Search

Radon is a chemically inert radioactive gas of natural origin, produced by the disintegration of uranium and radium located in the earth’s crust. Radon exposure, at various levels, is omnipresent for the general public. Radon inhalation is the main source of exposure to radioactivity for most people throughout the world [National Research Council’s (NRC) Committee on the Biological Effects of Ionizing Radiation (BEIR) 1999; National Council for Radiation Protection and Measurements 1984a, 1984b; U.S. Environmental Protection Agency (EPA) 2003; United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2000]. Most inhaled radon is rapidly exhaled, but the inhaled decay products—readily deposited in the lung epithelium—irradiate sensitive cells in the airways and thereby enhance the risk of lung cancer. In 1988, the International Agency for Research on Cancer (IARC) declared radon to be carcinogenic for humans (lung cancer) and classified as a group 1 carcinogen (IARC 1988), based on the results of experimental animal and epidemiologic studies, in particular among uranium miners. In 1988, the available results came from studies of high exposure levels. Extrapolation of this risk to the general population, who are exposed to lower levels in residential settings, raised numerous questions. In recent years, the average annual exposure of uranium miners has fallen to levels similar to the concentrations inhaled in some homes, and discussion today focuses on the transposition of the risk from occupational to general populations. Miners are almost all adult males, exposed in conditions different from residential exposure: they perform substantial amounts of heavy labor in an atmosphere polluted by dust and fumes. Several case-control studies of residential radon have tested the validity of this risk transposition in the past decade (Auvinen et al. 1996; Kreienbrock et al. 2001; Letourneau et al. 1994; Schoenberg et al. 1990), but lack of statistical power prevented most of them from showing a significant risk. To deal with this problem, several joint analyses have been conducted in recent years. They report a significant lung cancer risk after domestic radon exposure (Darby et al. 2005; Krewski et al. 2005; Lubin 2003). Scientists have used all of these data to assess the lung cancer risk associated with indoor radon. The principal risk assessments come from the United States, the United Kingdom, and Canada (BEIR 1999; Darby et al. 2005; Krewski et al. 2005). These studies have two principal methodologic problems. The first is related to the choice of the exposure–response relation and its use in the context of general population exposure. Past risk assessment studies generally used exposure–response relations derived from miners’ cohorts as recommended by BEIR (1990, 1999). The second methodologic problem involves the role of the uncertainty analysis in the risk assessment process. Uncertainty analysis is an essential step that is too seldom performed. The aim of this study was to assess the lung cancer risk associated with indoor radon exposure in France on the basis of French measurements and the major epidemiologic results available. Specifically, we applied several different exposure–response relations obtained from miners’ cohorts and from joint analyses of residential case-control studies to estimate the number of lung cancer deaths in 1999 that may have been associated with residential radon exposure. The analysis considers the variability of indoor radon exposure in France and allows the quantification of uncertainties related to each of the exposure–response relations.

The objective of this study was to evaluate the ecological association between indoor radon concentration and acute leukaemia incidence among children under 15 years of age in the 348 geographical units (zones d'emploi, ZE) of France between 1990 and 1998. During that period, 4015 cases were registered by the French National Registry of Childhood Leukaemia and Lymphoma. Exposure assessment was based on a campaign of 13 240 measurements covering the whole country. The arithmetic mean radon concentration was 85 Bq/m (range, 15-387 Bq/m) and the geometric mean, 59 Bq/m (range: 13-228 Bq/m). A positive ecological association, on the borderline of statistical significance (P=0.053), was observed between indoor radon concentration and childhood leukaemia incidence. The association was highly significant for acute myeloid leukaemia (AML) (P=0.004) but not for acute lymphocytic leukaemia (ALL) (P=0.49). The standardized incidence ratio (SIR) increased by 7, 3 and 24% for all acute leukaemia, ALL and AML, respectively, when radon concentration increased by 100 Bq/m. In conclusion, the present ecological study supports the hypothesis of a moderate association between indoor radon concentration and childhood acute myeloid leukaemia. It is consistent with most previous ecological studies. Since the association is moderate, this result does not appear inconsistent with the five published case-control studies, most of which found no significant association.