TEMPERATURE EFFECTS ON CADMIUM AND MERCURY KINETICS IN FRESH-WATER MOLLUSKS UNDER LABORATORY CONDITIONS

The temperature effects on Cd and Hg kinetics between the short-lived gastropod Viviparus georgianus (Lea) and the pelecypod Elliptio compla nata (Lightfoot) were compared under laboratory conditions. A first or der kinetic model was used to estimate, for different age classes and exposure temperatures, the following kinetic parameters; (1) the conce ntration at steady state conditions, (2) the depuration rate constant, (3) the uptake rate constant, and (4) the theoretical bio-concentrati on factor calculated from steady state conditions. The results show th at the uptake and depuration rate constants were not clearly correlate d with an increase of temperature for both species. However, the Cd an d Hg bioconcentration factors for the gastropods increased with temper ature, independent of the age class. For the pelecypods in most of the age classes, there was no clear correlation between the bioconcentrat ion factor and the exposure temperature. This low physiological respon se to temperature suggests that the bioconcentration of the metals in the mussel studied is controlled possibly by physical mechanisms or by biochemical and enzymatical processes of lower intensity.