Effects of environmental parameters on the elimination of cadmium by eastern oysters, Crassostrea virginica.

Abstract

Laboratory studies were conducted to test the effects of salinity, humic acid, and temperature on the rate of elimination of109Cd from laboratory-dosed juvenile oysters,Crassostrea virginica. After 140 days, oysters maintained at 34 parts per thousand (ppt) salinity retained 67% of the109Cd dose (CPM), oysters in 20 ppt salinity retained 72% and those in 6 ppt salinity retained 80%. The presence of humic acid in 14 ppt salinity water enhanced the amount of109Cd eliminated in 140 days relative to oysters in control tanks without humic acid: oysters exposed to 10 parts per million (ppm) humic acid retained 65%, oysters exposed to 1 ppm humic acid retained 67%, controls retained 72%. Temperature had a significant effect on the rate of Cd elimination. Oysters held at 28°C and 20 ppt for 28 days retained 75%, oysters at 20°C and 20 ppt retained 81% and those at 12°C and 20 ppt retained 88% of109Cd dose. The effects of a strong Cd-chelator, ethylenediamine tetraacetic acid-sodium salt (EDTA), were compared with those of the relatively weaker chelator, humic acid, on the rate of Cd elimination by oysters. No difference was observed between the two chelators over a 28 day depuration period. Cadmium concentrations were monitored in the water and Cd, Cu, Zn, Mg, and Fe concentrations were determined in the animals on the final day of the studies. Particle clearance assays were performed to determine if the rate of filtration by the oysters held in each of the test treatments correlated with the rates of Cd depuration. No direct correlation was observed.