Since the 1950s, the U.S. Public Health Service (and subsequently the National Institute for Occupational Safety and Health) has conducted a cohort study of more than 4000 uranium miners on the Colorado Plateau (CP) in the southwest United States. These miners were obtaining raw uranium to supply the U.S. nuclear weapons industry from the 1940s to the late 1980s. Initially, researchers administered questionnaires and physical examinations among the miners (both white and American Indian), who are a subset of a much larger group of miners employed during the cold war era. Thousands of measurements were made of radon progeny in hundreds of mines over a period of decades. Since the 1970s, the CP cohort has been followed for mortality and morbidity outcomes and smoking assessment. The unique features of the CP cohort include its high doses, extensive dosimetry, near-complete smoking information, and long follow-up. The cohort has contributed extensively to knowledge of lung cancer risk from radon exposure, including understanding of inverse dose-rate effects, changes in risk with time since exposure, and the form of interaction with smoking. As of the last follow-up in 2005, 75% of the cohort was deceased. Despite the anticipation that lung cancer rates would decline in the late follow-up, published findings suggest that attributable risk of lung cancer continues to be high in the cohort, particularly for miners who smoked little or not at all. The form of interaction of radon dose with smoking appears to remain sub-multiplicative but super-additive. Outcomes other than lung cancer, such as idiopathic pulmonary fibrosis, and some forms of renal disease, have shown associations with radon exposure. With a final wave of follow-up, the CP cohort continues to provide key information to support the development of protective standards to minimise lifetime lung cancer risk from occupational radon exposure.
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