Health Risks of Ionizing Radiation: - Clark University

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in a linear-quadratic curve (Figure 1-6, curve C). In this case the linear term predominates at lower doses and the quadratic term predominates at higher doses. This model has been applied to some types of leukemia in the atomic bomb survivors, for example 6 . It seems to fit the data at relatively low doses but is less appropriate for high doses. A sigmoid curve (Figure 1-6, curve D) is concave-up at low doses and concave-down at higher doses. This is not commonly used although it is good at describing the response pattern at higher doses where cell-killing becomes an important consideration. The supralinear model (Figure 1-6, curve E) has been found to fit some data sets well, especially those focusing on low doses, and there are biological reasons why we might expect this kind of curve in some cases. In this model, the line is steeper at lower doses (the effect per dose is greater at low doses). Figure 1-6. Examples of dose-response relationships. Introduction 11 The standard model used by agencies responsible for radiation protection is the linear no-threshold model. As we mentioned, this model assumes that risk is directly proportional to dose and that every dose carries some amount of risk. This is the simplest model, and although there is evidence for departure from the model in some cases it tends to fit the data reasonably well. 1.9 Overview structure Epidemiological studies based on low-dose radiation exposure are often inconclusive and it is difficult or impossible to show links of causation with certainty. The best way to assess the reality of risk is to examine the overall body of studies, pool the many years of research, and weigh the evidence. We have tried to make this task easier by collecting the 6 There are biological reasons why this shape would be chosen, aside from the fact that it tends to fit the data. Little (2000), for example, suggested that the shape of the dose-response curve for leukemia in the atomic bomb survivors is similar to that for radiation-induced chromosome damage in blood cells (although the comparison was highly uncertain).
12 Introduction available information and presenting the essence of each study with a minimum of interpretation. The optimal organization scheme depends on the intent and interest of the reader; some readers may be interested in a particular disease, others may be interested in a particular type of radiation, and others may be interested in specific sources of radiation. We have organized the overview primarily by radiation source. Natural background exposure and medical exposure are covered in sections 2 and 3, exposure to fallout from the atomic bombs and from weapons testing are covered in sections 4 and 5, and sections 6-9 deal with various occupational exposures. Section 10 addresses the risks of exposure prior to conception of a child (also mainly occupational exposures). Section 11 deals with the accidents at Chernobyl and Three Mile Island and Section 12 covers studies of communities near nuclear power and nuclear weapons facilities. We have also included appendices that deal with specific diseases, leukemia and thyroid cancer, and an appendix that presents an analysis of the risks associated with preconceptional exposure (following up on section 10). Each section includes a brief introduction followed by a review of the available epidemiological studies for that source of exposure. At the end of each section we have included a table where we list both quantitative and qualitative information about each study. We have not attempted any kind of comprehensive summary; the effects of radiation vary by dose, by age at exposure, and so on, and so such a simple answer to the question at hand would be misleading. Our concluding section (section 13) is a discussion that returns the focus to low doses and considers some possible interpretations of the data. A few notes on the conventions we adopted for writing this overview: • Several acronyms appear regularly throughout the overview. We have supplied a list of acronyms along with the glossary. The most common will be the risk units described above (RR, ERR, OR) and the names of certain agencies (National Cancer Institute, NCI, and Department of Energy, DOE). Types of leukemia are often refered to by their common acronyms (Acute Lymphocytic Leukemia, ALL, Chronic Myeloid Leukemia, CML, etc.) and we also periodically adopt a convention for grouping leukemia and non-Hodgkin’s lymphoma as LNHL. • The difference between absolute and relative risk rests on important biological assumptions. If we assume that radiation increases an underlying probability of cancer then we use the relative risk. For example, the number of stomach cancer cases that we expect might depend on the underlying stomach cancer risk. This is different between the US and Japan because of diet and maybe other factors. If, on the other hand, we assume that radiation confers an independent risk, not affected by the underlying risk, then we use the absolute risk concept. Under absolute risk assumptions a certain dose would produce the same number of cancers in any population. We have kept our emphasis on the relative risk model, rather than the absolute risk model, based on a belief that the relative risk model is more plausible biologically and in order to keep the presentation of results less cluttered. • The 95% confidence level is by far the most common degree of confidence; we have simplified the notation by dropping the ‘95% CI’ when the confidence interval is 95%, writing out the confidence level only in those cases where the author uses another percentage. For example ‘RR 2.13 (2.00-2.26)’ should be read as ‘a relative risk of 2.13 with a 95% confidence interval of 2.00 to 2.26’. • We have chosen to use units of Gy or Sv for dose. Where the primary source used rad or rem we have made the appropriate conversion. We have also frequently used units of mGy (thousandth of a Gray) or mSv (thousandth of a Sievert). If you read through the overview in order you might notice small differences from section to section. This is because we wrote this as a large and revolving team and authorship varied by section. We have done our best to preserve the document’s fluidity and intent throughout. Any questions, suggestions for updates, or comments can be addressed to Octavia Taylor at the George Perkins Marsh Institute.
Page 1 and 2: Health Risks of Ionizing Radiation:
Page 3 and 4: Contents List of Tables ...........
Page 5 and 6: Contents iii Rocky Flats ..........
Page 7 and 8: Contents v APPENDIX A .............
Page 9 and 10: List of Figures Figure 1-1 Average
Page 11 and 12: We are indeed grateful to those who
Page 13 and 14: 2 Introduction 1.2 A brief history
Page 15 and 16: 4 Introduction Figure 1-2. The evol
Page 17 and 18: 6 Introduction Figure 1-5(a). Alpha
Page 19 and 20: 8 Introduction In epidemiological s
Page 21: 10 Introduction precision to detect
Page 25 and 26: 14 Background Radiation Figure 2-1.
Page 27 and 28: 16 Background Radiation Figure 2-3.
Page 29 and 30: 18 Background Radiation
Page 31 and 32: 20 Medical Exposures Fi
Page 33 and 34: 22 Medical Exposures
Page 35 and 36: 24 Medical Exposures with national
Page 37 and 38: 26 Medical Exposures localized expo
Page 39 and 40: 28 Medical Exposures (2.1-28.7). Th
Page 41 and 42: 30 Medical Exposures posed 2.69 tim
Page 43 and 44: 32 Medical Exposures with diagnosti
Page 45 and 46: 34 Medical Exposures Table 3-1. Stu
Page 55 and 56: 44 Atomic Bomb Survivors Figure 4-2
Page 57 and 58: 46 Atomic Bomb Survivors
Page 59 and 60: 48 Atomic Bomb Survivors approximat
Page 61 and 62: 50 Atomic Bomb Survivors (ALL), acu
Page 63 and 64: 52 Atomic Bomb Survivors of the 8 t
Page 69 and 70: 5 Nuclear Weapons Testing Over 500
Page 71 and 72: 60 Nuclear Weapons Testing by disti
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62 Nuclear Weapons Testing Figure 5
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64 Nuclear Weapons Testing near the
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66 Nuclear Weapons Testing
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68 Nuclear Weapons Testing
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6 RADIATION WORKERS Introduction Th
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72 Radiation Workers • 50 rem (0.
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74 Radiation Workers work, reports
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76 Radiation Workers Figure 6-5. A
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78 Radiation Workers Figure 6-8. To
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82 Radiation Workers Feed Material
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84 Radiation Workers by Beral et al
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88 Radiation Workers Table 6-1. Leu
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90 Radiation Workers No
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92 Radiation Workers N
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94 Radiation Workers S
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96 Radiation Workers ERR estim
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98 Mayak Workers Table 1. Dose (Gy)
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100 Mayak Workers workers at the ra
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102 Mayak Workers
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104 Uranium Miners enrichment facil
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106 Uranium Miners Samet et al. (19
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108 Uranium Miners were selected 12
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Uranium Miners 111
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9 RADIATION EXPOSURE IN FLIGHT The
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DNA damage (a chemical change in DN
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10 PRECONCEPTION EXPOSURES Several
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of risk in the lowest dose groups,
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found elevated solid cancer risk wi
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preconception doses between 2.5 and
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Table 10-1. Preconception irradiati
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Preconception Exposures 127
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Tracheoesophageal fistula and conge
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cancer were both associated with th
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0.10-4.71) while respiratory system
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elationship was not significant for
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times higher than in less-contamina
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Nuclear Power Accidents 139
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12 COMMUNITIES NEAR NUCLEAR FACILIT
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levels (this could not in itself be
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Figure 12-3. Native Americans from
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of leukemia was measured over a lar
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(RR 1.06; 1.00-1.11) and risks of s
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more that we can say about this app
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Communities Near Nuclear Facilities
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54 observed vs. 46.1 expected death
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13 DISCUSSION Our intention in crea
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myeloid leukemia) was significantly
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0.1-3.5 WLM; this is roughly equiva
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adon (Lubin et al. 1997). These res
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Leukemia Leukemia, a general term t
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vical cancer. The doses to these pa
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England have found it convenient to
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Thyroid disease Thyroid cancer is a
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1986 through 1995. These workers sh
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dence of this disease includes elev
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Analysis of preconception exposure
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Paternal age, education, drinking O
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Gardner et al. 1990 Employed at Sel
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we consider this group of a few hun
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Leukemia risk (excluding CLL) among
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Glossary of Terms for Epidemiology
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Glossary 199 Beta radiation: Stream
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Dosimetry: Measurement or estimatio
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Glossary 203 Hypothyroidism: The cl
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Glossary 205 Metastasis: 1. Movemen
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Glossary 207 waves, ultra violet (U
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Glossary 209 Thyroid Disease: disea
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Bibliography ATSDR. Public Health A
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Bhatia S, Sklar C. Second cancers i
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Bibliography 215 Cavallo D, Tomao P
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Bibliography 217 Department of Ener
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Bibliography 219 Gardner MJ, Hall A
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Haldorsen T, Reitan JB, Tveten U. C
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Bibliography 223 Howe GR, Nair R, N
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of Mayak, A comparison of numerical
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Bibliography 227 Laird NM. Thyroid
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control population. International J
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Bibliography 231 Neel JV, Schull WJ
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2003.160:381-407. Bibliography 233
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Bibliography 235 Saccomanno G, Auer
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Bibliography 237 analysis of cancer
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Bibliography 239 Tokarskaya ZB, Sco
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Journal of Epidemiology 1987.125(2)
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Actinium, 84 Acute lymphocytic leuk
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and Nevada Test Site, 60-61, 62 nuc
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Hashimoto’s thyroiditis, 185 Heal
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studies, 101-2 Medical exposure, 19
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(RERF), 43 Radiation Exposure Compe
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Viruses, 118, 154, 193 West Germany
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