Chronic Effects of Waterborne Silver on the Physiology and Reproduction of the Manila Clam Ruditapes philippinarum

To evaluate the potential toxicity of waterborne silver (Ag), we analyzed the chronic effects of Ag on the physiological and reproductive responses of the Manila clam Ruditapes philippinarum. Clams were exposed to dissolved Ag (AgNO3) at concentrations of 0 (control), 0.03, 0.06, and 0.12 µmol L–1 for 6 weeks. The clearance rate, food absorption efficiency, and respiration rate of clams exposed to Ag were measured to determine their scope for growth (SFG). Histological assays were conducted to investigate gonad development in the clams. Despite considerable Ag accumulation in tissues at all test concentrations, no mortality occurred during the experiment, indicating that even an Ag concentration of 0.12 µmol L–1 did not have lethal effects within 6 weeks. However, the clearance rate and absorption efficiency markedly decreased in clams exposed to 0.12 µmol Ag L–1, resulting in a decline in SFG. Gonadal development was significantly delayed in female clams exposed to 0.06 and 0.12 µmol Ag L–1 for 6 weeks. These data suggest that the SFG and reproductive condition of clams analyzed in this study reflect the physiological status of R. philippinarum exposed to sublethal concentrations of Ag.