Cadmium and copper accumulation in the common mussel Mytilus edulis in the Western Scheldt estuary: a model approach

The Western Scheldt of the Dutch Delta area is severely contaminated with trace metals. Accumulation models of trace metals in the mussel Mytilus edulis are required to predict the biological efficiency of reductions in the metal and organic matter load. Two models are constructed: a black-box model and a physiologically structured model. The black-box model predicts metal accumulation in mussels from uptake and elimination parameters. The physiological model attempts to improve predictions by taking into account the kinetics of individual uptake and elimination routes. These in turn, are taken as depending upon two more general physiological processes, the ventilation rate and the metabolic rate. Metal uptake via food and water are expressed as relative fractions. Metal input is differentiated into particulate adsorbed, and dissolved species.The reliability of the two models is evaluated by comparing predicted concentrations for mussels with measurements. Model predictions for copper deviate less than 100% from measured concentrations, but neither model appears to predict cadmium concentration with sufficient accuracy since deviations of more than 100% occured. The introduction of physiological refinements did not improve performance. Food mediated contributions for cadmium and copper to total body burden had been overestimated in the model by a factor of 100 when compared to literature values. The physiological model did predict that the ratio of food mediated contribution to total body burden is probably different for cadmium and copper and decreases with increasing salinity for both. As yet there are no measurements available to confirm such predictions.We conclude that additional laboratory experiments should be done for a better understanding of why there is poor agreement between the few field observations and the simulations. In these experiments mussels grown under different environmental condition can be tested for their accumulation capacity of trace metals. More field observations are needed.