A pre-screening technique for bioavailable metals in sediments

In this study, a novel application of the diffusive gradients in thin films (DGT) technique as a monitoring tool for bioavailable metals in sediments is presented. DGT was tested using a wide range of marine and fresh water sediments that possessed a variety of chemical and physical properties. These were tested in both the laboratory and in the field. In the laboratory, the use of naturally contaminated sediments allowed the evaluation of the performance of the DGT technique under realistic environmental conditions (i.e. exposure to contaminant mixtures). Strong dose-response relationships were found between DGT-labile metal fluxes and toxicity to the marine amphipod Melita plumulosa. The combined flux of metals (Cd, Cu, Ni, Pb and Zn) measured at the sediment water interface (SWI) provided a robust measure of the bioavailable pool of metals present in the sediment and overlying water. A flux normalisation approach was adopted in an attempt to account for different toxicity caused by different metals, and this significantly improved the relationship between DGT and toxicity. The performance of the DGT technique to predict metal bioavailability was also investigated by comparing DGT-labile metal fluxes from identical metal contaminated sediments deployed in the field and under laboratory conditions with metal bioaccumulation in Tellina deltoidalis (marine bivalve) and Hyridella australis (freshwater bivalve). The combined laboratory and field results indicated that DGT-labile metal fluxes measured at the SWI provide robust predictions of metal bioaccumulation in Tellina deltoidalis (marine bivalve) and Hyridella australis (freshwater bivalve), irrespective of the type of exposure (laboratory vs field). There was a mismatch between laboratory and field bioassay results for both species which emphasised the importance of performing in situ tests for environmental risk assessments.