[The precautionary principle applied to lung cancer risk caused by residential radon]

Residential radon seems to represent a major health hazard. The studies, which investigate the pulmonary risk of cancer caused by radon, are of different nature and their results are divergent. Thus, there persist scientific uncertainties concerning the real size of this risk. The application of the precautionary principle is based on an analysis of these uncertainties. Studies on miners, studies concerning residential radon (at individual and ecological level), as well as experimental data allow for the organisation of the uncertainty of each one of these specific approaches taking into account their proper limitations. The first risk that is linked to radon is the risk of pulmonary cancer. Miner occupational exposure studies appear compatible with the results of case-control studies concerning residential radon. However, the case-control studies, where the risk appears more present, are contradicted by ecological studies, often not very convincing about the existence of a risk. The case-control studies have an intrinsic advantage over the ecological studies because they limit the classification errors by the individualization of the relation-exposure effect. In addition, the experimental data are not in contradiction with the existence of effects for very small exposures. Consequently, the inherent scientific uncertainties of the totality of these data, can be classified and permit the application of the precautionary principle in a better proportioned way. The utilisation of the precautionary principle implies the necessity to limit, as far as possible, the exposure to residential radon. Precautionary principle is based on the debated hypothesis of no threshold linear relation between radon exposition and health consequences. This relation has been established on professional and residential exposures. The implementation of this epidemiological model shows the "residential radon" risk as the second cause of pulmonary cancer and responsible of about 10% of these specific cancers.