Bioavailability of pyrene to the deposit-feeding polychaete Arenicola marina: importance of sediment versus water uptake routes

The bioavailability of the PAH (polycyclic aromatic hydrocarbon) model compound pyrene to the deposit-feeding polychaete Arenicola marina was studied at pyrene concentrations ranging from 0 to 10 ppm. By manipulating the sediment organic content, different distributions of pyrene between particle-associated pyrene, pyrene bound to dissolved organic matter (DOM) and freely dissolved pyrene were obtained at the same pyrene concentration in bulk sediment. The results showed that organic matter influenced the partitioning of pyrene in the sediment matrix. The concentration of dissolved pyrene in porewater and overlying water was higher in sediment with a high organic content, probably due to an increased DOM concentration. In contrast, the concentration of freely dissolved pyrene was, as expected, higher in sediment with low organic content. Bioaccumulation of pyrene correlated very well with the amount of pyrene passing through the gut, indicating that particle-associated pyrene is bioavailable and that ingestion is an important uptake route. Body burden was correlated neither with total dissolved pyrene nor with freely dissolved pyrene, leading one to reject the hypothesis that pyrene uptake is due to simple diffusion processes from water to sediment. Furthermore, no relation between bioaccumulation and dissolved pyrene passing through the gills via irrigation was observed. Bioconcentration factors relative to sediment and water declined with increasing external pyrene concentrations, enhancing the likelihood of sediment toxicity being underestimated when using these factors in risk assessment.