TRACE-METALS IN THE MARINE BIVALVE MACOMA-BALTHICA IN THE WESTERSCHELDE ESTUARY, THE NETHERLANDS .2. INTRACELLULAR PARTITIONING OF COPPER, CADMIUM, ZINC AND IRON - VARIATIONS OF THE CYTOPLASMIC METAL CONCENTRATIONS IN NATURAL AND IN IN-VITRO CONTAMINATED CLAMS

The intracellular distribution of copper, cadmium, zinc and iron in the marine bivalve Macoma balthica has been studied for 18 months at two locations from the Westerschelde estuary. Metal concentrations in the soluble fraction (cytosol) and in the particulate phase of the soft tissues were measured by atomic absorption spectrometry. Considering all data, heat-stable cytosolic metal accounts for 10-33% of total Cu, almost-equal-to 0-28% of total Cd, 7-17% of total Zn and 2-8% of total Fe. The case of non-essential cadmium is extremely interesting since the average difference in total concentration between the two stations (factor of 4) induces a much more marked average difference in cytosolic metal (factor of 15). Short term metal exposures carried out in the laboratory show a high sensitivity of this clam to Cd, a moderate sensitivity to Cu and no uptake of Zn. For the essential elements, the intracellular partitioning is not significantly affected. On the contrary, the extra load of cadmium provokes a large increase of the proportion of cytosolic metal, especially obvious when the natural cadmium concentration is low.