Analysis of Cancer Risks in Populations Near Nuclear Facilities Phase 1 (2012) / Chapter Skim
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Appendix A: Radiation as a Carcinogen
Appendix A: Radiation as a Carcinogen
Pages 271-330
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From page 271... ...
. In other words, as ionizing radiation exposure induces DNA damage to the tissue, that tissue will already carry some damaged cells from other stressors.
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From page 272... ...
Data provided by the updated report of the atomic bombing survivors in Japan continue to be in support of the LNT model across the entire dose range. However, a concave curve was the best fit for data restricted to doses of 0-2 Gy.
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From page 273... ...
Some scientists have argued that DNA repair capabilities are effective at low doses, preventing the accumulation of DNA damage and mutations following low-dose exposures, while others have argued that low doses may be even more damaging per unit dose than high doses. Major discussion on the biological consequences of low-dose radiation despite being controversial has also led to the identification of pathways of radiation damage that are evident at low doses but difficult to measure at high doses in light of overwhelming DNA damage.
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From page 274... ...
, that is, factors used to convert risk estimates from populations exposed in larger acute doses such as the atomic bombing survivors to populations who are exposed to lower low-rate doses. The ICRP derived estimates of the excess cancer risk after low-dose exposures and after exposures with higher doses but low-dose rates by reducing the corresponding risk value for the atomic bombing survivors by a DDREF of 2.0 (ICRP, 2007)
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From page 275... ...
A.4 EPIDEMIOLOGIC STUDIES OF IONIZING RADIATION A.4.1 Studies of Residents near Nuclear Facilities A British television program in 1983 reported a cluster of childhood leukemia in Seascale, a village 3 km from the nuclear fuel reprocessing facility Sellafield on the Cumbrian coast, then known as Windscale. The television team discovered seven childhood leukemia cases over the previous 30 years, while less than one case was expected (Urquhart et al., 1984)
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From page 276... ...
Studies on the cancer risks associated with living near nuclear facilities have come to different conclusions, with some suggesting a positive association between living in proximity to a nuclear facility and cancer risk and others suggesting that there is not a risk, or that the risk is too small to be detected with the methodology used. The power of a study to detect an effect, if there is one, depends highly on the hypothesized strength of the association to be detected and the sample size.
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From page 277... ...
. It is expected that a study in the United States would contain a larger number of exposed individuals than those in the European studies because the number of nuclear power plants in the United States is larger than that in any of the European countries.
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A better term for flawed studies would be "uninformative." In absence of biological plausibility, a positive or somewhat positive association may be underinterpreted. In studies that assess cancer risks associated with releases from nuclear facilities, there are examples where investigators are hesitant to conclude that evidence supported the hypothesis when they find a positive association between risk and exposure associated with nuclear facilities (Baker and Hoel, 2007; Hatch et al., 1990; Kaatsch et al., 2008; Nuclear Safety Council and the Carlos III Institute of Health, 2009)
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. The authors discuss that although the meta-analysis showed an increase in childhood leukemia near nuclear facilities, it "does not support a hypothesis to explain the excess" (Baker and Hoel, 2007)
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In other words, although the one excess case could have occurred due to chance alone, it is highly unlikely that an excess of 100 incident cases has occurred by chance. This is a common issue in interpreting studies of risks in populations near nuclear facilities where the number of excess can cers in the exposed region is particularly small when rare diseases such as childhood leukemia are examined (see Table A.1)
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From page 281... ...
For example, in the Life Span Study (LSS) follow-up of the Japanese atomic bombing survivors the ERR for leukemia is the highest among the various cancer effects of radiation exposure (RR approximately 5 for a dose of 1 Gy, which translates into an ERR of about 4)
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282 APPENDIX A SIDEBAR A.1 Continued or EAR risk estimates from the Japanese atomic bomb survivors to the U.S. popula tion.
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A.4.1.1 Great Britain In Great Britain the first multisite study came immediately as a response to the reported cluster in Sellafield. In 1984, Baron examined cancer mortality trends for the small areas around 14 nuclear installations in England and Wales using census and survey data for the years 1974-1979 (Baron, 1984)
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1.02 (possible sites) Scotland Sharp et al., 1996 7 1968-1993 0-14 I 25 km National rates 399 1.99 (reprocessing plant)
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1.00 (<25 km) NOTE: I, incidence; M, mortality; SIR, standardized incidence ratio; SMR, standardized mortality ratio; OR, odds ratio; RR, relative risk; NPP, nuclear power plant.
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From page 286... ...
The authors report an excess mortality due to leukemia in young people who lived near potential sites similar to that in young people who lived near existing sites, implying the presence of unidentified risk factors associated with the sites where nuclear stations reside or are selected to reside but not associated with the nuclear installations themselves. A study aiming to examine the contribution of potential risk factors to the observed excess of childhood leukemia (< 25 years of age)
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Observed and expected numbers of cases were calculated and analyzed by standard methods based on ratios and by linear rank score test. Overall, there was no evidence of an increase of childhood leukemia or of non-Hodgkin's lymphoma around nuclear installations.
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(1990) , who reported a possible association between paternal employment and development of leukemia by the offspring, detailed information on father's occupation, father's employment at Dounreay, and radiation dose preconception exposure to nonionizing radiation of the father was collected.
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From page 289... ...
Still, the Kinlen hypothesis of population mixing is well perceived today and, although it has not been explicitly examined, it is part of the discussion of the studies on cancer risks in populations around nuclear facilities published the past 2 years (COMARE, 2011; Sermage-Faure et al., 2012; Spycher et al., 2011)
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From page 290... ...
, and together with that of Sellafield and Dounreay (both fuel reprocessing plants) was a confirmed cluster of childhood leukemia near nuclear facilities (Laurier et al., 2008b)
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. The study is known as the KiKK study and was carried out by researchers from the German Childhood Cancer Registry in Mainz, on behalf of the Federal Office of Radiation Protection.
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Exposure to ionizing radiation due to medical diagnostic or therapeutic radiation was also assessed. The NLL study did not find an elevated risk with the radiation doses assessed to have been received as a result of routine discharges from the nuclear power plants.
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. An extended multisite study that included observed leukemia deaths for the years 1988 and 1989 around 13 nuclear installations, of which 11 were nuclear power plants, also showed no excess in mortality (Hattchouel et al., 1995)
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around 23 French nuclear installations (18 nuclear power plants, 2 nuclear fuel-cycle plants, 1 nuclear fuel reprocessing plant, 2 research centers) using a geographic zoning based on estimated doses to the bone marrow due to gaseous radioactive discharges.
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The study results were essentially negative. No general increase in cancer mortality was found in counties with or near nuclear power plants and, unlike some reports in Britain (Black, 1984; COMARE,
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Lucie nuclear power plant in Florida, the Department of Energy's Hanford nuclear facility in Washington, and the uranium mining and milling facilities in Montrose County, Colorado. The team investigated cancer mortality rates among residents of counties near the facilities and found no evidence for increased risk compared to control counties that could be attributed to radiation exposures.
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. One of the largest and most comprehensive studies conducted in the United States regarding the risk of cancer near a nuclear facility, in this case thyroid disease, is the Hanford Thyroid Disease study.
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. The investigators concluded that there was no evidence of a relationship between Hanford radiation dose and thyroid cancer incidence or other thyroid diseases.
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(1990) because it tested the hypothesis of an association between childhood leukemia and the occupational exposure of fathers to ionizing radiation before a child's conception.
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A.4.1.7 Sweden The existence of leukemia clusters among those less than 15 years of age living near four nuclear facilities was examined for the period 19801990. No consistent evidence was found for childhood leukemia clusters associated with living in the proximity of nuclear power plants (Waller et al., 1995)
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From page 301... ...
Results presented little evidence for an association between residence at birth or diagnosis near nuclear power plants and risk of leukemia or other childhood cancers. Potential confounders that were considered included background ionizing radiation, electromagnetic radiation from power lines and other sources, carcinogens related to traffic, pesticide exposure, socioeconomic status, and proxies of population mixing and exposure to childhood infection (average number of children per household in the community and degree of urbanization)
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From page 302... ...
However, rates of mortality due to leukemia for the population overall were higher among those populations living in proximity to nuclear power plants in Japan. A.4.2 Atomic Bombing Survivor Studies The atomic bombs that exploded over the city of Hiroshima and three days later over Nagasaki, Japan, in August 1945 exposed the people of each city to whole-body doses of penetrating ionizing radiation.
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(2007) on solid cancer incidence in atomic bombing survivors for the period 1958-1998 showed that an excess of 11 percent of solid cancers are attributed to exposures >0.005 Gy (mean 0.23 Gy)
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There is very little information about who among the atomic bombing survivors may have received such exposures. In addition, the risk estimates may be affected by sociodemographic factors such as rural and urban differences and by selection effects having to do with the hardiness of the survivors of acute radiation effects.
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From page 305... ...
-- evaluated the dose-response relationship for incident thyroid cancers using measurement-based individual 131I thyroid dose estimates taken within 2 months after the accident. The 12,000 individuals who were part of the prospective cohort study were <18 years of age at the time of the accident and resided in three contaminated regions of Ukraine.
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The European Childhood Leukemia-Lymphoma Incidence Study examined trends in leukemia based on cancer registration data from 23 countries among children aged 0-14 years (Parkin et al., 1996)
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, study group demographics, and health of exposed populations. Studies of cancer risk assessment among workers in the nuclear industry could provide more relevant estimates of the effects of protracted, low-level ionizing radiation exposure.
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Workers in the nuclear plants are at potential risk of exposure to ionizing radiation both externally from radioactivity in the working environment and internally from radionuclides which enter the body by inhalation, ingestion, or through accidents that result in percutaneous wounds. The exposures may accumulate over a lifetime to doses of the order of 100 mGy.
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(2007) combined the data from five nuclear facilities in the United States to evaluate leukemia mortality risk from ionizing radiation using a nested case-control study design.
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A.4.4.2 The British National Registry of Radiation Workers Perhaps the most precise estimates to date of mortality and cancer risks following occupational radiation exposure come from the third analysis of the British National Registry of Radiation Workers (Muirhead et al., 2009)
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The cancer risk estimates obtained were consistent with values used to set radiation protection standards. A.4.4.3 Emergency Chernobyl Workers Cancer incidence (as opposed to mortality)
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. A recent report from the NCRP entitled "Ionizing Radiation Exposure of the Population of the United States" indicated that in 2006, people in the United States were exposed to more than seven times as much ionizing radiation from medical diagnostic procedures than in 1980; the increase is fueled largely by the use of CT scans (NCRP, 2009)
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From page 313... ...
. Results from maternal or paternal radiation exposure from medical diagnostic procedures before conception were not associated with childhood cancer in some (Patton et al., 2004)
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. Even in the offspring of male atomic bombing survivors in Hiroshima and Nagasaki, no increase in childhood cancer risk was observed (Izumi et al., 2003; Schull and Neel, 1959)
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A reason for doubt of a causal relationship between cancer risk in childhood following prenatal exposure to ionizing radiation is the lack of evidence of a corresponding increased risk in cohort studies, most notably the atomic bombing survivors. Observations of those exposed in utero following the atomic bombings have been published since 1970.
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From page 316... ...
Outside the atomic bombing studies, there is mixed epidemiologic evidence to support the notion that exposure to low doses of ionizing radiation increases risk of cardiovascular diseases (Little et al., 2008b, 2010; McGale and Darby; 2005; UNSCEAR, 2006b)
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. A study evaluated the prevalence of thyroid diseases and their radiation dose responses in atomic bombing survivors, some 55 years after the bombings.
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From page 318... ...
. Distribution of childhood leukaemias and non Hodgkin's lymphomas near nuclear installations in England and Wales.
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. Effects of low doses and low dose rates of external ionizing radia tion: Cancer mortality among nuclear industry workers in three countries Radiat.
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. Death rates from childhood leukaemia near nuclear sites.
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. Childhood leukaemia incidence around French nuclear installations using geographic zoning based on gaseous discharge dose estimates.
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. Radiation dose-response relationships for thyroid nodules and autoimmune thyroid diseases in Hiroshima and Nagasaki atomic bomb survivors 55-58 years after radiation exposure.
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. Solid cancer incidence and low-dose-rate radiation exposures in the Techa River cohort: 1956-2002.
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. Low doses of ionizing radiation and circulatory diseases: A systematic review of the published epidemiological evidence.
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. Cancer incidence in atomic bomb survivors.
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. Solid cancer incidence in atomic bomb survivors exposed in utero or as young children.
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. Radiation exposure and circulatory disease risk: Hiro shima and Nagasaki atomic bomb survivor data, 1950-2003.
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. Childhood leukaemia around the La Hague nuclear waste reprocessing plant.
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From page 329... ...
. Cancer risks near nuclear facilities: The importance of research design and explicit study hypotheses.
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