Abstract. The amount of copper taken up via algae and water by Macoma balthica from the Oosterschelde sea arm, S.W. Netherlands, was established using the radioisotope 64Cu. As far as we know, this isotope has never been used before in marine food chain studies. As a model food source the marine diatom Phaeodactylum tricornutum was allowed to accumulate 64Cu for 1 d.These labelled algae were fed to the clams in the presence of the complexing agent EDTA (0.27 raM). EDTA was added to prevent uptake of dissolved 64Cu that could be leaking from the labelled diatoms. In control experiments, unlabelled diatoms were fed to M. balthica in the presence of dissolved 64Cu (with and without EDTA) in order to assure a similar filtration activity. In repeated experiments with varying particulate/dissolved copper ratios, uptake through food always turned out to be at least as efficient as uptake from the water. It was concluded that Cu, associated with food, is well available for uptake by M. balthica.

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The radiotracer 64 Cu was used to assess the influence of natural organic ligands on the bioavailability of copper. Biological availability of the 64 Cu-complexes was measured by accumulation in the bivalve Macoma balthica. The experiments were carried out in April as well as in February with water from the relatively clean Oosterschelde Sea arm and the relatively polluted Westerschelde estuary. Adsorption onto shells, as well as uptake in tissues was assessed at salinities of 10%o and 30%o. Simultaneously with the exposure experiments, ligand characteristics of the natural waters were assessed. High ligand concentrations, as occurring in the Westerschelde around February, reduced 64 Cu (320 nM) uptake by more than 50%, in spite of the much lower salinity in the Westerschelde water. At the low salinity, uptake was increased slightly in Westerschelde water, but considerably in Oosterschelde water. This implies that at low ambient ligand concentrations (during the whole year in Oosterschelde water and in the summer period also in Westerschelde water) the influence of salinity on 64 Cu uptake is more pronounced.

Abstract.To study the role of food in Cu accumulation by bivalves, algae spiked with Cu can be used. With spiked algae, however, redistribution of Cu between the dissolved and the particulate phase hampers the assessment of the contribution of food. This occurred in efforts to label algae with the radiotracer 64Cu. A method was designed to overcome this problem of redistribution. By adding excess EDTA to seawater, the biological availability of dissolved Cu was minimized. The effectiveness of complexation by EDTA was controlled through adsorption on Macoma balthica shells and uptake in M. balthica tissue.