Bioavailability of particle-associated silver, cadmium, and zinc to the estuarine amphipod Leptocheirus plumulosus through dietary ingestion

We conducted experiments to determine effects of particle type on assimilat ory metal bioavailability to Leptocheirus plumulosus, an infaunal, estuarin e amphipod that is commonly used in sediment toxicity tests. The following particles were used to represent natural food items encountered by this sur face-deposit and suspension-feeding amphipod: bacterial exopolymeric sedime nt coatings, polymeric coatings made from Spartina alterniflora extract, am orphous iron oxide coatings, the diatom Phaeodactylum tricornutum, the chlo rophyte Dunaliella tertiolecta, processed estuarine sediment, and fresh est uarine sediment. Bioavailability of the gamma-emitting radioisotopes Ag-110 m, Cd-109, and Zn-65 was measured as the efficiency with which L. plumulosu s assimilated metals from particles using pulse-chase methods. Ag and Cd as similation efficiencies were highest from bacterial exopolymeric coatings. Zn assimilation efficiency exhibited considerable interexperimental variati on; the highest Zn assimilation efficiencies were measured from phytoplankt on and processed sediment. In general, Ag and Cd assimilation efficiencies from phytoplankton were low and not related to the proportion of metal asso ciated with cell cytosol or cytoplasm, a phenomenon reported for other part icle-ingesting invertebrates. Amphipod digestive processes explain differen ces in Ag and Cd assimilation efficiencies between exopolymeric coatings an d phytoplankton. Results highlight the importance of labile polymeric organ ic carbon sediment coatings in dietary metals uptake by this benthic invert ebrate, rather than recalcitrant organic carbon, mineralogical features suc h as iron oxides, or phytoplankton.