COMPARATIVE-STUDY OF THE CADMIUM AND MERCURY KINETICS BETWEEN THE SHORT-LIVED GASTROPOD VIVIPARUS-GEOGIANUS (LEA) AND PELECYPOD ELLIPTIO-COMPLANATA (LIGHTFOOT), UNDER LABORATORY CONDITIONS

A laboratory study of the cadmium and mercury accumulation and elimina tion kinetics was conducted on the pelecypod Elliptio complanata (Ligh tfoot) and the short-lived gastropod Viviparus georgianus (Lea), accor ding to age-classes. Preliminary results (metal concentration vs time of exposure) have demonstrated that uptake of Cd and Hg, in the two mo lluscs studied, follow a biphasic pattern, whereby a steady state is r eached after approximately 16 days' exposure and then accumulation inc reases again for the rest of exposure period. The elimination of the t wo metals is also characterized in a biphasic way: fast excretion for the first four days followed by a slower depuration for the rest of ex posure time. A two-compartment bioaccumulation model has been used to describe the different kinetic parameters: (1) the rate constant for d epuration; (2) the rate constant for uptake; (3) the theoretical bioco ncentration factor extrapolated to steady-state conditions; and (4) th e biological half-life of the metals.