THE RELATION BETWEEN SALINITY AND COPPER COMPLEXING CAPACITY OF NATURAL ESTUARINE WATERS AND THE UPTAKE OF DISSOLVED CU-64 BY MACOMA-BALTHICA

The radiotracer Cu-64 was used to assess the influence of natural orga nic ligands on the bioavailability of copper. Biological availability of the Cu-64-complexes was measured by accumulation in the bivalve Mac oma balthica. The experiments were carried out in April as well as in February with water from the relatively clean Oosterschelde Sea arm an d the relatively polluted Westerschelde estuary. Adsorption onto shell s, as well as uptake in tissues was assessed at salinities of 10 parts per thousand and 30 parts per thousand. Simultaneously with the expos ure experiments, ligand characteristics of the natural waters were ass essed. High ligand concentrations, as occurring in the Westerschelde a round February, reduced Cu-64 (320 nM) uptake by more than 50%, in spi te of the much lower salinity in the Westerschelde water. At the low s alinity, uptake was increased slightly in Westerschelde water, but con siderably in Oosterschelde water. This implies that at low ambient lig and concentrations (during the whole year in Oosterschelde water and i n the summer period also in Westerschelde water) the influence of sali nity on Cu-64 uptake is more pronounced.