Benthic invertebrates may be exposed to metals in pore water, overlying water, ingested sediments, and other food particles. Rates and routes of metal exposure have important implications for predicting toxicity and interpreting toxicity test results. For the standard test amphipod Leptocheirus plumulosus, radiotracer techniques were used to quantify rates of Cd, As, Hg(II), and CH(3)Hg bioaccumulation from water and from suspension feeding on labeled microalgae. Measured parameters were incorporated into a bioaccumulation model to predict steady-state metal concentrations in L. plumulosus and to evaluate the relative importance of aqueous and dietary uptake pathways across a range of ingested particle types and ingestion rates. Results indicate that ingested particles contribute strongly to metal bioaccumulation and that feeding plasticity could strongly influence metal exposure. As L. plumulosus switches from suspension feeding to deposit feeding or selectively feeds on particles for which it has a high assimilation efficiency, metal exposure and body burden will increase. At ingestion rates previously reported for deposit feeding (3 g/g/d), dietary metal sources dominate metal bioaccumulation and can be responsible for greater than 90% of metal bioaccumulated, regardless of metal partitioning or ingested particle type. These results suggest that more research on L. plumulosus feeding behavior is needed to produce a more complete mechanistic understanding of metal bioaccumulation.
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