Lung Cancer Risk Associated with Low Chronic Radon Exposure: Results from Epidemiology and Animal Experiments in France

An increased lung cancer risk associated with radon exposure has been reported both in underground miner cohort studies and in animal experiments. However a large proportion of these results came from populations who received high radon exposure for a short period of time. Our aim is to analyse the effects of radon in populations exposed to low level and low rates over long periods. In France, research was developed in parallel both in the field of epidemiology through the cohort of uranium miners, and in that of animal experiments. We present here recent results underlying the points of agreement between epidemiological and experimental approaches. The French cohort of uranium miners includes 5098 miners with low cumulative radon exposure protracted over a long duration. Results show a significant increase of lung cancer risk with cumulative exposure to radon. Period of exposure appears as an important modifier of the exposurerisk relationship (reflecting historical changes in radiation protection and measurement methods), but no effect of exposure rate is observed. Recent animal experiments were conducted in France by CEA and COGEMA at low levels of exposure. More than 4600 rats have been exposed to various exposure rates and durations under controlled conditions, and followed-up over their life span. Results show that the risk increases with cumulative exposure. In this experiments, an inverse exposure rate effect is observed at the highest level of exposure. Such effect is not observed at the lowest level. Epidemiological and animal data are consistent to show an increase of risk with cumulative exposure protracted at low exposure rates. Animal data are also consistent with previous studies of underground uranium miners showing an inverse exposure rate effect at high level, but this effect disappears at low levels of exposure.