Comparative bioaccumulation of polycyclic aromatic hydrocarbons from sediment by two infaunal invertebrates

Bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) from field-contaminated sediments by 2 infaunal invertebrates, Rhepoxynius abronius (a non-deposit feeding amphipod) and Armandia brevis (a non-selective, deposit-feeding polychaete), was examined. Sediments were selected over a large geographical area of the Hudson-Raritan estuary (New York, USA) to assess the potential for bioaccumulation from a typical urban estuary. Assessment of bioaccumulation in these invertebrates is important because of the need to understand their health and role in ecosystem functioning and because they are vectors of sediment-associated contaminants to demersal fish. Our study compared the response of these 2 species over a wide range of PAH concentrations to learn how feeding mode may affect contaminant accumulation. After 10 d of exposure to sedirnents, we assessed the tissue concentrations of 24 PAHs and found no significant differences for the low molecular weight PAHs (LPAHs) between R. abronius and A. brevis. There was, however, a large differential observed between species for bioaccumulated high molecular weight PAHs (HPAHs). Because we assumed that the amphipod was not feeding and most of its tissue burden was received through ventilation of interstitial water (IW), we concluded that IW was probably the major route of uptake for the LPAHs for both species and that sediment ingestion was a much more important uptake route of HPAHs for the polychaete. Analysis of correlations between amphipod and polychaete tissue burdens found that the species were responding similarly to a gradient of PAH concentrations in sediment; however, when the associations between concentrations in tissue and exposure matrix (e.g. sediment, IW) were examined the interpretations were less clear. Concentrations of PAHs in IW and sediment indicated that the partition coefficient (&,) was generally 2 orders of magnitude higher than expected for LPAHs and highly variable between sites for HPAHs. When K,, was re-calculated using free PAH, i t became much less variable and was uniformly elevated above the predicted values. The BAF,,, (lipid/organic carbon normalized bioaccumulat~on factor) in the polychaete was generally consistent over the series of PAHs, as expected, and when metabolism and pre-steady state conditions were considered, partitioning of PAHs between tissue and sediment was relatively close to the theoretical maximum. Despite much lower than predicted 1W concentrations, the LPAH bioconcentration factors (BCF) for the amphipod were close to expected, but the HPAH BCFs were close to the predicted values only when expressed in terms of the free PAH. From these data, and previous studies, we conclude that there was a significant reduction in bioavailability of HPAHs to R. abronius due to partitioning of HPAHs to dissolved organic carbon.