Bioaccumulation of waterborne selenium in the Asiatic clam Corbicula fluminea: influence of feeding-induced ventilatory activity and selenium species.

A set of experiments was performed to investigate the bioavailability and the effect of Se on the ventilatory activity of the bivalve Corbicula fluminea, under different conditions of both algal cell densities and dissolved Se chemical forms and concentrations. A first set of experiments was conducted without selenium to investigate the changes in the ventilatory flow rate as a function of the concentration of the unicellular alga Chlamydomonas reinhardtii (10(5)-10(6) cells mL(-1)). For algal concentrations below 2-3x10(5) cells mL(-1), ventilatory activity was highly stimulated whereas it was independent of algal densities for higher values (up to 10(6) cells mL(-1)). To investigate the influence of this first ventilatory drive on selenium contamination process, bivalves were exposed to waterborne selenium at two different algal concentrations, selected to provide contrasting reference ventilatory activities. Three different selenium forms were studied [selenite Se(+IV), selenate Se(+VI) and selenomethionine SeMet] and were added into the water at concentrations of 50 and/or 500 microg L(-1). Each selenium form induced a specific behavioural response, an increase, a decrease or no change of ventilation being observed for Se(+IV), SeMet and Se(+VI), respectively. Selenium accumulation by the organisms was investigated at the organ level for the different exposure conditions. Selenomethionine was the most bioaccumulated form, followed by selenate and selenite, respectively. Despite the bivalves displaying different ventilatory behaviours at low or high algal density, there was no evidence showing reduction or enhancement of Se uptake in the chemical domain investigated.