Effects of copper and cadmium exposure on functional responses of hemocytes in the clam Tapes philippinarum

The effects of Cu and Cd on functional responses of hemocytes in Tapes philippinarum, a Veneridae clam widespread in the lagoon of Venice, were evaluated. Bivalves were exposed for 7 days to various concentrations of CuCl2 z 2H2O (0, 10, 60, and 110 mg/L) and CdCl2 z H2O (0, 150, 300, and 450 mg/L). Hemocytes were collected from exposed clams, and the effects of Cu and Cd on phagocytosis, Neutral Red retention capacity, superoxide dismutase, and cytochrome oxidase activities were investigated. Hemocytes from animals exposed to Cu showed a significant decrease in phagocytic activity, whereas no inhibition was observed in cells from Cd-exposed animals. Diffusion of Neutral Red into the cytosol, an index of lysosomal membrane alteration, was enhanced by high concentrations of both metals. Different results in biochemical parameters were observed. Exposure to 60 and 110 mg Cu/L caused a significant reduction in hemocyte superoxide dismutase activity, whereas no changes resulted after Cd exposure. Increased cytochrome oxidase activity was observed in hemocytes from mollusks exposed to 60 mg Cu/L and 300 mg Cd/L; no significant differences were found in cells from bivalves exposed to 110 mg Cu/L and 450 mg Cd/L. These results suggest a relationship between heavy metal exposure and alterations in functional responses of hemocytes in T. philippinarum and indicate that the type of observed effects vary with the nature and concentration of heavy metals. Moreover, the data obtained in the analyzed clam support the possibility of using it as sentinel organism in biomonitoring studies, even if used biomarkers will be further evaluated in field conditions.