Modeling cadmium uptake from water and food by the freshwater bivalve Pyganodon grandis

For this study, the unionid bivalve Pyganodon grandis was either exposed to dissolved cadmium (Cd) or fed Cd-contaminated algae ( Pseudokirchneriella subcapitata ) during short-term laboratory experiments. Cadmium accumulated largely in the digestive gland after a dietary exposure, or in the gills after an aqueous exposure; in these latter experiments, Cd accumulation from the dissolved phase increased as bivalve filtration rates increased. The results of these uptake experiments were used to parameterize a biodynamic model, which was then used to estimate the relative importance of water and food as sources of Cd for this bivalve, and to predict steady state Cd concentrations in the gills and digestive gland of native bivalves. In comparisons between the simulations and data obtained from earlier field studies on P. grandis, the model adequately predicted Cd concentrations in P. grandis gills, except in Ca-rich lakes, whereas it tended to overestimate Cd concentrations in the digestive gland. The field simulations indicate that water is the main source of Cd for both the gills (relative importance water:food::99:1) and the digestive gland (water:food::80:20). These results will facilitate the interpretation of spatial and temporal variations in Cd concentrations in free-living P. grandis, which is a promising metal biomonitor.