A risk assessment of the potential impacts of radon, terrestrial gamma and cosmic rays on childhood leukaemia in France

Natural radioactivity (NR) is an ubiquitous phenomenon and exhibits large geographic variations. Recommended risk models for radiation-induced leukaemia prediction, which are issued from the Life Span Study (LSS) of Hiroshima and Nagasaki A-bomb survivors, suggest that NR could induce some leukaemia cases. This work estimates the percentage of childhood leukaemia that might be related to 3 sources of NR (radon, cosmic and terrestrial gamma rays) in France. National rates of childhood leukaemia over period 1990-2004 were provided by the French registry of childhood malignancies. Risk models proposed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the US National Research Council (BEIR VII) to predict radiation-induced leukaemia cases were used. Estimated annual red bone marrow doses for the average French child due to radon, terrestrial gamma and cosmic rays are 0.27, 0.49 and 0.28 mSv respectively. The percent of leukaemia cases that might be attributed to these combined exposures varies from 4 to 18 % according to UNSCEAR models, depending on whether the additive or multiplicative version is used. It is about 11% according to BEIR VII models, whatever the version. These preliminary point estimates results suggest that a sizeable percentage of childhood leukaemia cases might be attributable to NR. However, the adopted risk assessment approach entails important uncertainties. Some are related to the transposition of risk models from acute (LSS) to chronic (NR) exposures and from external to less accurately known internal doses. Uncertainties related to risk estimates issued from the LSS are also important and will be considered at further steps. Beside, a planned INSERM-IRSN epidemiological study of the relation between NR and childhood leukemia in France as part of the Geocap project will aim at reducing uncertainties by providing direct observations.