Methodology and results of the Nord-Cotentin radioecological study.

Epidemiological studies have shown a trend towards an excess number of leukaemia cases in the region of Nord-Cotentin (France) where, in particular, the La Hague nuclear reprocessing plant is located. In 1997, it was suggested that the risk of leukaemia was associated with some aspects of lifestyle, in particular, the consumption of local seafood and use of local beaches. To respond to public concern, the French Ministries of the Environment and Health decided to commission complementary epidemiological studies and a detailed radioecological analysis. The radioecological study was entrusted to a group of experts with various backgrounds (inspectors, governmental experts, operators, experts from non-governmental laboratories and foreign experts)--the Nord-Cotentin Radioecology Group. Its principal objective was to assess realistically the exposure to ionising radiation of young people from 0 to 24 years of age who had lived near the La Hague nuclear reprocessing plant and to estimate their risk of radiation-induced leukaemia from 1978 through 1996, the period covered by the epidemiological studies. The Group chose to use a three-stage approach: reconstruction of the population of young people from 0 to 24 years who resided in the region between 1978 and 1996, assessment of their exposure to all sources of ionising radiation, and estimation of the risk of radiation-induced leukaemia attributable to this exposure. The collective red bone marrow dose due to the discharges from the local nuclear facilities from Nord-Cotentin has thus been estimated at approximately 0.5 man-Sv, which is less than 0.2% of the total exposure to ionising radiation, including natural and medical sources and fallout from atmospheric testing and the accident at Chernobyl. The number of cases of radiation-induced leukaemia attributable to discharges from the local nuclear facilities based on the estimated level of exposure was around 0.002 over this period. This is the best estimate, in the current state of knowledge, of the incidence of radiation-induced leukaemia attributable to environmental exposure to ionising radiation among the young people living in the vicinity of the La Hague reprocessing plant based on mean habits for the population. This estimate must be interpreted in the light of the limitations inherent in the risk assessment process, and some participants in the Nord-Cotentin Radioecology Group have expressed reservations about it. Nonetheless, the number of cases estimated here is low in comparison to the four cases of leukaemia observed during the same period. It is thus very improbable that exposure attributable to local nuclear facilities is implicated to any salient degree in the elevated incidence of leukaemia observed in this region among young people.