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Radon is recognized as a public health concern for indoor exposure. Precise quantification derived from occupational exposure in miners is still needed for estimating the risk and the factors that modify the dependence on cumulated exposure. The present paper reports on relationship between radon exposure and lung cancer risk in French and Czech cohorts of uranium miners (n = 10,100). Miners from these two cohorts are characterized by low levels of exposure (average cumulated exposure of less than 60 WLM) protracted over a long period (mean duration of exposure of 10 years) and by a good quality of individual exposure estimates (95% of annual exposures based on radon measurements). The modifying effect of the quality of exposure on the risk is analyzed. A total of 574 lung cancer deaths were observed, which is 187% higher than expected from the national statistics. This significantly elevated risk is strongly associated with cumulated radon exposure. The estimated overall excess relative risk per WLM is 0.027 (95% CI: 0.017-0.043, related to measured exposures). For age at exposure of 30 and 20 years since exposure, the ERR/WLM is 0.042, and this value decreases by approximately 50% for each 10-year increase in age at exposure and time since exposure. The present study emphasizes that the quality of exposure estimates is an important factor that may substantially influence results. Time since exposure and simultaneously age at exposure were the most important effect modifiers. No inverse exposure-rate effect below 4 WL was observed. The results are consistent with estimates of the BEIR VI report using the concentration model at an exposure rate below 0.5 WL.

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The follow-up of the French cohort of uranium miners has been extended to 1994, and a new source of information for causes of death has been used. The paper presents the new results regarding the risk of death among the cohort, and analyses the impact of the methodological changes on these results. The extension of the follow-up results in a substantial increase in statistical power compared with previous analysis (+25% for person-years and +74% for the number of deaths). The use of the National Mortality Database as the principal source for causes of death allows to reduce the potential bias in the calculation of standardized mortality ratios (SMR). As a consequence, an excess risk of deaths from laryngeal cancer, suggested in the first analysis, is not confirmed. The analysis shows the existence of an excess risk of deaths from lung cancer among French uranium miners (85 observed deaths, SMR = 1.9, 95% confidence interval CI: 1.5-2.3), and an increase of this risk with cumulative exposure to radon (excess relative risk per 100 working level month = 0.6, 95% CI: 0.1-1.2). These results confirm the existence of a risk of death from lung cancer in a population chronically exposed to relatively low levels of radon.