Radon Exposure of the U.S. Population-Status of the Problem (Ncrp Commentary)

NCRP COMMENTARY No.6

RADON EXPOSURE OF THE U.S. POPULATIONSTATUS OF THE PROBLEM

Issued March 15, 1991 National Council on Radiation Protection and Measunnents 7910 WOODMONT AVENUE / BETHESDA, MARYLAND 20814

This report was prepared by the National Counci1,on Radiation Protection and Measurements (NCRP). The Council strives to provide accurate, complete and useful information in its reports. However, neither the NCRP, the members of NCRP, other persons contributing to or assisting in the preparation of this report, nor any person acting on the behalf of any of these parties: (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness or usefulness of the information contained in this report, or that the use of any information, method or process disclosed in this report may not infringe on privately owned rights; or (b) assumes any liability with respect to the use of, or for damages resulting from the use of any information, method or process disclosed in this report, u n d e r t h e C i v i l R i g h t s A c t o f 1 9 6 4 , S e c t i o n 7 0 1 e t seq. a s amended 42 U . S . C . S e c t i o n 2 0 0 0 e e t s e q . ( T i t l e VIIJ or a n y o t h e r s t a t u t o r y or common l a w t h e o r y g o v e r n i n g l i a b i l i t y .

Library of Congress Cataloging-in-Publication Data

National Council on Radiation Protection and Measurements. Radon exposure of the U.S. population, status of the problem Pcm. - - (NCRP commentary; no. 6) Includes bibliographical references. ISBN 0-929600-17-7: $15.00 (est.) 1. Lungs--Cancer--UnitedStates--Risk factors. 2. Radon--Health aspects--United States. 3. Indoor air pollution--United States. I. Title. 11. Series. RC280.L8N37 1991 363.17'99--dc20

Copyright O National Council on Radiation Protection and Measurements 1991 All rights reserved. This publication is protected by copyright. No part of this publication may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotation in critical articles or reviews.

ace The exposure of the U.S. population to radon and its decay products appears to pose a significant risk. The magnitude of this risk has been estimated to range from approximately 5,000 to 20,000 lung cancer deaths annually. The NCRP last reviewed the risk of radon to the U.S. population in 1984. At that time, the NCRP recommended that remedial action to reduce the individual exposure from radon in houses be taken if such annual exposure was 2 WLM (7 x Jh m-3)or greater. This commentary reviews the present state of knowledge and consolidates in succinct form information and guidance on the radon problem. Although a number of important studies have been updated since 1984, perspective on radon risks and on radon levels has not changed greatly. As a result, the recommendation of 1984 on a remedial action level is unchanged for the present. However, a number of important studies are currently underway that are expected to produce results during the next few years. These studies will require definitive review. With this in mind, the Council has established Scientific Committee 85 to perform a new review of available information. This commentary was approved by the NCRP Board of Directors and made available to the Council membership for information prior to publication. Many of the Council members provided useful comments. The Council wishes to express its appreciation to Naomi H. Harley and John H. Harley for their efforts in preparing the first draft and also to William M. Beckner, NCRP Secretariat, for his staff work.

Bethesda, Maryland December 31, 1990

Warren K. Sinclair President, NCRP

Contents Preface ...................................................... 1 Background ..............................................

iii 1 2 Radon Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 Outdoor Radon Concentrations...................... 2 2.2 Indoor Radon Concentrations. . . . . . . . . . . . . . . . . . . . . . . 3 2.3 Radon Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 Epidemiological Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Underground Miner Studies . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.3 General Population Studies . . . . . . . . . . . . . . . . . . . . . . . . 10 4 Estimated Health Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.1 Miner Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2 General Population Risks .......................... 12 5 . Guidelines for Exgosure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 6 . Control of Radon in Houses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7 . Summary and Recommendations ............................... 19 References .................................................... 22 THE NCRP ...................................................... 26 NCRP Cownentaries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

. . . .

1. Background The National Council on Radiation Protection and Measurements (NCRP) published two reports in 1984 that ,focusedattention on the need for better information concerning the exposure of the U.S. population from radon and its decay products and the estimated lung cancer risks from such exposure (NCRP, 1984a; 1984b). The purpose of this commentary is to consolidate information fromthose reports and from some more recent studies into a document that summarizes information on radon and the Council's recommendations for a wide readership. Exposure of the general population to indoor radon was first noted as a public health concern in the United States in Grand Junction, Colorado, where uranium milling wastes were used as earth fill under and around buildings. Later, concern was expressed for residents in land areas of Florida reclaimed,following mining for phosphate rock. A study of phosphate wastes in Montana led to the discovery that the high levels of radon found in some homes came from natural sources and not from mine wastes. As additional surveys were made, it was evident that many geographical areas had homes with elevated natural levels of radon. The Reading Prong area in Pennsylvania, New Jersey, and New York has received the greatest public attention, although it is not known how exceptional this area is. It is clear, however, that there is a considerable potential for widespread exposure to radiation from radon and its decay products.

2.

Radon Concentrations 2.1

Outdoor Radon Concentrations

Radon is the immediate decay product of radium which is present at low concentrations in most materials. For example, soils and rocks contain radium at a concentration of about 40 Bq kg-'. Some of the radon produced by radium escapes into the air spaces around soil particles and then diffuses into the atmosphere. Average soil releases about 0.02 Bq m-2 s-' so that the earth's surface contributes about 100 EBq annually to the atmosphere. This leads to an average outdoor air concentration of approximately 8 Bq m-3over the northern hemisphere continents. This calculated value is in agreement with measured values. Releases from the oceans are much smaller, with the result that air concentrations at sea are about one .percent of those over land. The radon released at the soil surface is dispersed upward by convection. Radon is found in the troposphere but stratospheric concentrations are too low to measure. Under inversion conditions, upward dispersion is limited, and most locations show a diurnal cycle of concentration, rising at night and falling in the morning when the inversion breaks up. There is also a seasonal cycle which is dependent on location. The concentration in air is also affected by ground freezing, rainfall and other factors. Both diurnal and seasonal factors cause radon concentration to vary by a factor of two to three in temperate areas. The diurnal factor may be larger in coastal areas where the change from offshore to onshore winds can produce greater swings.

2.2

Indoor Radon Concentrations

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3

Radon decay products outdoors are at about 70 percent of equilibrium e , the concentration of the short lived decay products of radon are about 70 percent of the concentration of the radon), with the unattached fraction1 at somewhat below 10 percent. With this degree of equilibrium, the estimated average outdoor concentration of 8 Bq m-3of radon would be equivalent to a working level ( w L ) ~ value of about 0.001 and an annual exposure of 0.08 for an individual outdoors full time. working level month ( W L M ) ~

2.2

Indoor Radon Concentrations

When radon is released into an enclosed space, it cannot disperse into the atmosphere and continued release results in a buildup in concentration. This is the case both in mines and in houses. The major source of radon in houses is that formed in the soil beneath and immediately around the house. Releases from building materials and domestic water are almost always secondary sources and natural gas is a negligible source of radon and radon decay products in houses (NCRP, 1984a).

l ~ h efraction of short lived radon decay products not attached to the ambient aerosol. 2

Any combination of short-lived radon decay products in one liter of air that will result in the emission of 1.3 x lo5 MeV of potential alpha energy. The SI unit of WL is J m-' or the radioactivity concentration of radon in Bq m-3may be used for WL when the equilibrium fraction of the short lived decay products of radon are known, i . e. , 2 1 8 ~ o2,1 4 ~and b 214~i. 30ne working level month (WLM) is equivalent to an exposure to an air concentration of 1 WL for a working month of 170 hours., The SI unit for exposure to the short lived decay products of radon is Jh m-' where 1 WLM is equal to 3.5 x Jh mT3.

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2.

Radon Concentrations

Measured values of indoor radon in houses show a log-normal distribution. NCRP Report No. 77 (NCRP, 1984a) presented data demonstrating that with a log-normal distribution a large number of houses will show concentrations of 10 or even 100 times the average value, which is not the case for a normal distribution. Different surveys have shown log-normal distributions but with a significantly different distribution of readings. This can have a large effect on the predicted number of houses with high concentrations as demonstrated by the data in Table 2.1.

TABLE 2.1

Reported distribution of radon in U.S. living areas

Average Radon Concentration ~q m3

Percent Greater than 150 Bq m3

Reference

37 55

7

260

23

Alter and Oswald (1987)

120

19

Cohen (1988)

Nero et al., (1986)

Living areas in close proximity to soil have the highest radon concentrations. In most cases, the basement of a house has the highest concentration with the radon concentration at successive higher floors decreasing by a small factor. Concentrations in public buildings, such as offices and schools, are generally lower than those in Table 2.1, largely because of greater ventilation along with a lower contribution from soil due to more substantial foundations. High-rise apartments are also lower since the living areas are well removed from soil.

2.2 Indoor Radon Concentrations

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5

Many indoor radon measurements have been made, but their value in estimation of the average exposure is doubtful. The United States Environmental Protection Agency (EPA) and the state programs that they support use radon screening measurements designed to determine the potential maximum radon concentration rather than the average exposure of the occupants. Their protocol requires measurement in the lowest livable level of the house under closed conditions that assures the accumulation of data that overestimates the exposure of the occupants. The data bases of commercial radon measurements made by vendors are biased by the fact that the customers often have a reason to believe the radon concentration is high in their houses. One vendor, the Radon Project in Pittsburgh, has attempted a random sampling by mail (Cohen and Pondy, 1987), but the low response rate maym have produced a bias toward higher values. Considering that many vendors have difficulty measuring radon concentrations below the EPA guideline of 4 pCi 1-I (150 Bq m-3),it is likely that the bulk of current data is biased toward high value^.^ There is a need for a program of random sampling, statistically stratified, to estimate the average exposure and the exposure distribution of occupants of'houses in the United States as was recommended in NCRP Report No. 77 (NCRP, 1984a) . The EPA has had such a national program in the planning stage for some time and it has now been implemented. Results from this study are planned for release in 1991.

4 ~ h estated unit followed by the S I unit in parentheses is utilized in those instances that refer to a specific guideline or recommendation.

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2.

Radon Concentrations

2.3

Radon Exposures

The annual exposure of workers working for 1 7 0 hours per month is 1 2 times the average WL they are exposed to during the year, i . e . twelve 1 7 0 hour periods in a year. For the general population, total outdoor plus indoor exposure is continuous for 7 3 0 hours per month, rather than 1 7 0 hours and, therefore, their annual exposure is about 5 0 times the average exposure rate they are exposed to for the year. A United States average indoor concentration of 8 x l o - ' J m-3,estimated from the measurement data of George and Breslin ( 1 9 8 0 ) , gives an annual exposure of 7 x Jh m-3 in 5 0 years ( e - g . , 8 x lo-' J m-) x 8 . 7 6 x Jh m-3 or 3 . 5 x l o 3 h y-I = 7 x Jh m-3y-l, and 7 x Jh m-3 y-' x 5 0 y = 3 . 5 x Jh m-3 in 5 0 years) . This estimate was based on a small sample of houses and the average exposure rate is probably higher, from 8 x l o - ' up to 2 x J m'3. This gives a 5 0 year exposure range of 3.5 x lo-' up to 9 x l o - ' Jh m-3.

ological Studies Introduction Epidemiological studies aimed at elucidating the lung cancer risk attributable to radon exposure have focused primarily on miners. However, because lung cancer incidence is high both in the miner groups that have been studied and in the general population, an excess incidence in the miner groups due to radon is difficult to ascertain accurately. Identification of appropriate control study groups that allow for age, sex, cigarette smoking history, age at exposure, magnitude of radon decay product exposure, etc., is exceedingly complicated and introduces considerable statistical variation. Nevertheless, estimation of the risk of exposure to radon decay products by epidemiological studies of the miner groups and then the projection of these risks to lifetime risk is the only method currently available to estimate the risk to the general population, provided the exposure of the population is known.

3.2

Underground Miner Studies

There have been four major retrospective epidemiological studies of underground miners for which there have been updates since NCRP Report No. 78 (NCRP, 1984b) was published. Three of these are of uranium miners, the Colorado Plateau series (Hornung and Meinhardt, 1987), the Ontario series (Muller et d l . , 1985) and

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3.

Epidemiological Studies

the Czechoslovakian series (Sevc e t al., 1988); the fourth study is of the Swedish iron miners (Radford and Renard, 1984). Table 3.1 indicates the size of the study groups, their average exposure, and their observed, expected and, excess lung cancer mortality. Two additional studies, the Eldorado (Canada) cohort (Howe e t dl., 1986) and the Newfoundland fluorspar cohort (Morrison et al., 1988) may provide further information when complete.

TABLE 3.1 Mortality from lung cancer i n major mining cohorts a s o f the most recent follow-up

Cohort

Number in Cohort

Averaqe Exposure

Lunq Cancer Deaths Observed Expected Excess

(Jh K I - ~ ) Colorado

3360

2.8

256

59

197

Ontario ( Canada )

10661

0.13

80

56

24

Czechoslovakia

3043

0.79

484

98

386

Malmberget ( Sweden )

1292

0.33

15

36

51

Total excess deaths

643

There are a number of problems with these retrospective studies that introduce uncertainties into the risk estimates. The exposures of the miners are poorly documented and, in fact, many early exposures were not measured. The contribution of cigarette smoking to lung cancer is high in some studies and the smoking histories are not well known. Epidemiologists have attempted to

3.2 Underground Miner Studies

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9

correct the risk of radon exposures derived from the miner data for the smoking history of the miners, but the relevant smoking information for individual miners is difficult to extract. The Colorado Plateau miners constitute the only study group with essentially complete smoking histories, thus an internal control group was available for smoking as well as radon exposure (Whittemore and McMillan, 1983; Hornung and Meinhardt, 1987; NAS/NRC, 1988). A small study of 780 Navaho Indian uranium miners, most of whom are non-smokers or very light smokers, has also shown an excess of lung cancer (Samet et al., 1984). This study shows a positive dose response with increasing radon exposure and demonstrates that radon decay product exposure can cause excess lung cancer in the absence of a significant smoking history. An additional recent study of non-smoking Colorado miners (Roscoe et al., 1989) also shows an excess of lung cancer. The existing data indicate, however, that the risk from radon to smokers is substantially greater than that to non-smokers. The selection of appropriate external control populations in some of the studies is difficult, making estimates of expected deaths in the associated cohorts somewhat uncertain. The necessary corrections for age-adjusted mortality and for competing causes of death are less serious problems. One source of additional data is that of the 19th century European miners who are estimated to have been exposed to an average concentration of 1.2 x lo5 Bq m'3 of radon for many years. These miners incurred lung cancer at a high rate, at a frequency of somewhat below 50 percent (Muller, 1986, private communication). It is not possible to make a good estimate of their integrated exposure, but it was certainly greater than 3.5 x 10-I Jh m-3 per year. These miners, however, were not cigarette smokers like those in the more recent studies.

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3. Epidemiological Studies

3.3

General Population Studies

There are many ongoing epidemiological radon studies addressing exposures in the general population. These studies suffer from the same flaws as retrospective miner studies and also must generally deal with lower exposures and consequent lower health effects. In most cases the statistical power (the ability to detect an effect) of the studies is not adequate. The Department of Energy has summarized the current studies (DOE/CEC, 1989). One study in New Jersey (Schoenberg and Klotz, 1989) indicated a positive but not statistically significant relationship between radon exposure and lung cancer mortality.

4. Estimated Health Risk 4.1

Miner Risks

Because the estimates of risk to the population from radon exposure are necessarily based on data from miners, it is necessary to examine this material in some detail. The estimates of exposures to radon decay products in mines were based on measurements of WL (J m-3)and exposures were recorded in WLM (Jh m'3) . Sizeable fractions of the mining populations under study are still alive and it is necessary to estimate their future lifetime lung cancer mortality to assess the total radon risk. Neither of the two simplest risk models, the constant absolute risk model, where a given past exposure yields a fixed risk of mortality per year, nor the constant relative risk model, where a given past exposure yields a risk of mortality that is a fixed percentage of the risk in the general population at the same age, adequately describes the observed mortality pattern in any of the mining cohorts. A very significant point is that aging miner populations have shown a decline in excess lung cancer risk with time since cessation of exposure (NCRP, 1984b; Hornung and Meinhardt, 1987; NAS/NRC, 1988). A similar reduction in lung cancer risk is seen upon cessation of cigarette smoking. The reduction in radon risk with time has a marked effect on the prediction of lifetime risk because lung cancer in the general population seldom appears before age 40 and the rate increases steadily to about age 70 when competing causes of death decrease the risk,of mortality due to lung cancer.

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4. Estimated Health Risks

NCRP Report No. 78 (NCRP, 1984b) demonstrated that a modified absolute risk model, where the risk is reduced with time after exposure, fits the observed lifetime total mortality in miners better than the constant absolute or constant relative riskmodels. No correction for smoking was included in NCRP Report No. 78 since the fit was for the total miner population. The National Academy of Sciences/National Research Council Committee on the Biological Effects of Ionizing Radiation, in the report denominated BEIR IV (NAS/NRC, 1988), selected a modified relative risk model with the risk varying as a step function with age and time after exposure. The Committee also introduced a multiplicative interaction between smoking and radon exposure although the interaction was found to be submultiplicative (between additive and multiplicative). The Environmental Protection Agency (EPA) has adopted this general model for its risk assessments (Puskin and Yang, 1988).

4.2

General Population Risks

At this time, the only choice for estimating radon risk to the population is to use the miner data. Results from epidemiological studies in the general population are several years away and, even when completed, may not be adequate to describe a dose-response relationship or to provide a quantitative estimate of risk. In basing estimates of the general population risk from radon exposure on that derived from the miner data, several differences have to be considered. Most important are the distributions by age and sex and the lifetime continuous exposure for the population versus the short-term exposure of miners during working hours and a working lifetime. Added complications arise in estimating the actual radiation dose delivered to the lungs because of differences in breathing rate and physical factors such as aerosol particle size and degree of radioactive equilibrium of the decay products in the air.

4.2 General Population Risks

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13

The effect of many of these differences can be estimated by modeling the radiation dose to the bronchial epithelium for the various conditions. This was done in NCRP Report No. 78 (NCRP, 1984b) and in material published later by Harley and Cohen, (1986) as well as by James (1986). It would appear that the dose per unit exposure is very similar for miners and most members of the general population. There is some enhancement in dose per unit exposure in late childhood but this is not a major contributor to total lifetime dose. To assess lifetime risks, it is critical to evaluate the apparent decline in risk with time since exposure. The form of the fallloff is not fully defined, but an exponential decrease in risk with time having a half-time of 10 to 20 years seems to fit the data (NCRP, 1984b; and Hornung and Meinhardt, 1987). Since lung cancer is rare before age 40, exposure during childhood may contribute very little to the chance of developing lung cancer. This factor may also be helpful in retrospective studies of environmental radon, since estimating childhood exposures may not be as important as estimating exposures received later in life. The study by Lubin et al., (1990)'on Chinese tin miners showed that those exposed before age 13 had reduced risk of lung cancer compared with those exposed at older ages. The reduction was not statistically significant but the data indicate that children are not more sensitive than adults.

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4.

Estimated Health Risks

Table 4.1 compares the risk estimates developed by the several groups (EPA, 1986a; ICRP, 1987; NAS/NRC, 1988 and NCRP, 1984b) as they would apply to exposures of the general population. Puskin and Yang (1988) have indicated that the EPA range should be reduced by 40 percent to 0.8 to 3, so the differences are not large considering the variation in assumptions and procedures. There is no reason to expect that any of the present models are correct for such a complex system, but improvements will only appear when more time has lapsed and most of the cohorts have died.

Table 4.1 Lifetime excess risk of lung cancer mortality for exposure from birth to a concentration 4 x J m-' of radon decay products

I II I I

1

Lifetime Excess Risk (percent)

I

Projection Model

I

1

0.9

1.3

-

I Modified

I

Reference

I

absolute risk

1 NCRP

(1984b)

Constant relative risk Absolute risk

ICRP (1987) ICRP (1987)

5.0

Constant relative risk

EPA (1986a)a

3.4 men 1.4 women

Modified relative risk Modified relative risk

NAS/NRC, 1988 NAS/NRC, 1988

1I 1I

"Puskin and Yang (1988) have indicated the range should be 0.8 to 3.0

5.

Guidelines for Exposure

The annual exposure limit for uranium miners in the U.S. 12 WLM before 1971 was (4.2 x Jh rn-)). This was reduced in 1971 to 4 WLM (1.4 x Jh rn-)). The average annual exposure measured in the mines had been reduced to between 3.5 x and 7 x Jh rn-) by 1971. When a contamination problem with uranium mill tailings involving public exposure was recognized in Grand Junction, Colorado, the Surgeon General of the Public Health Service recommended that remedial action be considered at a radon daughter exposure rate (above background) of 0.01 WL (2 x J m-3)and be mandated at 0.05 WL (1 x J m-3) (Surgeon General, 1970). These exposure rates translate to annual exposures of 1.75 x lo-) Jh m-3 Jh m') if 100 percent occupancy is assumed. and 8.76 x When the State of Florida asked for EPA assistance on guidelines for the phosphate mining areas, the annual exposure recommended for remediation was 1 WLM (3.5 x Jh rn-)). The EPA translated this into 4 pCi 1-I (150 Bq m-)) of radon in air at an assumed 50 percent equilibrium of radon with its short-lived decay products . The NCRP, in Report No. 77 (NCRP, 1984a), recommended that lifetime exposures to individual members of the public above an annual rate of 2 WLM (7 x lo-) Jh m-)) be avoided. With the assumed 50 percent equilibrium of radon with its short-lived decay products, this translates into an average radon concentration of 8 pCi 1-I (300 Bq m-)) or, with the measured average equilibrium of approximately 40 percent, into approximately 400 Bq m-). The NCRP estimate for such a lifetime exposure (400 Bq m-)) was that the added lifetime risk of lung cancer was two percent, about twice the observed lung cancer value for non-smokers. This guideline is

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5.

Guidelines for Exposure

comparable with some of the miner exposures since an indoor exposure of 7 x Jh m-3per year can accumulate to approximately 4 x 10-I Jh m-3 in 50 years. The EPA guideline is being applied to the concentration in a specific house rather than to the li'fetime exposure of an individual. This is corrected for by assuming a 75 percent occupancy factor when calculating the risk. For a house with 3.5 x Jh m-' annual exposure, the lifetime mortality risk is 1.3 to 5 percent with the EPA prediction model shown in their Citizen's Guide to Radon (EPA, 1986a) or 0.8 to 3.0 percent as summarized by Puskin and Yang (1988). These guidelines have no legal standing for controlling indoor exposure, but they are entering the legal system. The Department of Housing and Urban Development offices in some areas have refused to guarantee mortgages for homes with high levels of radon. Also, several states have legislation or legislation in preparation which is based on the EPA guideline. The situation outside the united States is more relaxed. Several countries are using the ICRP guidelines (ICRP, 1987) of 200 Bq m-3for new housing and 400 Bq m-), at 50 percent equilibrium, for existing housing. Sweden has notably high radon levels and has adopted the guideline of 800 Bq m-3,at 50 percent equilibrium, for existing housing (Swedjemark, 1986). The 4 pCi 1 - I (150 Bq m-3) EPA guideline presents certain economic problems. Even the lowest estimate for the average concentration and distribution of radon in houses in the United States (NCRP, 1987a) indicates that about 1.5 percent of current housing would exceed the guideline. Other estimates approach 20 percent, which would mean that about 16 million houses should have remediation. The measured concentration distributions and the current risk estimations require careful scrukiny.beforesuch large scale action is undertaken.

6.

Control of Radon in Houses

The subject of remediation will only ,betreated briefly here, since it seems that generalized simple methods that always work have not been developed. The NCRP has recently issued a detailed report on this subject, Control o f Radon I n s i d e Houses (NCRP, 1989). Radon remediation may include blocking entry of the radon from the soil, or diversion or removal after entry. Simple blocking by caulking openings does not seem to offer long-term protection. Diversion through sub-floor ventilation almost always works but is expensive for existing structures. Ventilation can be good or bad; for example, depressurizing a house with exhaust ventilation can often pull in more soil radon. Present conventional wisdom is that each house is different and may require a different approach. This makes it difficult to predict the total cost of a nationwide remediation program or to establish costbenefit guidelines. Another remedial measure that may be applicable is the removal of decay products from the indoor space by cleaning the air (NCRP, 1989). This technique can reduce the decay product concentration in a room by several fold regardless of the source of radon, although the dose reduction may be smaller than the decrease in the concentration of decay products would suggest. The log-normal distribution of indoor radon concentrations has some significance in remediation. For public health purposes,

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6.

Control of Radon in Houses

assuming a linear response to radiation exposure and no threshold, the average exposure of the population should be reduced. This may best be done by small improvements in the bulk of the housing stock. For individual concerns, it is more desi'rable to reduce exposures in the homes with high levels of radon, which may have different economic implications. Available, in addition to the NCRP report on radon control men'tioned above, is an EPA homeowner's guide on the subject (EPA, 1986b). There are also a number of programs supported by Federal and State funds to test the effectiveness of remediation measures in homes with high radon concentrations.

7.

Summary and Recommendations

That radon decay product exposure contributes to excess lung cancer in underground miners is generally accepted. Miners were usually heavy cigarette smokers and were also exposed to other noxious agents but the appearance of the cancer excess with increasing exposure to radon and its decay products, in various miner groups, serves to firm up the role of radon as a major carcinogenic agent. The contribution of cigarette smoking to the total lung cancer rate in miners is considerable, but excess lung cancers are reported after correction for this factor to the extent that the data will allow. The current risk models developed from the miner data are quite varied but the resulting estimates of lifetime excess risk do not differ widely. Some additional information will be available from the present mining populations as they mature, but few new underground miners are expected to be added to the cohorts. In translating the miner experience to the general population, mathematical dose models indicate that the radiation dose per unit exposure is not greatly different for the two groups. The major obvious difference not accounted for is the rate of exposure, but any effect of rate of exposure, if any difference exists, cannot be evaluated at the present time. The general population epidemiology studies may give some answers in a few years. Epidemiological studies, however, are more likely to establish some upper limit of risk than to provide an exposure-

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7.

Summary and Recommendations

response model, particularly since individual unlikely to be estimated with any certainty.

exposures

are

Even if risk estimates per unit exposure were well known, they would not be very useful in estimating the overall risk to the U.S. population because there are inadequate data on average exposure and exposure distribution for the U.S. population. One step in approaching this problem is the EPA national survey that is expected to provide results in 1991. Radiation protection is based on a cautious approach, assuming Linear dose response and no threshold for stochastic effects such as lung cancer. This approach leads to the prediction that indoor radon exposures in houses will produce a number of excess lung cancers in the population. The estimate in NCRP Report No. 78 (NCRP, 1984b) was about 9,000 lung cancer deaths per year due to radon and its decay products in the U.S. with an average annual exposure of 7 x ~h m-3. Most other estimates are based on somewhat higher estimates of average exposures and higher risk coefficients, but the predictions of annual lung cancer deaths differ by only a factor of approximately two. For example, the BEIR IV data (NAS/NRC, 1988) may be used to derive an estimate of 13,300 deaths per year (Lubin and Boice, 1989). The recommendation in NCRP Report No. 77 (NCRP, 1984a) that remedial measures should be considered for an annual individual exposure greater than 2 WLM (7 x Jh m-3)included the estimate that a lifetime exposure of this magnitude would give an excess risk of lung cancer of approximately two percent. This may be compared with the observed average lifetime lung cancer risks of about one percent for non-smokers and six percent for cigarette smokers. The overall uncertainties in both the estimates of radon exposure levels in the United States and the risk per unit exposure are such that radical measures for exposure reduction for the entire population do not seem warranted at this time. On the other

7. Summary and ~ecornmendations

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hand, sensible approaches to the problem are certainly called for. The NCRP has already recommended, in NCRP Report No. 77 (NCRP, 1984a1, a national survey with follow-up measurements and continued r evaluation of lung cancer risks as the most important priorities with respect to radon. The EPA is now conducting the national survey and the NCRP expects to initiate a further evaluation of the lung cancer risks in the future. As noted previously, the contribution of smoking to the lifetime population risk from radon exposure is not clear at this time except that the risk is greater for smokers. No matter what relationship exists between smoking and radon exposure, the NCRP recommends that the risk from radon exposure which represents the most significant exposure of the U.S. population, should be vigorously studied. The earlier recommendation of the NCRP that an annual individual exposure above 7x Jh m-3 " . . .should be reduced by appropriate remedial action" has not been changed here but because of the risk level it represents, a lower level may be appropriate as more information on both risk and exposure become available. Furthermore, if attention is paid to remediation of homes with higher levels, and if good construction practices for new homes are observed, the population exposure will decrease with time.

References Alter, H.W., and Oswald, R.A. (1987). "Nationwide distribution of indoor radon measurements: A preliminary data base," J. Air Pollut. Control Assoc. 37, 227. Cohen, B.L. (1988). Radon L e v e l s by S t a t e s and C o u n t r i e s , R e p o r t o f t h e Radon P r o j e c t , Data t h r o u g h F e b r u a r y , 1 9 8 8 (Radon Project, Pittsburgh). "Comparison of purchased Cohen, B.L., and Pondy, P. (1987). measurements in randomly selected houses as a source of information on Rn-222 levels in homes," Health Phys. 53, 409. DOE/CEC (1989). Department of EnergylCommission of European Communities. International Workshop on Residential Radon Epidemiology, CONF-890717 (National Technical Information Service, Springfield, Virginia). EPA (1986a). Environmental Protection Agency. A C i t i z e n s Guide to Radon, U.S. EPA Report OPA-86-004 (Environmental Protection Agency, Washington). EPA ( 1986b) . Environmental Protection Agency. Radon R e d u c t i o n Methods: A Homeowner's G u i d e , U.S. EPA Report EPA-86-005 (Environmental Protection Agency, Washington). George, A.C., and Breslin, A.J. (1980). "The distribution of ambient radon daughters in residential buildings in the New York-New Jersey area," page 1272 in N a t u r a l R a d i a t i o n E n v i r o n m e n t 111, Gesell, T . and Lowder, W. Eds., United States Department of Energy Series 51, CONF 780422 (National Technical Information Service, Springfield, Virginia). Harley, N.H., and Cohen, B.S. (1986). "Updating radon daughter dosimetry," page 419 in A m e r i c a n C h e m i c a l S o c i e t y S y m p o s i urn on Radon and I t s D e c a y P r o d u c t s , Hopke, P.K., Ed. (American Chemical Society, Washington). Hornung, R.W., and Meinhardt, T.J. (1987). "Quantitative risk assessment of lung cancer in U.S. uranium miners," Health Phys. 52, 417.

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Howe, G.R., Nair, R.C., Newcombe, H.B., Miller, A.B. and Abbatt, J.D. (1986). "Lung cancer mortality (1950-1980) in relation to radon daughter exposure in a cohort of workers at the Eldorado Beaverlodge uranium mine, " J. Natl . Cancer Inst. 77(2), 357. ICRP (1987). International Commission on Radiological Protection. Lung Cancer Risk from Indoor Exposures to Radon ~aughters, ICRP Publication 50 (Pergamon Press, New York). James, A.C. (1986). "A reconsideration of cells at risk and other key factors in radon daughter dosimetry," page 400 in American Chemical Society Symposium on Radon and Its Decay Products, Hopke, P.K. Ed. (American Chemical Society, Washington) . Lubin, J.H., and Boice, J.D. (1989). "Estimating Rn-induced lung cancer in the United States," Health Phys. 57, 417. Lubin, J.H., You-Lin, Q., Taylor, P.R., Shu-Xiang, Y., Schatzkin, A., Bao-Lin, M., Jian-Yu, R., and Xiang-Zhen, X. (1990). "Quantitative evaluation of the radon and lung cancer association in a case control study of Chinese tin miners,"Cancer Res. 50, 174. Morrison, H.I., Semenciw, R.M., Mao, Y., and Wigle, D.T. (1988). "Cancer mortality among a group of fluorspar miners exposed to radon progeny," Am. J. Epidemiol, 128, 1266. Muller, J., Kusiak, R., and Ritchie, A.C. (1985). Factors Modifying Lung Cancer Risk in Ontario Uranium Miners, 19551981. Ontario Ministry of Labour Report (Ministry of Labour, Toronto) . NASINRC (1988). National Academy of Sciences/National Research Health Risks of Radon and Other Internally Council. Deposited Alpha-Emitters, BEIR IV Report (National Academy Press Washington). NCRP (1984a). National Council on Radiation Protection and Exposures From the Uranium Series With Measurements. Emphasis on Radon and Its Daughters, NCRP Report No. 77 (National Council on Radiation Protection and Measurements, Bethesda, Maryland) .

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(1984b). National Council on Radiation Protection and Measurements. E v a l u a t i o n o f O c c u p a t i o n a l and Environmental Exposures t o Radon and Radon Daughters i n t h e U n i t e d S t a t e s , NCRP Report No. 78 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). NCRP (1989). National Council on Radiation Protection and Measurements. C o n t r o l o f Radon In Houses, NCRP Report No. 103 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). Nero, A.V., Schwehr, M.B., Nazaroff, W.W., and Revzan, K.L. (1986). "Distribution of airborne radon-222 concentrations in U.S. homes," Science 234, 992. Puskin, J.S., and Yang, Y. (1988). "A retrospective look at Rninduced lung cancer mortality from the viewpoint of a relative risk model," Health Phys. 54, 635. Radford, E.P., and Renard, K.G.S. (1984). "Lung cancer in Swedish iron miners exposed to low does of radon daughters," N. Engl. J. Med. 310, 1485. Roscoe, R.J., Steenland, K., Halperin, W.E., Beaumont, J.J., and Waxweiler, R.J. (1989). "Lung cancer mortality among nonsmoking uranium miners exposed to radon," J. Am. Med. Assoc. 262, 629. Samet, J.M., Kutvirt, O.M., Waxweiler, R.J., and Key, C.R. (1984). "Uranium mining and lung cancer in Navaho men," N. Engl. J. Med.-310, 1481. Sevc, J., Kunz, E., Tomasek, L., Placek, V., and Horacek, J. (1988). "Cancer in man after exposure to Rn daughters," Health Phys. 54, 27. Schoenberg, J. and Klotz, J. (1989). A c a s e - c o n t r o l S t u d y o f Radon and Lung Cancer Among New J e r s e y Women, New Jersey State Department of Health Technical Report, Phase I. (New Jersey Department of Health, Trenton, New Jersey).

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Surgeon General (1970). "Recommendations of action for radiation exposure levels in dwelling constructed on or with uranium mill tailings," page 52 in Use of Uranium Mill Tailings for Construction Purposes, Hearings of the Joint Committee on Atomic Energy, October 1971, (Government Printing Office, Washington) . Swedjemark, G.A. (1986). "Swedish limitation schemes to decrease Rn daughters in indoor air," Health Phys. 51, 569. Whittemore, A.S. and McMillan, A. (1983). "Lung cancer mortality among U.S. uranium miners," J. Nat. Cancer Inst. 71, 489.

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K r y p t o n - 8 5 i n t h e A t m o s p h e r e - W i t h S p e c i f i c Reference t o the P u b l i c H e a l t h S i g n i f i c a n c e o f the Proposed C o n t r o l l e d R e l e a s e a t Three M i l e I s l a n d

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P r e l i m i n a r y E v a l u a t i o n o f C r i t e r i a f o r the Disposal o f Transuranic Contaminated Waste

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S c r e e n i n g Technique for Determining Compliance w i t h Environmental Standards

4

G u i d e l i n e s f o r the R e l e a s e o f W a s t e W a t e r f r o m N u c l e a r F a c i l i t i e s w i t h S p e c i a l Reference t o t h e P u b l i c H e a l t h S i g n i f i c a n c e o f the P r o p o s e d R e l e a s e o f T r e a t e d W a s t e W a t e r s a t Three M i l e I s l a n d

5

Review o f the P u b l i c a t i o n , L i v i n g W i t h o u t L a n d f i l l s

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Radon E x p o s u r e o f t h e U.S. P o p u l a t i o n , S t a t u s o f t h e Problem

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