BIOAVAILABILITY OF DISSOLVED ZINC TO THE COMMON MUSSEL MYTILUS-EDULISIN COMPLEXING ENVIRONMENTS

The bioavailability oi dissolved zinc to the common mussel Mytilus edu lis was studied in chemically defined seawater containing 5 different organic ligands. Zinc uptake shows saturable kinetics, indicating that it is a facilitated process. The uptake of zinc from solution is near ly Linear over a 24 h period for mussel tissues exposed to a 5 mu mol l(-1) concentration. In most cases, metal complexation decreases zinc uptake by reducing the activity of the free metal ion. Zinc uptake rat es are similar for 4 of the 5 ligands studied when the free zinc ion a ctivity is kept constant. Complexation of zinc with histidine facilita tes the uptake of zinc. Whether the mechanism of facilitation involves the direct uptake of zinc-histidine complexes across the membrane can not be deduced from the present study. For the same free zinc ion acti vity, the availability of zinc is higher in the digestive system than in the gills. The observed differences can be caused by changes in the chemical speciation of the metals in the layers lining the exchange s urfaces where conditions may deviate considerably from seawater.