Canadian Nuclear Safety Commission contract 87055-13-0577 MORTALITY RISKS IN THE POOLED ANALYSIS OF THE CANADIAN AND GERMAN URANIUM PROCESSING WORKERS

Nuclear fuel cycle workers are exposed to a variety of hazardous materials. Uranium processing is one of the stages of the nuclear fuel cycle and, together with uranium underground mining, employs the largest number of workers, with much smaller groups of workers involved in uranium enrichment and reprocessing and reactor operation. To date, epidemiological studies of uranium underground miners showed significantly increased risks of lung cancer from exposures to radon decay products (RDP). Uranium enrichment workers also have been shown to have increased risks of lung cancer from exposures to reprocessed uranium compounds. Large pooled studies of nuclear reactor workers showed significantly increased risks of solid cancers and leukemia, and, more recently and controversially, of cardiovascular (CVD) and non-malignant respiratory diseases. Workers engaged in uranium processing are exposed to a wide range of radioactive (e.g., gamma-ray) and non-radioactive (e.g., fine or silica dust) exposures from the ore dust, but less to RDP exposures, typical for uranium underground miners. Data from recent studies of the physicochemical characteristics of uranium isotopic types from the nuclear fuel cycle provide additional evidence for an emerging consensus that exposures of workers in the uranium processing industry are substantially different from those of uranium underground miners or enrichment workers or nuclear reactor workers, and that they should be carefully evaluated in separate studies. The purpose of this study was to develop an understanding of the long-term health risks of occupational exposures in the uranium processing industry. The pooled cohort consisted of 7,431 workers from Port Hope, Canada and Wismut, Germany who were exposed to uranium processing, which includes milling and refining, and had detailed annual exposure information. This is one of the largest cohort analyses comprised of workers exposed to a unique combination of RDP exposures and gamma-ray doses as a result of the refining and processing of uranium. Over 90% of workers were followed-up for at least 20 years, allowing sufficient time for occupationally-induced cancers to develop. RDP exposures were broadly similar in the two cohorts, but gamma-ray doses almost four-fold higher among male Port Hope compared to male Wismut workers. We determined that radiation risks of all cancer and noncancer outcomes were similar in the two cohorts, indicating that the cohorts were suitable for pooling. We observed small and not statistically significant increases in risks of lung cancer due to RDP exposures and of CVD due to both RDP exposures and gamma-ray doses among males. Higher CVD risks among males were observed among those with duration of employment less than 8 years and among those with the youngest age at first WLM exposure. Radiation risks of solid cancers excluding lung cancer were increased both for RDP exposures and for gamma-ray doses, significantly so among women. All other causes of death among males and females were not associated with occupational RDP exposures and gamma-ray doses. Significant findings should be interpreted with caution and could be due to a large number of statistical tests. Continued follow-up of the cohorts and pooling with other cohorts of workers exposed to uranium processing could provide valuable insights into risks from occupational uranium exposures and gamma-ray doses and into suspected differences in risks with other groups of workers involved in the nuclear fuel cycle.