Metal fluxes from porewaters and labile sediment phases for predicting metal exposure and bioaccumulation in benthic invertebrates

The use of diffusive gradients in thin films (DGT) for predicting metal bioavailability was investigated by exposing the bivalve Tellina deltoidalis to an identical series of metal-contaminated sediments deployed simultaneously in the field and laboratory. To understand the differences in metal exposure occurring between laboratory and field-based bioassays, changes in metal fluxes to DGT probes in sediments, and metal concentrations and partitioning to porewaters and overlying waters were investigated. DGT-metal fluxes (Cu, Pb and Zn) were lower in the overlying waters of most field-bioassays compared to the laboratory, causing differences in Pb and Zn bioaccumulation between bivalves exposed to laboratory and field conditions. Overall, DGT-metal fluxes provided predictions of metal bioaccumulation similar to those obtained using dilute-acid extractable metal measurements. This study demonstrates that, irrespective of the physicochemical properties of the sediment and type of exposure (laboratory or field), sediments pose a significant risk of bioaccumulation by T. deltoidalis when the Cu, Pb and Zn DGT flux exceeds 3.5, 1.3 and 156 µg/h/m2, respectively. The results presented here support the use of the DGT technique for sediment quality assessment and the hypothesis that DGT-metal fluxes may potentially be useful surrogates for the lability of metals for all exposure routes.