Application of diffusive gradients in thin films (DGT) and simultaneously extracted metals (SEM) for evaluating bioavailability of metal contaminants in the sediments of Taihu Lake, China.

The toxicities of heavy metals in sediments are related to their bioavailability, which is critical for deriving reliable sediment quality guidelines. To evaluate the bioavailability of the metals (Cd, Cu, Ni, Pb and Zn), sediments were collected from Taihu Lake, one of the largest and most important freshwater lakes in China. Concentrations of simultaneously extracted metals (1-M HCl extraction, C SEM) in the sediments, metals released from sediment to pore waters and accumulated by diffusive gradients in thin films (DGT, C DGT), and dissolved metals in the overlying water (C OLW) were measured separately. Sediment toxicity was assessed with tubificids (Monopylephorus limosus) and chironomids (Chironomus kiiensis and Chironomus tentans). Significant relationships existed between the total metal concentrations and C SEM , C DGT , and C OLW measurements (r ² = 0.43–0.95, n = 27, p < 0.001), with stronger relationships with C SEM (r ² = 0.91–0.95) than C DGT (r ² = 0.56–0.85) and C OLW (r ² = 0.43–0.71). Risk quotients were derived by dividing C SEM by sediment quality guideline values (SQGVs), and by dividing both C DGT and C OLW by water quality criteria (WQC). Toxicity of the sediments to the three species was better explained by the C SEM -based risk quotient than those derived from C DGT and C OLW. The study indicated that DGT piston probes deployed face down in sediments did not accumulate metals in proportion to the bioavailable metal fraction that caused toxicity to these freshwater benthic organisms, and that single measurements of metals in overlying waters are not adequate for predicting risks of toxicity from sediments. The measurement of C SEM was determined to be effective for assessing the risk posed by the metals in the Taihu Lake sediments, but offered limited improvement over measurement of total metal concentrations. • DGT and SEM were used to measure the bioavailable metal contaminants in the freshwater sediments of Taihu Lake, China. • DGT and SEM concentrations of the metals of Cd, Cu, Ni, Pb and Zn significantly correlated with the total concentrations. • Risk quotients derived by normalizing SEM with SQGV showed significant correlations with the toxicity of the sediments. [ABSTRACT FROM AUTHOR]