Lung cancer risk associated with low chronic radon exposure. Results from the French uranium miners cohort and the European project
Proceedings of the 10th international congress of the International Radiation Protection / Association on harmonization of radiation, human life and the ecosystem Tokyo (Japan), Japan Health Physics Society, May 2000, P-2a-56.
Comprehensive results from miners cohort studies had been published on the risk of lung cancer death associated to radon exposure. However a large proportion of these miners had cumulated high radon exposure and often during a short period of exposure. A European collaborative work on uranium miners has been initiated in 1996, with the objectives to estimate the risk of lung cancer linked to radon when low cumulative exposures are protracted over large periods, and to test the influence of other components present in the mining atmosphere. The project includes a total of several tens of thousands of miners from Czech republic, France and Germany. This paper presents results from the French cohort and the framework of the European project. The French cohort includes 5098 miners employed at least one year since 1947, and followed up to 1994. The number of lung cancer deaths is 126, for a total of 133,500 person-years. Mean cumulative exposure to radon is 36.5 WLM, protracted over a mean duration of 11.5 years. A significant excess of lung cancer deaths is observed, as well as an association of this risk with cumulative exposure to radon (Excess Relative Risk=0.8 per 100 WLM). Within this cohort, more than 3000 miners have been employed only after 1955, when mean annual exposure to radon was always below 5 WLM. In this subcohort, exposure to gamma rays and to uranium ore dust were also recorded. Both are correlated to radon exposure. Risks of lung cancer and leukaemia among this subcohort have been analyzed. These results are consistent with those previously published. In the frame of the European collaboration, a joint analysis of European miners will increase the statistical power for the demonstration of a potential lung cancer risk linked to low levels of exposure. The analysis will be restricted to miners having experienced only low exposure rates, with a precise individual measurement of this exposure. Furthermore, the European project will allow to consider the modifying effects of confounding factors, present in the mines but absent in houses. Especially, gamma rays or uranium dust may interact in the radon-lung cancer risk relationship by increasing the lung dose. Risk will be analyzed after calculation of the <> organ dose associated to these three radiological components. Tobacco consumption will be considered through a nested case-control approach. A parallel analysis of human and animal data is also planned in this framework.