Health Risks of Ionizing Radiation: - Clark University

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When we look at an analysis of SMRs, for example, we should consider each estimate in the context of the overall SMR for the cohort. If workers at a facility have an SMR of 0.8 overall then they are a healthy cohort with mortality rate 20% lower than average. Judging SMRs for specific diseases by whether or not they are significantly greater than 1 is misleading in this case, because they should in fact be lower than 1 in a healthy cohort. Any SMRs that are significantly greater than 1 become very strong evidence of an effect. Another common factor involves time; researchers often represent workplace exposure with a proxy variable like years of employment. This is affected by the fact that sick people are weeded out of employment over the years. A person with lung cancer, for example, is unlikely to remain working for very long. This results in a situation where the people who have been working the longest can be expected to be unusually healthy. This is known as the healthy survivor effect. Baillargeon and Wilkinson (1999) studied the healthy survivor effect among workers at Hanford; they found that there was a stepwise decline in the standardized mortality ratios of workers with increasing employment length and that workers in the highest employment duration category showed a significant survival advantage over other workers. Other methodological limitations associated with occupational exposure studies include: • relatively low numbers of excess deaths, reducing precision in risk estimation • missing or incomplete workplace employment and exposure records (this is especially true for older data) • confounding variables such as smoking that are difficult to control • poor records of disease incidence leading to a reliance on mortality data Despite these limitations, many researchers look to studies of occupational exposure as a key resource for data on health effects of chronic, lowlevel radiation exposure. These workers constitute a large population for whom exposure monitoring, although far from ideal, is relatively thorough. Furthermore, the majority of doses received by these workers are relatively low. The mean dose Radiation Workers 73 in a study of workers from three countries was 40 mSv and 80% of workers had doses below 0.05 Sv (Cardis et al. 1995). In a large Canadian study the mean dose was even lower (6.6 mSv) because it included exposure in medical professions; in this case 97% of workers had doses below 0.05 Sv (Sont et al. 2001). Sections 6.2 and 6.3 discuss studies of worker health by facility. Examining facilities individually can reveal information and risks that “a common estimator” from a multi-site study may obscure (Ritz 1999). On the other hand, many facility-specific studies have been inconclusive because the cohorts are small and because the healthy worker effect limits meaningful comparisons to analyses within the cohort. Because of this, a number of large pooled analyses have been undertaken, some general and some focused on specific disease endpoints. These are addressed in Section 6.4. Section 6.5 presents a summary and discussion of health effects in nuclear workers. 6.2 US facilities Hanford. Hanford, managed by the DOE, is located in Richland, Washington and covers 560 square miles. From 1944 to the late 1980s, Hanford operated as a plutonium production facility for the nuclear weapons complex. More than 100,000 people have worked at Hanford over the years. In our literature review for Hanford it became clear that there had been something of an academic battle over interpretation of the occupational exposure research for this facility. Stewart and Kneale (1991) provide some background as follows: In the early years of standard setting for occupational radiation exposure there was a lot of fluctuation and disagreement. The Atomic Energy Commission (AEC) lowered its exposure limits as risk awareness increased. However, after hearing that significant risk was difficult to detect in low-dose survivors of the atomic bomb, the AEC wished to relax its standards. In 1964 the AEC agreed to sponsor a lifetime health mortality study of all of its employees in order to gather more definitive information by which to set standards. They hired Thomas Mancuso, of the University of Pittsburgh School of Public Health, to lead the study and Mancuso decided to focus on data from Hanford. Shortly after Mancuso began his
74 Radiation Workers work, reports from another researcher indicated that there was significant health risk related to exposure at Hanford. The AEC contacted Mancuso and asked him to refute these claims and Mancuso responded that he would be unable to do so until he completed his own research. Mancuso was shortly thereafter told that his contract would not be renewed; with two years left on his contract he invited British epidemiologists Alice Stewart and George Kneale to help conduct the remaining research. At the end of Mancuso’s contract, the DOE appointed Ethel Gilbert as chief scientist of the Hanford study. Mancuso, Stewart and Kneale were able to continue their work with a grant from the National Institute of Occupational Safety and Health (NIOSH). Gilbert et al. published an analysis of the mortality risk in Hanford employees in 1989, covering employee data from 1945-1981, and then published a follow-up analysis in 1993, covering 1945-1986. The 1989 analysis found a strong healthy worker effect, with low standardized mortality ratios (SMRs), and cancer was generally not significantly related to dose. This study did find a significantly elevated risk of multiple myeloma and a significant trend with dose for this disease 4 . The 1993 analysis generally confirmed the results of the 1989 analysis and aside from the multiple myeloma association there was no significant evidence of a health risk. It was also clear, however, that the results were very uncertain and not inconsistent with atomic bomb survivor data. For example, the solid cancer ERR estimate was –0.04/Sv but had a 90% CI of –1.7 to 1.25/Sv (compared to the atomic bomb survivor estimate of 0.47/Sv; Preston et al. 2003). Mancuso, Stewart and Kneale also published a series of studies examining cancer mortality at Hanford (Mancuso et al. 1977, Kneale et al. 1981, Figure 6-3. Located at the Hanford site in Washington and completed in September 1944, the B Reactor was the world’s first large-scale plutonium production reactor (http://ma.mbe.doe.gov/me70/history/b_reactor.htm). Kneale and Stewart 1993) as well as a review of the issues of age, exposure and dose recording (Stewart and Kneale 1993). In a preliminary analysis Mancuso et al. (1977) used methods involving cumulative mean doses and proportional mortality. They found that workers who died of cancers that might be related to radiation (leukemias and myelomas, lung cancer, etc.) had higher mean doses than workers who died of other cancers. They also found that the death from these cancers occurred more frequently, as a proportion of total mortality, than in the general population 5 . In addition, risk was found to be higher for those exposed at younger and older ages. This study was controversial because of the methods used and also because it estimated higher risks than would be expected based on the atomic bomb survivor data. Life tables and regression models were used by Kneale et al. (1981) and Kneale and Stewart (1993) for follow-up through 1977 and then 4 In exposure categories 0-19, 20-49, 50-149 and 150+ mSv the RR estimates were 1.0, 0.0 (no deaths), 8.5 (based on two deaths) and 14.7 (based on one death). Multiple myeloma had by this time also been associated with exposure to radiation at the Sellafield facility in England (Smith and Douglas 1986). 5 This proportional mortality method assumes that, for example, if 10% of cancers in the general population are prostate cancers then 10% of workers’ cancers should also be prostate cancers. This avoids the healthy worker effect because the overall mortality rate is not compared across populations. According to this method, Mancuso et al. found 11 myeloid leukemia deaths where 5.8 would be expected; similar excesses were apparent for cancers of the lung (192 vs. 144 expected), kidney (21 vs. 15) and pancreas (49 vs. 37) and for multiple myeloma (11 vs. 7.6) and lymphoma (34 vs. 27.7). 6 Life tables are a way of arranging data to allow for year-to-year accounting of exposure and mortality; regression models are used to account for a variety of confounding factors.
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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
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
Page 73 and 74: 62 Nuclear Weapons Testing Figure 5
Page 75 and 76: 64 Nuclear Weapons Testing near the
Page 77 and 78: 66 Nuclear Weapons Testing
Page 79 and 80: 68 Nuclear Weapons Testing
Page 81 and 82: 6 RADIATION WORKERS Introduction Th
Page 83: 72 Radiation Workers • 50 rem (0.
Page 87 and 88: 76 Radiation Workers Figure 6-5. A
Page 89 and 90: 78 Radiation Workers Figure 6-8. To
Page 93 and 94: 82 Radiation Workers Feed Material
Page 95 and 96: 84 Radiation Workers by Beral et al
Page 99 and 100: 88 Radiation Workers Table 6-1. Leu
Page 101 and 102: 90 Radiation Workers No
Page 103 and 104: 92 Radiation Workers N
Page 105 and 106: 94 Radiation Workers S
Page 107 and 108: 96 Radiation Workers ERR estim
Page 109 and 110: 98 Mayak Workers Table 1. Dose (Gy)
Page 111 and 112: 100 Mayak Workers workers at the ra
Page 113 and 114: 102 Mayak Workers
Page 115 and 116: 104 Uranium Miners enrichment facil
Page 117 and 118: 106 Uranium Miners Samet et al. (19
Page 119: 108 Uranium Miners were selected 12
Page 122 and 123: Uranium Miners 111
Page 124 and 125: 9 RADIATION EXPOSURE IN FLIGHT The
Page 126 and 127: DNA damage (a chemical change in DN
Page 128 and 129: 10 PRECONCEPTION EXPOSURES Several
Page 130 and 131: of risk in the lowest dose groups,
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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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