Effect of carbon dioxide on uranium bioaccumulation in the freshwater clam Corbicula fluminea

This paper presents the results of a study examining the impact of CO2 variations in water on uranium bioaccumulation in the bivalve Corbicula fluminea. The objectives were to evaluate the effect of CO2 on bivalve behavior (valve activity and ventilation rate) that are related to bioaccumulation and on the bioavailability of uranium carbonate complexes to the bivalve. It was demonstrated that at a total inorganic carbon concentration of Cco2 = 276 micromol/L, the daily valve opening duration and ventilation rate are significantly (p < 0.05) lower than those obtained at 27.6 micromol/L (-28 and -47%, respectively). For both Cco2 values, exposure to uranium at 0.25 micromol/L had no impact on valve activity; however, ventilation decreased significantly compared to the reference condition, down to the same lower level for the two Cco2 conditions. Consequently, the quantity of uranium passing through the bivalve was identical for both Cco2 conditions. Thus, bivalve ventilatory and valve activity could not explain increased bioaccumulation in the gills and mantle measured under the low-Cco2 condition. Consequently, we suggest that the quantity of carbonate bound to the U fraction must be less bioavailable than other U species such as the free-ion UO(2)2+, which is in accordance with the biotic ligand model.