Ecological Association Between Natural Ionizing Radiation And Childhood Leukemia Incidence In France, 1990-1998
AS Evrard, D Hémon, S Billon, D Laurier, E Jougla, M Tirmarche, J Clavel, Sixtennth conference of the international society for environmental epidemiology, 01-04/08/2004, New-York, USA.
The aim of the study was to evaluate the ecological association between natural ionizing radiation (indoor radon and terrestrial gamma radiation) and acute leukemia incidence among children under 15 years of age in France between 1990 and 1998.
During that period, 4015 cases were registered by the French National Registry of Childhood Leukemia and Lymphoma: 3270 acute lymphoblastic leukemia (ALL) and 697 acute myeloid leukemia (AML). Exposure assessment was based on measurement campaigns covering the whole country, including 13240 indoor radon concentration measurements and 8737 indoor gamma dose rate measurements. Analyses were conducted using Poisson regressions, at the level of "employment areas" (348 geographical units called zones d'emploi in France).
The arithmetic mean radon concentration was 85 Becquerel per m3 (Bq/m3) (range: 15-387 Bq/m3) and the arithmetic mean gamma dose rates was 54 nanosievert per hour (nSv/h) (range: 14-124 nSv/h). A positive ecological association, on the borderline of statistical significance (p=0.053), was observed between indoor radon concentration and childhood leukemia incidence. The association was highly significant for AML (p=0.004) but not for ALL (p=0.49). The Standardized Incidence Ratio (SIR) increased by 7%, 3% and 24% for all acute leukemia, ALL and AML, respectively, when radon concentration increased by 100 Bq/m3. The results were stable over age, gender and period for all acute leukemia and ALL, but the association with AML seemed restricted to cases aged less than 10 years. The positive association between indoor radon concentration and AML remained significant when ecological covariates were included in the Poisson regression model. Conversely, there was no evidence of an ecological association between indoor gamma radiation and childhood leukemia incidence, for AML or for ALL. This observation may be related to the fact that the geographical variability of indoor exposure to gamma radiation turned out to be much smaller than that of radon concentration. The results did not change when the association between radon and leukemia was adjusted on indoor gamma radiation or when the association between indoor gamma radiation and leukemia was adjusted on radon.
The present study supports the hypothesis of a moderate association between indoor radon concentration and childhood leukemia incidence. On the basis of these results, and with the hypothesis of a causal association, 5.4% of the cases of childhood leukemia in France might be due to radon.