It is well established that high radon exposures increase the risk of lung cancer mortality. The effects of low occupational exposures and the factors that confound and modify this risk are not clear and are needed to inform current radiation protection of miners. The risk of lung cancer mortality at low radon exposures (< 100 working-level months) was assessed in the joint cohort analysis of Czech, French, and Canadian uranium miners, employed in 1953 or later. Statistical analysis was based on linear Poisson regression modeling with grouped cohort survival data. Two sensitivity analyses were used to assess potential confounding from tobacco smoking. A statistically significant linear relationship between radon exposure and lung cancer mortality was found. The excess relative risk per working-level month was 0.022 (95% confidence intervals: 0.013-0.034), based on 408 lung cancer deaths and 394,236 person-years of risk. Time since exposure was a statistically significant modifier; risk decreased with increasing time since exposure. A tendency for a decrease in risk with increasing attained age was observed, but this was not statistically significant. Exposure rate was not found to be a modifier of the excess relative risk. The potential confounding effect of tobacco smoking was estimated to be small and did not substantially change the radon-lung cancer mortality risk estimates. This joint cohort analysis provides strong evidence for an increased risk of lung cancer mortality from low occupational radon exposures. The results suggest that radiation protection measures continue to be important among current uranium miners.

Department of Epidemiology and Biostatistics School of Medicine University of California San Francisco 550 16th St San Francisco CA 94158 USA

Institute for Radiological Protection and Nuclear Safety B P 17 92262 Fontenay aux Roses Cedex France

National Radiation Protection Institute Bartoskova 28 140 00 Prague Czech Republic

School of Epidemiology and Public Health Faculty of Medicine University of Ottawa Room 101 600 Peter Morand Crescent Ottawa ON K1G 5Z3 Canada

School of Epidemiology and Public Health Faculty of Medicine University of Ottawa Room 101 600 Peter Morand Crescent Ottawa ON K1G 5Z3 Canada Centre for Practice Changing Research Ottawa Hospital Research Institute Children's Hospital of Eastern Ontario Research Institute 401 Smyth Rd Ottawa ON K1H 8L1 Canada

School of Epidemiology and Public Health Faculty of Medicine University of Ottawa Room 101 600 Peter Morand Crescent Ottawa ON K1G 5Z3 Canada Directorate of Environmental and Radiation Protection and Assessment 280 Slater Street Station B P O Box 1046 Ottawa ON K1P 5S9 Canada

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