Bioavailability of dissolved zinc to the common mussel Mytilus edulis in complexing environments

Abstract

The bioavailability of dissolved zinc to the common mussel Mytilus edulis 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 nearly linear over a 24 h period for mussel tissues exposed to a 5 μmol l-1 concentration. In most cases, metal complexation decreases zinc uptake by reducing the activity of the free metal ion Zinc uptake rates are similar for 4 of the 5 ligands studied when the free zinc ion activity is kept constant. Complexation of zinc with histidine facilitates the uptake of zinc. Whether the mechanism of facilitation involves the direct uptake of zinc-histidine complexes across the membrane cannot be deduced from the present study. For the same free zinc ion activity, 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 surfaces where conditions may deviate considerably from seawater.