A COMPARISON BETWEEN PARTICULATE (ELEMENTAL) ZINC AND SOLUBLE ZINC (ZNCL2) UPTAKE AND EFFECTS IN THE MUSSEL, MYTILUS-EDULIS

The uptake of particulate (elemental) and soluble (ZnCl2) zinc was compared in whole animals and individual organs in the mussel Mytilus edulis. Analysis of seawater showed that the addition of particulate zinc resulted in a maximum concentration of 0.7 mu g/g dissolved zinc being present in the aquaria. Mussels exposed to either form of zinc at 10 mu g/g accumulated it readily, although considerable mortality was experienced after 14 days. After loading with particulate zinc, depuration for 48 h significantly lowered (p < 0.001) the concentration of zinc in whole mussels. Mussels loaded at 2 mu g/g showed a similar pattern of accumulation to those exposed at 10 mu g/g, although with a lower mortality. Greater whole body concentrations were obtained with particulate zinc than with soluble zinc. On an organ basis, the kidney, gill, hepatopancreas, and mantle were the major sites of accumulation following both soluble and particulate zinc loading, although generally the levels were lower with particulate loading, indicating the possible presence of two different uptake pathways. The flesh condition index of mussels subjected to 10 mu g/g particulate zinc declined compared to the control animals. Degeneration of the digestive tubules and the stomach was visible in zinc-loaded mussels while no such tissue damage was seen in control animals. Tissue damage, as indicated by the presence of large quantities of lipofuschin, occurred in the hepatopancreas and gonads of particulate zinc-loaded mussels. The results indicate that soluble zinc is both absorbed and taken up by the tissues far more readily than is particulate zinc, and these results may be of significance with regard to zinc loading in the mussel Mytilus edulis.