Cadmium kinetics in freshwater clams. V. Cadmium-copper interaction in metal accumulation by Anodonta cygnea and characterization of the metal-binding protein.

Freshwater clams were exposed for 6 1/2 weeks to cadmium chloride, at 48 ppb1 Cd, or to copper chloride, at 47 ppb Cu, or to a mixture of the salts, at 122 ppb Cd + 139 ppb Cu. The Cd-accumulation factor (AF) for whole animal was reduced by 90% in the presence of Cu. Cu-AF was reduced by 50% in the presence of Cd. Copper did not influence the in vitro uptake of Cd by the excised gill but increased the elimination of previously accumulated Cd. However, decrease of the ventilation rate probably accounts for the greater part of the Cu effect on Cd accumulation. In the cytosol, the two metals were partitioned between two protein fractions in gel permeation. Except for hepatopancreas, Cu was for the greater part bound to the high-molecular-weight fraction. Cadmium was mainly bound to a specific metal-binding, carbohydrate-containing protein fraction of Mr approximately 11,000. Co-exposure to copper increased the portion of Cd bound to this fraction.