Selenium bioaccumulation in Chlamydomonas reinhardtii and subsequent transfer to Corbicula fluminea:: Role of selenium speciation and bivalve ventilation

The uptake of Se by the freshwater alga Chlamydomonas reinhardtii and the subsequent transfer to the Asiatic clam Corbicula fluminea was investigated. The objective was to investigate the bioavailability of algal-bound Se for C. fluminea while taking into account Se speciation and bivalve ventilation. First, uptake rates of waterborne Se (selenite, selenate, and selenomethionine) in the algae during a 1-h exposure period were determined for a range of concentrations up to 2,000 mu g/L. Fluxes for selenite uptake were constant in the range of concentrations tested, whereas fluxes for selenate and selenomethionine uptake decreased with increasing concentrations, suggesting a saturated transport system at high concentrations (similar to 1,000 mu g/L for selenate and 100 mu g/L for selenomethionine). These data were used to set the algal contamination for the study of trophic transfer to the clam. Three parameters were studied: The Se form, the algal density, and the Se burden in the algae. The results show that for a fixed algal density, an Se-contaminated algal diet does not modify ventilation. In this case, the driving factor for ventilation is the algal density, with ventilation being enhanced for low algal densities. On the basis of ventilatory flow rate measurements and Se burdens in algae, it was found that bioaccumulation of Se in C. fluminea was proportional to the total quantity of Se passing through the whole organism, but with a lesser extraction coefficient for selenomethionine than for the inorganic forms. These results underline the importance of both physiological factors and speciation in understanding the trophic transfer of Se.