Évolution spatio-temporelle des concentrations, des rapports isotopiques et des facteurs de concentration du plutonium dans une espèce d'algue et deux espèces de mollusques en Manche

Variation of activity levels, isotope ratios, concentration factors in space and the of plutonium in seaweed and mollusc species along the coast of the English Channel. A study was carried out on the spatial and temporal variation of plutonium iso- topes (2wrh~39~2%) in hioindicator species (Fucus serraius, Patella sp., Mytilus edulis) sampled along the coast of the English Channel. Several penods of the were considered, covering 1982-1983, 1990-1993 and the year 1996. The activity levels of the radionuclides in question were les than 1 Bq kg-'dry basis. A decrease in these activities has been ohserved over a number of years in relation to a reduc- tion in the amounts of plutonium released from the establishment of La Hague. 1,ongshore gradients are apparent in the radionuclide distribution for Fucus. The discrepancy between the isotope ratios measured in the bioindicator species and the releases from industrial sources leads to a discussion of the vanous source-terms affecting plutonium activities. Then concentration factors are defined.