The influence of sediment, food and organic ligands on the uptake of copper by sediment-dwelling bivalves

The sediment-dwelling bivalve Macoma balthica was exposed to dissolved copper ina flow-through system in long-term experiments. Unlike another sediment-dwelling bivalve, the suspension feeder Cerastoderma edule (cockle), M. balthica accumulated copper from the sediment, while the cockles did not. When dwelling in silty, organic-rich sediment, M. balthica accumulated less from the water, whereas accumulation in the cockle was not influenced by the sediment type. In water from the Oosterschelde sea-arm, total organic ligand concentrations were around 100 nanoequivalent copper, with a free Cu2+ concentration of 6.3 x 10(-14) M (pCu 13.20). Addition of 400 nM Cu (25 mu g l(-1)) resulted in a free Cu2+ concentration of 2.19 x 10(-8) M (pCu 7.66); Addition of low concentrations of EDTA caused a reduction of Cu uptake, which was confirmed with the calculated cupric ion activity. In water with 400 nM Cu, M. balthica accumulated more copper when fed on copper-enriched algae than without the addition of the algae. This accumulation occurred despite a decrease in filtration rates and indicates an important contribution of food-associated copper to the overall accumulation by Macoma balthica.