Chernobyl: Catastrophe and Consequences (Springer Praxis Books Environmental Sciences)

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Chernobyl ± Catastrophe and Consequences

Jim T. Smith and Nicholas A. Beresford

Chernobyl ± Catastrophe and Consequences

Published in association with

Praxis Publishing Chichester, UK

Dr Jim T. Smith Centre for Ecology and Hydrology Winfrith Technology Centre Dorchester Dorset UK Dr Nicholas A. Beresford Radioecology Group Centre for Ecology and Hydrology Lancaster Environment Centre Cumbria UK

SPRINGER±PRAXIS BOOKS IN ENVIRONMENTAL SCIENCES SUBJECT ADVISORY EDITOR: John Mason B.Sc., M.Sc., Ph.D.

ISBN 3-540-23866-2 Springer-Verlag Berlin Heidelberg New York Springer is part of Springer-Science + Business Media (springeronline.com) Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available from the Internet at http://dnb.ddb.de Library of Congress Control Number: 2005928344 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers. # Praxis Publishing Ltd, Chichester, UK, 2005 Printed in Germany The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Cover design: Jim Wilkie Project management: Originator Publishing Services, Gt Yarmouth, Norfolk, UK Printed on acid-free paper

Contents

List of contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xi

Editors and principal authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xiii

Contributing authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xv

List of ®gures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xvii

List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xxi

List of abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xxv

1

Introduction (Jim T. Smith and Nick A. Beresford) . . . . . . . . . . . . . . 1.1 History of the accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 Emergency response and early health effects. . . . . . . . . 1.1.2 Emergency clean up and waste disposal. . . . . . . . . . . . 1.1.3 Radionuclides released and deposited . . . . . . . . . . . . . 1.2 Radiation exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Health effects of radiation . . . . . . . . . . . . . . . . . . . . 1.2.2 Exposure pathways and change of dose over time after Chernobyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Limiting the long-term dose to the population . . . . . . . 1.2.4 Unof®cial resettlement of the abandoned areas . . . . . . . 1.3 Chernobyl in context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Previous radioactive releases to the environment . . . . . . 1.3.2 Natural radioactivity in the environment and medical radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 5 7 11 16 16 19 23 24 25 25 27 31

vi Contents

2

Radioactive fallout and environmental transfers (Jim T. Smith and Nick A. Beresford) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Pattern and form of radioactive depositions . . . . . . . . . . . . . . 2.1.1 Element isotope ratios and `hot' particles. . . . . . . . . . . 2.1.2 Break up of hot particles . . . . . . . . . . . . . . . . . . . . . 2.2 Environmental transfers of radionuclides . . . . . . . . . . . . . . . . 2.2.1 Migration of radionuclides in the soil . . . . . . . . . . . . . 2.2.2 Rates of vertical migration . . . . . . . . . . . . . . . . . . . . 2.2.3 Change in external dose rate over time . . . . . . . . . . . . 2.2.4 Resuspension of radioactivity . . . . . . . . . . . . . . . . . . 2.2.5 Transport of radioactivity by rivers . . . . . . . . . . . . . . 2.3 Bioavailability, bioaccumulation and effective ecological half-lives 2.3.1 Aggregated Transfer Factor and Concentration Ratio . . 2.3.2 Physical, biological and ecological half-lives . . . . . . . . . 2.3.3 Changes in radiocaesium bioavailability over time . . . . . 2.3.4 Temporal changes in radiostrontium bioavailability . . . . 2.4 Characteristics of key Chernobyl radionuclides . . . . . . . . . . . . 2.4.1 Radioiodine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Radiostrontium . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Radiocaesium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Plutonium and americium . . . . . . . . . . . . . . . . . . . . . 2.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Radioactivity in terrestrial ecosystems (Jim T. Smith, Nick A. Beresford, G. George Shaw and Leif Moberg) . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Agricultural ecosystems. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Interception of radioactive fallout by plants . . . . . . . . . 3.2.2 Transfer of radionuclides to crops and grazed vegetation 3.2.3 Transfers to animal-derived food products . . . . . . . . . . 3.2.4 Time changes in contamination of agricultural systems . . 3.2.5 Very long-lived radionuclides in agricultural systems . . . 3.3 Forest ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Cycling of radioactivity in the forest ecosystem. . . . . . . 3.3.2 Transfer of radionuclides to fungi, berries and understorey vegetation . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Transfer of radionuclides to game and semi-domestic animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Radionuclides in trees . . . . . . . . . . . . . . . . . . . . . . . 3.4 Radiation exposures from ingestion of terrestrial foods . . . . . . . 3.4.1 Reference levels of radioactivity in foodstuffs . . . . . . . . 3.4.2 Radiation exposures from agricultural foodstuffs . . . . . . 3.4.3 People now living in the abandoned areas . . . . . . . . . . 3.4.4 Radiation exposures via the forest pathway . . . . . . . . . 3.4.5 Time dependence of exposures . . . . . . . . . . . . . . . . . .

35 35 37 40 41 41 44 46 48 53 54 54 55 57 64 65 65 67 69 71 73 81 81 85 85 86 93 103 107 108 108 110 116 118 119 119 121 122 124 126

Contents

3.5 4

3.4.6 Comparison of radiocaesium transfers to various products References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Radioactivity in aquatic systems (Jim T. Smith, Oleg V. Voitsekhovitch, Alexei V. Konoplev and Anatoly V. Kudelsky) . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Distribution of radionuclides between dissolved and particulate phases . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Radionuclides in rivers and streams . . . . . . . . . . . . . . . . . . . 4.2.1 Early phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Intermediate phase . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Long-term 137 Cs contamination of water . . . . . . . . . . . 4.2.4 Processes controlling declines in 90 Sr and 137 Cs in surface waters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.5 In¯uence of catchment characteristics on radionuclide runoff. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Radioactivity in lakes and reservoirs . . . . . . . . . . . . . . . . . . . 4.3.1 Initial removal of radionuclides from the lake water . . . 4.3.2 The in¯uence of lake water residence time . . . . . . . . . . 4.3.3 The in¯uence of lake mean depth d . . . . . . . . . . . . . . 4.3.4 The in¯uence of sediment±water distribution coef®cient Kd . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.5 Transport of 90 Sr in lakes. . . . . . . . . . . . . . . . . . . . . 4.3.6 Transport of 131 I in lakes . . . . . . . . . . . . . . . . . . . . . 4.3.7 Transport of Ruthenium in lakes . . . . . . . . . . . . . . . . 4.3.8 Radionuclide balance in water of open lakes . . . . . . . . 4.3.9 Closed lake systems . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Radionuclides in sediments . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Uptake of radionuclides to aquatic biota . . . . . . . . . . . . . . . . 4.5.1 137 Cs in freshwater ®sh . . . . . . . . . . . . . . . . . . . . . . 4.5.2 In¯uence of trophic level on radiocaesium accumulation in ®sh. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Size and age effects on radiocaesium accumulation . . . . 4.5.4 In¯uence of water chemistry on radiocaesium accumulation in ®sh . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 131 I in freshwater ®sh. . . . . . . . . . . . . . . . . . . . . . . . 4.5.6 90 Sr in freshwater ®sh . . . . . . . . . . . . . . . . . . . . . . . 4.5.7 Radiocaesium and radiostrontium in aquatic plants . . . . 4.5.8 Bioaccumulation of various other radionuclides. . . . . . . 4.6 Radioactivity in marine systems . . . . . . . . . . . . . . . . . . . . . . 4.6.1 Riverine inputs to marine systems . . . . . . . . . . . . . . . 4.6.2 Transfers of radionuclides to marine biota . . . . . . . . . . 4.7 Radionuclides in groundwater and irrigation water. . . . . . . . . . 4.7.1 Radionuclides in groundwater . . . . . . . . . . . . . . . . . . 4.7.2 Irrigation water . . . . . . . . . . . . . . . . . . . . . . . . . . .

vii

128 128 139 139 141 143 144 149 149 150 152 154 155 157 159 159 160 161 162 162 163 165 168 168 170 170 171 173 173 174 174 175 177 178 179 179 180

viii

Contents

4.8 4.9 5

Radiation exposures via the aquatic pathway . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

180 181

Application of countermeasures (Nick A. Beresford and Jim T. Smith). . 5.1 Countermeasure techniques . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.1 Methods of reducing uptake of radioiodine to the thyroid 5.1.2 Methods of reducing the soil-to-plant transfer of radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.3 Methods of reducing the radionuclide content of animalderived foodstuffs . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1.4 Countermeasures for freshwater systems . . . . . . . . . . . 5.1.5 Reduction of the external dose in residential areas . . . . 5.1.6 Social countermeasures. . . . . . . . . . . . . . . . . . . . . . . 5.2 Countermeasures to reduce internal doses applied within the agricultural systems of the fSU . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Key foodstuffs contributing to ingestion doses . . . . . . . 5.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

191 191 192

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192 193 197 200 201 204 207 208 209

6

Health consequences (Jacov E. Kenigsberg and Elena E. Buglova) 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Radiation-induced health effects . . . . . . . . . . . . . . . . . . 6.3 Deterministic health effects after the Chernobyl accident . . 6.4 Stochastic health effects after the Chernobyl accident . . . . 6.4.1 Leukaemia. . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Thyroid cancer . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Non-thyroid solid cancer . . . . . . . . . . . . . . . . . 6.4.4 Non-cancer diseases. . . . . . . . . . . . . . . . . . . . . 6.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . .

217 217 218 219 220 220 222 231 232 232 233

7

Social and economic effects (Ingrid A. Bay and Deborah H. Oughton). . 7.1 Social and economic effects and their interactions . . . . . . . . . . 7.2 Health detriments and associated harms due to radiation exposure 7.2.1 Radiation exposure of the Chernobyl `liquidators' . . . . . 7.2.2 Physiological health effects . . . . . . . . . . . . . . . . . . . . 7.2.3 Psychological and social effects . . . . . . . . . . . . . . . . . 7.3 Economic impact. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Expenditures related to countermeasures . . . . . . . . . . . 7.3.2 Capital losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Rural breakdown . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Social costs of countermeasure implementation . . . . . . . . . . . . 7.4.1 Evacuation and resettlement . . . . . . . . . . . . . . . . . . . 7.4.2 Countermeasures in agricultural food chains. . . . . . . . . 7.4.3 Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . .

239 239 242 243 244 245 247 247 249 250 251 252 254 254

Contents ix

7.5 7.6 8

9

7.4.4 Communication and information . . 7.4.5 The European response . . . . . . . . 7.4.6 Risk perception . . . . . . . . . . . . . 7.4.7 Factors in¯uencing risk perception . 7.4.8 Control . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . .

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Effects on wildlife (Ivan I. Kryshev, Tatiana G. Sazykina and Nick A. Beresford). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Terrestrial biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.1 Radiation effects in forests . . . . . . . . . . . . . . . . . . . . 8.1.2 Radiation effects in herbaceous vegetation . . . . . . . . . . 8.1.3 Radiation effects in soil faunal communities and other insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1.4 Radiation effects in mammal populations . . . . . . . . . . 8.1.5 Radiation effects in bird populations . . . . . . . . . . . . . 8.2 Freshwater biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.1 Exposure of aquatic biota. . . . . . . . . . . . . . . . . . . . . 8.2.2 Radiation effects in aquatic biota. . . . . . . . . . . . . . . . 8.3 The Chernobyl exclusion zone ± a nature reserve? . . . . . . . . . . 8.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

255 257 258 258 260 261 262 267 268 268 272 274 275 276 277 277 279 280 282

Conclusions (Jim T. Smith and Nick A. Beresford) . . . . . . . . . . . . . . 9.1 Contamination of the environment . . . . . . . . . . . . . . . . . . . . 9.1.1 Current radiation exposures in the Chernobyl affected areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1.2 Future environmental contamination by Chernobyl . . . . 9.1.3 Countermeasures and emergency response . . . . . . . . . . 9.2 Consequences of the accident. . . . . . . . . . . . . . . . . . . . . . . . 9.2.1 Damage to the ecosystem . . . . . . . . . . . . . . . . . . . . . 9.2.2 Direct health effects of the accident . . . . . . . . . . . . . . 9.2.3 Social and economic consequences . . . . . . . . . . . . . . . 9.2.4 Future management of the affected areas. . . . . . . . . . . 9.2.5 Chernobyl and the Nuclear Power Programme . . . . . . . 9.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

289 289 289 290 293 294 294 296 298 300 301 302

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

307

Contributors

EDITORS AND PRINCIPAL AUTHORS Jim Smith Centre for Ecology and Hydrology, Winfrith Technology Centre, Dorchester, Dorset, DT2 8ZD, UK. E-mail: [email protected] Nick Beresford Centre for Ecology and Hydrology, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, UK. E-mail: [email protected]

CONTRIBUTING AUTHORS Ingrid Bay-Larsen Nordland Research Institute, MoerkvedtraÊkket 30, 8049 Bodé, Norway. E-mail: [email protected] Elena Buglova Protection in Interventions Unit, Division of Radiation, Transport and Waste Safety, International Atomic Energy Agency, Wagramerstrasse 5, A-1400 Vienna, Austria. E-mail: [email protected] Jacov Kenigsberg National Commission of Radiation Protection, Komchernobyl, 23 Masherov Ave., Minsk 220004, Belarus. Email: [email protected] Alexei Konoplev Science & Production Association `Typhoon', 82 Lenin Ave., Obninsk, Kaluga Region, 249020, Russia. E-mail: [email protected]

xii

Contributors

Ivan Kryshev Science & Production Association `Typhoon', 82 Lenin Ave., Obninsk, Kaluga Region, 249020, Russia. E-mail: [email protected] Anatoly Kudelsky Institute of Geochemistry and Geophysics, 7 Kuprevich Str., Minsk 220141, Belarus. E-mail: [email protected] Leif Moberg Swedish Radiation Protection Institute, S-171 Stockholm, Sweden. E-mail: [email protected] Deborah Ougton The Ethics Programme, Forskningsparken, GaustadalleÁen 21, 0349 Oslo, Norway. Email: [email protected] George Shaw Division of Agricultural & Environmental Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK. Tatiana Sazykina Science & Production Association `Typhoon', 82 Lenin Ave., Obninsk, Kaluga Region, 249020, Russia. E-mail: [email protected] Oleg Voitsekhovitch Ukrainian Hydrometeorological Institue, 37 Nauka Ave., Kiev 252028, Ukraine. Email: [email protected]

Editors and principal authors

Dr. Jim Smith is an expert in modelling radioactive pollution in terrestrial and freshwater ecosystems. He has coordinated three multi-national projects on the environmental consequences of Chernobyl and regularly works in the Chernobyl exclusion zone. He has worked with Ukrainian, Belarussian and Russian scientists on the Chernobyl accident for fourteen years and speaks Russian. Currently he is leading an EC INTAS project to evaluate the ecological e€ects of remediation of the Chernobyl Cooling Pond. Jim Smith has 53 papers on environmental radioactivity in the refereed scienti®c literature. Together with Nick Beresford and colleagues, he made the ®rst long-term predictions of general ecosystem contamination by Chernobyl radiocaesium, for the ®rst time quantitatively linking soil sorption kinetics to environmental mobility and uptake. He is a member of the International Atomic Energy Agency (IAEA) Expert Group on Chernobyl and Chairman of the UK Coordinating Group on Environmental Radioactivity. Dr. Nick Beresford has 20 years experience as a radioecologist. His areas of expertise include the study of mechanisms controlling radionuclide and heavy metal transfer/ metabolism in (predominantly farm) animals and the development of countermeasures to reduce the entry of radioactivity into the human food chain. Recently he has worked, both nationally and internationally, on the development of guidance and methodologies to ensure protection of the environment from ionising radiation. In relation to the Chernobyl accident, he conducted extensive studies on upland sheep farms in the UK, tested and developed countermeasures and conducted experiments in the Chernobyl exclusion zone. He has also contributed to the development of approaches for sustainable management strategies for radioactively contaminated environments. He has published 62 papers in the refereed literature.

Contributing authors

Professor George Shaw holds the Chair in Environmental Science at Nottingham University. He has carried out research into the behaviour of radionuclides in agricultural and semi-natural ecosystems since 1987, and has studied semi-natural ecosystems in the Chernobyl 30-km exclusion zone. He has contributed to the IAEA's work on contaminated forests and timber products, as well as being a member of the IAEA/WHO Chernobyl Forum. Dr. Leif Moberg is the principal radioecologist at the Swedish Radiation Protection Authority (SSI) where he has worked for more than 20 years. He has worked on the consequences of the Chernobyl accident since 28 April, 1986 and for a number of years has been the spokesman for SSI on these issues. He is closely involved in the radiation-related work of a number of international organisations, including the EU, UNSCEAR, IAEA and OSPAR. Dr. Oleg Voitsekhovitch is deputy director of the Ukrainian Hydrometeorological Institute and was responsible for monitoring radioactivity in aquatic systems after the Chernobyl accident and for advising on aquatic countermeasures. Dr. Alexei Konoplev is Head of the Centre for Environmental Chemistry at SPA `Typhoon' in Russia. He is a leading expert on radionuclide interactions with soils and sediments, fuel particle disintegration and on radionuclide transfers to and in aquatic systems. He has worked on radioactivity in the Chernobyl area since 1986. Professor Anatoly Kudelsky is Head of the Hydrogeology Laboratory at the Institute of Geochemistry and Geophysics in Belarus. He is an expert in mobility of radioactivity in soils, groundwaters and surface water systems and has worked on Chernobyl problems since the accident. Professor Jacov Kenigsberg is Chairman of the National Commission of Radiation Protection of the Republic of Belarus. He is a leading expert in radiation protection, radiation medicine and dosimetry. He has more than 200 scienti®c publications on the health consequences of the Chernobyl accident and radiation protection of the population. Dr. Elena Buglova is an expert on the

xvi Contributing authors

health e€ects of ionising radiation. Formerly Head of the Laboratory of Radiation Hygiene and Risk Analysis at the Institute of Radiation Medicine and Endocrinology of Belarus, Dr. Buglova is currently working as a radiation protection specialist at the International Atomic Energy Agency. Ingrid Bay has a Masters in radioecology and has worked on social and ethical issues of radioactive contamination in a number of international projects. She has held a scholarship in the Ethics Programme (University of Oslo) and is currently an associated researcher to Nordland Research Institute. Professor Deborah Oughton is a Research Fellow with the University of Oslo's Ethics Programme and Professor in Environmental Chemistry at the Norwegian University of Life Sciences. Her main scienti®c research interests lie within radioecology, particularly experimental studies on the transfer and biological e€ects of long-lived radionuclides. At the University of Oslo, her studies have focused on ethical issues within radiation protection, including the non-human environment, and the ethical, legal and social aspects of risk assessment and management in general. Professor Ivan Kryshev is Head of Environmental Modelling and Risk Analysis at SPA `Typhoon', Russia. He has 29 years experience in modelling the transfer of radionuclides in the environment, ecological dosimetry and analysis of countermeasures following the Chernobyl and Kyshtym accidents. He is an Academician of the Russian Academy of Natural Sciences, a Member of the Russian Scienti®c Commission of Radiation Protection and an Expert of the United Nations Scienti®c Committee on the E€ects of Atomic Radiation. He is author of 280 scienti®c publications, including 18 books. Dr. Tatiana Sazykina is a leading research scientist at SPA `Typhoon' in Obninsk, with 28 years experience in radioecological and ecosystem modelling. She is a key member of a number of international research projects into the e€ects of radiation on wildlife.

Figures

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8

1.9 1.10 1.11 1.12 1.13 1.14 1.15 1.16

2.1 2.2 2.3

The destroyed Unit 4 reactor building at the Chernobyl Nuclear Power Plant Aerial view of the destroyed reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The abandoned town of Pripyat with the Chernobyl Nuclear Power Station in the background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Satellite photo of the area around Chernobyl NPP. . . . . . . . . . . . . . . . . . . . Sarcophagus construction, early September 1986 . . . . . . . . . . . . . . . . . . . . . Sarcophagus photographed in 2003. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimated daily releases of 131 I from the reactor for the period from the initial explosion to the extinction of the ®re . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (a) Percentage of the initial radioactivity remaining in the environment at di€erent times after the Chernobyl accident, based on release data given in Table 1.2. (b) Changes in the amounts of some key radionuclides over time due to radioactive decay. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Cs fallout in Ukraine, Belarus and Russia . . . . . . . . . . . . . . . . . . . . . . . . 137 Cs fallout in Europe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Sr and 239;240 Pu fallout in the Ukrainian part of the 30-km zone . . . . . . . . . (a) Fatal solid cancer; (b) leukaemia rates in the follow up group of people exposed to radiation from the Hiroshima and Nagasaki atomic bombs . . . . . E€ective dose to the populations of Belarus, Russia and the Ukraine (excluding thyroid dose) during the period 1986±1995 . . . . . . . . . . . . . . . . . . . . . . . . . Thyroid dose to children less than 18 years old in the two most a€ected regions of Belarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Change in external gamma dose rate over time after the accident . . . . . . . . . Contrasting contributions of internal and external dose rates to overall dose in areas of di€erent soil types, Bryansk Region, Russia . . . . . . . . . . . . . . . . . . Electron micrograph of a uranium fuel particle from Chernobyl. . . . . . . . . . . Concentration of di€erent radionuclides in the air and deposition as a function of distance from Chernobyl, expressed as a ratio of radionuclide : 137 Cs . . . . . Half-time of dissolution of fuel particles as a function of soil pH . . . . . . . . .

3 3 6 7 9 9 12

14 15 16 17 18 20 21 22 23 36 38 41

xviii 2.4 2.5 2.6 2.7 2.8 2.9 2.10 2.11 2.12 2.13 2.14

2.15 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12

Figures Examples of activity±depth pro®les of various radionuclides in soils . . . . . . . Decline in the observed dispersion coecient as a function of time in a grassland soil at Veprin, Belarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . External dose rate 0.05 m above the ground as a function of 137 Cs inventory in the soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Change in annual e€ective external dose for rural indoor workers living in wood-framed houses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Change in resuspension factor as a function of time after fallout at a number of sites around Europe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Annual mean 137 Cs resuspension factors measured at 20 di€erent sites around Europe at large distances from Chernobyl for two di€erent time periods. . . . . Illustration of Cs sorption to speci®c FES on illitic clay minerals and competition for sorption sites by ions of similar hydrated radius (K‡ , NH‡ 4) but not ions with much larger hydrated radius such as Ca2‡ , Mg2‡ . . . . . . . . Illustration of the dynamic model for radiocaesium sorption to illitic clay minerals showing rapid uptake to `exchangeable' sites and slower `®xation' in the mineral lattice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Schematic diagram indicating timescales of release of radiocaesium from soils to terrestrial and aquatic ecosystems during the years after a fallout event . . . . . Illustration of changes in radiocaesium in milk in a system with declining activity concentrations in vegetation and relatively rapid rates of uptake and removal from milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (a) Examples of changes in 137 Cs activity concentration in di€erent ecosystem components after Chernobyl. (b) Frequency distribution of e€ective ecological half lives in di€erent ecological components during the ®rst ®ve years after Chernobyl. (c) Long-term changes in 137 Cs in brown trout, Norway, and perch, terrestrial vegetation and water, UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Change in CR of wheat on soddy±podzolic soil . . . . . . . . . . . . . . . . . . . . . . Ranges in 137 Cs activity concentration in various products from the Luginsk district, Zhitomir region, Ukraine in 1995 . . . . . . . . . . . . . . . . . . . . . . . . . . Plot of Tag vs. organic matter content in soils in 5 catchments in Cumbria, UK CR of 90 Sr and 137 Cs in various vegetables in Finland, clay and silt soils, 1987 Comparison between calcium intake and Fm for strontium with additional recent data for cattle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variation in 137 Cs activity concentration in 1,144 sheep, Cumbria, UK . . . . . Increase in feed±milk transfer coecient over time at a farm in Bavaria. . . . . Time changes in (a) 131 I and (b) 137 Cs in air, grass and milk in north-western Italy during the ®rst month after the accident . . . . . . . . . . . . . . . . . . . . . . . Time changes in the aggregated transfer factor of 137 Cs in the decade after the accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seasonal trends in the 137 Cs activity concentrations of study ewes at one of the farms of Beresford et al. (1996) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Major storages and ¯uxes in radionuclides in contaminated forest ecosystems Radiocaesium pro®les in forest soils in (a) the Chernobyl 30-km zone at two di€erent times after the accident and (b) in a forest soil in Germany (in 1996) contaminated by Chernobyl and weapons test fallout . . . . . . . . . . . . . . . . . . Aggregated transfer factor for 137 Cs in a very highly accumulating mushroom species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

43 44 47 48 49 50 57 57 58 59

60 65 84 88 93 96 99 101 104 106 106 110 111 113

Figures xix 3.13 3.14 3.15

4.1 4.2 4.3 4.4 4.5

4.6 4.7 4.8 4.9

4.10 4.11 4.12 4.13 4.14 4.15 5.1 5.2 5.3

Change in 137 Cs activity concentration in roe deer meat in a spruce forest, Ochsenhausen, Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A summary of the 137 Cs activity concentration measured in the milk of cattle owned by people living within the 30-km exclusion zone. . . . . . . . . . . . . . . . A comparison of the consumption rate of fungi and the whole body 137 Cs burden determined in people living in an urban area of Russia . . . . . . . . . . . Pripyat±Dnieper River±Reservoir system showing Chernobyl and Kiev with the Kiev Reservoir in between . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fraction of a radionuclide absorbed to particulates as a function of suspended solids concentration in water for di€erent values of Kd . . . . . . . . . . . . . . . . . The change in activity concentration of 137 Cs and 90 Sr in the Pripyat River over time after the accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The initial activity concentrations of radionuclides in various rivers vs. the total amount released from the reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (a) Normalised activity concentration of 137 Cs in the dissolved phase of di€erent rivers after Chernobyl. (b) Correlation between the normalised 137 Cs activity concentration and the percentage catchment coverage of organic, boggy soils in six di€erent catchments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radionuclide transfers in a catchment±lake system . . . . . . . . . . . . . . . . . . . . Comparison of initial 137 Cs activity concentration in 15 lakes determined from measurements with that estimated from a simple dilution model . . . . . . . . . . Change in the 137 Cs activity concentration in water and ®sh of: (a) a small shallow lake in Germany, Lake Vorsee and; (b) the large, deep Lake Constance (a) The relationship between 137 Cs removal rate from 14 lakes and the removal rate of water through the out¯ow. (b) The relationship between the fraction of the total 137 Cs transferred to the out¯ow and the lake water residence time. (c) The relationship between 137 Cs removal rate and the lake mean depth . . . . . . Changes in average annual content of 137 Cs and 90 Sr in the water of the ®rst (Vishgorod, Kiev Reservoir) and last (Novaya Kahovka, Kahovka Reservoir) reservoirs of the Dnieper cascade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graphs of 137 Cs activity±depth pro®les in sediments in (a) Baltic Sea, muddy and sandy sediments; (b) Lake Constance; (c) Lake Svyatoe, Kostikovichy, Belarus. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Illustration of a simple model for uptake in ®sh via the food chain . . . . . . . . Radiocaesium in ®sh in the Kiev Reservoir after Chernobyl, illustrating the `size e€ect' in predatory perch, but not in the non-predatory roach. . . . . . . . . . . . Relationship between 137 Cs concentration factor in ®sh and the potassium concentration in 17 lakes around Europe. . . . . . . . . . . . . . . . . . . . . . . . . . . Radiocaesium in the Baltic and Black Seas . . . . . . . . . . . . . . . . . . . . . . . . . Nick Beresford live-monitoring a sheep in upland west Cumbria in 1993 to determine Cs-137 activity concentration in muscle . . . . . . . . . . . . . . . . . . . . Decrease in 137 Cs activity concentrations in perch in Lake Svyatoe over a 15year period after a potassium countermeasure was applied . . . . . . . . . . . . . . Variability within the 137 Cs activity concentration of private milk within the Belarussian village . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

117 124 125

140 143 145 147

153 154 155 156

158 161 167 169 171 172 177

196 199 208

xx 6.1 6.2

Figures Increase in thyroid cancer in children (aged 0±18 years at the time of the Chernobyl accident) in Belarus during the period 1986±2002 . . . . . . . . . . . . . Increase in excess thyroid cancer risk in the period 1991±1995 in children born between 1971 and 1986 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

229 230

7.1

Interaction between health, social and economic e€ects. . . . . . . . . . . . . . . . .

241

8.1 8.2 8.3

Area of Red Forest where coniferous trees were killed as a consequence of acute irradiation but deciduous trees continued to grow . . . . . . . . . . . . . . . . . . . . Pripyat sports stadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kestrels nesting on the roof of a tower block, Pripyat . . . . . . . . . . . . . . . . .

268 281 281

9.1 9.2

Rise in world primary energy consumption from 1970±2025 . . . . . . . . . . . . . World consumption of nuclear energy from 1970 and projected future use . . .

301 302

Tables

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10 1.11 1.12 2.1

Con®rmed cases of acute radiation sickness in emergency workers. . . . . . . . . Physical half-lives and amounts of radionuclides released from Chernobyl . . . Estimates of releases of some additional radionuclides compared with 137 Cs . . Main pathways and nuclides contributing to the population exposure after the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiation exposures of di€erent groups after Chernobyl. . . . . . . . . . . . . . . . Population dynamics within abandoned settlements of Belarus in selected years after Chernobyl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of previous major releases of radioactive material to the environment Examples of some measurements of 137 Cs in the environment before the Chernobyl accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Population average doses from natural radiation sources and average dose in various European and North American countries from medical diagnostic procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Doses from various X-ray medical diagnostic procedures . . . . . . . . . . . . . . . Primordial radionuclides and some of their decay products . . . . . . . . . . . . . . Concentrations of natural radioactive potassium in various foodstu€s . . . . . .

Radionuclide resuspension factors from agricultural activity, trac and forest ®res compared with natural wind resuspension. . . . . . . . . . . . . . . . . . . . . . . 2.2 Summary of mean values of rate of decline in 137 Cs activity concentrations in di€erent environmental compartments, and comparison with rate of di€usion of 40 K into the illite lattice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radioiodine Isotope data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of stable iodine concentrations in the environment . . . . . . . . . . . . . . . . . Radiostrontium isotope data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of stable strontium concentrations in the environment . . . . . . . . . . . . . . . Radiocaesium isotope data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of stable caesium concentrations in the environment . . . . . . . . . . . . . . . . Plutonium and americum isotope data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 12 13 20 21 25 26 27 28 28 29 30 52 61 65 67 67 68 69 70 71

xxii 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26

Tables Average ratio of fresh weight : dry weight of various products . . . . . . . . . . . . Illustrative productivities and radiocaesium transfer factors of food products derived from di€erent ecosystem types . . . . . . . . . . . . . . . . . . . . . . . . . . . . Percentage of the total plant contamination from di€erent contamination pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Soil±grass aggregated transfer factor for radiocaesium . . . . . . . . . . . . . . . . . 137 Cs and 90 Sr soil-to-grass aggregated transfer coecient for di€erent soil groups, Bragin, Belarus, 1994±1995. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregated transfer factors of 90 Sr and 137 Cs to various crops . . . . . . . . . . . Recommended factors for radiocaesium to convert CR or Tag values for cereals to values for other crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommended factors for radiostrontium to convert CR or Tag values for cereals to values for other crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recommended transfer coecients for radiocaesium and dry matter feed intake rates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiocaesium transfer coecients to various organs of cows, goats and sheep Examples of radioactivity concentrations in milk and meat of domestic animals in various parts of Europe contaminated by the Chernobyl accident. . . . . . . . Feed±milk transfer coecient following intake of contaminated herbage by cows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ratios of activity concentrations of 90 Sr and 137 Cs in milk products to those in milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimated activity concentrations in milk and beef from a hypothetical pasture located in an area very highly contaminated by transuranium elements . . . . . Estimated activity concentrations of cereals and potatoes grown on hypothetical agricultural land in an area very highly contaminated by transuranium elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Cs in various components of a pine forest, Bourakovka, Chernobyl in 1990. 90 Sr (from weapons tests) in di€erent components of a pine forest in Sweden in 1990. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregated transfer factors of 137 Cs in various species of edible fungi collected in Belarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of mean Tag values for 137 Cs and 90 Sr in fungi in the Bragin district of Belarus, 1994±1995 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparison of concentration ratios of 137 Cs with other radionuclides in understorey vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Range in transfer factors and e€ective ecological half-lives observed in game during the ®rst few years after Chernobyl . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Cs and 90 Sr in game animals in the Bragin district of Belarus, 1994±1995 . . Radiocaesium transfer factors in di€erent parts of trees at Dityatki, 28 km south of Chernobyl during 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agreed CFILs of radionuclides in foods in place in the EC. . . . . . . . . . . . . . Intervention limits for the 137 Cs activity concentration in foodstu€s within Belarus, Russia and the Ukraine as in place in 1999 . . . . . . . . . . . . . . . . . . . Average annual consumption of foodstu€s by the population of a village in Bryansk, Russia, before and after the Chernobyl accident . . . . . . . . . . . . . . . Example of consumption rates of di€erent foodstu€s and the contribution of each foodstu€ to the daily 137 Cs intake, as determined during June/July 1997 in Milyach, the Ukraine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

83 84 87 89 90 92 93 94 95 97 98 100 103 108 108 109 112 113 114 117 118 118 120 121 122 123

Tables 3.27 3.28

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14

5.1 5.2 5.3 5.4

6.1 6.2 6.3 6.4 6.5

Mean e€ective dose in 15 forest units region, Russia . . . . . . . . . . . . . . . . . . 137 Cs transfer factors and illustrations foodstu€s from measurements made in

in the Novozybokov district, Bryansk ............................ of activity concentrations of di€erent the early 1990s . . . . . . . . . . . . . . . . .

Kd values for radiostrontium, radioiodine, radiocaesium and plutonium in freshwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radionuclide levels in the Pripyat River at Chernobyl . . . . . . . . . . . . . . . . . Temporary allowable levels of radionuclides in drinking water in the Ukraine at di€erent times after Chernobyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimates of the initial rate of decline of radionuclides in river water after Chernobyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rates of change in 137 Cs and 90 Sr activity concentrations in di€erent rivers in the medium to long term (1987±2001) after Chernobyl . . . . . . . . . . . . . . . . . Comparison of radiocaesium Kd determined from removal rate measurements with Kd measured in the ®eld or laboratory . . . . . . . . . . . . . . . . . . . . . . . . . Mean 137 Cs and 90 Sr activity concentration in in¯ow streams compared with concentrations in the lake water/outlet of di€erent lakes . . . . . . . . . . . . . . . . Normalised water concentrations of 137 Cs and 90 Sr in various water bodies 4±10 years after fallout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radionuclides in Chernobyl Cooling Pond bed sediments approximately one month after the accident, expressed as a percentage of the total amount in both sediments and water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Typical radionuclide activity concentrations in the most contaminated silty sediments of the Cooling Pond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 Sr concentration factors in freshwater ®sh after Chernobyl . . . . . . . . . . . . . Mean CF of radiocaesium in aquatic plants. . . . . . . . . . . . . . . . . . . . . . . . . Radionuclide CFs in biota of the Dnieper River in June 1986 . . . . . . . . . . . . Radionuclides in marine macroalgae and fallout compared to 137 Cs in July 1986 and August±September 1987 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The reduction achieved in the radiocaesium content of fungi following commonly used cooking procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of the e€ectiveness of di€erent agricultural countermeasures to reduce 137 Cs activity concentrations employed within the fSU . . . . . . . . . . . . Suggested feeding regime for beef cattle at various times prior to slaughter and the e€ect on the activity concentration in meat . . . . . . . . . . . . . . . . . . . . . . Changes in the amount of meat and milk produced by collective farms with 137 Cs activity concentrations in excess of intervention limits . . . . . . . . . . . . . The most critical radiation-induced health e€ects resulting from a radiation exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples of stochastic health e€ects from exposure to radiation . . . . . . . . . . Emergency workers with ARS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distribution of external doses to emergency workers as recorded in the registry of emergency workers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results of studies of the risk of thyroid cancer development following acute

xxiii

125 127

142 146 147 148 150 160 163 164 165 166 173 175 176 178

203 205 205 206

218 219 220 222

xxiv

6.6 6.7 6.8 6.9 6.10 7.1 7.2 7.3

7.4 7.5 7.6 7.7 8.1 8.2 8.3 8.4 8.5 8.6 8.7 9.1 9.2

Tables external radiation from atomic bombs and from radiation therapy at an age of 555 kBq m 2 (15 Ci km 2 ) {

270,000 {

50

`General population of the contaminated territories' ± people living in regions of 137 Cs contamination >37.5 kBq m 2 (1 Ci km 2 ) {

6,400,000

5±16**

* Other studies give a higher number, but the ®gure given here is for those working in and around the reactor during 1986±1987; { population estimate at the time of the accident; ** range in estimates of the average dose. { The authors (Cardis et al., 2001) do not specify the time interval over which these exposures apply. Our interpretation of their source (Balonov et al., 1996) suggests that they are for the period 1986±1995

Introduction External γ dose) (µSv yr-1 per kBq m-2)

22

[Ch. 1 20 18 16 14 12 10 8 6 4 2 0 0

2

4

6

8

Time after accident (years)

Figure 1.15. Change in external gamma dose rate over time after the accident. This data accounts for occupancy of di€erent locations during the day: the dose rate during time spent in the home, for example, is much lower than when working in a contaminated ®eld. Adapted from Balonov et al. (1996).

(see Figure 1.14), nor does it include doses to the emergency workers exposed during the accident (see Table 1.1). External gamma-ray exposures declined signi®cantly over time (Figure 1.15): it was estimated (Balonov et al., 1996) that approximately 60% of the external gamma dose was received during the ®rst 10 years after the accident, with 40% of the dose remaining in the years 1996±2056. This decline in exposure over time is due to radioactive decay and migration of radionuclides into deeper layers of the soil. Doses from ingestion of contaminated food also declined signi®cantly over time as a result of radioactive decay, migration and `®xation' of radiocaesium to the soil, and the implementation of countermeasures (see Chapters 2±5). The relative importance of external and internal doses is strongly dependent on dietary habits and on the soil type on which food products are grown. Using data from Balonov et al. (1996), Figure 1.16 illustrates that on black earth soils (which have the ability to strongly ®x radiocaesium) average doses were dominated by external exposures. In contrast, on turf±podzol soil (where radiocaesium transfer to grass for cattle grazing and agricultural products is high), ingestion doses dominate the average exposures. Note also that high consumption of certain `wild' foods (mushrooms, berries, freshwater ®sh) leads to relatively high ingestion doses (see Chapter 3 for more details). From measurements of the resuspension of contaminated dust (see Chapter 2 for a discussion of resuspension rates), Jacob et al. (1996) estimated inhalation doses from Pu isotopes and 137 Cs. The study focused particularly on tractor drivers who may be exposed to high concentrations of contaminated dust during agricultural work, and concluded that, although there are uncertainties, `with sucient care it can be concluded that even at sites inside the 30-km zone, lifetime doses per year of

1.2 Radiation exposures

Sec. 1.2] Black earth soil

23

Turf-podzol (sandy) soil

Internal dose 33% External dose 67%

Internal dose 74%

External dose 26%

Figure 1.16. Contrasting contributions of internal and external dose rates (in the absence of countermeasures) to overall dose in areas of di€erent soil types, Bryansk Region, Russia. From data in Balonov et al. (1996).

work will hardly exceed . . . 35 mSv e€ective dose for agricultural workers' (Jacob et al., 1996). This implies that doses from inhalation of resuspended material make a negligible contribution to radiation exposures in comparison with external and ingestion doses. 1.2.3

Limiting the long-term dose to the population

In 1988 a plan known as the `350 mSv Concept' was developed to limit the lifetime radiation dose to the populations in the Chernobyl a€ected areas (Belyaev et al., 1996). The aim of this concept was to better de®ne the evacuated areas using more comprehensive information than was available in 1986. The proposal de®ned 350 mSv as the safe lifetime dose to the most exposed people in a particular area. Previously evacuated areas which would give rise to lifetime doses less than 350 mSv could be resettled, while those areas not previously evacuated which could exceed the limit would be evacuated. Although the 350 mSv Concept was not formally adopted by the USSR, it illustrates the thinking behind dose control measures at the time. Following the break-up of the Soviet Union, control of dose limitation fell to the governments of the separate a€ected countries ± the Ukraine, Belarus and Russia. The situation therefore became more complex with, in some cases, di€erent regulatory limits being adopted in the di€erent countries. The general approach, however, was the same for all three countries and was based on the `Chernobyl 1991 Concept' (Belyaev et al., 1996). This concept was based on the following principles (Belyaev et al., 1996): . .

No restrictions or countermeasures need be applied in areas where the annual effective dose in 1991 was less than 1 mSv yr 1 . Where doses were above 1 mSv yr 1 , measures should be put in place to reduce contamination of foodstuffs in order to ensure that the individual effective dose was less than 5 mSv yr 1 and that, over time, maximum doses reduced to 1 mSv yr 1 or less.

24

Introduction

[Ch. 1

.

If necessary more people would be relocated: `Each person living in a contaminated territory shall have the right to make their own decision about continuing to live in the given territory . . . based on unbiased information about the radiation situation, socio-economic and other aspects of life' (Belyaev et al., 1996).

In practice, relocations, compensation for a€ected people and countermeasure applications were largely based on zones of di€erent surface contamination by 137 Cs. These zones, based on curies (Ci) per square kilometre (1 Ci ˆ 3.7  1010 Bq) were de®ned as follows (UNDP/UNICEF, 2002): . . . . . .

1480 kBq m 2 ): zone of obligatory resettlement. Territories adjacent to Chernobyl which were evacuated in 1986±1987. Zone of evacuation or `30-km exclusion zone'.

The zones in which strict radiation controls are in place (>15 Ci km 2 ) cover an area of approximately 7,000 km2 of Belarus, 2,660 km2 of Russia and 1,290 km2 of the Ukraine (De Cort et al., 1998). In 1995, approximately 150,000 people lived in these areas (UNSCEAR, 2000). Currently, it is the policy within the three most a€ected countries of the former Soviet Union (fSU) to implement protective measures where the total (external ‡ internal) dose exceeds 1 mSv y 1 (Balonov et al., 1999; Kenik et al., 1999). 1.2.4

Unof®cial resettlement of the abandoned areas

There are people who are living within settlements which are ocially abandoned in all three a€ected fSU countries. Information concerning the population dynamics and radiation exposures of these people was summarised in Beresford and Wright (1999). Some of the resettlers have returned to where they used to live, whereas, others who did not previously live in the area have decided to settle. In Russia, a large proportion of people unocially living within abandoned settlements (in 1999) were ethnic Russians originating from Asian republics of the fSU. Changes in the populations of abandoned settlements within Belarus are presented in Table 1.6. Following the initial reduction in population there is no apparent trend. The population of abandoned areas of the Ovruch, Narodichi and Polesskoje regions of the Ukraine in 1998 was 5,534, approximately 13% of whom were children below the age of 14 (Ukrainian Institute of Agricultural Radiology, unpublished). There are

1.3 Chernobyl in context 25

Sec. 1.3]

Table 1.6. Population dynamics within abandoned settlements of Belarus* in selected years after Chernobyl. From Beresford and Wright (1999).

Region

1986

1987

1988

1989

1990

1991

1992

1994

1996

1998

Gomel Mogilev

44,457 9,578

19,614 n/a

17,923 n/a

18,084 8,567

17,627 n/a

7,076 3,112

2,836 1,133

1,947 ,31

1,703 , 15

1,769 n/a

* Collated from the annual census data of the State Committee on Analysis and Statistics of Republic of Belarus, Minsk. n/a ± not available.

also a number of settlements unocially inhabited within the 30-km exclusion zone (in addition to the town of Chernobyl which provides temporary accommodation for people ocially working within the zone). The inhabited settlements within the 30km zone are in the relatively less contaminated southern area. 1.3 1.3.1

CHERNOBYL IN CONTEXT Previous radioactive releases to the environment

The Chernobyl accident was on a much greater scale than previous accidental releases of radioactivity to the environment. The largest nuclear accident prior to Chernobyl was the explosion in 1957 of a high-level waste tank at the Mayak plutonium production and reprocessing facility in Siberia. Releases of a mixture of radionuclides, including long-lived 90 Sr (with a physical half-life of 28 yr) resulted in evacuation and removal from agricultural production of approximately 1,000 km2 of land. By 1997, 82% of this land had been reclaimed (Joint Norwegian±Russian Expert Group, 1997). Releases from Mayak, and other previous releases of radioactivity to the environment, are summarised in Table 1.7. Following the 1957 ®re at the Windscale nuclear reactor in the UK, a ban on the consumption of milk because of high 131 I activity concentrations was implemented over an area extending to a maximum of 518 km2 (Jackson and Jones, 1991). It is probable that, at present-day intervention levels, temporary precautionary bans on foodstu€s, including meat and milk, would also have been implemented as a consequence of radiocaesium contamination (Wright et al., 2003). This may also have been the case for some food products in some areas as a consequence of fallout from the atmospheric nuclear weapons testing era (predominantly 1952±1963). The accident at Three Mile Island in the USA did not result in signi®cant contamination of the environment and food chain; the highest activity concentration in a food product determined in a sample of goats milk was only 1.5 Bq l 1 of 131 I, collected 2 km from the site (Katherine, 1984). Nuclear weapons explosions have also released radioactivity into the environment. Long-term environmental contamination from the Hiroshima and Nagasaki bombs was not signi®cant: the high-radiation doses to survivors came primarily from

26

Introduction

[Ch. 1

Table 1.7. Summary of previous major releases of radioactive material to the environment. Note that the summary is not comprehensive, and only data for three radionuclides are presented. These release data should not be interpreted in terms of signi®cance of the releases to environmental or human health: the impact of radionuclide releases is not solely determined by the amount of radioactivity released. Release of some key radionuclides to the environment (PBq) 137

90

131

Release event

Area*

Chernobyl, 1986a

Signi®cant part of Europe

85

Hiroshima atomic bomb, 1945{b

Few km radius around epicentre

0.1

Atmospheric nuclear weapons testing, 1952±1981**c

Global, primarily northern hemisphere

949

578

USA atmospheric weapons tests, Nevada Test Site**d

USA states, particularly Nevada

**

**

5,550 released to atmosphere, 1,390 deposited to ground

Three Mile Island, USAe

No signi®cant environmental contamination

±

±

Negligible

Mayak, discharges to the Techa River, 1949±1956f

Techa and Ob rivers

13

12

±

Mayak accident, 1957f

Approximately 300 km  50 km area of Siberia

40

±

Waste discharges from Sella®eld, 1964±1992g

Irish Sea

6

±

Windscale accident, 1957g

518 km2 area of northern England

Cs

0.3

41

0.022

Sr

10

1,760

0.085

7:4  10

I

52 **

5

0.74

{ Note that the radiation health effects of the Hiroshima and Nagasaki bombs resulted primarily from gamma and neutron radiation from the initial explosion. Radioactive fallout to the environment (detailed here for Hiroshima) was minor in comparison. * Indicative area only ± the contaminated area depends on how you de®ne `contaminated'. ** 131 I data is given for the US atmospheric weapons tests only: 137 Cs and 90 Sr data are global totals for the period 1952±1981. a From UNSCEAR (2000), see Table 1.2; b Gudiksen et al. (1989); c Cambray et al. (1989); d NCI (1997); e Katherine (1984); f NATO (1998); g Gray et al. (1995).

1.3 Chernobyl in context 27

Sec. 1.3]

Table 1.8. Examples of some measurements of 137 Cs in the environment before the Chernobyl accident. 137

Product

Cs activity concentration (Bq kg 1 )

Notes

Root crops Barley

0.5±2 d.w.* 90% organic matter) at Devoke Water, UK is signi®cantly more disperse than in the unsaturated mineral soils. Modelling of 137 Cs activity±depth pro®les in saturated peats (Smith et al., 1995; Kudelsky et al., 1996) has shown that its vertical migration is consistent with rates of di€usion in the solution phase. In these saturated systems, the soilwater distribution coecient (Kd ) values are relatively low (of order 103 l kg 1 ) (Kudelsky et al., 1996) compared with unsaturated soils, so a much greater proportion of radiocaesium di€uses in the aqueous phase. Such behaviour was observed after NWT fallout: at peat soil sites across the UK, Cawse and Baker (1990) reported that about 50% of 137 Cs deposited from NWT had been lost over a period of 20 years as a consequence of water ¯ow and lack of clay minerals.

46

Radioactive fallout and environmental transfers

[Ch. 2

In unsaturated, mineral soils, long-term vertical migration is believed to be primarily due to the movement of radioactivity attached to soil particles rather than by di€usion in solution (Anspaugh et al., 2002). MuÈller-Lemans and van Dorp (1996) argue that the bioturbation of soil by earthworms can signi®cantly redistribute radionuclides in the topsoil. These workers estimate that `in grasslands it will take around 5±20 years for the earthworms to turn over the topsoil once, resulting in an intensive and more or less homogeneous mixing'. Most earthworm activity is in the soil surface to a depth of 10 or 20 cm, though some species can be found at depths of up to 3 m (MuÈller-Lemans and van Dorp, 1996). It was shown for unsaturated soils that, given even relatively low binding of a radionuclide to soil particles, advection and dispersion of radionuclides in soil water would play a minor role in their long-term redistribution in comparison to bioturbation (MuÈller-Lemans and van Dorp, 1996). In summary, the available empirical evidence suggests a relatively rapid in®ltration of radionuclides into the soil during and shortly after deposition. This is likely to have depended in a complex way on initial environmental and soil conditions at the time of fallout. During the ®rst year after Chernobyl, the vast majority of the radioactivity was observed within the surface (top 5-cm layer or less) of the soil. Following this initial period, there was a long-term redistribution of radionuclides in the soil, though the majority of radioactivity is expected to remain in the top 0±15-cm layer (and therefore potentially available for root uptake by plants) for long periods (decades) after fallout. In unsaturated mineral soils, where long-lived radionuclides (e.g., 134;137 Cs, 237 Np, 239‡240 Pu and 241 Am) are strongly bound to soil particles, bioturbation is believed to be the key transport mechanism. In saturated, highly organic soils, redistribution by advection and dispersion in solution has been found to be important for radiocaesium. In some peat and sandy soils, radiostrontium was observed to be relatively mobile, with signi®cant quantities observed at depths of around 50 cm. 2.2.3

Change in external dose rate over time

Radioactive decay and the migration of radioactivity in the soil signi®cantly reduces the external dose rate over time after deposition. As was shown in Chapter 1 (Figure 1.15), the external dose to the population declined by more than an order of magnitude from late 1986 to 1993. This was mainly due to the physical decay of relatively short-lived radionuclides such as 106 Ru and 134 Cs. After this period, 137 Cs formed the major part of the external dose, so declines in external dose (due to physical decay and vertical migration) were relatively slow. Measurements of external dose in a number of di€erent locations in Belarus (Timms et al., 2004) during the year 2000 showed a very strong correlation between external dose rate and radiocaesium inventory in the soil (Figure 2.6). The observed relationship was: Dose …mSv hr 1 † ˆ 1:14D …2:4† where D is the deposition (inventory) of

137

Cs in the soil in MBq per square metre.

2.2 Environmental transfers of radionuclides

Sec. 2.2]

47

4.5

External dose (µSv hr-1)

4 3.5 2

R = 0.98

3 2.5 2 1.5 1 0.5 0 0

1 137

2

3

4 -2

Cs inventory in soil (MBq m )

Figure 2.6. External dose rate 0.05 m above the ground as a function of 137 Cs inventory in the soil. From Timms et al. (2004).

The dose was measured at 0.05 m above the ground: dose measured at a height of 1 m was approximately 80% of the value at 0.05 m. Note that this relationship and Figure 2.6 are for observed external dose rates above soils ± they do not represent average external doses received by people, since they do not account for occupancy factors (i.e., proportion of time spent in a contaminated area, see Figures 1.15 and 2.7). The strong correlation between external dose rate and soil 137 Cs inventory indicates that, for the sites studied, di€erent vertical migration rates played only a minor role in in¯uencing external dose rate. Using estimates of the long-term migration of radiocaesium, Balonov et al. (1995) and Jacob et al. (1996) calculated the average annual dose to various population groups in rural areas of Ukraine, Belarus and Russia. Doses per unit of deposition were approximately 25% higher relatively close to the Chernobyl NPP ( carrot, potato > cereals, onion (Paasikallio et al., 1994). There is wide variation between radionuclide accumulation in crops according to soil characteristics and agricultural practices. Analysis of a large database on the accumulation of radiocaesium in various crops (Frissel et al., 2002), however, showed that `it was clear that if the uptake for a speci®c soil system was relatively high for one crop, it was high for all crops, or if it was low for one crop, it was low for all crops'. On the basis of this observation, the authors developed a system of conversion factors which allow transfer factors or CRs for di€erent crop groups to be calculated if the transfer factor or CR for one crop group is known. The developed system is based on cereals: if the Tag or CR is known (or can be estimated) for cereals, the Tag or CR for other crops can be estimated by multiplying by the conversion factors given in Table 3.7 (reproduced from Frissel et al., 2002). For systems in which the transfer factor to cereals is not known, Frissel et al. (2002) give recommended values for generic soil types and conditions. Note that Table 3.7 implies greater accumulation of 137 Cs in potatoes than in cereals, in contrast to ®ndings in Ukrainian, Belarussian and Russian systems, but in agreement with studies in Finland (Paasikallio et al., 1994). This again may be due to the fact that transfer factors for potatoes in the Ukraine, Belarus and Russia are commonly presented per unit fresh weight, whereas the ratios in Table 3.7 and in the Finnish study are based on dry weights of crops. The CF for potatoes (tubers) on a fresh weight basis would be approximately 5 times lower than the value for dry weight presented in Table 3.7.

92

Radioactivity in terrestrial ecosystems

[Ch. 3

Table 3.6. Aggregated transfer factors of 90 Sr and 137 Cs to various crops. Tag for cereals and rape are on a dry weight basis, for potato and other vegetables fresh weight is used. Crop

Time period

Tag (10

3

m2 kg 1 ) 90

Notes

Reference

Sr

Cereal grain

1994

0.7{

Bragin region, Belarus

(1)

Potato

1994 1993

0.06{ 0.056±0.095* 0.068±0.176*

Bragin region, Belarus Collective farm, Russia Private farm, Russia

(1) (2) (2)

137

Cs

Cereal grain

1994 1992±1994 1993 1992±1994

0.1 0.2±1.3 0.005 0.11** 0.03

Bragin region, Belarus Bryansk region, Russia Central Europe Sweden, peat soil Sweden, sandy loam

(1) (3) (4) (5) (5)

Potato

1994 1992±1994 1993 1993

0.05 0.03±0.05 0.0075 0.028±0.034 0.019±0.05

Bragin region, Belarus Bryansk region, Russia Central Europe Collective farm, Russia Private farm, Russia

(1) (3) (4) (2) (2)

Vegetables

1993

0.0035

Central Europe

(4)

Oilseed rape

1992±1994

0.55**

Sweden, peat soil

(5)

{

The in¯uence of fuel particles on 90 Sr CFs is expected to be minor at this time after the accident (see Chapter 2). * Negligible in¯uence of fuel particles. ** Mean value estimated from data given for a number of farms in RoseÂn et al. (1996). (1) Zhuchenko et al. (2002); (2) Korobova et al. (1998); (3) Alexakhin et al. (1996); (4) MuÈck (2003); (5) RoseÂn et al. (1996).

In the study in Finland discussed above (Paasikallio et al., 1994), CR values for Sr were generally signi®cantly higher than for 137 Cs (Figure 3.3) and varied signi®cantly between di€erent soil groups. 90 Sr CRs in organic soils were approximately 5 times lower than in mineral soils (Paasikallio et al., 1994). Di€erent crop types exhibit di€ering accumulation of 90 Sr, even given the same soil conditions. Conversion factors relating radiostrontium Tag and CR for cereals to values for other crops were estimated by Frissel (2001), as shown in Table 3.8. In contrast to these estimates, the 90 Sr values estimated for the Ukraine, Belarus and Russia (Table 3.6), as with 137 Cs, showed a much lower Tag for potatoes (tubers) than cereals. This is again likely to be due to the fact that transfer factors for potatoes in the Ukraine, Belarus and Russia are presented per unit fresh weight, whereas the ratios here are based on dry weights of crops. The ratios in Table 3.8 broadly agree with di€erences in CR shown in the Finnish study (Figure 3.3; 90

3.2 Agricultural ecosystems

Sec. 3.2] 10

93

Cs-137

Concentration ratio

Sr-90 1

0.1

0.01

Figure 3.3. CR (dry mass basis) of silt soils, 1987.

90

Sr and

137

ni on O

ls er ea C

Po

ta to

t ar ro C

C

Le

ab ba

ttu

ge

ce

0.001

Cs in various vegetables in Finland, clay and

From data in Paasikallio et al. (1994).

Table 3.7. Recommended factors for radiocaesium to convert CR or Tag values (dry weight basis) for cereals to values for other crops. From Frissel et al. (2002).

Radiocaesium Conversion factor Range

Green Legumes Cereals Cabbage veg. (pods)

Root Fodder Tubers crops Grass crops Fruita Onions

1

7

9

5

4

3

4.5b

3±11

4±14

1±11

1±7

1±5

1±10

4

5

1

Frissel et al. (2002) note that: a `the use of one factor for fruit is a simpli®cation; it may have to be split into fruit categories'; b for application to Tag rather than CR, the conversion for grass is 9 instead of 4.5 because of an assumed rooting depth for grass of 10 cm (cf. 20 cm for crops). Frissel et al. (2002) further note that `the conversion factor of Cs for tea, herbs of woody species, leaves of trees and new wood seems to be about 20'.

Paasikallio et al., 1994) though in the latter, onions show much lower uptake than other crops. It is clear from the large ranges in values given in Table 3.8, that there is signi®cant variation around the recommended values. 3.2.3

Transfers to animal-derived food products

In the most a€ected areas of the Ukraine, Belarus and Russia, milk and (to a lesser extent) meat are the main contributors to an internal dose from agricultural systems (Alexakhin et al., 1996). Ingestion of contaminated feed by farm animals results in transfers of radionuclides to meat and dairy products. Though inhalation of airborne radionuclides is also a potential uptake pathway, it is of minor signi®cance in

94

Radioactivity in terrestrial ecosystems

[Ch. 3

Table 3.8. Recommended factors for radiostrontium to convert CR or Tag values (dry weight basis) for cereals to values for other crops. From Frissel (2001).

Radiostrontium Conversion factor Range

Green Legumes Cereals Cabbage veg.a (pods)

Root Tubers crops Grass Fodder Fruitb Onion

1

1

12 2.5±79

10

5

7

5

4

2

7

2.6±71

Frissel (2001) note that: a `values for spinach are usually higher than for other vegetables'; b `the use of one factor for fruit is a simpli®cation; it may have to be split into fruit categories'.

comparison with ingestion. Following ingestion, radionuclides may be absorbed via the gastrointestinal tract and transferred to various organs via the blood. The transfer of radionuclides from an animal's diet to milk or meat is most often expressed as the equilibrium transfer coecient (Ff or Fm for meat or milk respectively, units: d kg 1 ), de®ned as the ratio of the activity concentration in a tissue to the rate of radionuclide ingestion: Ff …or Fm † ˆ or

Activity concentration in tissue …or milk† …Bq kg 1 † Cf …m† ˆ Cv If Radionuclide ingestion rate …Bq d 1 † Cf …m† ˆ Ff …m† Cv If

…3:5† …3:6†

1

where Cf is the activity concentration in the tissue (Bq kg , fresh weight) (Cm for milk), Cv is the activity concentration in vegetation (i.e., feed, Bq kg 1 , dry matter) and If (kg d 1 , dry matter) is the feed intake rate. Thus, the activity concentration of the radionuclide in meat or milk may be predicted using the transfer coecient and the daily radionuclide ingestion rate. Table 3.9 presents transfer coecients for radiocaesium as advised for a range of animal-derived food products (IAEA, 1994). These imply, for animals ingesting the same amount of radiocaesium daily, that the radiocaesium activity concentration in meat will be higher than that in milk or eggs. The lower CR of radiocaesium in milk and eggs mirrors the lower potassium concentration in these foodstu€s in comparison to meat (Table 3.9). It can also be seen that radiocaesium transfer coecients generally decrease with increasing animal mass (and consequently dry matter intake). However, this does not necessarily imply that radionuclide transfer to larger animals is less ecient. If we rearrange Equation 3.6 in terms of the equilibrium CR (kg kg 1 ), the ratio of activity concentration in tissue (fresh weight) to that in feed, then: CR ˆ

Activity concentration in tissue …or milk† …Bq kg 1 † Cf …m† ˆ ˆ Ff …m† If …3:7† Cv Activity concentration in feed …Bq kg 1 †

Equation 3.7 implies that, unless CR changes in inverse proportion to dry matter intake, then the transfer coecient would be expected to decrease with increasing dry

3.2 Agricultural ecosystems

Sec. 3.2]

95

Table 3.9. Recommended transfer coef®cients for radiocaesium and dry matter feed intake rates. These are used to calculate typical radiocaesium CRs (see Equation 3.7) for various animal products. Typical potassium concentrations of these products are also shown. From IAEA (1994).

Foodstuff

Feed ingestion Transfer coef®cient rate by animal If Ff or Fm (kg d 1 ) (d kg 1 )

Milk Cow Goat Sheep

16.1 1.3 1.3

Meat Beef Lamb Pork Chicken

7.2 1.1 2.4 0.07

Eggs Hen

0.1

7.9  10 0.1 5.8  10 5  10 0.49 0.24 10 0.4

2

3 2

CR (dimensionless)

Typical potassium concentration (mg kg 1 )

0.13 0.13 0.075

1,430 1,930 1,370

0.36 0.54 0.58 0.7

3,040 3,060 3,765 2,570

0.04

1,260

matter ingestion rate. The transfer coecient is not a measure of any one process but an amalgam of processes including absorption and tissue turnover rates: radiocaesium absorption from feed does not appear to be in¯uenced by animal size. Using advised feeding rate values (IAEA, 1994), Table 3.9 also presents estimated CR values: these can be seen to vary considerably less between species than transfer coecients. Thus, for example, the observation that chickens tend to have much higher Ff values than cows (IAEA, 1994) may primarily be because their dry matter intake rate is much lower. Therefore, the apparent di€erences in transfer between animals of di€erent size (which may be implied by di€erent Ff ) are largely a consequence of the method of calculation of the transfer coecient. A comparison of potassium concentrations in Table 3.9 further demonstrates that the large di€erences in radiocaesium uptake between animals which are sometimes implied by the use of transfer coecients are a consequence of the method of their calculation. Another study on individual species has demonstrated that the transfer coecient of radiocaesium to sheep tissues decreases with increasing dry matter intake (Beresford et al., 2002a) Beresford (2003) has hypothesised that CR should be a constant for a range of radionuclides across animal species. It should also be acknowledged, however, that other authors have reported that estimation of transfer as Ff rather than CR reduced variability within study groups of animals of the same species (Ward et al., 1965); this being the initial justi®cation for using transfer coecients rather than the CR. The transfer of radiostrontium to milk is strongly in¯uenced by the amount of calcium in the diet. Studies prior to the Chernobyl accident (Comar, 1966) showed

96

Radioactivity in terrestrial ecosystems 0

50

100

[Ch. 3 150

200

250

300

350

1.E-01 Goat Cattle Sheep Predicted 2.6 g/kg Ca Predicted 1 g/kg Ca

FmSr

1.E-02

1.E-03

1.E-04 -1

Dietary calcium intake (g d )

Figure 3.4. Comparison between calcium intake and Fm for strontium  with additional recent data for cattle { . The lines represent predicted values from Equation 3.9 based upon calcium contents in milk of 1 g kg 1 (typical for cattle) and 2.6 g kg 1 (typical for sheep). 

Adapted from Beresford et al. (1998). { From Beresford et al. (2000a).

that the radiostrontium feed±milk transfer coecient Fm was proportional to the feed±milk transfer coecient of calcium: Fm ˆ

‰SrŠmilk ‰CaŠmilk ˆ OR ISr ICa

…3:8†

where ISr is the ingestion rate (Bq d 1 ) of 90 Sr, ICa is the ingestion rate (g d 1 ) of calcium and ‰SrŠmilk and ‰CaŠmilk are the concentrations of Sr and Ca in milk in units of Bq l 1 and g l 1 respectively. OR is the `observed ratio', an empirically determined coecent with mean value 0.11 and range 0.03±0.4 (Howard et al., 1997) for cow milk. The fact that OR is less than 1.0 implies that calcium is preferentially transferred to milk compared to strontium. Since the calcium concentration in cow milk varies within a relatively narrow range, and assuming an average OR value of 0.11, Howard et al. (1997) obtained the following relationship between Fm of strontium in cows and dietary calcium intake: 0:127 Fm ˆ …3:9† ICa Predictions using this model were in good agreement with empirical observations, as shown in Figure 3.4 which also expands the comparison to sheep and goat milk. In contrast to radiostrontium, there is little evidence that the uptake of radiocaesium to milk is signi®cantly in¯uenced by the amount of its competitor ion (potassium) in the diet. As with humans, uptake and retention of 131 I in animals is dependent on dietary stable iodine intake. Iodine is an important trace element required by the thyroid for hormone synthesis, and the metabolism and excretion of radioiodine is controlled by the individual's stable iodine status. Absorption of radioiodine in the gut is complete,

3.2 Agricultural ecosystems

Sec. 3.2]

97

regardless of dietary iodine intake rates, and there is a subsequent rapid transfer to the thyroid and milk (Beresford et al., 2000b). As the stable dietary iodine increases, the proportion of the daily radioiodine intake which is transferred to the thyroid declines because of the constant rate of uptake of iodine by the thyroid. Thus, a smaller fraction of the daily iodine intake (stable iodine and radioiodine isotopes) is transferred to the thyroid and the proportion available for transfer to the mammary gland increases. At high stable iodine daily intakes, this e€ect is o€set by the saturation of the transfer from plasma to milk (Crout et al., 2000). This was demonstrated in a study in which goats fed 0.5 mg of stable iodine six hours before being fed 131 I had approximately 50% less radioiodine in their milk than under normal conditions (Crout et al., 2000). In another study, cows given di€erent levels of stable iodine in their diet (from 4 to 75 mg d 1 ) showed only a marginal di€erence in the 131 I transfer coecient to milk (Vandecasteele et al., 2000).

Distribution of radioactivity within the animal Studies of radiocaesium in various organs of cows, goats and sheep (Table 3.10) showed similar transfer coecients in muscle and most internal organs, with slightly elevated levels in the kidney and signi®cantly lower levels in the blood, brain and fat. Whilst radiocaesium is relatively evenly distributed throughout most organs of the animal, other radionuclides may be concentrated in particular tissues. As is the case with humans, radioiodine is strongly concentrated in the thyroid of animals: Kirchner (1994) quotes studies showing that `between 10% and 50% of the 131 I ingested by a cow accumulates in the thyroid'. Again, as with humans, radiostrontium is accumulated in the bones of animals and is only released from bone at a slow rate (although this is dependent on the calcium status of the animal). Table 3.10. Radiocaesium transfer coef®cients{ (calculated using fresh weight of tissue) to various organs of cows, goats and sheep. From Assimakopoulos et al. (1995).

Compartment

Cows (d kg 1 †

Whole blood Blood cells Muscle Lung Liver Kidney Heart Brain Gut Fat

1.9  10 2.0  10 22  10 3 24  10 3 28  10 3 47  10 3 31  10 3 7.7  10 13  10 3 2.3  10

3 3

3 3

Goats (d kg 1 † 5.2  10 6.8  10 84  10 2 51  10 2 53  10 2 89  10 2 64  10 2 33  10 2 50  10 2 10  10 2

2 2

Sheep (d kg 1 † 3.1  10 3.5  10 71  10 2 41  10 2 56  10 2 96  10 2 53  10 2 23  10 2 34  10 2 7.4  10

2 2

2

{ Data are averages of 6 lactating and non-lactating animals fed with contaminated hay at Pripyat, close to Chernobyl. Standard errors were less than 20% of the mean.

98

Radioactivity in terrestrial ecosystems

[Ch. 3

Table 3.11. Examples of radioactivity concentrations in milk and meat of domestic animals in various parts of Europe contaminated by the Chernobyl accident. { Activity concentration (Bq kg 1 ) Notes

Radionuclide Date

Cow milk (f.w.) 90

Sr

131

I*

137

Cs

1993

210

May 1986 May 1986 May 1986 May 1986 May 1986 July 1986 1987 1993

250 870 300 (max.) 250 180 Most