Health Risks of Ionizing Radiation: - Clark University

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0.1-3.5 WLM; this is roughly equivalent to a range of 1-20 mSv lung dose according to the conversions suggested by UNSCEAR (2000). Uncertainty and judgement. At low doses, with low associated risks, it is difficult for epidemiology to detect an excess incidence of disease. Background variations in the rate of a disease, caused by variations in demographic characteristics, unknown risk factors, and the stochastic nature of cancer, create situations where it is often impossible to say with any statistical certainty that an observed outcome is attributable to a particular exposure. This problem is exacerbated by small study populations. Land (1980) presents a good discussion of statistical power. Studies with low expected risks tend to have low power because the size of a cohort needed to detect the risk is unrealistic. In these cases we introduce a bias when we only consider risk estimates that are significantly greater than zero (Land 1980). As an example of this problem we might consider atomic bomb survivors who were exposed to radiation in utero. In this group there were two cases of childhood cancer; based on the background cancer rate less than one case was expected. This is not a statistically significant excess and one might say something like “atomic bomb survivors exposed in utero did not demonstrate an increase in childhood cancer”. On the other hand, the excess relative risk estimate based on these two cases could be as high as 44 per Gy 13 . Another example is multiple myeloma incidence among veterans of the 1957 nuclear test “Smoky”; although one case of the disease was expected, none were observed. This outcome might have occurred by chance even if the true relative risk was as high 2.8 14 . The most truthful assessment of data such as these is that they are insufficient to tell us anything specific and they are consistent with a wide range of possibilities. Synthesis of information. Although many individual studies of low doses are inconclusive by themselves they become more meaningful when they are considered together with other information. With a set of uncertain information in hand we can Discussion 171 attempt to describe our understanding in terms that are meaningful if not precise. As an illustration we can consider the leukemia risk of adult exposures to low doses of radiation. We have seen convincing evidence that there is a leukemia risk in children exposed to low doses of radiation in utero, from Chernobyl, or from the Nevada Test Site (above and in the leukemia section). There are physiological reasons why adult risks might be different, including different rates of blood production; we can see evidence of this difference in the fact that childhood leukemia is often the acute lymphocytic type and adult leukemia is often the chronic myeloid type. It is therefore worthwhile to examine adult risks independently, keeping in mind what we know about childhood risks. The best sets of data on adult exposures come from nuclear workers and the atomic bomb survivors, and we might also consider veterans who participated in nuclear weapons testing. As noted above, Cardis et al. (1995) found a significant dose response for non-CLL leukemia mortality among workers in three countries. This dose-response estimate included doses over 0.4 Sv and so it is not, by itself, evidence of a risk at low doses. The authors note, however, that although the slope is not significant at lower doses it is compatible with the estimate for the full cohort (unfortunately this data is not shown in the report). In a study of Canadian workers, over 98% of whom received doses less than 0.1 Sv, a similar estimate of the leukemia risk (for incidence) was derived (Sont et al. 2001), and a compatible mortality risk estimate was also derived (Ashmore et al. 1998). Gilbert (2001) compares these estimates to the male atomic bomb survivors who were exposed as adults and an estimate from the National Registry of Radiation Workers (UK) 15 . Table 13-2 is based on a table presented by Gilbert (2001). Although three of the estimates presented in Table 13-2 are not significant there is notable consistency; the estimate of Cardis et al. (1995) is stronger in this context. The vast majority of these workers were exposed to low doses. In addition to these dose-response estimates we 13 The ERR estimate for childhood cancer incidence following in utero exposure to the atomic bombs was reported to be 11/Gy with a 95% confidence interval of –1 to 44 (Wakeford and Little 2003). 14 The RR for multiple myeloma incidence was 0.0 (0.0-2.8; Caldwell et al. 1983). 15 There is some overlap between the UK study and the three-country study.
172 Discussion Table 13-2. Estimated risk of non-CLL leukemia in adults Cohort ERR Sv -1 Canadian workers (incidence) Sont et al. 2000 Canadian workers (mortality) Ashmore et al. 1998 UK workers (mortality) Muirhead et al. 1999 Three-country workers (mortality) Cardis et al. 1995 Adult male atomic bomb survivors (mortality) Gilbert 2001 have a couple of examples of significant risks in the low-dose region. • Wilkinson and Dreyer (1991) found a significantly positive rate ratio of 2.1 (1.4- 3.3) in workers with doses of 0.01-0.05 Sv. • Caldwell et al. (1983) found a significantly positive relative risk of 2.5 (1.2-4.6) in nuclear test veterans exposed to less than 0.1 Sv. These estimates of risk are substantially higher than what we would expect based on the dose-response estimates presented in Table 13-2. What can we learn from the data presented in this example? We might characterize this information as a relatively robust dose-response estimate and two risk estimates at low doses that deviate from this dose-response curve. Concluding anything from this information is largely a value-based decision and there is not one right answer. Based on a precautionary approach we might assume that the low dose risk estimates are valid, and that the leukemia risk might be as high as 3- or 4-fold with exposures to less than 0.1 Sv in some situations. We might also look at these data and consider the possibility that the dose-response relationship is not linear and that the risk at low doses is higher, per sievert, than the risk at moderate doses. The ankylosing spondylitis analysis of Weiss et al. (1995) (90% CI) 2.7 (
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Health Risks of Ionizing Radiation:
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Contents List of Tables ...........
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Contents iii Rocky Flats ..........
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Contents v APPENDIX A .............
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List of Figures Figure 1-1 Average
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We are indeed grateful to those who
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2 Introduction 1.2 A brief history
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4 Introduction Figure 1-2. The evol
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6 Introduction Figure 1-5(a). Alpha
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8 Introduction In epidemiological s
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10 Introduction precision to detect
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12 Introduction available informati
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14 Background Radiation Figure 2-1.
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16 Background Radiation Figure 2-3.
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18 Background Radiation
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20 Medical Exposures Fi
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22 Medical Exposures
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24 Medical Exposures with national
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26 Medical Exposures localized expo
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28 Medical Exposures (2.1-28.7). Th
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30 Medical Exposures posed 2.69 tim
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32 Medical Exposures with diagnosti
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34 Medical Exposures Table 3-1. Stu
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44 Atomic Bomb Survivors Figure 4-2
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46 Atomic Bomb Survivors
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48 Atomic Bomb Survivors approximat
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50 Atomic Bomb Survivors (ALL), acu
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52 Atomic Bomb Survivors of the 8 t
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5 Nuclear Weapons Testing Over 500
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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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Page 134 and 135: preconception doses between 2.5 and
Page 136 and 137: Table 10-1. Preconception irradiati
Page 138 and 139: Preconception Exposures 127
Page 140 and 141: Tracheoesophageal fistula and conge
Page 142 and 143: cancer were both associated with th
Page 144 and 145: 0.10-4.71) while respiratory system
Page 146 and 147: elationship was not significant for
Page 148 and 149: times higher than in less-contamina
Page 150 and 151: Nuclear Power Accidents 139
Page 156 and 157: 12 COMMUNITIES NEAR NUCLEAR FACILIT
Page 158 and 159: levels (this could not in itself be
Page 160 and 161: Figure 12-3. Native Americans from
Page 162 and 163: of leukemia was measured over a lar
Page 164 and 165: (RR 1.06; 1.00-1.11) and risks of s
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Page 168 and 169: Communities Near Nuclear Facilities
Page 176 and 177: 54 observed vs. 46.1 expected death
Page 178 and 179: 13 DISCUSSION Our intention in crea
Page 180 and 181: myeloid leukemia) was significantly
Page 184 and 185: adon (Lubin et al. 1997). These res
Page 186 and 187: Leukemia Leukemia, a general term t
Page 188 and 189: vical cancer. The doses to these pa
Page 190 and 191: England have found it convenient to
Page 192 and 193: Thyroid disease Thyroid cancer is a
Page 194 and 195: 1986 through 1995. These workers sh
Page 196 and 197: dence of this disease includes elev
Page 198 and 199: Analysis of preconception exposure
Page 200 and 201: Paternal age, education, drinking O
Page 202 and 203: Gardner et al. 1990 Employed at Sel
Page 204 and 205: we consider this group of a few hun
Page 206 and 207: Leukemia risk (excluding CLL) among
Page 208 and 209: Glossary of Terms for Epidemiology
Page 210 and 211: Glossary 199 Beta radiation: Stream
Page 212 and 213: Dosimetry: Measurement or estimatio
Page 214 and 215: Glossary 203 Hypothyroidism: The cl
Page 216 and 217: Glossary 205 Metastasis: 1. Movemen
Page 218 and 219: Glossary 207 waves, ultra violet (U
Page 220 and 221: Glossary 209 Thyroid Disease: disea
Page 222 and 223: Bibliography ATSDR. Public Health A
Page 224 and 225: Bhatia S, Sklar C. Second cancers i
Page 226 and 227: Bibliography 215 Cavallo D, Tomao P
Page 228 and 229: Bibliography 217 Department of Ener
Page 230 and 231: 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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