Report of the Committee Examining Radiation Risks of Internal Emitters (CERRIE)
Total Page:16
File Type:pdf, Size:1020Kb
Report of the Committee Examining Radiation Risks Internal Emitters (CERRIE) Report of the Committee Examining Radiation Risks of Internal Emitters (CERRIE) Further copies available from: National Radiological Protection Board Chilton Didcot Oxon OX11 0RQ ISBN 0-85951-545-1 Report of the Committee Examining Radiation Risks of Internal Emitters (CERRIE) Chairman Professor Dudley Goodhead OBE Members Mr Richard Bramhall Dr Chris Busby Dr Roger Cox Professor Sarah Darby Dr Philip Day Dr John Harrison Dr Colin Muirhead Mr Peter Roche Professor Jack Simmons Dr Richard Wakeford Professor Eric Wright Secretariat Dr Ian Fairlie Mr Paul Dorfman © Crown Copyright 2004 Produced by the Committee Examining Radiation Risks of Internal Emitters, London www.cerrie.org ISBN 0-85951-545-1 October 2004 Preface In July 2001, the then Environment Minister, Michael Meacher MP, announced the establishment of a group with the remit “to consider present risk models for radiation and health that apply to exposure to radiation from internal radionuclides in the light of recent studies and to identify any further research that may be needed”. The Committee thus formed, commenced its work in December 2001 and has held 16 meetings, during which it examined evidence from radiobiology and epidemiology. In June 2003, the Committee prepared a Preliminary Report that was considered by a Workshop of invited delegates in Oxford in July 2003. This final Report has been published and sent to the Committee on Medical Aspects of Radiation in the Environment (COMARE) for its consideration. It is expected that COMARE will wish to inform Ministers of its views on the Report. Contents Preface iii 1 Introduction 1 1.1 Background 1 1.2 Format 3 1.3 Consensus Aim of the Committee 4 1.4 Dissenting Views 5 2 Risks from Internal Emitters 6 Part 1 6 Introduction 6 What Are Internal Emitters? 6 How Are Radiation Risks Estimated? 7 How Do We Quantify Radiation? 8 Uncertainties in Current Risk Estimates 9 Uncertainties in External Radiation Risks 9 Uncertainties in Internal Radiation Risks 10 Part 2 11 2.1 Introduction 11 2.2 Relative Biological Effectiveness 14 2.3 Risk Estimates 17 2.4 Biokinetic Models 21 2.5 Dosimetric Models 22 2.6 ICRP Dose Coefficients 23 2.7 Uncertainties 25 2.8 Conclusions 29 ANNEX 2A Microdosimetric Considerations 32 Introduction 32 ‘Proportional-counter’ Microdosimetry 33 Hit Frequencies 34 ANNEX 2B Tritium Doses and Risks 35 Introduction 35 ICRP Dose Coefficients 36 Adequacy of ICRP Dose Coefficients 36 Tritiated DNA Precursors 37 Conclusions 37 v Contents ANNEX 2C Auger Emitter Doses and Risks 39 Significant Auger Emitters 40 Conclusions 40 ANNEX 2D Alpha Emitter Doses and Risks 42 Introduction 42 Heterogeneous Dose from Alpha Emitters 42 Transfer of Inhaled Particles to the Fetus 43 Conclusions 44 3 Biological Evidence 45 3.1 Introduction 45 3.2 Genomic Instability 45 3.3 Bystander Effects 45 3.4 Minisatellite Mutations 46 3.5 Implications for Radiological Protection 47 3.6 Carcinogenic Risks of Particulates 48 3.7 Dose Thresholds for Cancer Risk 49 3.8 Second Event Theory 50 3.9 Biphasic (Bimodal) Dose–response Relationships 52 3.10 Artificial versus Natural Radionuclides 52 3.11 Conclusions 52 3.12 Specific Recommendation for Biological Research 54 ANNEX 3A Biophysical and Biological Aspects of the Second Event Theory 55 Recalculation of SET Probabilities for 90Sr–90Y Decays and Consideration of 132Te–132I Decays 56 Review of the Biological Plausibility of the SET and Other Relevant Radiobiological Data 57 Calculation of Second Event Probabilities for Plutonium Oxide Particles 57 Biological Data Relevant to the SET 58 Mitotic Activation of G0/G1 Cells by Ionising Radiation 58 Extreme Radiosensitivity in G2 Phase 58 Binding of 90Sr to Cellular DNA 59 ANNEX 3B Minisatellite DNA Mutations in Germ Cells 60 Human Data 60 Mouse Data 60 Current Estimates of Human Genetic Risks from Radiation 62 4 Epidemiological Evidence 63 4.1 Introduction 63 4.2 Possible Dose–response Relationships 65 4.3 Radon, Radium and Thorotrast 66 vi Contents 4.4 Exposure to Radioactive Fallout 66 4.4.1 After Chernobyl 66 Infant Leukaemia 67 Mainland Europe 67 United States of America 67 Great Britain 67 Summary 68 Childhood Leukaemia 68 Childhood Thyroid Cancer 69 Other Cancers 69 4.4.2 Exposures from Atmospheric Nuclear Weapons Testing 70 United States of America 70 Nordic Countries 71 Great Britain 71 Summary 72 Conclusion 72 4.5 Cancer Rates in Areas near Nuclear sites and in Coastal and Estuarine Areas 73 4.5.1 Cancer Rates in Areas near Nuclear Sites 73 Sellafield and Dounreay 73 Other Nuclear Sites 74 4.5.2 Cancer Rates in Coastal and Estuarine Areas in Great Britain 74 4.5.3 Conclusion 76 4.6 Nuclear Industry Workers and Their Children 76 4.7 Non-cancer Effects 77 4.8 Conclusions on Epidemiological Evidence 78 4.9 Recommendations on Future Epidemiological Studies 79 ANNEX 4A Post-Chernobyl Epidemiology 82 Mainland Europe and USA 82 Great Britain 84 Comparison of Findings 88 ANNEX 4B Weapons Test Fallout Epidemiology 89 Nordic Countries 89 USA 95 Great Britain 96 ANNEX 4C Epidemiological Studies of UK Coastal and Estuarine Areas 100 Studies around Nuclear Installations 100 Hinkley Point 100 Bradwell 100 Studies of Coastal and Estuarine Areas 101 Wales 101 Leukaemia Research Fund Analyses 102 vii Contents ANNEX 4D Sir Austin Bradford Hill’s Tests of Causality 105 ANNEX 4E P-values and Confidence Intervals 110 ANNEX 4F Statistical Power 112 5 Conclusions 113 From Chapter 2 on Risks of Internal Emitters 113 From Annex 2B on Tritium 115 From Annex 2C on Auger Emitters 116 From Annex 2D on Alpha Emitters 116 From Chapter 3 on Biological Evidence 116 From Chapter 4 on Epidemiological Evidence 117 6 Recommendations 119 From Chapter 2 on Risks of Internal Emitters and Chapter 3 on Biological Evidence 119 From Chapter 4 on Epidemiological Studies 120 General Recommendations 120 Specific Recommendations 120 References 122 Appendix A Abbreviations and Acronyms 139 Appendix B Report of CERRIE Workshop, July 2003 141 CERRIE Workshop Participants 147 Tables and Figures Table 2C.1 Calculated ratio of dose to the nucleus 39 Table 2C.2 Occurrence and physical characteristics of Auger emitters (from Bingham et al, 2000; with addition of 137mBa) 41 Table 3A.1 Second event probabilities for decay of 90Sr and 132Te 56 Table 4A.1 Infant leukaemia following the Chernobyl accident by birth cohort 82 Table 4A.2 Leukaemia incidence in young children (1–3 or 1–4 years of age) following the Chernobyl accident, by birth cohort 83 Table 4A.3 Leukaemia incidence in infants and children (0–14 years of age) following the Chernobyl accident, by dose category, in ECLIS (Parkin et al, 1996) 83 Table 4A.4 Infant leukaemia in Great Britain, by birth cohort (using the Petridou et al definition of periods of birth) and geographical region 86 Table 4A.5 Infant leukaemia in Great Britain, by birth cohort (using the CERRIE definition of periods of birth) and geographical region 87 Table 4A.6 Excess relative risks of infant leukaemia estimated in four birth cohort studies 88 viii Contents Table 4B.1 Classification of calendar years by bone marrow dose equivalent for fetus or 1 year old and by testis dose equivalent for adult, as used by Darby et al (1992) 93 Table 4B.2 Relative risk of childhood leukaemia incidence in Nordic countries for categories of exposure to weapons fallout 95 Table 4B.3 Leukaemia death and registration rates per 100,000 persons per year in wet and dry regions of Great Britain, based on post-natal dose equivalent to red bone marrow (Haynes and Bentham, 1995) 96 Table 4C.1 Summary of results of the studies of Alexander et al (1990) and Lloyd et al (2002) 102 Figure 2.1 Possible dose–response curves describing the excess risk of stochastic health effects at low doses of radiation 19 Figure 4A.1 Rate of incidence of infant (<1 year of age) leukaemia in Great Britain by three periods of birth and by three areas of birth, categorised by the level of Chernobyl contamination (see Table 4A.4). Error bars show 95% confidence intervals on rates 85 Figure 4A.2 Rate of incidence of infant (<1 year of age) leukaemia in Great Britain by four periods of birth and by three areas of birth, categorised by the level of Chernobyl contamination (see Table 4A.5). Error bars show 95% confidence intervals on rates 85 Figure 4B.1 Average annual effective dose in the Northern Hemisphere from radionuclides produced in atmospheric nuclear weapons testing (UNSCEAR, 2000) 90 Figure 4B.2 Incidence rate of all leukaemias among children aged 0–4 years, 1950–1990. Incidence data from eight cancer registries. Error bars show 95% confidence intervals on rates 91 Figure 4B.3 Leukaemia incidence in Denmark, ages 0–4 years, by year of birth. Line A shows the recorded number of cases by year of birth (the average, 26, ±2 x standard deviation are shown as dashed lines); line B shows the number of cases standardised to a population of 100,000 92 Figure 4B.4 Annual rate of incidence of all leukaemias among infants (<1 year of age) in Denmark, Norway, Finland and Sweden, by year of diagnosis, 1948–1987 94 Figure 4B.5 Annual rate of incidence of all leukaemias among young children (1–4 years of age) in Great Britain and the Nordic countries, by year of diagnosis, 1948–1997. Solid lines show linear temporal trends of annual incidence rates 97 Figure 4B.6 Annual rate of incidence of all leukaemias among infants (<1 year of age) in Great Britain, by year of diagnosis, 1953–1997.