Modeling metal bioaccumulation in a deposit-feeding polychaete from labile sediment fractions and from pore water

Estuarine sediments are often highly enriched in particle-reactive metal contaminants and because aquatic animals have often been shown to acquire metals predominantly from their diet, benthic animals feeding on deposited or resuspended sediments may also accumulate metals through this uptake pathway. Laboratory experiments were performed in which the surface deposit-feeding polychaete, Nereis succinea, was exposed to As(+5), Cd, and Cr(+3) in pore water or in estuarine sediments with and without enrichment with algal debris. These experiments generated metal uptake parameters (assimilation efciency of ingested metal [AE], uptake rate constant of dissolved metal, efflux rate constants following dietary or aqueous metal exposures) used in a kinetic model of metal bioaccumulation. The model showed that N97% of the body burden of these metals is accumulated through ingested sediment. The kinetic model was further modied to consider the geochemical fractionation of themetals in the sediments becausemetals bound to some fractions were shown to be unavailable to these polychaetes. The modied model substituted the AE term for each metal by the percentage of metal extracted in neutral and weak acid exchangeable fractions (termed "carbonex" fraction) multiplied by the slope of the regression between themetal AE and its fractionation in carbonex. Themodied model generated predictions of As, Cd, and Cr body burdens in polychaetes at three different estuarine sites that matched independent eld observations at these sites (r ² =0.84 for sediments without organic enrichment, r ² =0.87 with organic enrichment). Model predictions that relied on total metal concentrations showed weaker relationships (r ² =0.11-0.50). This study adds to the evidence for the dominance of dietary uptake of metals in aquatic animals and identies a key sedimentary fraction of metals that can account for bioavailability of sediment-bound metals.