Dietary metal bioavailability in razor clam Sinonovacula constricta under fluctuating seston environments

To understand the potential risks of dietary metals to marine bivalves, it is important to study the interaction between dietary metal bioaccumulation and bivalve feeding behavior. Key processes in affecting the dietary metal influx are the selection of different particles during the ingestion process as well as the differential assimilation of metals during the digestion process. In this study, we quantified the influences of seston quality and quantity on the dietary assimilation of Cd and Zn as well as pre-ingestion particle selectivity in a razor clam Sinonovacula constricta following feeding on radiolabeled diatoms and sediments with different mixtures at four food concentrations. Bioavailability of ¹⁰⁹Cd and ⁶⁵Zn from seston was measured by assimilation efficiency (AE) using a pulse-chase feeding technique. The AEs of Cd and Zn were significantly affected by the seston quantity and quality (higher for Zn than they were for Cd and higher for diatoms than for suspended sediments), but were independent of the presence of other particles during the feeding process. Dual gamma radiotracer technique was further employed to study pre-ingestion particle selectivity. Particle selectivity was weak during pre-ingestion in razor clams, although there was evidence that clams might be able to differentiate particles during the process of pseudofeces production. Our study demonstrated that seston composition and quantity substantially affected the bioavailability of Cd and Zn to the razor clams. The results are important to understand the bioaccumulation of metals in clams living in dynamic food environments of estuary.