ALTERNATIVE METHODOLOGIES FOR PREDICTING METAL TRANSFER IN MARINE FOOD WEBS INCLUDING FILTER-FEEDERS

A methodology was developed in order to evaluate the role of suspended matter as a vector of metals in food chains. An experimental model was tested for Ag and Cu accumulation in oysters. After short-term exposures (Ag : 2 weeks; Cu : 3 weeks), metal levels in the soft tissues of oysters showed a preponderance of the direct uptake from water over metal transfer through microalgae or sedimentary particles. However, oysters retained a significant percentage of metals from particulate sources and these vectors could get significant in chronic exposures. The major difficulty to overcome in order to generalize this methodology of contamination is to determine the alimentary demands of filter-feeders since responses to a kind of particles may vary considerably from species to species. Another approach consists of determining metal speciation in the most representative organisms at each trophic level in an ecosystem. The limiting factor of metal absorption is often the diet not in terms of the total mineral but the presence of more or less bioavailable metallic compounds as hypothesized for Ag2S in oysters. The predictive value of this alternative method needs to be evaluated by determining directly the metal transfer in an experimental food chain including a small mammal.