Comparative experimental study of cadmium and methylmercury trophic transfers between the Asiatic clam Corbicula fluminea and the crayfish Astacus astacus

Cadmium (Cd) and methylmercury (MeHg) trophic transfers were analyzed betwe en the Asiatic clam Corbicula fluminea and the crayfish Astacus astacus. Me tal bioaccumulation in crayfish was quantified after 5, 10, and 15 days of exposure via daily ingestion of soft bodies of C. fluminea, previously expo sed during 7 days to Cd (20 mu g . L-1) and MeHg (4 mu g . L-1). Bioaccumul ation kinetics in the predator were investigated at organ and tissue levels : hemolymph, tail muscle, hepatopancreas, gills, stomach/mesenteron, intest ine, green gland, carapace. Trophic transfer races were estimated at the wh ole organism level. Results showed marked differences (1) in assimilation e fficiencies, mean transfer rates being 5% for Cd and 16% for MeHg; and (2) in the metal distribution within the different tissue compartments of the c rayfish: for Cd, the trophic uptake leads to high concentrations in the hep atopancreas and small accumulation in the muscle tissue; for MeHg, the high est levels of bioaccumulation occur in the green gland and in the tail musc le. From an ecotoxicological point of view, these experimental data suggest a small risk of Cd transfer between the crayfish and predators, humans inc luded; on the other hand, Hg distribution in the muscle and accumulation tr ends in this tissue represent an obvious risk of transfer.