Field transplantation of the freshwater bivalve Corbicula fluminea along apolymetallic contamination gradient (river Lot, France): I. Geochemical characteristics of the sampling sites and cadmium and zinc bioaccumulation kinetics

Specimens of the Asiatic clam Corbicula fluminea were transplanted from a c lean lacustrine site to four stations along a polymetallic gradient in the river Lot (France), downstream from an old Zn ore treatment facility. The b ivalves were held in benthic cages for a 5-month exposure period, April to September 1996: mollusk growth and metal bioaccumulation kinetics (Cd, Zn w ere followed by subsampling the cages at t = 0, 21, 49, 85, 120, and 150 d. Rates of Cd bioaccumulation in the whole soft bodies and in individual org ans were greater at the upstream stations located close to the pollution so urce, but there was no direct proportionality between Cd in the bivalves an d in the unfiltered or filtered river water samples. Unlike the case for Cd , rates of Zn bioaccumulation did not reflect the contamination gradient. M arked growth differences were measured among the four stations, reflecting both nutritional differences and changes in the degree of metal contaminati on; these growth differences produced markedly different trends when metal bioaccumulation was expressed in terms of burdens rather than concentration s.