K l i n e and French; Wisconsin Alumini Research Foundation. Reactions

I n t e r f a c i a l Condensation Polymerization - Pennwalt Chemical Company. In S i t u I n t e r f a c i a l Condensation Polymerization S t a u f f e r Chemical Company I n t e r f a c i a l A d d i t i o n Polymerization - Stanford Research I n s t i t u t e ; National Cash Register Company.

Physical Methods a. b.

M u l t i o r i f i c e C e n t r i f u g a l - Southwest Research Institute. E l e c t r o s t a t i c - I IT Research I n s t i t u t e .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SCHER

Microencapsulated

Pesticides

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

132

C O N T R O L L E D R E L E A S E PESTICIDES

Microcapsule Dispersion

Atomizer

Exaust Air

Microcapsule Powder Encyclopedia of Polymer Science and Technology

Figure 5. Spray dryers are direct, dispersion-type dryers which operate on the principle of atomizing a fluid feed to form a spray of droplets which mix with hot gases to evaporate a liquid and produce a dispersed, dry product. Spray dryers find extensive application in the process and food industries. They can be characterized as follows: (1) an atomizing device disperses the liquid into a spray of droplets with a range of drop sizes. Drops can range in diameter from 100-600 μ depending on the type of atomizer used, the capacity, and atomizing conditions. (2) Hot gases, introduced by a variety of gas-inlet configurations, contact the spray and evaporate moisture from the individual drops. (3)The mixture of hot gases and spray droplets which produce a dry, paniculate product has a residence time in the dryer which is highly statistical in character. (4) The dry product and drying gases must be separated to obtain the desired dry product in the form of finely divided material. (5) Any residual product must be recovered from the exhaust gases.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

SCHER

Microencapsulated

Pesticides

133

Aqueous Phase Separation (complex c o a c e r v a t i o n ) , I n t e r f a c i a l Condensation Polymerization and In S i t u I n t e r f a c i a l Condensation Polymerization are the most widely used processes f o r microencapsulating pesticides. The r e s u l t i n g product of a l l three o f these processes i s an aqueous d i s p e r s i o n o f p e s t i c i d e microcapsules. The National Cash R e g i s t e r Company (5_) has used an aqueous phase separation process (complex coacervation) to microencaps u l a t e p e s t i c i d e s f o r 20-years. The complex coacervation process c o n s i s t s o f the f o l l o w i n g s t e p s . 1. D i s s o l v e g e l a t i n ( i s o e l e c t r i c p o i n t = 8) i n aqueous phase (pH > 8 . 0 ; 50°C). 2. Emulsify p e s t i c i d e l i q u i d i n aqueous phase. 3. Add gum a r a b i c s o l u t i o n to aqueous phase (pH > 8 . 0 ; 50°C) 4. Mutual p r e c i p i t a t i o n (complex coacervation) of gum a r a b i c and g e l a t i n around p e s t i c i d e p a r t i c l e s i s induced by dropping pH Figure 4 ) . 5. Gel complex coacervate by c o o l i n g to 5-10°C. 6. Harden complex coacervate by a d d i t i o n o f glutaraldehyde or formaldehyde and adjusting pH to 9-10. Organic Phase Separation (6) and Meltable D i s p e r s i o n (7) processes are the inverse o f Aqueous Phase Separation and are used to microencapsulate h y d r o p h i l i c substances. Organic phase s o l u b l e polymers are p r e c i p i t a t e d around the h y d r o p h i l i c core by the a d d i t i o n o f a nonsolvent or c o o l i n g . Since p e s t i c i d e s are p r i m a r i l y l i p o p h i l i c substances, these processes are g e n e r a l l y not s u i t a b l e f o r the microencapsulation o f p e s t i c i d e s . Spray Drying (8) and F l u i d i z e d Bed Spray Coating (9j are useful processes f o r the microencapsulation of p e s t i c i d e s o l i d particles. In the spray d r y i n g p r o c e s s , a f i l m forming polymer i s d i s s o l v e d i n the aqueous continuous phase o f a p e s t i c i d e d i s persion. The d r y i n g process (see Figure 5) causes the water to evaporate and the polymer coats the p e s t i c i d e p a r t i c l e . The r e s u l t i n g microcapsule product i s a f r e e - f l o w i n g , dry powder. In the Wurster process ( F l u i d i z e d - B e d Spray C o a t i n g ) , a f l u i d i z e d bed o f sol id p e s t i c i d e p a r t i c l e s i s sprayed with an aqueous polymer s o l u t i o n . Coating o f the p e s t i c i d e p a r t i c l e s occurs when the water i s evaporated. A d d i t i o n a l coats of polymer can be a p p l i e d to the p e s t i c i d e p a r t i c l e s by r e c i r c u l a t i o n through the spraying and d r y i n g zones (see Figure 6). Pennwalt Corporation has pioneered i n microencapsulation by i n t e r f a c i a l condensation polymerization (10). Pencap M (microencapsulated Methyl Parathion) i s produced by the i n t e r f a c i a l r e a c t i o n o f sebacoyl c h l o r i d e ( i n the organic phase) and e t h y l enediamine and di e t h y l e n e t r i ami ne ( i n the aqueous phase). The r e a c t i o n product (microcapsule w a l l ) i s a cross l i n k e d polyamide (see Figure 7). S t a u f f e r Chemical Company has developed a microencapsulation process based on i n s i t u i n t e r f a c i a l condensation polymerization (11). The process i s capable o f producing an aqueous d i s p e r s i o n

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

FIRST, CHARGE WITH • CONTINUOUS AND DISCONTINUOUS LIQUIDS INCLUDING FIRST REACTANT

PESTICIDES

THIRD, LOWER RATE

I

'

OF AGITATION WHILE ADDING SECOND REACTANT

SECOND, RAPIDLY AGITATE TO FORM DISPERSION U.S. Patent 3,577,515

Figure 7. Interfacial condensation polymerization (10)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

SCHER

Microencapsulated

Pesticides

135

of microcapsules c o n t a i n i n g 4-pounds o f a c t i v e i n g r e d i e n t per gallon. The f i r s t step o f the process c o n s i s t s o f d i s p e r s i n g an organic p e s t i c i d e phase (containing isocyanate monomers) i n t o a aqueous phase. The isocyanate monomers used i n the process are polymethylene polypheny! isocyanate (PAPI) and toluene d i i s o cyanate (TDI). The wall forming r e a c t i o n i s i n i t i a t e d by heating the batch to an elevated temperature at which point the i s o cyanate monomers are hydrolyzed at the i n t e r f a c e to form amines, which i n turn r e a c t with unhydrolyzed isocyanate monomers to form the polyurea microcapsule w a l l . The process and wall form ing r e a c t i o n i s described i n Figure 8. The r e l e a s e rate o f t h i s microcapsule system can be v a r i e d by varying microcapsule p a r t i c l e s i z e ( i . e . , t o t a l surface area per pound o f p e s t i c i d e ) cyanate monomers i n organi wall p e r m e a b i l i t y can be v a r i e d by varying the cross l i n k d e n s i t y o f the polyurea ( r a t i o of PAPI to TDI). E l e c t r o n scanning photo micrographs o f the microcapsules produced by t h i s process are shown i n Figures 9-11. Microencapsulation by i n t e r f a c i a l a d d i t i o n polymerization (12) involves 1) d i s s o l v i n g v i n y l monomers i n p e s t i c i d e 1 i q u i d , 2T~emulsifying p e s t i c i d e s o l u t i o n i n aqueous phase, 3) c o n t a c t ing surface o f p e s t i c i d e p a r t i c l e with a d d i t i o n polymerization catalyst. P e s t i c i d e microcapsule powders can be produced by (13) m u l t i o r i f i c e c e n t r i f u g a t i o n (see Figure 12) or (14) e l e c t r o s t a t i c encapsulation (see F i g u r e 13). The diameters o f the microcapsules produced by these p h y s i c a l methods are l i m i t e d to 80 μ and l a r g e r . The f a c t o r s a f f e c t i n g the rate o f r e l e a s e o f the core m a t e r i a l from a microcapsule were smmarized by (15) Fanger (see Figure 14). The f o l l o w i n g examples show the v a r i e t y o f a p p l i c a t i o n s for microencapsulated p e s t i c i d e s . 1. Microencapsulated Methyl Parathion (Pencap M produced by Pennwalt Corp.)

2.

3.

4.

Microencapsulating Methyl Parathion reduces i t s mammalian t o x i c i t y and extends i t s a c t i v i t y (16) Microencapsulated j u v e n i l e hormone JK\tosid produced by Zoecon) Microencapsulation p r o t e c t s t h i s j u v e n i l e hormone from environmental degradation (J7.) Microencapsulated D i s p a r l u r e (gypsy moth sex a t t r a c t a n t ) Mi croencapsulation c o n t r o l s the evaporation or m s p a r i u r e and extends i t s a c t i v i t y (18) Microencapsulated Mi rex Microencapsulis o f 2% Mi rex i n vegetable o i l are very a t t r a c t i v e to the imported f i r e ant and give a high degree o f c o n t r o l . The a b i l i t y o f microencapsulated

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

136

C O N T R O L L E D R E L E A S E PESTICIDES

NCO

PAPI

PROCESS

HEATING

DISPERSING Organic

Phase

queous

Phase

WALL FORMING REACTION Η0 - Ν = C = 0 + H 0 2

Heat, ^

1

Η

11

-N-C-OH carbamic acid

Isocyanate

- N' V

+ CO, H

2

amine

Η Ο Η - Ν = C = Ο+ - Ν Isocyanate

Η amine

I II I -N-C-N polyurea

Great Britain Patent 1,371,179

Figure 8. In situ interfacial condensation polymerization (11)

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SCHER

Microencapsulated

Pesticides

Figure 9. Magnification: lOOOX; particle size distribution = 10-40 μ. Note the smooth membrane-like outer wall surface and the crushed capsules in upper left corner revealing thin wall.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

138

CONTROLLED RELEASE

PESTICIDES

Figure 10. Magnification: 6000χ. Note the smooth membrane-like outer wall surface and the sponge-like nature of the wall interior.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

SCHER

Microencapsulated

Pesticides

Figure 11. Microcapsules on cellulose filter. Magnification: ΙΟΟΟχ. Note the cellulose fibers and the collapse of capsules as the pesticide diffuses through wall.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

139

140

C O N T R O L L E D R E L E A S E PESTICIDES

filler fluid

shell

head

Ci

nozzle

Chemical Engineering

Figure 12. Multiorifice centrifugation. The centrifugal extruder consists of a rotating head with nozzles on the periphery. Capsule filler, pumped into the inner chamber, flows through the tubes that project into orifices at the periphery of the head. Fluid-shell formulation, pumped into the head, flows through the anuli formed by the orifices and filler tubes. The result, in effect, is the extrusion of fluid "rods" of filler sheathed in fluid-shell formulions. These rods subsequently break into individual fluid capsules that are hardened by chemical reactions, evaporation, cooling, or other means.

filler shell

1

carrier

fluid Chemical Engineering

Figure 12 (continued). The extrusion nozzle device has two concentric tubes mounted axially in a tubular duct. Capsule filter is pumped through the center tube and fluidshell formulation through the anulus of the nozzle so as to extrude a coated filler "rod" which breaks into individual capsules that are carried away in the stream of nonreactive carrier fluid. Capsule size is a function of the rehtive velocities of carrier fluid and extruded materials.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

SCHER

Microencapsulated

Pesticides

Coating p a r t i c l e s

141

Core

particles

Chemical Engineering

Figure 13. The principle of electrostatic encapsulation. The two aerosols, produced separately in atomizers, bear opposite electric charges that greatly increase the attraction of core and coating particles. After coalescing, the coating droplets flow together to form a continuous film on the core. A subsequent cooling step then solidifies the coating, and capsules are gathered as a dry powder. Wet collection may also be used.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICIDES

POI VMFRTf. UAI I MATFBTAI

FOR LOWER PERMEABILITY

PARAMETERS (1) Density

Increase

Crystal U n i t y

Increase

Orientation

Increase

Crossflinking

Increase

P l a s t i c i z e r Level

Decrease

Solvents Used i n Film Preparation S o l u b i l i t y Paramter (2)

Use Good Solvents Versus Poor One the Opposite Side o f SP Scale From Core Material

CAPSULAR PARAMETERS Size

Increase

Wall Thickness

Increase

Configuration Confornri t y Post Treatments

As Spherical As Possible As Regular As Possible Utilize

(Crosslinking, Sintering) M u l t i p l e Coatings

Utilize

ENVIRONMENTAL PARAMETERS Temperature, Storage

Decrease

P a r t i a l Pressure D i f f e r e n t i a l

Decrease

(Inside and Outside of Capsule Wall) Microencapsulation Processes and Applications

Figure 14.

Parameters affecting capsular wall permeability

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

12.

SCHER

Microencapsulated

Pesticides

143

b a i t to withstand weathering makes i t s u p e r i o r to c o r n cob g r i t s b a i t i n c o n t r o l l i n g the ant during c e r t a i n seasons. A e r i a l a p p l i c a t i o n o f microencapsulated b a i t i s f e a s i b l e (19). 5 . Microencapsulated B a c i l l u s T h u r i n g i e n s i s

(Bacterium)

The bacterium B a c i l l u s t h u r i n g i e n s i s , encapsulated by several processes, retained i t s v i a b i l i t y and patho g e n i c i t y f o r the European corn borer. In f i e l d t e s t s the capsule formulation was a p p l i e d dry and i n spray form, g i v i n g good c o n t r o l i n both ( 2 0 ) . The uses and examples discussed above seem to i n d i c a t e that p e s t i c i d e microcapsule formulations have a b r i g h t future i n agriculture.

Abstract Controlled release of pesticides can be achieved by micro encapsulation. Pesticide microcapsule systems can be designed to reduce mammalian toxicity and extend activity; reduce evaporative losses; reduce phytotoxicity; protect pesticides from environ mental degradation; reduce leaching; reduce pesticide levels in the environment. An aqueous dispersion of pesticide microcapsules is a particularly useful controlled release formulation because it is composed of discrete microcapsules; i t can be diluted with water or liquid fertilizers and sprayed using conventional equipment; it requires less polymeric component per pound of pesticide than monolithic devices; it is capable of establishing a constant pesticide release rate; pesticide release rate can be varied over wide limits by varying microcapsule particle size distribution, wall thickness, and wall permeability; additives such as film forming agents can be added directly to the formulation. Microencapsulation processes are grouped into three categor ies (Phase Separation, Interfacial Reactions and Physical Methods) and reviewed with respect to application to pesticides. Factors affecting the permeability of a pesticide through a microcapsule wall are also summarized. Examples are given to show the variety of agricultural uses to which microencapsulated pesticides can be applied. Literature Cited (1) (2)

Baker, R. W. and Lonsdale, Η. Κ., "Controlled Release of Biological Active Agents", Tanquary, A. C., and Lacey, R. Ε., editors, P. 15, Plenum Press, New York (1974). Baker, R. W. and Lonsdale, Η. Κ., Chem. Tech. (1975), 5, 668-674.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

144

(3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20)

CONTROLLED RELEASE

PESTICIDES

Flinn, J . E. and Nack, H., Chem. Eng. (1967), 74, 171-178. Wolfgang, S., Angew. Chem. Internat. Edit. (1975), 14, 539-550. Gutcho, Μ. Η., "Microcapsules and Microencapsulation Tech niques", P. 8, Noyes Data Corporation, Park Ridge, N.J., (1976). Reyes, Z., U.S. Patent 3,173,878 (1965). Herbig, J . A. and Hanny, J . F., U.S. Patent 3,161,602 (1964). Macaulay, N., U.S. Patent 3,016,308 (1962). Hall, H.S., and Hinkes, T.M., "Microencapsulation Processes and Applications", Vandegaer, J . Ε., editor, P. 145, Plenum Press, New York (1974). Vandegaer, J . E., U.S. Patent 3,577,515 (1971) Scher, H. B., Great Britain Patent 1,371,179 (1975). Brynko, C., U.S. Patent 2,969,330 (1961). Goodwin, J . T., an Processes and Applications", Vandegaer, J . Ε., editor, Ρ 155, Plenum Press, New York (1974). Berger, Β. Β., Miller, C. D., and Langer, G., U.S. Patent 3,208,951 (1965). Fanger, G. O., "Microencapsulation Processes and Applica tions", Vandegaer, J . Ε., editor, Ρ l, Plenum Press, New York (1974). Ivy, Ε. E., J . of Econ. Ent. (1972), 65, 473-474. Chem. and Eng. News, March 17, 1975, Ρ 5. Plimmer, J . R., Bierl, Β. Α., DeVilbiss, E. D. and Smith, B. L., "Proceedings of the 1976 International Controlled Release Pesticide Symposium", Akron, Ohio. Markin, G. P., and H i l l , S.O., J . of Econ. Ent. (1971), 64, 193-196. Rarn, E. S., and Jackson, R. D., J . of Econ. Ent. (1966), 59, 620-622.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

13 Effects of W a l l Parameters on the Release of Active Ingredients from Microencapsulated Insecticides J. R. LOWELL, JR. and W. H. CULVER Pennwalt Corp., 1630 E. Shaw Ave., Suite 179, Fresno, Calif. 93710 C. B. DeSAVIGNY Pennwalt Corp., P. O. Box 3608, Bryan, Tex. 77801

Application o technology t o methy commercial microencapsulated p e s t i c i d e , PENNCAP-M I n s e c t i c i d e . In the course of our encapsulation development programs a s u b s t a n t i a l body o f i n f o r m a t i o n has been c o l l e c t e d regarding the e f f e c t s of v a r i o u s w a l l parameters on r e l e a s e r a t e s o f microencapsulated formulations. The polymer system used in preparation of PENNCAP-M is a c r o s s l i n k e d nylon-type polymer produced from sebacoyl c h l o r i d e , ethylenediamine (EDA), d i e t h y l e n e t r i a m i n e (DETA), and polymethylenepoly-phenylisocyanate ( P A P I ) . The a c t i v e i n g r e d i e n t , d i a c i d c h l o r i d e and PAPI form a homogeneous mixture, which is dispersed in an aqueous medium. When brought i n t o contact w i t h an aqueous s o l u t i o n of the diamines, a shell of c r o s s - l i n k e d nylon forms around each i n d i v i d u a l d r o p l e t . The product is typically formulated as an aqueous suspension, as w i t h PENNCAP-M. While m a t e r i a l s encapsulated may i n c l u d e liquids, s o l u t i o n s , suspensions, o r solids, our efforts have been most s u c c e s s f u l w i t h the two former c a t e g o r i e s . Encapsulation in similar polymers has produced e f f e c t i v e i n s e c t i c i d e formulations of Diazinon®, parathion, v a r i o u s p y r e t h r o i d s , and malathion. In this paper some observations will be presented on the e f f e c t s of capsule w a l l t h i c k n e s s , c r o s s l i n k i n g , and a c i d c h l o r i d e s on r e l e a s e r a t e s o f active ingredients. I v y has p r e v i o u s l y reported on the r e d u c t i o n i n mammalian t o x i c i t y and the extension o f i n s e c t i c i d a l a c t i v i t y r e s u l t i n g from encapsulation of methyl parathion. As p r e s e n t l y marketed, PENNCAP-M i s a t l e a s t 6 times l e s s t o x i c o r a l l y and 12 times l e s s t o x i c dermally than e m u l s i f i a b l e concentrate formu®

1

145 In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

146

CONTROLLED

Figure 1.

RELEASE

Effect of wall thickness on bioactivity of encapsulated parathion

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PESTICIDES

13.

LOWELL

ET AL.

Effects of Wall Parameters

147

on Release

l a t i o n s o f methyl parathion, on an a c t i v e i n g r e d i e n t basis. I n s e c t i c i d a l a c t i v i t y i s e x t e n d e d , u p t o 2% times, depending on t h e crop and weather c o n d i t i o n s . DeSavigny and I v y have r e p o r t e d f u r t h e r on t h e Pennwalt microencapsulation process, r e v i s i n g t h e t o x i c o l o g y f i g u r e s a s p r o d u c t i o n e x p e r i e n c e was o b tained. Additional insect control reports confirmed t h e g r e a t e r r e s i d u a l a c t i v i t y o f PENNCAP-M a s c o m p a r e d w i t h EC f o r m u l a t i o n s . We h a v e a l s o r e p o r t e d o n t h e u s e o f PENNCAP-M f o r e f f e c t i v e i n s e c t c o n t r o l on tobacco p l a n t s , and on t h e e c o n o m i c s o f m i c r o e n c a p s u l a t i o n a s d e m o n s t r a t e d b y o u r e x p e r i e n c e w i t h PENNCAP-M . K o e s t l e r has proposed a mechanism f o r t h e a c t i o n o f m i c r o e n c a p s u l a t e d h e r b i c i d e s and i n s e c t i c i d e s suggestin tha t h e h i g h number o f and h i g h l o c a l c o n c e n t r a t i o n responsible f o rthe e f f e c t i v e n e s s o f t h e microencapsulated products. D u r i n g d e v e l o p m e n t o f a new m i c r o e n c a p s u l a t e d pesticides i n our l a b o r a t o r i e s , candidate preparat i o n s a r e s c r e e n e d b y means o f a b i o a s s a y technique. The b i o a s s a y c o n s i s t s o f s p r a y i n g a s u i t a b l e s u r f a c e , u s u a l l y bean f o l i a g e o r cardboard, w i t h a standard amount o f t h e i n s e c t i c i d e . The s u r f a c e i s t h e n infested a t suitable intervals with insects, generally crickets. Percent m o r t a l i t y i s determined as a function o f time a f t e r spraying. Corrected percent m o r t a l i t y f i g u r e s f o rt h e d u r a t i o n o f t h e t e s t a r e averaged, g i v i n g a " B i o a c t i v i t y " f i g u r e which a p p r o a c h e s 100 f o r a m a t e r i a l w h i c h i s i n s e c t i c i d a l l y a c t i v e and p e r s i s t s f o rt h e d u r a t i o n o f t h e t e s t . Low b i o a c t i v i t y r e s u l t s m o s t o f t e n i n d i c a t e a r a p i d r e l e a s e and lowp e r s i s t e n c e , b u t o c c a s i o n a l l y a formulation w i l l produce a lowpercent m o r t a l i t y which p e r s i s t s f o rthe duration o f the t e s t , i n d i c a t i n g very slow r e l e a s e . 2

3

4

5

The t h i c k n e s s o f t h e c a p s u l e w a l l c a n b e estimated by simple geometry c a l c u l a t i o n s t o be d i r e c t l y p r o p o r t i o n a l t o t h e percentage o f polymerforming i n g r e d i e n t s i n t h e formulation. F o r any f o r m u l a t i o n , then, t h e "percent w a l l " c a nbe r e p r e sented as a r e l a t i v e w a l l thickness. I n F i g u r e 1, the b i o a c t i v i t y o f parathion encapsulated i n three d i f f e r e n t w a l l systems i s d e p i c t e d as a f u n c t i o n o f wall thickness. I ti s r e a d i l y apparent t h a t i n each case t h e b i o a c t i v i t y dropped as t h e w a l l t h i c k n e s s increased. I n t h e c a s e o f W a l l A, i n p a r t i c u l a r , t h e d a t a showed t h a t t h e p e r c e n t m o r t a l i t y was i n c r e a s i n g with time f o ra l l three w a l l thicknesses, i n d i c a t i n g American Chemical Society Library

1155 18th St.,

N.W.

In Controlled Release Pesticides; Scher, H.; Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

148

C O N T R O L L E D R E L E A S E PESTICIDES

t h a t t h e l o w b i o a c t i v i t y f o r t h i s w a l l was due t o very slow release. I n F i g u r e 2, i t c a n b e s e e n t h a t f o r D i a z i n o n encapsulated i n Wall D b i o a c t i v i t y on f o l i a g e increased with increasing w a l l thickness u n t i l a p l a t e a u was r e a c h e d . When t e s t e d i n s o i l , h o w e v e r , t h e same f o r m u l a t i o n s h o w e d i n c r e a s e s i n b i o a c t i v i t y w i t h i n c r e a s i n g w a l l t h i c k n e s s u n t i l a p e a k was reached, a f t e r which the b i o a c t i v i t y decreased. F o l i a r b i o a c t i v i t y with malathion encapsulated in Wall D increased with increasing wall thickness. In F i g u r e 3, r e s u l t s f o r e n c a p s u l a t e d m e t h y l p a r a t h i o n s h o w e d a n i n s e n s i t i v i t y t o w a l l t h i c k n e s s when e n c a p s u l a t e d i n W a l l D. Another major f a c t o r i n f l u e n c i n g the release of a c t i v crosslinking. In Figur a p e a k i n b i o a c t i v i t y a t 2 5 % c r o s s l i n k i n g f o r W a l l E, u s i n g b o 1 1 w o r m s a s t h e t e s t i n s e c t . The increased b i o a c t i v i t y i n t h i s c r o s s l i n k i n g s t u d y was associated w i t h lower release r a t e s . DeGennaro e t a l . h a v e shown t h a t t h e r e l e a s e o f sodium p e n t o b a r b i t a l i n c r e a s e d w i t h i n c r e a s i n g c r o s s l i n k i n g b y i n c r e a s i n g p r o p o r t i o n s o f DETA. The i n c r e a s e was a t t r i b u t e d t o i n c r e a s i n g p o r o s i t y a s t h e p r e p a r a t i o n became more h i g h l y c r o s s l i n k e d . It s h o u l d be n o t e d , h o w e v e r , t h a t t h e i r s t u d i e s u t i l i z e d an i o n i c a c t i v e i n g r e d i e n t , w h i l e o u r preparations have used r e l a t i v e l y n o n p o l a r o r g a n i c m a t e r i a l s . C r o s s l i n k i n g i n t h e i r s y s t e m was a c h i e v e d w i t h a p o l y f u n c t i o n a l amine, w h i l e i n ours, a p o l y f u n c t i o n a l isocyanate i s the p r i n c i p a l source of c r o s s l i n k i n g . E f f e c t s of the i d e n t i t y of the a c i d c h l o r i d e have not been e x t e n s i v e l y i n v e s t i g a t e d i n our l a b o r a tories. As shown i n F i g u r e 5, t h e b i o a c t i v i t y v a r i e d w i t h the chain length of the d i c a r b o x y l i c a c i d . In W a l l F, a s s h o w n , t h e b i o a c t i v i t y was l o w e s t w i t h a z e l a o y l c h l o r i d e , w h i l e a d i p o y l and s e b a c o y l c h l o r i d e b o t h gave s i g n i f i c a n t l y g r e a t e r a c t i v i t y i n t h i s w a l l formulation. In c o n c l u s i o n , the data presented here have shown t h a t b i o a c t i v i t y v a r i e s i n a n i r r e g u l a r m a n n e r w i t h i n c r e a s i n g w a l l t h i c k n e s s and i n c r e a s i n g c r o s s linking. The a c i d c h l o r i d e c h o s e n a l s o a f f e c t e d a c t i v i t y , b u t t e s t i n g has been i n s u f f i c i e n t t o draw any c o n c l u s i o n s . I t m u s t t h u s be c o n c l u d e d , t h e n , t h a t p r o d u c i n g an optimum e n c a p s u l a t e d p e s t i c i d e f o r m u l a t i o n by t h e P e n n w a l t p r o c e s s s t i l l r e q u i r e s an e m p i r i c a l approach. F o r each p r o d u c t w h i c h has reached the f i e l d development stage, a p a i n s t a k i n g l a b o r a t o r y i n v e s t i g a t i o n of each of these v a r i a b l e s f

6

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

LOWELL

Effects

ET AL.

of Wall

Parameters

on

Release

M - Wall D -Foliage ID - Wall D -Foliage

D - Wall D - S o i l

l

ι 1

ι 2

· 3

ι 4

Relative Wall Thickness

Figure 2. Effect of wall thickness on bioactivity of encapsulated Diazinon (D) and mahthion (M)

50

25

h

1

2

3

4

Relative Wall Thickness

Figure 3.

Effect of wall thickness on bioactivity of encapsulated methyl parathion

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

Figure 5. Effect of acid chloride chain length on bioactivity of encapsulated parathion

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PESTICIDES

13.

LOWELL

ET

AL.

Effects of Wall Parameters

on

Release

151

has

been necessary. One a s p e c t o f t h e e f f e c t o f c r o s s l i n k i n g i s worth noting here. With regard to the suggestion of DeGennaro e t a l . t h a t t h e e f f e c t o f i n c r e a s i n g c r o s s l i n k i n g i n t h e i r capsule formulations increased the r e l e a s e r a t e b y i n c r e a s i n g p o r o s i t y , we generally have found the o p p o s i t e e f f e c t w i t h the r e l a t i v e l y n o n p o l a r p e s t i c i d e s w h i c h we h a v e e n c a p s u l a t e d , when c r o s s l i n k i n g was e f f e c t e d b y a p o l y f u n c t i o n a l isocyanate. I t may b e t h a t t h e e f f e c t s o b s e r v e d w i t h i n c r e a s i n g amounts o f p o l y f u n c t i o n a l isocyanate r e l a t e t o changes i n the s o l v e n t p r o p e r t i e s of the capsule w a l l polymer, a l t e r i n g the s o l u b i l i t y of the d i f f u s i n g s u b s t a n c e i n t h e w a l l , and t h u s c h a n g i n g its diffusion characteristics s w e l l i n g or hydratio i n m i c r o p o r o s i t y s h o u l d be s i m i l a r i n d i r e c t i o n f o r i o n i c or nonionic materials. I f the e f f e c t of the polymer composition i s to a l t e r the s o l u b i l i t y of the encapsulated m a t e r i a l i n the polymer, then opposite e f f e c t s f o r i o n i c and n o n p o l a r s p e c i e s , as o b s e r v e d h e r e , m i g h t be e x p e c t e d . We o f f e r t h i s a s a w o r k i n g hypothesis deserving of further study. PAPI i s a trademark o f Upjohn Diazinon i s a trademark of Ciba-Geigy

Literature Cited 1. Ε. E. Ivy, J . Econ. Entomol., 65(2), 473 (1972). 2. C. B. DeSavigny and Ε. E. Ivy, in J . E. Vandagaer, E d i t o r , "Microencapsulation: Processes and A p p l i c a t i o n s , " Plenum P u b l i s h i n g Corp. 3. J . R. L o w e l l , J r . and J . L. Frizzell, Reprints of Papers from the Symposium "Chemical Require ments of the Tobacco Industry," 169th Meeting of the American Chemical Society, P h i l a d e l p h i a , PA, April, 1975. 4. J . R. L o w e l l , J r . and J . J . Murnighan, Reprints of Papers from the Symposium "Economics and Market Opportunities f o r C o n t r o l l e d Release Products," 172nd Meeting of the American Chemical S o c i e t y , San F r a n c i s c o , CA, August, 1976. 5. R. C. K o e s t l e r , i n N. F. Cardarelli, E d i t o r , "Proceedings 1976 C o n t r o l l e d Release P e s t i c i d e Symposium," Akron, OH, September, 1976. 6. M. DeGennaro, et al., i n D. R. Paul and F. W. H a r r i s , Ed., " C o n t r o l l e d Release Polymeric Formulations," ACS Symposium S e r i e s , American Chemical Society, Washington, D.C., 1976, pp. 195-207.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14 The Effect of Some Variables on the Controlled Release of Chemicals from Polymeric Membranes AGIS F. KYDONIEUS Hercon Products Group, Herculite Protective Fabrics Corp., 1107 Broadway, New York, N.Y. 10010

Controlled release processes to the dispensin chemicals. Nature, Naivete and ingenuity have provided a number of well known examples of permeation controlled processes. Some well known processes which depend on permeation are: respiration, osmosis, and the "bloom" or "patina" on grapes and other fruit. Inspection of these examples reveal that gases, liquids, and solids may be observed to pass through various membrane materials. The manner in which permeation takes place through the HERCON laminated polymeric membrane system and the factors affecting such permeation will be discussed. ®

1. The HERCON Dispensing System A schematic cross-section of a typical HERCON laminated membrane structure is shown in Figure 1. The specially formulated inner layer, which behaves as the reservoir, contains dissolved insecticide or other active agent which then migrates continually, due to imbalance of chemical potential, through one or more initially inert outer layers to the surface, rendering it biologically or physico-chemically active. At the surface, the insecticide is removed by volatilization, thermal or ultraviolet degradation, alkaline or acid hydrolysis, or mechanically by humans, insects, rainfall, wind or other agents. The construction and composition o£ the laminated insecticidal membranes vary , o£ course, with the active agent used, release rate and effective life span desired. However, materials containing from 0.5 to 40%, by weight, active agent have been successfuEy prepared and have been shown by laboratory and field tests to be efficacious in a number o£ applications (1, 2).

152 In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

KYDONiEus

Effects of Some Variables

153

on Release

2. The Mathematics of Transport The class of membranes used with the H E R C O N technology is the nonporous, homogeneous polymeric films. These membranes are usually referred to as solution-diffusion membranes. Silicone rubber, polyethylene, polyvinylchloride and nylon films are typical examples. The penetrant is able t o pass through the membrane material in the absence of pores or holes by a process of absorption, solution, diffusion down a gradient of t her mo-dynamic activity and desorption. The process of permeation thus is divisible into a number of indepen dent processes governed primarily by Henry s law and Fick s law (3, 4). Transport of active chemical from the reservoir through the barrier membrane is governed by Fick s f i r s t law: 1

f

1

j

,p

[1] dx

where J is the flux in g/cm^-sec, C is the concentration of permeant in the membrane in g/cm^, d C / d x is the gradient in concentration, and D is the diffusion coefficient of the permeant in the membrane in cmVsec. M

m

(a) The Steady State. As shown in Figure 2, the concentration just inside the membrane surface can be related t o the concentration in the reservoir C by the expressions: Cm (0)

=

K C /Q) at the upstream surface (x = Q) [2]

C (l)

= KC (j) at the downstream surface (x =%)

m

here, Κ is a distribution coefficient and is analogous to the familiar liquid-liquid partition coefficient. In Figure 2, for purposes of illus tration, i t has been assumed that the distribution is less than unity for barrier membrane I, and more than unity for membrane II. Throughout the following, we will assume diffusion coefficients and distribution coefficients to be constant. This is a safe assumption for most polymer-permeant systems. Thus, in the steady state, Equation [1] can be integrated to give: C

C

J = D m(0) - m(l) = D 1

Δ

C

M

[3]

1

where 1 is the thickness of the membrane. Since the concentration within the membrane is usually not known, Equation [3] is frequently

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

154

CONTROLLED RELEASE

PESTICIDES

CONTROLLED AMOUNTS OF PESTICIDE . MOVE FROM RESERVOIR LAYER TO SUSTAIN ACTIVE SURFACE

φ ACTIVE SURFACE ' φ PROTECTIVE PLASTIC LAYER φ PESTICIDE RESERVOIR LAYER ' φ PROTECTIVE PLASTIC BARRIER Figure 1.

Schematic

T H R E E - LAYER

LAMINATE

FLUID

FLUID

DILUTE SOLUTION SIDE

THICKNESS

Figure 2.

Schematic of the concentration gradient across a three-layer laminate

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

KYDONiEus

Effects of Some Variables

155

on Release

written: J = f^t dt

= DKAC

[4]

1

dMt where M t is the mass of agent released,—gftr is the steady state release rate at time t and A C is the difference in concentration (C(0) - C(i)) between the reservoir concentration and the fluid concentration adjacent t o the barrier membrane. It is significant t o note that the rate of release is proportional to diffusivity (a kinetic constant ) and to distribution coefficient (a thermodynamic constant). Equation [4] can be integrated between the limits: Mt

to give:

t = t

= Mt

[5]

= ADK ÀCf. 1

When the distribution coefficient between the reservoir layer and the barrier membrane is much smaller than unity, as is the case of membrane I in Figure 2, the system has excellent release kinetics and the release rate can be maintained constant f o r extended periods of time (pseudo-zero order delivery). Equation [5] is then governing the process and a straight line is obtained when the mass of agent released (Mt) is plotted against time (t). This is shown in Figure 3, with a polyvinyl chloride-polyester system. (b) The Unsteady State. When the distribution coefficient between the reservoir layer and the barrier membrane i s approximately unity, or larger than unity, as i s the case with membrane II of Figure 2, the HERCON system will approximate the "dissolved system", i.e., the reservoir - barrier membrane system forms a single homogeneous polymeric f i l m . The concentration in the reservoir will not remain constant but will f a l l continuously with time. The system remains continuously under unsteady state conditions and the mass of agent released varies as a function of time (first order delivery). The transport equations have been described by several investigators (5,6, 7). The two useful equations are the early time approximation, which holds over the initial portion of the curve: Mt

= 4/Dt \

1 / 2

n

A l t

/

0.6

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

[6]

CONTROLLED RELEASE

PESTICIDES

2 -, 10 m i l P V C 8 mil MYLAR

RESERVOIR BARRIER MEMBRANE Moo Κ

= «

4.24 m g / i n

2

1

-4

ι

Τ 20

T 40

T "

T

60

80

~ l

100

120

TIME IN DAYS Figure 3.

Release of fly repellent MGK R-874—reservoir-type system

4-1

3 H

RESERVOIR BARRIER MEMBRANE Moo Κ

0 Figure 4.

20 20

"T

40 6o" 60 40 TIME IN DAYS

=4.23 =

10 m i l P V C 10 m i l P V C

mg/irr

1

80 80

Τ"

lOO 100

Release of fly repellent MGK R-874—dissolved-type system

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1

120

14. KYDONiEus

Effects of Some Variables

on Release

157

and t h e l a t e t i m e approximation, which holds over the f i n a l p o r t i o n o f the release curve, exp (-TT*Pt)

M£=l-J

0 . 4 / L . O

[7]

As i t can be seen f r o m equation [ 6 ] , a p l o t o f mass o f agent released versus t i m e w i l l give a parabolic curve. T h i s i s the case f o r the P V C - P V C s y s t e m shown i n Figure 4. When t h e same data are p l o t t e d versus (time)-*/ , a l i n e a r curve i s obtained, (Figure 5), i n accordance w i t h Equation [6]. 2

3. F a c t o r s A f f e c t i n g the Release Looking a t equations [5], [6], and [7], i t becomes apparent t h a t t h e release o f a c t i v e ingredients f r o m H E R C O N laminated membrane s t r u c t u r e s i s controlled by molecular and s t r u c t u r a l f a c t o r s . F o r a given combination o f polymer s t r u c t u r e and a c t i v e agent where energy t o f r e e r o t a t i o n s , f r e e volume, and i n t e r m o l e c u l a r a t t r a c t i o n s a r e constant, a t l e a s t t w o p a r a m e t e r s are available t o regulate t h e r a t e o f t r a n s f e r : r e s e r v o i r concentration and membrane t h i c k n e s s . D i f f u s i v i t y D and reservoir/membrane d i s t r i b u t i o n c o e f f i c i e n t Κ are also d i r e c t l y p r o p o r t i o n a l t o the permeation r a t e . In p o l y m e r s , d i f f u s i v i t y i s s t r o n g l y s e n s i t i v e t o the molecular weight o f t h e d i f f u s a n t and t o t h e s t i f f n e s s o f the backbone o f the polymeric mem brane. Simply speaking, the d i f f u s a n t molecule w i l l have t o r e o r i e n t s e v e r a l segments o f polymer chain t o allow i t s passage f r o m s i t e t o s i t e . T h e higher t h e molecular weight, t h e more the segments t h a t need t o be reoriented f o r passage t o be possible; and t h e s t i f f e r the polymer (glassy and high c r y s t a l l i n i t y ) , the more d i f f i c u l t f o r i t s segments t o undergo large r e o r i e n t a t i o n s . T h e r e f o r e , variables t h a t could a f f e c t the s t i f f n e s s o f polymer membranes such as c o - d i f f u s ants t h a t would s o f t e n , p l a s t i c i z e o r p a r t i a l l y dissolve the membrane would have an e f f e c t on d i f f u s i v i t y and p e r m e a t i o n r a t e . The reservoir/membrane d i s t r i b u t i o n c o e f f i c i e n t Κ can be e s t i m a t e d f r o m the s o l u b i l i t y p a r a m e t e r o f the d i f f u s a n t . S o l u b i l i t y p a r a m e t e r s can be calculated using Hilderbrand s s o l u b i l i t y theory. When t h e s o l u b i l i t y p a r a m e t e r f o r t h e d i f f u s a n t and polymer mem brane i s t h e same, t h e polymer w i l l be soluble i n t h e d i f f u s a n t . T h e s o l u b i l i t y p a r a m e t e r s and d i s s o l u t i o n a r e s t r o n g l y a f f e c t e d by molecular weight and the chemical f u n c t i o n a l i t y o f the molecule, i . e . , hydrogen bonding and p o l a r i t y . L i k e dissolves l i k e i s s t i l l a good r u l e o f thumb. I would l i k e t o t a k e a f e w minutes now t o discuss the e f f e c t f

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

158

CONTROLLED

R E L E A S E PESTICIDES

C

0

1

2 1 t

Figure 5,

3

4

5

/ 2 ( DAYS1/2 )

Release of fly repellent MGK R-874—dissolved-type

system

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

KYDONiEus

Effects of Some Variables

on

Release

159

o f : 1) r e s e r v o i r c o n c e n t r a t i o n , 2) m e m b r a n e t h i c k n e s s , 3) p o l y m e r s t i f f n e s s , 4) c o - d i f f u s a n t s , 5) m o l e c u l a r w e i g h t o f d i f f u s a n t a n d 6) c h e m i c a l f u n c t i o n a l i t y o n t h e t r a n s p o r t o f a c t i v e i n g r e d i e n t s through H E R C ON laminated membranes. F o r purposes o f i l l u s t r a t i o n and s i m p l i c i t y i n a l l examples t h a t f o l l o w , t h e r e s e r v o i r i s made o f flexible polyvinylchloride. R e s e r v o i r C o n c e n t r a t i o n . In F i g u r e s 6 and 7, t h e r e l e a s e o f t h e p e s t i c i d e chlordane and t h e i n s e c t r e p e l l e n t D E E T a r e i l l u s t r a t e d . In b o t h c a s e s , z e r o o r d e r release r a t e s were obtained. A c l o s e r look i n d i c a t e s t h a t doubling t h e c o n c e n t r a t i o n i n t h e r e s e r v o i r does not double t h e m a s s o f agent r e l e a s e d . T h i s d e v i a t i o n i s m o r e pronounced a t higher concentrations, presumably because t h e i n t e r - m o l e c u l a r attraction of the diffusan concentration. W i t h the exception o f these minor differences, the data in g e n e r a l t e r m s f o E o w e q u a t i o n s [5] a n d [6]. M e m b r a n e T h i c k n e s s . B o t h e q u a t i o n s [5] a n d [6] i n d i c a t e t h a t t h e mass o f agent released should be i n v e r s e l y p r o p o r t i o n a l t o t h e t h i c k n e s s o f t h e membrane. T h i s i s shown t o be t h e case w i t h t h e r e p e E e n t D E E T and t h e p h e r o m o n e s dodecenyl a c e t a t e and H e x a d e c y l A c e t a t e ( F i g u r e s 8 and 9 ) . Polymer Stiffness. The distribution coefficient Κ for several p o l y m e r m e m b r a n e s o f d i f f e r e n t b a c k b o n e s t i f f n e s s and P V C w a s studied, by adhering large r e s e r v o i r layers o f P V C t o said membranes. T h e t r a n s p o r t o f a c t i v e agent f r o m t h e r e s e r v o i r t o t h e membrane was s t u d i e d b y s e p a r a t i n g t h e l a y e r s and d e t e r m i n i n g t h e a m o u n t o f a c t i v e agent b y c h e m i c a l a n a l y s i s . T h i s i s shown i n T a b l e A f o r t h e active agents: Captan-an a n t i b a c t e r i a l agent, Malathion-an i n s e c t i c i d e , and Z i n e b - a n a g r i c u l t u r a l f u n g i c i d e . F o r a l l t h r e e a g e n t s , t h e amount transported into the membranes becomes progressively s m a E e r , g o i n g f r o m P V C t o r i g i d v i n y l , p o l y p r o p y l e n e , n y l o n and m y l a r , which also corresponds t o i n c r e a s e i n backbone s t i f f n e s s . D i s t r i b u t i o n c o e f f i c i e n t s w e r e n o t c a l c u l a t e d b e c a u s e 20 w e e k s a f t e r t h e e x p e r i m e n t s w e r e i n i t i a t e d , i t was not c e r t a i n t h a t e q u i l i b r i u m had been reached i n m o s t c a s e s . T h e amount o f a c t i v e c h e m i c a l t r a n s p o r t e d w i t h t i m e f o r a few cases is shown i n Table B , In a second e x p e r i m e n t , t h e d i f f u s i o n i n t o f i l m s o f d i f f e r e n t backbone s t i f f n e s s was m o n i t o r e d b y t h e p r o p e r t i e s i m p a r t e d t o said f i l m s . T h e a n t i b a c t e r i a l a g e n t , C a p t a n , t h e g e r m i c i d e , v i n a z e n e , and t h e a n t i s t a t i c agent, Ethoquad, were used. The r e s u l t s , shown i n Table C , indicate t h a t the effectiveness of the f i l m s was, i n general,

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

160

CONTROLLED RELEASE

1/2 t

1/2 DAYS

Figure 8. Effect of film thickness on release of repellent

DEET

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

PESTICIDES

KYDONiEus

Effects

of Some Variables

on

Release

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

161

162

C O N T R O L L E D R E L E A S E PESTICIDES

best for flexible PVC, followed by rigid PVC, acrylic, polyproplene, nylon and polyester. This order is the same as that of the dats shown in Table A , with effectiveness reduced as the backbone stiffness was increased. Table A Distribution of Active Agents between Flexible PVC and Polymer Increasing Backbone Stiffness ACTIVE AGENT TRANSPORTED (ppm) Flex PVC Rigid PVC Polyprop Nylon Polyester 250 109 36 3 0 1200 1600 568 62 63 9 1

Captan Malathion Zineb

* A l l Polymer films were 5 mils thick. The t o t a l amount of Captan, Malathion and Zineb in the system were 500, 24000 and 4000 ppm, respectively. Readings were taken 20 weeks after the initiation of Experiment.

Table Β Active Agent transported as a Function of Time (ppm)

Malathion Rigid PVC Nylon Polyprop Captan Rigid PVC Polyprop Zineb Rigid PVC Nylon

2 weeks

7 weeks

20 weeks

6300 6 387

9000 12 334

9700 23 498

29 1

55 26

109 36

303 67

619 60

568 62

Co-diffusants. Chemical agents that are capable in altering the structure (e.g., stiffness) of a polymer would have a pronounced effect on the diffusion of active chemicals that are aEowed t o

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

KYDONiEus

Effects of Some Variables

on

Release

163

c o - d i f f u s e . T h e s e " c a r r i e r " m a t e r i a l s m u s t have t h e a b i l i t y t o s w e l l , s o f t e n a n d / o r d i s s o l v e t h e p o l y m e r m a t r i x . A good e x a m p l e i s t h e i m p a r t m e n t o f a n t i s t a t i c p r o p e r t i e s t o n y l o n and p o l y e s t e r c a r p e t s b y u s i n g t h e c o - d i f f u s a n t s phenol and ethylene g l y c o l p h e n y l e t h e r , r e s p e c t i v e l y (8). T a b l e D s h o w s t h a t 3 f o l d and 100 f o l d i m p r o v e m e n t s i n a n t i s t a t i c r e s i s t i v i t y c a n b e o b t a i n e d f o r n y l o n and p o l y e s t e r respectively b y using the co-diffusants mentioned above. Table

C.

P r o p e r t y Improvement by Diffusion o f A c t i v e Chemicals Flex PVC Vinazene [germicide] Captan [antibacterial] Ethoquad [antistatic]

7.0

Rigid P V C A c r y l i c Polyprop Nylon Polyester 12

1

99.9+

2

99.9+

10000

3

4200

88.2

2100

15

0

0

97.8

42.3

48.2

1100

420

73

^ Zone o f Inhibition i n m m R e d u c t i o n o f b a c t e r i a o v e r u n t r e a t e d c o n t r o l (NYS-63) 3 Reduction i n Surface R e s i s t i v i t y (Ohmsj over untreated c o n t r o l 2

Molecular Weight. T h e m o l e c u l a r weight o f t h e d i f f u s a n t is very i m p o r t a n t because i t i s d i r e c t l y related t o t h e d i f f u s i v i t y . T o i n v e s t i g a t e t h e e f f e c t o f molecular weight on t h e t r a n s p o r t t h r o u g h p o l y m e r m e m b r a n e s , f i v e (5) i n s e c t p h e r o m o n e s w e r e c h o s e n . A l t h o u g h not e x a c t l y o f t h e same homologous s e r i e s , t h e y w e r e a l l a c e t a t e s r a n g i n g f r o m 12 c a r b o n a t o m s t o 20 c a r b o n a t o m s . T h e release through a 2 m i l flexible polyvinylchloride membrane i s shown i n F i g u r e 10. T h e s t r o n g i n f l u e n c e o f m o l e c u l a r w e i g h t i s a p p a r e n t f r o m t h i s graph, w i t h sharp decreases i n release r a t e as t h e m o l e c u l a r w e i g h t i n c r e a s e d f r o m 198 t o 310 i n s t e p s o f 28 u n i t s . C h e m i c a l F u n c t i o n a l i t y . L i k e dissolves l i k e i s equally a p p l i c able i n t h e polymer a r e a . D i s s o l u t i o n o f the p o l y m e r m a t r i x by t h e d i f f u s i n g molecules i s i m p o r t a n t i n t h e t r a n s p o r t process because i t increases t h e value o f the d i s t r i b u t i o n c o e f f i c i e n t . T o s t u d y t h i s v a r i a b l e , t w o s e t s o f p h e r o m o n e s w i t h 16 and 20 c a r b o n a t o m s , respectively, were investigated. The results are depicted i n Figures U and 12 a n d s h o w t h a t f u n c t i o n a l i t y h a s a s u b s t a n t i a l e f f e c t o n t h e

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

PESTICIDES

DODECENYL ACETATE 1 4 C ' s

TETRADECENYL ^ACETATE 16C's

ΔΓΡΤΓΤ 18Πο ACETATE 1 8 C s Ρ

2

4

t1/z Figure 10.

OCTADECENYL ACETATE 20C»s

€Υ

(DAYS 1 / 2 )

Effect of molecular weight on mass of agent released

0

2

4

t Figure 11.

V z

6

DAYS

8

72

Effect of functionality on release rate

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14.

KYDONiEus

Effects of Some Variables

on Release

165

Table D.

The E f f e c t o f C o - D i f f u s a n t s on t h e A n t i s t a t i c P r o p e r t i e s o f C a r p e t s CARPET FIBER

Antistatic Agent

CoA c t i v e Agent Diffusant Concentration

NYLON (Bigelow)

A d v a s t a t 50

Phenol

14.7

Volume Resistivity (ohms) 7.0x108

A d v a s t a t 50

None

14.8

2.2 χ 10

None

None

None

l.lxl0

17.6

7.0 x l O

POLYESTER (DuPont)

Dowanol E P h

A d v a s t a t 50

9

U

A d v a s t a t 50

None

16.9

8.0 x l O

None

None

None

l.lxl0

1 0

U

Reservoir Polymer Matrix: VULCANOL 5023

Ο

1

2 t

Figure 12.

%

3

4

5

(DAYS1/2)

Effect of functionality on release rate

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

6

166

C O N T R O L L E D R E L E A S E PESTICIDES

Table Ε Some Commercial Products Using the HERC ON technology Product STAPH-CHEK®

Membrane I 4 mil PVC

INSECT APE®

2 m i l mylar

Membrane II Function Antibacterial 4 mil PVC hospital fabric Roach control 5 m i l PVC

LURE-N-KILL™ FLYTAPE Attractant Pesticide

2 m i l mylar 2 m i l PVC

8 m i l PVC 2 m i l PVC

SCENTSTRIP™I SCENT S T R I P ™ Π

2 m i l mylar cloth

5 m i l PVC cloth

A i r freshener (consumer)

SCENTCOIL™

vinyl

vinyl

A i r freshener (industrial)

2 m i l vinyl

2 m i l vinyl

Houseflycontrol

TM LURETAPE Disparlure Gossyplure Orfralure Multilure Grandlure

m

monitoring gypsy moth monitoring pink 5 m i l vinyl 5 m i l vinyl bollworm 6 mil acrylic 6 m i l acrylic Control of oriental f r u i t moth Control of elm mylar mylar bark beetle 16 m i l rigid 16 m i l rigid Monitoring of boE weevil PVC PVC

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

14. KYDONiEus

Effects of Some Variables

on Release

167

release rate. As a matter o£ fact, octadecane had a much faster release rate than hexadecyl acetate as well as a l l of the 16 carbon atom pheromones shown in Figure E. 4. Flexibility of the HERC ON Process. It has been shown that a large variety of factors affect the release through polymer films. The HERCON process with i t s flex ibility in controlling release by varying membrane polymer thickness, membrane polymer matrix, reservoir polymer matrix and diffusant concentration as well as co-diffusants is capable in controlling the release of chemical agents t o produce consumer and industrial products with improved properties inexpensively Table Ε describe use the HERCON technology. Thickness and type of films are given for each product. The reservoir layer which is perhaps the most important aspect of the technology varies from product to product and i t is of proprietary nature. Our company is looking forward to the continuous expansion of the market f o r controlled release products and we are aggressively exploring new product applications using the technology mentioned herein.

LITERATURE CITED (1) Kydonieus et al., "Marketing and Economic Considerations for HERCON Consumer and Industrial Controlled Release Products", ACS Proceedings-Chemical Marketing and Economics Division-1976, pp. 140-165. (2) Kydonieus et al., "Controlled Release of Pheromones through Multi-layered Polymeric Dispensers", ACS Symposium Series 33, pps. 283-294, 1976. (3) Crank, J. and G.S. Park, ed. "Diffusion in Polymers" Academic Press, N.Y. (4) Richards, R.W., "The Perme ability of Polymers to Gases, Vapours and Liquids; ERDE (Ministry of Defense) Tech. Report No. 135, March 1973, NTIS AD-767 627. (5) Baker, R.W. and H.K. Lonsdale, "Controlled Release of Biologically Active Agents, A.C. Tanquary and R.E. Lacey (Eds.), Plenum Press, N.Y., 1974. (6) Crank, J., "The Mathematics of Diffusion", Oxford University Press, London, 1956. (7) Barrer, R.M., Diffusion in Polymers", Academic Press, London, 1968. (8) Kydonieus, et al., U.S. Patent 3,961,117 (1976).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15 Controlled Release of Pheromone in the Gypsy Moth Program J. R. PLIMMER, B. A. BIERL, and R. E. WEBB Beltsville Agricultural Research Center, U.S. Department of Agriculture, Beltsville, Md. 20705 C. P. SCHWALBE Animal and Plant Health Inspection Service, U.S. Department of Agriculture, Otis Air Force Base, Mass. 02542

Progress in development and practical application of behavior-modifying chemicals has continued since research on the control of the gypsy moth, Lymantria Dispar (L.) and other insects with behavior-modifying chemicals was summarized in 1975 (1), and there has been considerable effort towards obtaining a greater understanding of the relationship between pheromone composition and the behavior associated with chemical stimuli (2). This is particularly true of the application of behavior-modifying chemicals in attempts to disrupt insect mating and thus to control pest populations. This appealing concept has many potential advantages. It is quite specific, and the quantity of material used (a few grams per hectare) i s so small that i t s impact on the environment and on non-target species should be minimal. Pheromones generally show very low toxicity towards living organisms (3). Most insect pheromones contain only carbon, hydrogen and oxygen, and they would not be expected to pollute the environment because they are readily biodegradable. Their value for detection and survey of insect pest infestations has already been demonstrated. If pheromones can be applied effectively they should play an important role in the management of economic species, and there are many situations in which pheromones might be used with advantage to supplement conventional insecticides. Sex pheromones are not expected to be effective in reducing insect populations in heavily infested areas (4); i t is therefore important to define by experiment the population level at which mating can be prevented. It must also be possible to monitor the progress of attempts to disrupt mating throughout the period of mating activity. When dealing with agricultural crops, economic benefit may be measured by reduction of crop damage in a treated plot compared with that observed in a control. However, i t i s often very difficult to define economic benefit that results from application to forest insects unless valuable timber resources are suffering attack. 168 In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLiMMER E T A L .

Controlled

Release of

Pheromone

169

In a d d i t i o n to e s t a b l i s h i n g methods of d e f i n i n g e f f e c t i v e ness of pheromone treatments i n terms of p o p u l a t i o n r e d u c t i o n , we must a l s o determine when and how pheromones should be used. These questions must be answered by c o n s i d e r i n g the behavior of the i n s e c t and by i n v e s t i g a t i n g the p h y s i c o - c h e m i c a l c h a r a c t e r i s t i c s of p o t e n t i a l methods of d e l i v e r i n g the pheromone. The Gypsy Moth [Lymantria d i s p a r ( L . ) ] :

Role of the Sex Pheromone

Since the i n s e c t was introduced i n t o the U.S. i n 1868 or 1869, gypsy moth i n f e s t a t i o n s have spread over the g r e a t e r p o r t i o n of the n o r t h e a s t e r n U n i t e d States where they have d e f o l i a t e d l a r g e areas of f o r e s t and shade t r e e s ( 5 ) . The gypsy moth i s a l s o found i n temperate areas throughout the world from North A f r i c a to Japan. I n the l a t e summer mass that may c o n t a i n 30 these egg masses e a r l y the f o l l o w i n g May consume l a r g e q u a n t i t i e s of f o l i a r m a t e r i a l . ( I n Japan, male l a r v a e consume 700 t o 1100 cm and females 110 t o 1800 cm of leaves) ( 6 ) . The f u l l y developed l a r v a e pupate and emerge as a d u l t moths from l a t e June to August, depending on l o c a l c l i m a t e . Mating a c t i v i t y extends over a p e r i o d of 6 t o 8 weeks. The female does not normally f l y and a t t r a c t s the male f o r mating purposes by e m i t t i n g a pheromone. Although o t h e r s t i m u l i , such as v i s u a l cues, are important i n mating, the sex pheromone of the moth ( d i s p a r l u r e , cis-7,8-epoxy-2-methyloctadecane) a c t s as a powerful a t t r a c t a n t . Pheromone emission f o l l o w s a d i e l p e r i o d i c i t y ( 7 ) . The females become a t t r a c t i v e a f t e r 0900 hours and remain a t t r a c t i v e u n t i l about 2000 hours. Male response c l o s e l y f o l l o w s t h i s p e r i o d i c i t y : peak response occurs between 0900 and 1500 hours. In our e f f o r t s to d i s r u p t mating, s y n t h e t i c racemic d i s p a r l u r e was used because i t could be manufactured f o r a reasonable cost and has proved t o be a good a t t r a c t a n t . However, i n 197A Japanese workers s y n t h e s i z e d the two o p t i c a l l y a c t i v e enantiomers of d i s p a r l u r e and found t h a t the (+) enantiomer (7R,8S-epoxy-2-methyloctadecane) was much more e f f e c t i v e as a t r a p p i n g agent than the o p p o s i t e enantiomer ( 8 ) . Other e x p e r i ments have confirmed i t s a t t r a c t i v e n e s s (9,10,11). T h e r e f o r e , i t seems l i k e l y that the (+) enantiomer i s i d e n t i c a l to the n a t u r a l l y o c c u r r i n g pheromone. However, the enantiomers have so f a r been a v a i l a b l e o n l y i n m i l l i g r a m q u a n t i t i e s (8,12), and t h e i r f u t u r e impact on mating d i s r u p t i o n experiments cannot be assessed u n t i l the p o s s i b i l i t i e s of an economical s y n t h e s i s have been explored. 2

2

Mating D i s r u p t i o n :

Use of Pheromone Formulations

The suggestion was made i n 1960 (13) that the a r t i f i c i a l r e lease of i n s e c t sex pheromones i n t o the atmosphere would i n t e r f e r e w i t h the process of m a t e - f i n d i n g and thus w i t h the mating

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

C O N T R O L L E D R E L E A S E PESTICIDES

170

process. The antennal s e n s i l l a e of the male f u n c t i o n as very s p e c i f i c receptors f o r t h e pheromone emitted by the female. The r e c e p t o r s i t e s are a c t i v a t e d by s p e c i f i c chemicals o r blends of chemicals, thus ensuring t h a t communication i s l i m i t e d t o members of the same s p e c i e s . However, the study of chemical s t i m u l i alone i s inadequate f o r understanding t h e complex phenomena a s s o c i a t e d w i t h mating. Superimposed on the chemical communication system of i n d i v i d u a l i n s e c t species i s a v a r i e t y of b e h a v i o r a l and p h y s i o l o g i c a l c h a r a c t e r i s t i c s . Techniques f o r d i s r u p t i o n of mating must be based not only on the use of chemical formulations but a l s o on knowledge of the behavior and b i o l o g y of the t a r g e t i n s e c t . The design o f chemical formulations demands t h a t c o n s i d e r a t i o n be given t o the i n t e r p l a y of many complex v a r i a b l e s . Most a t t r a c t a n t pheromones a r of which r e a d i l y decompos ment of areas i n f e s t e d by the gypsy moth should be l i m i t e d t o one o r two a p p l i c a t i o n s i f pheromone use i s t o be economical. F o r t u n a t e l y , pheromones possess extremely high b i o l o g i c a l a c t i v i t y and, i f they can be used t o maximum e f f e c t , a p p l i c a t i o n s of only a few grams per acre should be adequate t o achieve mating d i s r u p t i o n (14). The requirements f o r a f o r m u l a t i o n that w i l l r e l e a s e s u f f i c i e n t pheromone t o permeate the a i r and achieve d i s r u p t i o n o f mating over a prolonged p e r i o d a r e q u i t e e x a c t i n g . F o r example, a constant r e l e a s e r a t e over a long p e r i o d seems d e s i r a b l e . Some formulations show apparent zero order r a t e o f emission ( i . e . , constant r e l e a s e r a t e independent of pheromone loading) i f the r e s e r v o i r o f pheromone i s so l a r g e that o n l y a s m a l l f r a c t i o n only i s emitted over a long p e r i o d (15). However, t o reduce the amount of expensive i n g r e d i e n t used, we designed types of f o r m u l a t i o n t h a t were intended t o r e l e a s e the major p o r t i o n o f t h e i r l o a d i n g o f pheromone over the f l i g h t season of the male gypsy moth (6-8 weeks). Formulation performance i s a f f e c t e d by environmental f a c t o r s such as temperature. Pheromone r e l e a s e r a t e from the formulat i o n should be c h a r a c t e r i z e d by a p o s i t i v e temperature c o e f f i c i e n t , because the mating a c t i v i t y o f the gypsy moth i s a t i t s most i n t e n s e a t mid-day and during t h e afternoon. D i u r n a l temperature v a r i a t i o n s w i l l favor the d e s i r e d performance. Pheromone emission w i l l i n c r e a s e as the temperature i n c r e a s e s during t h e day, whereas very l i t t l e o f the pheromone w i l l be r e l e a s e d during t h e c o o l e r p e r i o d throughout t h e n i g h t . However a f o r m u l a t i o n possessing these c h a r a c t e r i s t i c s would probably be l e s s e f f e c t i v e against i n s e c t s that showed maximum mating a c t i v i t y i n the dark. Controlled release

formulations

C o n t r o l l e d r e l e a s e formulations have proved t h e i r worth as a source of pheromone f o r use i n t r a p s . The USDA d e t e c t i o n and

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLIMMER

ET

AL.

Controlled

Release of

Pheromone

171

survey t r a p ( d e l t a trap) (Figure 1) c o n s i s t s of an open-ended cardboard tube of t r i a n g u l a r cross s e c t i o n (16). The i n t e r i o r i s coated w i t h a s t i c k y m a t e r i a l and contains a dispenser that s l o w l y r e l e a s e s d i s p a r l u r e , thus p r o v i d i n g a b a i t . The d i s penser c u r r e n t l y i n use (the Hereon ® dispenser, manufactured by the H e a l t h Chem. Corp., New York, N.Y. 10010 I/) i s a t h r e e l a y e r p l a s t i c laminate (17). The two outer p l a s t i c l a y e r s cover an inner l a y e r impregnated w i t h d i s p a r l u r e . We have determined the e f f e c t s of l o a d i n g , w a l l t h i c k n e s s , and temperature on the r a t e of emission of d i s p a r l u r e from t h i s dispenser (18). A d i s penser of 6 m i l s t h i c k n e s s c o n t a i n i n g 6 mg of d i s p a r l u r e emitted 0.24 \ig of pheromone/hr at 80°F i n a constant flow of a i r of 100 ml/min. An i n c r e a s e of 10°F almost doubled the r a t e of emission. Although the r a t e of emission should be dependent on the weight of l u r e present 80°F. Since t h i s i s a ver t e n t , we may regard the emission r a t e as constant during the p e r i o d of male f l i g h t . By c o n t r a s t , i f we w i s h to use a broadcast f o r m u l a t i o n to d i s r u p t mating, more e f f i c i e n t use of the expensive pheromone i s p r e f e r a b l e . In a d d i t i o n , unnecessary increases i n the environmental burden of s y n t h e t i c b i o l o g i c a l l y a c t i v e compounds are u n d e s i r a b l e . I t must be borne i n mind t h a t the amount of a c t i v e i n g r e d i e n t a p p l i e d per hectare i s i r r e l e v a n t i n terms of our o b j e c t i v e when we use pheromones to permeate the a i r ; the amount of m a t e r i a l r e l e a s e d by the f o r m u l a t i o n during the p e r i o d of mating i s more s i g n i f i c a n t , and t h i s q u a n t i t y i s dependent on the type of the f o r m u l a t i o n . However, f o r comparison during f i e l d t r i a l s we maintained the r a t e of a p p l i c a t i o n constant at 20 grams of d i s p a r l u r e per hectare (8 g/acre). S e v e r a l f o r m u l a t i o n types were s e l e c t e d f o r l a b o r a t o r y e v a l u a t i o n . W i t h i n each f o r m u l a t i o n type, p o s s i b l e m o d i f i c a t i o n s can i n c r e a s e f a c t o r i a l l y the number of candidates f o r t e s t i n g . In 1975, l a r g e s c a l e f i e l d t e s t s were r e s t r i c t e d to microencapsulated f o r m u l a t i o n s . In 1976, on the b a s i s of l a b o r a t o r y r e s u l t s s e v e r a l other formulations were i n c l u d e d i n the f i e l d program (Table I ) .

If Mention of a manufacturer or a p r o p r i e t a r y product does not imply endorsement by the USDA.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

CONTROLLED RELEASE

PESTICIDES

SX

t5

Ο

tup

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLIMMER ET

AL.

Controlled

Release of

Pheromone

173

TABLE I Formulations Used i n F i e l d T e s t i n g

Formulation designation

Manufacturer

1976-NCR-2 1976-NCR-4

N a t i o n a l Cash R e g i s t e r N a t i o n a l Cash R e g i s t e r

1976-NCR-10 1975-NCR-2 Stauffer MGK Conrel

% Lure in Particles

Particle s i z e (μ) 50-250 50-250

N a t i o n a l Cash R e g i s t e r N a t i o n a l Cash R e g i s t e r S t a u f f e r Chemical Co.

2 : 2 : 10 10 2 3/4 : 2

50-250 50-400 10-40

McLaughli Albany I n t e r n a t i o n a l Co.

30

Fibers

3/4 1/4

Microencapsulated f o r m u l a t i o n s based on g e l a t i n - w a l l e d capsules ( N a t i o n a l Cash R e g i s t e r Corp., Dayton, O h i o ) , and on p o l y u r e a w a l l e d capsules ( S t a u f f e r Chemical Co., Richmond, C a l i f . ) w e r e examined. A l s o t e s t e d were a " m a t r i x " f o r m u l a t i o n (McLaughlin, Gormley, King and Co., M i n n e a p o l i s , Minn.) and h o l l o w f i b e r s c o n t a i n i n g d i s p a r l u r e ( C o n r e l , Albany I n t e r n a t i o n a l Co., Norwood, Mass.). A l l the f o r m u l a t i o n s w i t h the e x c e p t i o n of the C o n r e l hollow f i b e r type, f o r which s p e c i a l equipment was necessary, were s u i t a b l e f o r c o n v e n t i o n a l spray a p p l i c a t i o n from a i r c r a f t . They were a p p l i e d from Spraying System No. 8010 t i p s on spray boom nozzles. Formulations f o r Broadcast A p p l i c a t i o n Previous experience (19) gave a good i n d i c a t i o n of the typés of f o r m u l a t i o n t h a t might be expected t o perform w e l l i n the f i e l d . Among the candidates s e l e c t e d f o r t e s t i n g were v a r i o u s types of microcapsules. Although the behavior of encapsulated pheromones would appear to be p r e d i c t a b l e j i p r i o r i , we l e a r n e d by experiment t h a t t h e i r l o n g e v i t y i n the f i e l d was g r e a t l y a f f e c t e d by environmental f a c t o r s . The r a t e a t which the pheromone i s r e l e a s e d was a f f e c t e d not only by the pheromone l o a d i n g and the chemical composition of the capsule w a l l and the other components of the f o r m u l a t i o n , but a l s o by humidity, temperature and s u n l i g h t . Microcapsules of d i f f e r e n t w a l l p e r m e a b i l i t y or s i z e can be made by changing the manufacturing process. Because changes i n d i s p a r l u r e content can a f f e c t r e l e a s e r a t e , d i s p a r l u r e was encapsulated a t two d i f f e r e n t c o n c e n t r a t i o n s (2% and 10%) i n s o l u t i o n . The d e s i g n a t i o n 2% and 10% r e f e r t o the c o n c e n t r a t i o n of d i s p a r l u r e i n the s o l v e n t ; the S t a u f f e r and 4% NCR f o r m u l a t i o n s comprised a 75:25 mixture of the

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

174

C O N T R O L L E D R E L E A S E PESTICIDES

2% and 10% m a t e r i a l s . The r e l e a s e r a t e of d i s p a r l u r e from a microcapsule should undergo approximately e x p o n e n t i a l decay as i t s c o n c e n t r a t i o n decreases. In p r a c t i c e , spray a p p l i c a t i o n of microcapsules i s sometimes f o l l o w e d by a 'burst' of pheromone, which may p o s s i b l y be a s c r i b e d to l o s s from a capsular membrane i n i t i a l l y saturated w i t h d i s p a r l u r e . A f t e r the i n i t i a l b u r s t , the slope of the p l o t of r e l e a s e r a t e versus time decreases. Some microcapsules, observed under a microscope, appeared to l o s e t h e i r contents r a p i d l y and become d i s t o r t e d . T h i s c o l l a p s e appeared to be r e l a t e d to high r e l a t i v e humidity. In consequence, we examined the e f f e c t of some of these v a r i a b l e s i n a s e r i e s of l a b o r a t o r y t e s t s before f i e l d e v a l u a t i o n . These t e s t s were c a r r i e d out as f o l l o w s : 1) P r e l i m i n a r y Screening t i o n s were a p p l i e d to microscope s l i d e s and aged outdoors i n s l i d e boxes hung under a canopy to p r o t e c t them from r a i n but not from wind and temperature changes. Other samples were aged i n doors. The r a t e of emission of pheromone was measured p e r i o d i c a l l y at constant temperature i n the apparatus p r e v i o u s l y des c r i b e d (20). The amount of pheromone remaining i n the formulat i o n was a l s o determined as a f u n c t i o n of exposure time. These two measurements d i d not always g i v e the same e v a l u a t i o n . The emission r a t e provided a b e t t e r guide to performance than measurement of r e s i d u a l pheromone, s i n c e we found t h a t some microencaps u l a t e d formulations ceased e m i t t i n g d i s p a r l u r e even though a s u b s t a n t i a l amount of the pheromone was s t i l l present i n the capsules. 2) E v a l u a t i o n of S t i c k e r : Microencapsulated formulations c o n t a i n capsules suspended i n water w i t h a s u r f a c t a n t and a t h i c k e n i n g agent ( u s u a l l y h y d r o x y e t h y l c e l l u l o s e ) to s t a b i l i z e the suspension. Microcapsules deposited onto f o l i a g e are r a p i d l y washed o f f by r a i n or d i s l o d g e d by the e f f e c t of wind; t h e r e f o r e s t i c k e r s are added to the formulations to ensure t h a t the capsules adhere t i g h t l y t o the f o l i a g e . Larger capsules seem to be dislodged more r e a d i l y than the smaller ones, and the choice of capsule s i z e was i n f l u e n c e d by t h i s knowledge. S t i c k e r s were t e s t e d i n the l a b o r a t o r y by a p p l y i n g the formulat i o n , i n c l u d i n g the s t i c k e r , to f o l i a g e and a l l o w i n g i t to dry f o r 1 to 2 hours. A spray of water was a p p l i e d to determine whether the f o r m u l a t i o n was r e a d i l y washed o f f . Because s t i c k e r s can form adhesive f i l m s , they reduce the r a t e of emission of pheromone from the microcapsules and, i n e f f e c t , prolong the e f f e c t i v e n e s s of the f o r m u l a t i o n . As f u r t h e r e v a l u a t i o n , the emission r a t e s of the formulations were measured w i t h and without a d d i t i o n of s t i c k e r .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLiMMER E T A L .

Controlled

Release of

Pheromone

175

3) E f f e c t of Environmental C o n d i t i o n s : In the f i e l d , formulations are u s u a l l y exposed to severe weathering. Wind, sun, and r a i n w i l l have c o n s i d e r a b l e i n f l u e n c e i n decreasing the l i f e t i m e of a microencapsulated pheromone f o r m u l a t i o n . Therefore, we measured the l i f e t i m e under a v a r i e t y of c o n d i t i o n s to provide a working guide f o r f i e l d t r i a l s . In t y p i c a l experiments, g l a s s s l i d e s were coated w i t h microencapsulated formul a t i o n s and exposed under l a b o r a t o r y and f i e l d c o n d i t i o n s . B i o assay and pheromone r e l e a s e measurements were used f o r comparat i v e assessment a f t e r exposure. We found that capsules l o c a t e d outdoors l o s t h a l f of t h e i r l u r e content i n 10 to 34 days, whereas about 123 days was r e q u i r e d under l a b o r a t o r y c o n d i t i o n s . The emission r a t e measurements showed t h a t , i n g e n e r a l , the microcapsule and m a t r i x formulations gave a h i g h r e l e a s e r a t e f o r the f i r s t few days more s l o w l y as a f u n c t i o the data obtained f o r both emission r a t e s and l u r e contents f o r samples aged outdoors i n Maryland i n s p r i n g 1976. S t i c k e r was not added to these t e s t samples. A much higher percentage of the a p p l i e d l u r e was emitted over a 9-week p e r i o d from the 2% NCR f o r m u l a t i o n than from the 10% NCR m a t e r i a l . The r a t e of emission d i d not i n c r e a s e i n prop o r t i o n to the i n c r e a s e i n l u r e content; i n s t e a d the 10% formulat i o n emitted l u r e at a r e l a t i v e l y h i g h r a t e f o r a longer p e r i o d . A f t e r 9 weeks of aging, the 10% NCR f o r m u l a t i o n emitted l u r e at 2 to 3 times the r a t e of the 2% m a t e r i a l per m i l l i g r a m of i n i t i a l l y a p p l i e d l u r e . Therefore the 2% NCR f o r m u l a t i o n e f f i c i e n t l y r e l e a s e d i t s l u r e during the moth f l i g h t season, but the 10% f o r m u l a t i o n had a longer a c t i v e l i f e t i m e . The S t a u f f e r f o r m u l a t i o n l i s t e d i n Table I I was modified t o improve i t s e f f i c i e n c y f o r f i e l d a p p l i c a t i o n ; a mixture of 3 p a r t s 2% capsules and 1 p a r t 10% capsules (average of 4%) was used f o r f i e l d t e s t s . The RA-1645 ® s t i c k e r (Monsanto Corp., Indian Orchard, Mass.) used w i t h the NCR and MGK m a t e r i a l s reduced the emission r a t e by over 50% when 2% of t h i s s t i c k e r was added to the formul a t i o n s . To minimize t h i s problem, we used only 1% f o r f i e l d applications. No emission measurements were made on Conrel

fibers.

1976

F i e l d T r i a l s f o r Comparative E v a l u a t i o n of Formulations Tests were conducted i n June and J u l y by the Animal and P l a n t H e a l t h I n s p e c t i o n S e r v i c e , the A g r i c u l t u r a l Research S e r v i c e , and the Maryland Department of A g r i c u l t u r e ; d u p l i c a t e experiments were run i n Maryland and Massachusetts (21). The formulations s e l e c t e d f o r f i e l d t e s t s are shown i n Table I . The NCR capsules c o n s i s t e d of a p l a s t i c - c o a t e d , g e l a t i n w a l l encasing a 3:1 xylene : amyl acetate s o l u t i o n of 2.2% or 11% d i s p a r l u r e ; s i n c e the w a l l m a t e r i a l i s 10% of the

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

0.1 0.2 0.2 0.08 0.3 0.1

0.4 0.6 0.3 0.2 0.4 0.3

0.05 0.2 0.08

0.005 0.02 0.02

Emission Rate Measurements yg/hr ** a f t e r aging 4 days 9 wks 4 wks

** P e r mg of l u r e o r i g i n a l l y present.

* Not the f o r m u l a t i o n a p p l i e d i n the f i e l d ; the f i e l d f o r m u l a t i o n contained 3/4 capsules w i t h 2% l u r e and 1/4 capsules w i t h 10% l u r e .

Lure Content Measurements mg l u r e i n t e s t sample a t % Loss % Lure i n t of l u r e 9 wks Capsules Manufacturer ο 2 1.0 73 3.7 NCR-1975 2 75 2.5 0.6 NCR-1976 60 3/4 : 2 1.9 NCR-1976 4.9 1/4 : 10 6.8 29 NCR-1976 10 9.6 13 4 1.3 Stauffer * 1.5 82 2 1.6 0.3 MGK

Emission of Lure from Aged Samples

TABLE I I

15.

PLiMMER

ET AL.

Controlled

Release of

Pheromone

177

capsule weight, the l u r e content of the capsules was 2% and 10% r e s p e c t i v e l y . The 4% f o r m u l a t i o n was a mixture of 3 p a r t s of the 2% f o r m u l a t i o n w i t h 1 p a r t of the 10% f o r m u l a t i o n . The capsules were suspended i n water c o n t a i n i n g a t h i c k e n i n g agent and an adhesive or s t i c k e r t o h o l d the sprayed capsules onto the f o l i a g e . The s t i c k e r f o r the 1975 NCR f o r m u l a t i o n was 1% Rhoplex B-15 © (Rohm and Haas, P h i l a d e l p h i a , Penn.); that f o r the 1976 NCR formulations was 1% RA-1645 Θ plus 0.1% T r i t o n X-202 ® (Rohm and Haas). The S t a u f f e r f o r m u l a t i o n was an aqueous sus pension of c r o s s - l i n k e d polyurea microcapsules of which 75% contained 2.2% d i s p a r l u r e and 25% contained 11% d i s p a r l u r e i n xylene; a t h i c k e n i n g agent and an adhesive were a l s o present. The MGK was an aqueous s l u r r y of p a r t i c l e s of a p a r a f f i n waxi n o r g a n i c s a l t m a t r i x c o n t a i n i n g 2% d i s p a r l u r e ; a t h i c k e n e r and an adhesive (same as used i 1976 NCR formulations) als added. The Conrel f i b e r 2.3 cm i n l e n g t h , f i l l e disparlur Test p l o t s were e s t a b l i s h e d i n both Maryland ( C e c i l County) and Massachusetts (near F a l l R i v e r ) . The p o p u l a t i o n l e v e l i n the t r e a t e d areas was estimated by pre-season counts of egg masses before f o l i a t i o n of t r e e s . I n Massachusetts, approximately 2 t o 3 egg masses/hectare was found; a much lower p o p u l a t i o n was present i n Maryland. Each f o r m u l a t i o n was a p p l i e d i n each s t a t e t o 4 r e p l i c a t e p l o t s of 16 ha a t a r a t e of 20 g of l u r e / h a . E i g h t check or c o n t r o l p l o t s were e s t a b l i s h e d i n each s t a t e . The i n c i d e n c e of mating i n the t r e a t e d p l o t s was compared w i t h that i n the check p l o t s by p l a c i n g v i r g i n female moths i n the f i e l d and r e t r i e v i n g them a f t e r 3 days t o determine the number mated. The recovered i n s e c t s were d i s s e c t e d i n the l a b o r a t o r y to determine whether sperm was present. Any egg masses deposited were c o l l e c t e d and examined f o r the presence of f e r t i l e eggs. The o v e r a l l r e s u l t s of these t e s t s are given i n Table I I I . The percent r e d u c t i o n i n mating i s 100 minus the r a t i o : percent mated i n t r e a t e d p l o t s times 100, d i v i d e d by percent mated i n c o n t r o l p l o t s . The ranking of the seven formulations t e s t e d was the same i n both t e s t l o c a t i o n s although the d i f f e r e n c e s among the top performers were not s t a t i s t i c a l l y s i g n i f i c a n t . The best performance was shown by the 1976 2% NCR microcapsule f o r m u l a t i o n w i t h mating r e d u c t i o n s of 98 and 83% r e s p e c t i v e l y , f o r Maryland and Massachusetts. The 4% NCR f o r m u l a t i o n was second w i t h 95 and 76% mating r e d u c t i o n f o r the two s t a t e s . The 1975-2% NCR microcapsules reduced mating by 80% i n Maryland and 68% i n Massachusetts; t h i s 80% f i g u r e f o r the 1976 t e s t s i s the same as that obtained i n t r i a l s c a r r i e d out i n Maryland i n 1975 over a much l a r g e r area (22). T h i s d u p l i c a t i o n of r e s u l t s was en couraging because i t provided an element of c o n t i n u i t y i n the t e s t i n g program and confirmed our p r e d i c t i o n s t h a t m o d i f i c a t i o n of t h i s f o r m u l a t i o n f o r the 1976 t e s t s would improve i t s per formance. We f e l t that the improved performance of the 1976 NCR f o r m u l a t i o n s i s due a t l e a s t i n p a r t t o the new RA-1645

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

260 101 121 149 91 76 128 132

124 2 5 7 9 7 31 49

47.7 2.0 4.1 4.7 9.9 9.2 24.2 37.1

Maryland Tests No. o f % moths Mated mated

* 8 Control plots, a l l formulations 4 plots.

Controls * 1976-NCR-2% 1976-NCR-4% 1976-NCR-10% 1975-NCR-2% Conrel Stauffer MGK

Material

No. of moths dissected

96 91 90 79 81 51 22

.

% Reduction i n mating 644 364 273 270 292 282 356 358

315 29 31 37 45 59 105 129

47.9 8.0 11.4 13.7 15.4 20.9 29.5 36.0

Massachusetts Tests No. o f No. of % moths moths mated mated dissected

Mating Reduction i n 1976 F i e l d Tests

TABLE I I I

83 76 71 68 56 38 25

_

% Reduction i n mating

15.

P O M M E R

ET AL.

Controlled

Release of

Pheromone

179

s t i c k e r , which proved t o be a more e f f e c t i v e adhesive than the Rhoplex B-15 used i n 1975; t h e RA-1645 a l s o provided an a d d i t i o n a l c o a t i n g t o the capsules that reduced the r e l e a s e r a t e of t h e l u r e and thus extended the a c t i v e l i f e of the capsules. In a d d i t i o n , the s m a l l e r average p a r t i c l e s i z e of the 1976 NCR capsules i n creased the number of capsules per acre and improved adhesion and r e t e n t i o n on f o l i a g e . Laboratory t e s t s of a l l formulations during the f i e l d season i n d i c a t e d that the poor performance of the MGK and S t a u f f e r formulations was due a t l e a s t i n p a r t t o the r a p i d l o s s o f l u r e during the i n i t i a l 1 t o 2 weeks a f t e r a p p l i c a t i o n , l e a v i n g i n s u f f i c i e n t l u r e f o r c o n t r o l d u r i n g peak mating. Midsummer aging t e s t s i n d i c a t e d t h a t the r e l e a s e r a t e of the MGK m a t e r i a l i n creased f a r more as a f u n c t i o n o f higher outdoor temperatures than d i d those o f the microencapsulated formulations I t i s important t season t o evaluate the degree of c o n t r o l a t the r e l a t i v e l y h i g h mid-season p o p u l a t i o n s . P l o t s o f percent mating vs number of days a f t e r a p p l i c a t i o n f o r the 1976-NCR-2 and 1976-NCR-4 f o r m u l a t i o n s and f o r the c o n t r o l s are shown i n F i g u r e s 2 and 3. A t h r e e p o i n t running average was used f o r t h e percent mating f i g u r e s . During t h e p e r i o d of peak mating (mid J u l y ) even the 2% NCR f o r m u l a t i o n d i d not adequately c o n t r o l mating. A second a p p l i c a t i o n o f the capsules or a i n i t i a l l u r e a p p l i c a t i o n r a t e higher than 20 g/ha may be necessary t o maintain mating below 10% throughout the f i e l d season. Future f i e l d plans w i l l i n c l u d e t e s t s t o determine the e f f e c t of a second a p p l i c a t i o n of the 2% NCR f o r m u l a t i o n . I n a d d i t i o n , a p p l i c a t i o n r a t e s s i g n i f i c a n t l y higher than the 20 g/ha w i l l be t e s t e d . Discussion Although a i r permeation w i t h pheromone presents a p o t e n t i a l method of c o n t r o l l i n g some pest p o p u l a t i o n s , there a r e many d i f f i c u l t i e s t o be overcome before the technique becomes economical and p r a c t i c a l . Our aim was t o provide a sprayable f o r m u l a t i o n t h a t would s u c c e s s f u l l y d i s r u p t mating throughout the f l i g h t p e r i o d of the gypsy moth i n the f o r e s t environment. This o b j e c t i v e met w i t h l i m i t e d success, and we s h a l l continue our research to improve the performance of our c o n t r o l l e d - r e l e a s e f o r m u l a t i o n s . O p t i m i z a t i o n of pheromone formulations w i l l depend on a number o f f a c t o r s . The f i r s t of these i s the behavior of the i n s e c t during the f l i g h t p e r i o d , and the second i s the physico-chemical behavior of a c o n t r o l l e d - r e l e a s e f o r m u l a t i o n i n a f o r e s t environment. McDonough (14) has discussed the t h e o r e t i c a l case i n which a f o r m u l a t i o n r e l e a s e s pheromone at a r a t e p r o p o r t i o n a l t o the amount remaining (a f i r s t order process) and has given an equation

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

180

CONTROLLED

R E L E A S E PESTICIDES

C Φ S20f

Days After Application Figure 2. Maryland tests; Ο — Ο control; Χ — X 1976-NCR-2; W7&-NCR-4

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLiMMER

ET AL.

Controlled

Release of

Pheromone

181

f o r the a p p l i c a t i o n l e v e l of the pheromone (C ) based on a desired h a l f - l i f e period, t ° /

9

where k = ( I n 2) t

1/2

(R i s the minimum r e l e a s e r a t e , t i s the p e r i o d of c o n t r o l des i r e d f o r the a p p l i c a t i o n , and e i s the n a t u r a l base of l o g a r i thms) . From data on the c o d l i n g moth, (Laspeyresia pomonella ( L . ) ) s o l u t i o n of t h i s equation g i v e s a f i g u r e f o r C of 13.1 g/ha f o r a 30-day p e r i o d of c o n t r o l . However, t h i s t h e o r e t i c a l treatment n e g l e c t s the to which the f o r m u l a t i o that temperature and wind v e l o c i t y had a c o n s i d e r a b l e e f f e c t on the emission r a t e . Rain and s u n l i g h t a l s o c o n t r i b u t e d towards u n p r e d i c t a b l e changes i n the l i f e t i m e of the f o r m u l a t i o n , and we found that the time i n which the l u r e content had decreased by 50% v a r i e d g r e a t l y depending on the c o n d i t i o n s of exposure. Microencapsulated formulations of a v o l a t i l e s o l u t e i n a s o l v e n t should show p r e d i c t a b l e r e l e a s e c h a r a c t e r i s t i c s f o r a p e r i o d a f t e r an i n i t i a l b u r s t of pheromone emission, because i n theory the r a t e of emission i s c o n t r o l l e d by d i f f u s i o n of s o l u t e through the capsule w a l l . However, i n p r a c t i c e , r a p i d l o s s of v o l a t i l e s o l v e n t r e s u l t s i n behavior u n l i k e t h a t t h e o r e t i c a l l y p r e d i c t e d . Our f i n d i n g s were p a r a l l e l e d i n l a b o r a t o r y s t u d i e s of emission r a t e by Roelofs e t a l . (23) who found that the r a t e of pheromone emission dropped from 0.7% per day t o 0.02% by the 16th day when only 3.7% of a mixture of 11-tetradecenyl acetates had been r e l e a s e d by a microencapsulated formulation. I n the f o r e s t , the s i t u a t i o n i s even more complex. A i r measurements of d i s p a r l u r e concentrations showed that a l a y e r i n g e f f e c t occurred. Most o f the pheromone appeared t o be near the ground and there was a c o n s i d e r a b l e d i f f e r e n c e between concentrat i o n s measured a t 0.5 m and 15.0 m h e i g h t . Measurement of d i s p a r l u r e i n a i r from a f o r m u l a t i o n a p p l i e d t o a f l a t , grass p l o t showed that over a p e r i o d o f 30 days, only 2% of the a p p l i e d d i s p a r l u r e could be accounted f o r i n the a i r (24). Thus i n a d d i t i o n t o the a i r , there are probably other " s i n k s " which r a p i d l y take up d i s p a r l u r e r e l e a s e d by the f o r m u l a t i o n . We suggest t h a t the surfaces of the s o i l , l e a v e s , and p l a n t s probably adsorb the pheromone r a p i d l y . The c l o s e resemblance of d i s p a r l u r e t o the long chain hydrocarbon s t r u c t u r e s common i n p l a n t l e a f waxes would be expected t o f a v o r i t s ready adsorpt i o n and r e t e n t i o n by such s u r f a c e s . Experience i n fumigation has taught that a i r permeation i s best achieved when v o l a t i l e chemicals are not h i g h l y sorbed by the s u b s t r a t e and that s p e c i a l techniques may be r e q u i r e d t o im-

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

182

CONTROLLED RELEASE

PESTICIDES

prove the d i s t r i b u t i o n o f h e a v i e r - t h a n - a i r vapors. These f a c t o r s w i l l be important i n the e f f i c i e n t use of pheromones, and i t seems l i k e l y t h a t the a b i l i t y of a f o r e s t or p l a n t s u r f a c e to adsorb pheromone w i l l s i g n i f i c a n t l y a f f e c t performance of a controlled-release formulation applied uniformly to f o l i a g e .

Literature Cited 1. Beroza, Μ., "Pest Management with Insect Sex Attractants and Other Behavior-controlling Chemicals",M. Beroza, ed. ACS Symposium Series No. 23. American Chemical Society, Washington, D.C. 1976 pp 99-118. 2. Roelofs, W. L., Miller, J. R., Baker, T. C., in "Perspectives in Forest Entomology", J. F. Anderson and H. K. Kaya, eds. Academic Press, New York 1976 pp 111-125 3. Knipling, E. F., Environ (1976). 4. Beroza, Μ., Knipling, E. F., Science 177, 19-27 (1972). 5. Pest Control: An Assessment of Present and Alternative Technologies." Vol. IV "Forest Pest Control. National Academy of Sciences, Washington, D. C. 1975, pp 114-120. 6. Leonard, D. Ε., Ann. Rev. Entomol. 19, 197-229 (1974). 7. Carde, R. T., Doane, C. C., Roelofs, W. L. Can. Entomol. 106, 479-484 (1974). 8. Iwaki, S., Marumo, S., Saito, T., Yamada, Μ., Katagiri, Κ., J. Amer. Chem.Soc. 96, 7842-7843 (1974). 9. Yamada, Μ., Saito, T., Katagiri, Κ., Iwaki, S., Marumo, S., J. Insect Physiol. 22, 755-761 (1976). 10. Vite, J. P., Klimetzek, D., Loskant, G., Hedden, R., Mori, Κ., Naturwissenschaften 63, 582-583 (1976). 11. Plimmer, J. R., Schwalbe, C. P., Paszek, E. C., Bierl, Β. Α., Webb, R. Ε., Marumo, S., Iwaki, S. (in preparation). 12. Mori, Κ., Takigawa, T., Matsui, Μ., Tetrahedron Lett. 3953-3956 (1976). 13. Beroza, Μ., Agr. Chem. 15, 37-40 (1960). 14. McDonough, L. M. presented at 172nd ACS National Meeting, Aug. 30-Sept. 3, 1976; Environ. Entomol. (submitted). 15. Plimmer, J. R., Bierl, B. A. DeVilbiss, E. D., Smith, B. L. Proc. Internatl. Controlled Release Pestic. Symp., Akron, Ohio, 1976. In press. 16. Mastro, V. C., Richerson, J. V., Cameron, Ε. A., Environ. Entomol. 6, 128-132 (1977). 17. Beroza, Μ., Paszek, E. C., DeVilbiss, E. D., Bierl, Β. Α., Tardif, J. G. R., Environ. Entomol. 4, 712-714 (1975). 18. Bierl, Β. Α., DeVilbiss, E. D., Plimmer, J. R., i n "Controlled Release Polymeric Formulations", D. R. Paul and F. W. Harris, eds. ACS Symposium Series No. 33. American Chemical Society, Washington, D. C. 1976. pp. 265-272. 19. Beroza, M., Stevens, L. J., Bierl, Β. Α., Philips, F. M., Tardif, J. G. R. Environ. Entomol. 2, 1051-1057 (1973).

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

15.

PLIMMER

ET AL.

Controlled

Release of

Pheromone

183

20. Bierl, B. A., DeVilbiss, E. D., Proc. Internatl. Controlled Release Pesti. Symp., Dayton, Ohio, 1975. pp. 230-246. 21. Schwalbe, C. P., Webb, R. E., McComb, C., Dull, C., Altman, R, Bierl, B. A. and Plimmer, J. R., (in preparation). 22. Webb, R. Ε., Plimmer, J. R., Bierl, Β. Α., Schwalbe, C. P., (unpublished results). 23. Roelofs, W. L., Carde, R. T., Taschenberg, E. F., Weires, R. W., Jr., ACS Symposium Series No. 23 (1976), 75-87. 24. Caro, J. Η., Bierl, Β. Α., Freeman, H. P., Glotfelty, D. Ε., Turner, B. C., presented at the 173rd ACS National Meeting, New Orleans, Louisiana, March 21-25, 1977. Acknowledgement : The work reported h e r e i Expanded Gypsy Moth Research & Development

program.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16 Controlled Release Formulations of Insect Growth Regulators and Pheromones—Evaluation Methods and Field Test Results J. W. YOUNG, T. M. GRAVES, and R. CURTIS Zoecon Corp., 975 California Ave., Palo Alto, Calif. 94304 M. M. FURNISS Forest Service, U.S. Department of Agriculture, Moscow, Idaho 83843 This third section of our Symposium has been entitled "Utility of Controlled Releas to share with you three instances in my experience in which controlled release techniques provided the key element of utility. In each case, the availability of a controlled delivery system made a product possible which would otherwise have been impossible. I will attempt to outline for you the formulation screening procedures which were used, and to indicate with some field data the effectiveness of the final delivery system. Mosquito Larvicide To properly introduce this first topic, I will need to describe briefly the mode of action of the active ingredient since that has an important bearing on the nature of the problem. The factors controlling insect growth and metamorphosis have been the subject of biological investigations since early in this century. By the 1960s, i t was known that particular glands secreted substances which initiated the molting process in insects, and which controlled the complex series of metamorphoses from egg, through larva and pupa, to adult (1). One hormone, secreted by a small pair of glands called the corpora allata, was known to be responsible for the maintenance of preadult characters throughout the immature life stages of insects. It is the lowering of titre of this material, called Juvenile Hormone, which allows for metamorphosis of immature insects into adults. It had been speculated that treatment of an insect with Juvenile Hormone at a time when the hormone should have been absent should cause i t to carry larval characteristics into the next developmental stage -- a derangement of the normal process which would in all likelihood be lethal. In 1967, a research group at the University of Wisconsin announced the structure of a Juvenile Hormone (JH I) (2). A closely related structure was identified soon afterward (JH II) (3). The third natural Juvenile Hormone (JH III) was discovered in our own laboratories using a novel tissue culture technique (4). 184

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG

ET AL.

Formulations

of Insect Regulators and Pheromones

185

JH I

JH

II

JH

III

In 1968, Zoecon wa among o t h e r s , o f developing from these d i s c o v e r i e s a new, hopeful l y s e l e c t i v e , i n s e c t c o n t r o l agent. One o f the f i r s t o f the J u v e n i l e Hormone-type m a t e r i a l s p r e pared i n Zoecon's l a b o r a t o r i e s which appeared f e a s i b l e f o r commerc i a l i z a t i o n now c a r r i e s the common name "methoprene" and our trademark "ALTOSID®."

methoprene ALTOSID® IGR Because o f t h e i r mode o f a c t i o n , methoprene and chemicals l i k e i t are now c a l l e d " I n s e c t Growth Regulators" (IGR). The e f f e c t s o f treatment with IGRs vary somewhat from one i n s e c t to another, but i n g e n e r a l , i n s e c t s e n s i t i v i t y to the compounds occurs l a t e i n l a r v a l development, with m o r t a l i t y due to morphological effects* and p h y s i o l o g i c a l imperfections delayed u n t i l the l a s t l a r v a l i n s t a r or the pupal stage. One o f the f i r s t a p p l i c a t i o n s o f methoprene which we explored, once i t s b i o l o g i c a l c h a r a c t e r i s t i c s were known, was i t s use as a mosquito l a r v i c i d e . The mode o f a c t i o n o f IGRs on mosquito larvae i s very d i f f e r e n t from c l a s s i c a l i n s e c t i c i d e s . Rather than t o x i c i t y to larvae soon a f t e r treatment, IGR-treated larvae develop normally through the pupal stage, but then f a i l to emerge as adults. This unusual s o r t o f a c t i v i t y has made necessary several new developments i n f i e l d t r i a l e v a l u a t i o n methods. It was not p o s s i b l e to simply count dead v s . l i v e larvae i n order to gauge the e f f e c t o f the treatment. In some c a s e s , t r e a t e d water c o n t a i n i n g larvae was sampled i n the f i e l d , brought i n t o the l a b o r a t o r y , and the larvae observed f o r i n h i b i t i o n o f a d u l t emergence. In other t r i a l s , larvae were introduced i n t o t r e a t e d water e i t h e r i n the l a b o r a t o r y or i n s p e c i a l l y designed f l o a t i n g cages.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

186

CONTROLLED RELEASE

PESTICIDES

Soon a f t e r we began f i e l d t e s t i n g o f methoprene, we noted r a p i d degradation — the inverse o f the problem encountered with sometimes t o o - p e r s i s t e n t conventional p e s t i c i d e s . The a c t i v e i n gredient was simply not l a s t i n g long enough under f i e l d exposure c o n d i t i o n s to be b i o l o g i c a l l y e f f e c t i v e . Chemical a n a l y s i s q u i c k l y confirmed that at l e a s t two d i f f e r e n t r e a c t i o n s were occuring which converted methoprene to i n a c t i v e m a t e r i a l s ( 5 j . The f i r s t o f these processes was found to be r a p i d u l t r a v i o l e t l i g h t - i n duced i s o m e r i z a t i o n to the much l e s s a c t i v e 2Z,4E isomer (B below). hv

I

A

^

Table I shows that a second p r o c e s s , i n v o l v i n g decomposition to nonisomenc products, occurs simultaneously. Table I Percent Methoprene Isomers Remaining A f t e r Exposure to S u n l i g h t %Β 10 30 39 36 27

Initial 1 hour 2 hours 4 hours 8 hours

%A

% A+B 100 95 89 78 62

90 65 50 42 35

It has s i n c e been determined (5} that s u n l i g h t i n i t i a t e s r a p i d de cay to the b i o l o g i c a l l y i n a c t i v e decomposition products shown below.

A

7

+

In these chemical experiments, the h a l f - l i f e of methoprene i n sun l i g h t was l e s s than one day as an aqueous emulsion and about four hours as a t h i n f i l m on g l a s s . The r a p i d decomposition i n d i c a t e d i n Table I merely served as chemical confirmation of the complete f a i l u r e of conventional f o r mulations of methoprene i n e a r l y f i e l d t e s t s , although the same formulations had been h i g h l y e f f e c t i v e i n l a b o r a t o r y t e s t s . Even though we were d e a l i n g with floodwater mosquitoes and synchronous p o p u l a t i o n s , the s u s c e p t i b i l i t y of fourth i n s t a r larvae to metho prene required p i n p o i n t a p p l i c a t i o n timing f o r e f f e c t i v e n e s s .

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG

ET AL.

Formulations

of Insect Regulators

and Pheromones

187

A formulation was thus needed which protected the a c t i v e i n gredient and released i t i n b i o l o g i c a l l y a c t i v e form, but d i d not leave residues beyond those required f o r e f f e c t i v e n e s s (see Table II). Table

II

P r o j e c t Goals — ALTOSID Mosquito Formulation 1. 2. 3. 4.

Decrease r a t e of i s o m e r i z a t i o n to the l e s s a c t i v e isomer. Decrease r a t e o f o x i d a t i v e degradation. Achieve e f f i c i e n t use o f a c t i v e i n g r e d i e n t — must be b i o l o g i c a l l y e f f e c t i v e f o r 4-10 days. Predictable residues.

In preparing candidat which we explored are those shown i n Table I I I . Formulations were f i r s t screened i n l a b o r a t o r y glassware. Aqueous d i l u t i o n s were subjected to aging under a r t i f i c i a l l i g h t , and then i n f e s t e d with s e n s i t i v e fourth i n s t a r l a r v a e (6). L a t e r t e s t s were conducted s i m i l a r l y , but i n s e r i e s of outdoor ponds e i t h e r one meter or 130 meters i n s i z e (7_). B i o l o g i c a l t e s t i n g revealed most s i g n i f i c a n t gains i n e f f e c t i v e l i f e t i m e o f the a c t i v e i n g r e d i e n t with a p o l y amide formulation which we now c a l l ALTOSID SR-10. The product i s an aqueous d i s p e r s i o n o f m i c r o p a r t i c l e s i n the 1-10 micron range, and contains 10% a c t i v e i n g r e d i e n t . Our formulation procedure does not y i e l d true microcapsules — o i l d r o p l e t s surrounded by a f i l m o f polymeric wall m a t e r i a l . ALTOSID SR-10 appears on m i c r o scopic examination to be a matrix which i s s p o n g e - l i k e i n c r o s s section. 2

2

Table Formulation

III Variables

1.

Capsule wall/matrix

2. 3. 4. 5.

Ratio o f polymer to a c t i v e Degree o f c r o s s - l i n k i n g Particle size P a r t i c l e specific gravity

material ingredient

The e f f e c t o f t h i s formulation on the rate o f i s o m e r i z a t i o n to the 2Z,4E isomer (B, Table I ) , i s shown i n Figure 1. Although t h a t process i s not stopped a l t o g e t h e r , i t s rate i s s u b s t a n t i a l l y decreased r e l a t i v e to that o f unprotected material s u p p l i e d as an e m u l s i f i a b l e concentrate ( E . C . ) f o r m u l a t i o n . Methoprene has a water s o l u b i l i t y of 1.4 parts per m i l l i o n (ppm). Its threshold of b i o l o g i c a l a c t i v i t y and the l e v e l o f d e t e c t i o n by our residue methods are both about 1 part per b i l l i o n (ppb). Figure 2 shows the cumulative e f f e c t on the p r o d u c t ' s l i f e t i m e o f the decrease

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

188

C O N T R O L L E D R E L E A S E PESTICIDES

both i n i s o m e r i z a t i o n rate and i n r a t e o f o x i d a t i v e degradation. Many o f our e a r l y formulation screening experiments i n v o l v e d twofold e v a l u a t i o n procedures. Water was sampled and analyzed chemically for residues o f methoprene a f t e r various aging p e r i o d s . At the same time, b i o l o g i c a l performance was monitored by p l a c i n g s e n s i t i v e fourth i n s t a r mosquito larvae i n the t r e a t e d water. We repeatedly saw instances o f complete b i o l o g i c a l e f f e c t i v e n e s s of the treatment while no methoprene was c h e m i c a l l y d e t e c t a b l e . It was not u n t i l we began to note the time o f day at which samples were taken f o r chemical a n a l y s i s that a pattern emerged. That pattern i s shown i n Figure 3. Our r a t i o n a l i z a t i o n o f t h i s r e s u l t i s that the rate o f decomposition o f released methoprene exceeds the r e l e a s e rate i t s e l f during the s u n l i t hours o f the day. Dur ing the c o o l , dark hours, r e l e a s e o f the a c t i v e i n g r e d i e n t c o n tinues and e s t a b l i s h e s a b i o l o g i c a l l y e f f i c a c i o u s pool of metho prene. A n a l y t i c a l Methods. E v a l u a t i o n o f the e f f i c i e n c y o f various mi c r o e n c a p s u l a t i on procedures i s a problem which has p e r s i s t e d throughout t h i s and a l l s i m i l a r p r o j e c t s with which we have been involved. It occurs i n the i n i t i a l stages of product development when one needs a r a p i d means o f e v a l u a t i n g the e f f e c t o f formu l a t i o n v a r i a b l e s , and p e r s i s t s throughout the l i f e t i m e of the product as a vitaΤ aspect o f q u a l i t y c o n t r o l . The problem, simply s t a t e d , i s not too d i f f e r e n t from one encountered by high energy p h y s i c i s t s — i n measuring t h i s p a r t i c u l a r property o f the p a r t i c l e , one cannot avoid changing the nature o f the p a r t i c l e i t s e l f . We have a r r i v e d at a method which, although i t undoubtedly does s u f f e r from t h i s d e f e c t , serves the purpose of y i e l d i n g h i g h l y r e p r o d u c i b l e data i n a r e l a t i v e l y r a p i d f a s h i o n . The method i t s e l f i s summarized i n Table IV, while the r e s u l t s o f two r e p r e s e n t a t i v e analyses are shown i n Figure 4. At short time i n t e r v a l s , the curve obtained i s very n o n l i n e a r , which i s undoubtedly due to d i s s o l u t i o n o f unencapsulated material along with a q u a n t i t y at or near the surface o f the p a r t i c l e s . At longer i n t e r v a l s , however, we f i n d that with the proper choice o f e x t r a c t i n g s o l v e n t , very r e p r o d u c i b l e s t r a i g h t l i n e s are obtained which allow the character i z a t i o n o f the p a r t i c u l a r batch o f product. For s i m p l i c i t y , the term " e n c a p s u l a t i o n e f f i c i e n c y " i s em ployed here. The method as o u t l i n e d appears to have v a l i d i t y i n a wide range o f formulations — true encapsulates as well as ma t r i x systems such as ALTOSID SR-10.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG

Formulations

ET AL.

of Insect Regulators

189

and Pheromones

70/30 ALTOSID SR-10 ALTOSID E . C . 0.1 ppm i n water

Figure 1.

Change of methoprene isomer ratio—sunlight

ι 1

ι 2

ι 3

ι 4

•

5

• 6

• 7

8

•

9

days Figure 2.

Methoprene

decomposition—sunlight

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

1

10

en

1

>

W

Figure 3. Effect of sampling time on methoprene residues detected

w

a

(Η

ο

ο

ο

ο

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

Formulions

YOUNG E T A L .

100

β

Pheromones

r

-A-

80 methoprene encap sulated

of Insect Regulators and

« Run #25 84% encapsulated

40

20

15

100

30 60 90 E x t r a c t i o n time, minutes

ι—

80

Run #26 22% encapsulated

methoprene encap60 sulated 40

20

15

30 60 90 E x t r a c t i o n t i m e , minutes

Figure 4. Encapsulation efficiency

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

192

C O N T R O L L E D R E L E A S E PESTICIDES

Table Analytical Step 1: Step 2:

Step 3:

Method - -

IV

Encapsulation E f f i c i e n c y

Analyze t o t a l A . I . a v a i l a b l e . High shear mixing to rupture p a r t i c l e s — strong solvent system. M i l d e x t r a c t i o n procedure A) D i l u t e c o n t r o l l e d r e l e a s e formulation i n water. B) Add s o l v e n t c o n t a i n i n g i n t e r n a l standard f o r GLC a n a l y s i s . Solvent chosen i s solvent f o r a c t i v e i n g r e d i e n t , nonsolvent f o r polymer, immiscible i n water. C) Shake the sample c o n t a i n i n g the solvent on a wrist-shaker. Remove a l i q u o t s o f the supernatant s o l v e n t f o r a n a l y s i s at standard i n t e r vals. D) Analyze (by GLC or other s u i t a b l e means) f o r % a c t i v e i n g r e d i e n t i n the s o l v e n t . Determine % encapsulated A . I . A) P l o t X v s . e x t r a c t i o n time. X = 100 B)

wt. detected [total wt. a v a i l a b l e

E x t r a p o l a t e to zero time.

F l y Control — P o u l t r y Feed Through Another area i n v e s t i g a t e d very a c t i v e l y with methoprene i s that o f f l y c o n t r o l i n p o u l t r y houses. In caged l a y i n g hen opera t i o n s i n p a r t i c u l a r , f l i e s present serious nuisance and disease vector problems. Managers o f these operations are forced to follow very r i g i d programs o f manure c l e a n - o u t and frequent i n s e c t i c i d e sprays to c o n t r o l t h e i r f l y p o p u l a t i o n s . Because o f the e x t r a o r d i n a r y safety o f ALTOSID, we f e l t i t could be incorporated i n t o the feed r a t i o n s o f the b i r d s . I f i t emerged i n t a c t i n the manure, and any f l y larvae developing there would not emerge as adults. In p r e l i m i n a r y t e s t s , small groups o f l a y i n g hens were fed with a r a t i o n t r e a t e d with t e c h n i c a l methoprene over a wide range o f c o n c e n t r a t i o n s . The manure was i n f e s t e d with housefly l a r v a e , and the various treatments were scored f o r percent i n h i b i t i o n o f a d u l t emergence. The r e s u l t s are shown i n Table V. In t h i s and i n subsequent work, the l e v e l o f methoprene i n t h e manure required f o r e f f e c t i v e c o n t r o l f e l l i n the range of 1-2 ppm.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG

ET AL.

Formulations

of Insect Regulators and Pheromones

193

Table V Rate o f Methoprene i n P o u l t r y Feed, ppm 10 25 50 75 100 125 200 400

Percent I n h i b i t i o n o f A d u l t House F l y Emergence 68 81 96 98 99+ 100 100 100

Level o f Methoprene Detected i n Manure, EË1 1.0 1.5 2.5

Economic a n a l y s i s i n d i c a t e d to us that the market would bear the c o s t o f the product only i f the l e v e l o f methoprene to be i n corporated i n t o the feed could be reduced to 10 ppm or l e s s and that >95% f l y c o n t r o l was r e q u i r e d . These f a c t o r s , t h e n , defined the t a r g e t f o r formulation work. When fed as t e c h n i c a l m a t e r i a l , the amount o f methoprene excreted i n t a c t was on the order o f 3%. I t was our task to formulate the product to y i e l d a f i v e - to t e n f o l d increase i n feed-through e f f i c i e n c y . Formulation screening involved both chemical and b i o l o g i c a l e v a l u a t i o n o f each candidate. Not only was i t necessary to d e t e r mine the l e v e l o f a c t i v e i n g r e d i e n t present i n the p o u l t r y manure, but i t s b i o a v a i l a b i l i t y had to be a s c e r t a i n e d . Small groups o f hens were fed r a t i o n s c o n t a i n i n g 10 ppm methoprene i n a v a r i e t y o f f o r m u l a t i o n s , and manure was sampled 10 and 14 days a f t e r t r e a t ment. Part o f the sample was i n o c c u l a t e d with house f l y l a r v a e , and methoprene residues determined by chemical a n a l y s i s were compared with the percent i n h i b i t i o n o f a d u l t f l y emergence. Figure 5 shows the r e s u l t s f o r several formulations t e s t e d e a r l y i n the program (numbers 1 through 7) and for the formulation ALTOSID PS-10 which u l t i m a t e l y emerged as s u i t a b l e f o r f u r t h e r t e s t i n g (number8). It should be noted t h a t the b i o l o g i c a l data i n d i c a t e s c o n s i d e r a b l y greater e f f i c a c y than would be expected at these residue l e v e l s . This probably r e f l e c t s the somewhat i d e a l i z e d c o n d i t i o n s o f the l a b o r a t o r y experiment. The e x c e l l e n t performance o f ALTOSID PS-10 i n s m a l l - s c a l e e f f i c a c y experiments prompted us to f i l e f o r an experimental permit r e g i s t r a t i o n to allow expanded t e s t i n g . Under the experimental permit, t e s t i n g involved extremely l a r g e numbers of b i r d s i n several s t a t e s . The r e s u l t s o f two o f the many t r i a l s conducted under the experimental permit are shown at the bottom o f Table VI. While i n 1974, the treatment y i e l d e d 90% or g r e a t e r c o n t r o l i n most i n s t a n c e s , e f f e c t i v e n e s s i n f u l l - h o u s e t r i a l s a year l a t e r was v a r i able and much lower.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977. 0.55

Celite

Celite/Polyurea

ALTOSID

6

7

8

Figure 5.

PS-10

100

98

96

98

97

84

93

25

% Control Avg. of 3 Reps

Formuhtion screening: poultry feed-through—10

2.00

0.39

0.62

Calcium S i l i c a t e / Polyamide Coating

5

Coating

0.21

Calcium

4

Silicate

0.22

Fumed S i l i c a

3

0.36

Technical

Residue (ppm)

2

Control

Type

Untreated

Formulation

1

Sample #

ppm in feed

2.50

0.32

0.62

0.94

0.26

0.29

100

92

98

97

71

71

92

12

0.39

% Control Avg. of 3 Reps

Residue (ppm)

n

CO

w

13

m >

s

α

Ο

8

ç£5

16.

YOUNG

ET AL.

Formulations

of Insect Regulators and Pheromones

195

Table VI ALTOSID PS-10 Manure Residue & E f f i c a c y

Date 1974 1974 1974 1974 1974 1975 1975

Test Location California California California Texas Texas California Texas

Feeding Rate 10 ppm 10 ppm 10 ppm 10 ppm 10 ppm 10 ppm 10 ppm

Formulation PS-10 PS-10 PS-10 PS-10 PS-10 PS-10 PS-10

Percent Control 97 95 98 90 89 42 39

ppm i n Manure 1.2 1.6 2.0 1.4 1.6 1.7 1.5

The c o n t r a s t i n g r e s u l t s are undoubtedly r e l a t e d to the d i f ference i n e v a l u a t i o n technique was necessary to judge the e f f e c t i v e n e s s o f the treatment by monit o r i n g i n h i b i t i o n o f a d u l t f l y emergence from small closed c o n t a i n e r s o f manure. In l a r g e r t e s t s , movement o f the natural popu l a t i o n of f l y larvae was not r e s t r i c t e d , and e v a l u a t i o n was made by actual f l y counts on a whole ranch or whole house b a s i s . The f a i l u r e o f l a r g e t e s t s to demonstrate the commercial v i a b i l i t y o f t h i s product r e s u l t s from f a i l u r e o f the IGR to act during e a r l y stages o f l a r v a l development. It was observed that f l y larvae developing i n wet areas i n the manure tend to move s h o r t l y before pupation to d r i e d areas — away from f r e s h l y deposited droppings. Since t h i s time i n the l i f e c y c l e o f the f l y c o i n c i d e s with the period o f s e n s i t i v i t y to the IGR, the time o f exposure to the a c t i v e i n g r e d i e n t i s i n s u f f i c i e n t . In many c a s e s , t h i s phenomenon was aggravated i n 1975 by an unusually r a i n y f l y season. Although these r e s u l t s were d i s a p p o i n t i n g , they serve to i l l u s t r a t e an important p o i n t . No matter how well one b e l i e v e s to have designed s m a l l - s c a l e experiments, the jump to commercial s i z e d t e s t i n g i n v a r i a b l y brings i n t o play a number o f v a r i a b l e s not present i n the smaller t r i a l s . Anti-Aggregative

Pheromone — Douglas F i r Bark Beetle

The Douglas F i r Bark Beetle i n f e s t s Douglas f i r f o r e s t s throughout much o f the Northwestern United S t a t e s . Its population o c c a s i o n a l l y reaches epidemic p r o p o r t i o n s , e s p e c i a l l y i n trees weakened by windthrow or d i s e a s e . It was discovered i n 1971 (8) that the f r a s s o f the female beetle contains a pheromone, 3-methyl-2-cyclohexen-1-one (MCH), which was l a t e r shown (9,10) to have a n t i - a g g r e g a t i v e e f f e c t s on a d u l t b e e t l e s . In 1974, F u r n i s s e t al (11) reported on f i e l d t r i a l s with f e l l e d host trees which showed t h a t , when released o p t i m a l l y , the pheromone served to r e duce beetle attacks upon s u s c e p t i b l e trees by 96%. The pheromone was dispensed i n t h i s experiment as neat material from small metal

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

196

CONTROLLED RELEASE

PESTICIDES

c a n i s t e r s mounted at even spacings around the t r e e on wooden stakes. T h i s t r i a l served to demonstrate the e f f e c t i v e n e s s o f the treatment, and r e f i n e d the optimum r a t e o f pheromone r e l e a s e to a narrow range. Q

3-methyl-2-cyclohexen-1-ι We became involved a t t h i s stage, and began work aimed a t de veloping a formulation f o r season-long release o f MCH, a h i g h l y v o l a t i l e and water s o l u b l e m a t e r i a l . The p r o p e r t i e s of the formu l a t i o n would i d e a l l y matc Table

VII

Goals - - MCH Formulation 1. 2. 3.

Project

Release MCH at r a t e o f 0 . 1 - 1 . 3 grams/acre/day E f f e c t i v e f o r 30-60 days S u i t a b l e f o r a p p l i c a t i o n by a i r - - must penetrate f o r e s t canopy Biodegradable Nontoxic Low c o s t

4. 5. 6.

The f i r s t step i n our program was the development o f a r e lease rate method s u i t a b l e f o r l a b o r a t o r y screening of the many formulations which would be necessary (12). The method as i t de veloped involved the use of t r i t i u m - l a b e l e d MCH. The formulation to be tested was placed i n a modified f l a s k (13) f i t t e d with i n l e t and o u t l e t f o r c a r r i e r gas flow. To the o u t l e t o f the f l a s k was attached a small g l a s s tube packed with 0.25 grams o f Porapak® QS (50-80 mesh) (14). Dry nitrogen c a r r i e r gas was passed through the f l a s k and trapping column for one hour at a rate of 175 ml/ minute. The trapping column was then removed, and the H-MCH r e leased from the formulation was e l u t e d i n t o a s c i n t i l l a t i o n v i a l with 10 c c * s o f hexane.. S c i n t i l l a t i o n f l u i d was added to the v i a l , and the H-MCH content was determined d i r e c t l y by s c i n t i l l a t i o n counting. Formulations were aged at ambient temperature and r e l a t i v e humidity f o r up to 60 days on p a p e r - l i n e d s t e e l t r a y s stacked i n a forced d r a f t fume hood with a constant a i r flow through the stack of t r a y s of 150 c u . f t . / m i n . Formulations were sampled f o r r e lease rate determination at the beginning of the aging period and weekly t h e r e a f t e r u n t i l the rate o f release o f H-MCH f e l l below 0.5 micrograms/hour. 3

3

3

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG E T A L .

Formulations

of Insect Regufators and Pheromones

Treatment

Method

Coated Molecular Sieve

1

Ρ

Granules

197

Douglas F i r Beetle Brood Attacks 3

0.1**

ι**

L i q u i d Standard

Ρ

0.2**

4**

Polyamide Granules A

Β

0.3*

33 NS

Β

0.6*

26 NS

Β

1.7 NS

51 NS

Β

3.5 NS

42 NS

Control

-

4.8

45

Coated Kobrite Granules

Β

4.9 NS

54 NS

Polyamide Granules Β Polyamide Granules C Coated Molecular Sieve

Granules

Coated Molecular Sieve

Granules

P_ = i n cans on stakes 4 f t .

1

B_ = broadcast

2

2

above ground, 10 by 10 f t . spacing

by hand.

A p p l i e d at a rate of 1/10 that of the other

granules.

d i f f e r e n c e from c o n t r o l i s s i g n i f i c a n t at the 0.01 0.5 l e v e l (*), or not s i g n i f i c a n t (NS). Figure 6.

(**),

Density (no/ft ) of Douglas Fir beetle attacks and brood by treatment 2

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

198

C O N T R O L L E D R E L E A S E PESTICIDES

T h i s formulation screening method was convenient and r a p i d enough to allow t e s t i n g o f r e l a t i v e l y l a r g e numbers o f formulation systems. We conducted r e l e a s e rate t e s t s with about 70 d i f f e r e n t formulations (several o f them r e p l i c a t e d three t i m e s ) . Release rates were run at an average o f f i v e aging i n t e r v a l s f o r each formulation. Most systems were e l i m i n a t e d from f u r t h e r c o n s i d e r a t i o n a f t e r the f i r s t few weeks of s c r e e n i n g , when the rate o f r e l e a s e o f MCH f e l l below 0.5 micrograms/hour. Twelve f o r m u l a t i o n s , however, showed promise and maintained a rate o f r e l e a s e o f H-MCH c l o s e to or above 1 microgram/hour f o r 30-60 days. These formul a t i o n s were evaluated by an independent l a b o r a t o r y (13), and e v e n t u a l l y f i v e formulations were s e l e c t e d f o r f i e l d t e s t i n g . The d e t a i l s o f t h i s f i e l d t e s t w i l l be reported s e p a r a t e l y (12). In g e n e r a l , the procedure involved treatment of i s o l a t e d , f e l l e d , host trees with the formulations at a rate o f 38 grams MCH per a c r e . The stake-mounte served as a standard. Each treatment was r e p l i c a t e d three times, and s i x untreated c o n t r o l p l o t s were reserved. Treatment was made p r i o r to the f i r s t beetle f l i g h t i n A p r i l , and f i n a l e v a l u a t i o n of treatments was made i n mid-August. The r e s u l t s o f the t e s t are shown i n Figure 6. As i n d i c a t e d i n Figure 6, one o f the formulations a p p l i e d to the ground by broadcast method gave e x c e l l e n t r e s u l t s — i n d i s t i n g u i s h a b l e from the standard treatment. T h i s m a t e r i a l , a dimer a c i d polyamide granular formulation (3-8 mesh), was judged s u f f i c i e n t l y e f f e c t i v e to be used i n l a r g e - s c a l e t r i a l s i n areas o f natural windthrow. These t r i a l s are s t i l l i n the planning stage. 3

One other f o r m u l a t i o n , 13X molecular sieve granules coated with a wax/polymer system, gave e x c e l l e n t performance when p r o t e c t e d i n metal cans on stakes above the ground, but f a i l e d e n t i r e l y when broadcast on the ground. It i s l i k e l y that exposure to the high r a i n f a l l of the area and constant contact with the moist f o r e s t f l o o r e x t r a c t e d the pheromone from that f o r m u l a t i o n . Acknowledgements The authors thank Robert Lowe and Loren Dunham f o r advice and a s s i s t a n c e i n the A n a l y t i c a l Chemistry aspects o f t h i s work. Edward Wenik developed the assay method f o r encapsulation e f f i c i e n c y , and Kenneth Horwege provided valuable t e c h n i c a l a s s i s t a n c e on a l l o f the p r o j e c t s d i s c u s s e d . The MCH formulation work was funded by the U . S . D . A . , Forest S e r v i c e Contract Number 12-11-205-09.

Literature Cited 1. Wigglesworth, V.B., "The Principles of Insect Physiology," Sixth Edition, E.P. Dutton & Co., New York, 1965. 2.

Röller, H., Dahm, K.N., Sweeley, C.C., and Trost, B.M., Angew. Chem. Internat. Ed., (1967), 6, 179.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

16.

YOUNG

3.

Meyer, A.S., Schneiderman, H.A., Hanzmann, Ε., Proc. Nat. Acad. Sci. USA, (1968), 60, 853.

ET AL.

Formulations

of Insect Regulators

and Pheromones

199

4. Judy, K.J., Schooley, D.A., Dunham, L.L., Hall, M.S., Bergot, B.J., and Siddall, J.B., Proc. Nat. Acad. Sci. USA, (1973), 70, 1509. 5.

Quistad, G.B., Staiger, L.E., and Schooley, D.A., J. Agr. Food Chem., (1975), 23, 299.

6.

Schaefer, C.H., and Wilder, W.H., J. Econ. Ent., (1972), 65, 1066.

7.

Schaefer, C.H., and Wilder, W.H., J . Econ. Ent., (1973), 66, 913.

8.

Kinzer, G.W., Fentiman, A.F. Jr., Foltz, R.L., Rudinsky, J.A., J. Econ. Ent., (1971), 64, 970.

9.

Rudinsky, J.A., Furniss, M.M., Kline, L.N., and Schmitz, R.F., Can. Entomol., (1972), 104, 815.

10. Furniss, M.M., Kline L.N., Schmitz, R.F., and Rudinsky, J.A., Ann. Entomol. Soc. Amer., (1972), 65, 1227. 11. Furniss, M.M., Daterman, G.E., Kline, L.N., McGregor, M.D., Trostle, G.C., Pettinger, L.F., and Kudinsky, J.A., Can. Entomol., (1974), 106, 381. 12. Furniss, M.M., Young, J.W., McGregor, M.D., Livingston, R.L, and Hamel, D.R., Can. Entomol., (1977), in press. 13. Look, M., Chem. Ecol., (1976), 2, 481. 14. The use of Porapak QS was suggested (private communication) by Dr. James Trudell, Stanford University. See also Byrne, K.J., Gore, W.E., Pearce, G.T., and Silverstein, R.M., J. Chem. Ecol., (1975), 1, 1.

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

INDEX A Acetyl copolymers Agent solubility Algicides Altosid mosquito formulations Antifoulants Antioxidant properties of lignin Aqueous phase separation Aromatic nature of lignin Arsenic, poisoning with Aspirin Atrazine Attractants

47 61 41 187 38 86 133 86 5 5 34 39

Β Bacillus thuringiensis, microencap sulated Beetle, Douglas fir bark Behavior-modifying chemicals "Bioactivity" figure Butylate formulations, percent weed control by delayed incorpora tion of

143 195 168 147 81

C Capsule formulations 151 Carbamates 87 Carbon black 61 «-Cellulose 2,4-diehlorophenoxyacetate 94 hydrolytic release of 2,4-dichlorophenoxyacetic acid from 100 α-Cellulose, esterification reactions of 95 Cellulose in soil, deterioration of 95 Cellulosic materials 45 Chemosterilants 57 Chlorinated hydrocarbon insecticides 55 Chloroprene polymers 47 Chlorpropham, microencapsulation of 32 Chlorpyrifos 39 "Chronicity" phenomenon 49 Classes of pesticides formulated as controlled release products 38 Clinical toxicology aspects of con trolled release pesticide formula tions 54 Co-diffusants 159,162 Codling moth 181

Commercially available controlled release pesticides, list of Commercial products using controlled release technology Complex coacervation Compounding of the controlled release formulation Concentration dependence of diffusion Coniferyl alcohol

42 166 133 61 24 84

advantages of 2 effect of some variables on 152 formulation, compounding of the .... 61 herbicides 94,102 of insect growth regulators and pheromones 184 from Kraft lignin carriers 84 materials, list of 44 mechanisms of 4 molluscicides 62 nematocides 90 pesticide(s) 1 formulations, clinical toxicology aspects of 54 formulations, environmental aspects of 37 list of commercially available 42 system, ideal 14 technology 30 of pheromones in the gypsy moth program ..... 168 products, list of 43 systems design of 6 polymeric materials in 17 reservoir ......... 6 technology, commercial products using 166 Copolymer(s) of 2-acryloyloxyethyl 2,4-dichlorophenoxyacetate and meth acrylic acid 103 of 2-acryloyloxyethyl 2,4-dichlorophenoxyacetate and trimeth ylamine methacrylimide 107 of 2-methacryloyloxyethyl 2,4-dichlorophenoxyacetate and methacrylic acid 106 Corpora allata 184 Cotton losses 1

201

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

202

C O N T R O L L E D R E L E A S E PESTICIDES

Cross-link density Cross-linked polyamide Cross-linking effect of Cucumbers

72 39 21,61 151 91

D DDT 55,113 DEET 159 Degradation of polymers, mecha nisms of 45 Design of controlled release systems .. 6 Diacid chloride 145 Diazinon 40,145 formulation, release properties of starch xanthide80 2,4-Dichlorophenoxyacetic acid esterification of «-cellulose Diethylenetriamine (DETA) 145 Diethyl-m-toluamide (DEET) 41 Diffusant molecular weight 163 Diffusion behavior, free volume .. 26 behavior in membrane systems ..... 17 coefficient 61 determination by water absorption 65 effect of the glass transition temperature (T ) on the 65 effect of test temperature and carbon black content on 66 concentration dependence of 24 against the concentration gradient.. 20 flux, / 19 Disparlure ...174,181 microencapsulated 135 Dispersed pesticide 7 Dissolved pesticide 7 Douglas fir bark beetle 195 Douglas fir tree 13 g

Ε Elastomers, matrix factors affecting the controlled release of pesti cides from Electrostatic encapsulation Encapsulation of methyl parathion of pesticides within a starch matrix Environmental aspects of controlled release pesti cide formulations effect on pheromone formulations .. impact of polymers problems, pesticides and Protection Agency

60 135 98 145 74 37 175 44 30 113

Environmental (Continued) testing government regulations for toxicological and tests for registering pesticides Erosion, release by Erythromycin Esterification of α-cellulose with 2,4-dichlorophenoxyacetic acid .... Esterification reactions of α-cellulose Ethylene-propylene polymers Ethylenediamine (EDA)

48 37 49 10 56 100 95 45 145

F Fick's law Flory-Huggins equation Fluidized-bed spray coating

6,19,153 22 133

Fly Tape Free volume diffusion behavior Fungicides

11 26 40

G Glass transition temperature (T g ) ... on the diffusion coefficient, effect of the Government regulations for toxico logical and environmental testing Gypsy moth program, controlled release of pheromones in the

61 65 37 168

H Henry's law 22 Herbicidal effectiveness of α-cellulose 2,4-dichlorophenoxyacetate, duration of 100 Herbicide(s) 32,40,79 controlled release 94,102 hydrolytic release of the 95 polymers containing pendant 112 in soils, leaching of 35 substituents, hydrolysis studies of polymer containing pendant .... 102 Highly selective toxicity 56 Hilderbrand equation 27 Hilderbrand's solubility theory 157 Home use, membrane-moderated diffusion systems for 11 Hydrogen bonding 21 Hydrolysis of methacrylic acid copolymers 104 studies of polymer containing pend ant herbicide substituents 102 of trimethylamine methacrylimide copolymer 108

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

203

INDEX

Hydrolytic release of 2,4-dichlorophenoxyaeetic acid from «-cellu lose 2,4-dichlorophenoxyacetate.. 100 Hydrolytic release of the herbicide .... 95 Hydrophobicity 98

I Insect growth regulators 39 and pheromones, controlled release of 184 Insecticides 39, 56 In situ interfacial condensation polymerization 133 Interfacial condensation polymeriza tion 133 Interfacial reactions of microencap sulation 130 J Juvenile hormone microencapsulated

184 135

Κ Kraft lignin carriers, controlled release of pesticides from

85 84

L Laminated insecticidal membranes .... 152 Laspeyresia pomoneUa ( L. ) 181 Leaching of herbicides in soils 35 Lead 54 Lignin antioxidant properties of 86 aromatic nature of 86 carriers, controlled release of pesticides from Kraft 84 —2,4-D composites 88 -ethoprop composites 89 -PCNB composites 91 Local chain segmental mobility of a polymer 21 Loss rate of pesticides 61 Lure 'N Kill .... 11 Lymantria Dispar (L.) 168,169

Mechanisms of degradation of polymers 45 Meltable dispersion ..... 133 Membrane -moderated diffusion, release by .... 6 -moderated diffusion systems for home use 11 permeability, factors affecting ....... 18 thickness 157,159 Methacrylic acid copolymers, hydrolysis of 104 Methoprene 39,57,192 isomers 186 in poultry feed ..... 193 structure of 185 3-Methyl-2-cyclohexen-l-one (MCH) 195 formulation 196 structure of 196 microencapsulated 135 Metribuzin as a model pesticide 115 from polymers, residual phyto toxicity of 117 rates of release of 115 Microencapsulated insecticides, effects of wall parameters on the release of active ingredients from 145 Microencapsulated pesticides 126 poisoning with 54 possible toxicologic problems with 58 Microencapsulation 12, 37 of chlorpropham 32 interfacial reactions of 130 of pesticides 58 phase separation methods of 130 physical methods of 130 Mirex 113 microencapsulated 135 Molecular weight, diffusant 163 Molluscicide(s) 38 controlled release 62 formulations, standard 63 Mosquito formulations, Altosid 187 Mosquito larvicide 184 Multiorifice centrifugation 135

Ν M Malathion .39,145 Mating disruption with pheromone formulations 169 Mating reduction 178 Matrix factors affecting the controlled release of pesticides from elastomers 60

National Clearing House for Poison Control centers Natural rubber Nematocide(s) controlled release formulations starch xanthide formulations of a .... Nicotine

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

56 45 41 90 89 79 54

204

CONTROLLED RELEASE

Ο Occupational pesticide poisoning in agriculture Organic molecules through a polymer matrix, permeability of pesticides phase separation phosphate intoxications Organophosphates Oysters

58 17 112 133 56 87 113

Ρ PAPI • 145 Paracelsus 57 Paraquat 5 Parathion 56,14 Peanuts 91 Penicillin 56 Permeability of organic molecules through a polymer matrix 17 Permeation 21,152 behavior in membrane systems 17 of large molecules in relatively nonswollen media 27 Pesticide(s) binding to soils 35 commercialization, new 113 controlled release 1 dispersed 7 dissolved 7 efficacy 30 from elastomers, matrix factors affecting the controlled release of 60 and environmental problems 30 environmental tests for registering .. 49 formulated as controlled release products, classes of 38 formulations, clinical toxicology aspects of controlled release ... 54 importance of 1 from Kraft lignin carriers, con trolled release of 84 law (FIFRA) 48 loss rate of 61 major toxicological tests for registration of 48 metribuzin as a model 115 microencapsulated 126 microencapsulation of 58 "persistence" levels 112 poisoning 54 prevention of 56 polymeric systems for controlled release of 114 rate of removal of 2

PESTICIDES

Pesticide (s) (C ontinued ) safety 30 within a starch matrix, encapsula tion of 74 synthetic methods for polymers containing pendant 114 Phase separation methods of micro encapsulation 130 Phenoxyacetics 87 Pheromone(s) 39,163 antiaggregative 195 controlled release of insect growth regulators and 184 formulations, effect of environ ment on 175 formulations, mating disruption with 169 in the gypsy moth program, tion 130 Phytotoxicity of metribuzin from polymers, residual 117 Phytotoxicity, residual 123 Poisoning with arsenic 54 Poisoning with microencapsulated pesticides 54 Polar group interactions 21 Polyacrylates 46 Polyacrylonitriles 46 Polyamides 46 cis-Polybutadiene 47 Polyesters 46 Polyethylene (PE) 46 Polyisobutylene and butyl rubber . . . . 46 Polymer(s) additives 47 chain reactivity of substituents attached to the backbone of a 103 segmental motion of a 61 "stiffness" 159 containing pendant herbicides 112 hydrolysis studies of 102 matrix, permeability of organic molecules through a 17 matrix, swelling of the 24 mechanisms of degradation of 45 Polymeric materials in controlled release systems 17 Polymeric systems for controlled release of pesticides 114 Polymethylenepolyphenylisocyanate (PAPI) 135,145 Polyurethanes 47 Polyvinyl chloride 47 -polyester system 155 Poultry feed, methoprene in 193 Predator control devices 41

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

INDEX

205

Prevention of pesticide poisoning 56 Pyrethroids .57,145

R Rates of release of metribuzin 115 Rayon 95 Registering pesticides, environmental tests for 48,49 Release by erosion 10 by membrane-moderated diffusion 6 by retrograde chemical reactions .... 10 Repellents 41 Reservoir concentration 157,159 Residual phytotoxicity 123 Retrograde chemical reactions, release by 10 Roach-Tape 1 Rodenticides 4 S Schistosomiasis 38 Sebacoyl chloride 145 Segmental motion of a polymer chain 61 Sex pheromones 168 Shelf life of the starch-encapsulated pesticides 77 Shell No-Pest Strip 11 Sinapyl alcohol 84 Sodium pentobarbital 148 Soil mobility studies 115 Solution behavior in membrane systems 17 -diffusion membranes 153 -diffusion model of transport ., 18 Spray drying 133 Starch -encapsulated pesticides, shelf life of the 77 matrix, encapsulation of pesticides within a 74 xanthate 74 xanthide -Diazinon formulation, release properties of 79, 80 formulations of a nematocide 79

Stickers Strychnine Styrene-butadiene copolymers Substituted benzoic acids Sustained release Swelling of the polymer matrix Synthetic methods for polymers con taining pendant pesticides

174 54 46 87 4 24 114

Τ

Test temperature and carbon black content on diffusion coefficient, effect of Tobacco plants Toluene diisocyanate (TDI) Tomatoes Toxicity, highly selective Toxicological and environmental testing, govern ment regulations for problems testing for registration of pesticides, major Toxicology aspects of controlled re lease pesticide formulations, clinical Trimethylamine methacrylimide copolymer, hydrolysis of

66 147 135 91 56

37 37 48 48 54 108

V Vancomycin van der Waal's attractions

56 21

W Wall parameters on the release of active ingredients from micro encapsulated insecticides, effects of Weed control by delayed incorporation of butylate formulations, percent

In Controlled Release Pesticides; Scher, H.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

145 32 81