Epidemiological studies in three corporations covering the Canadian nuclear fuel cycle

Three Canadian corporations, Eldorado Nuclear Ltd (uranium mining and refining), Ontario Hydro (nuclear reactor operation) and Atomic Emergy of Canada Ltd (nuclear research and radioactive waste management) have established long-term health studies of their employees. Together they cover the Canadian nuclear fuel cycle. Their purpose is to define mortality patterns among employees occupationally exposed to ionizing radiation and, where possible, develop risk estimates. For tracing causes of death, two studies depend very heavily and one to a lesser extent on the National Mortality Data Base operated by Statistics Canada since 1950. Computerized record linkage techniques between lists of identified employees and the National Mortality Data Base have been found both reliable and cost effective. The three studies described will in the long term provide mortality data for a population of approximately 40,000 radiation workers, some of whom were first exposed to ionizing radiation during mining operations in the 1930s. An important feature of each study is that data analysis and reporting are done by independent epidemiological consultant groups. The purpose of this paper is to describe the philosophy behind and the methodology applied to these three ongoing epidemiological studies. Results to date have been limited. However, in the Ontario Hydro study, analysis since 1970 has shown no indication of excess cancer deaths among employees or pensioners exposed to ionizing radiation within the current permissible limits. (author)