Predicting trace metal bioavailability to chironomids in sediments by diffusive gradients in thin films

The technique of diffusive gradients in thin films (DGT) has been developed as a promising tool to assess metal bioavailability in sediment. However, it has yet to be determined whether the DGT-labile metal in sediment is representative of bioavailable fraction for benthic organisms. In this study, the performance of DGT for predicting metal bioavailability was evaluated by exposing DGT and chironomids Chironomus tentans to a series of metal-contaminated natural sediments in the laboratory. Conventional methods, including acid-volatile sulfides and simultaneously extracted metals method, and total recoverable and dilute-acid extractable metal concentrations were also used to assess the availability of Zn, Cu and Pb to chironomids. The bioassay results showed that >70% of the larvae (73 ± 1.7%-98 ± 0.5%) survived in all sediment samples, however, an enhanced uptake of Zn, Cu and Pb by C. tentans in contaminated sediments was observed compared to control sediments. The correlation analyses indicated that the total recoverable metal concentrations and DGT-metal fluxes in the surficial sediment (-1 cm) were all significantly associated with metal bioaccumulation in C. tentans (p < 0.01). Given the advantages of DGT devices for in situ and time-averaged measurement of the potentially bioavailable fraction, DGT-metal fluxes were proved to be a better surrogate to predict C. tentans response to metal contamination. The results further supported the applicability of the DGT technique as an alternative method to assess the bioavailability of metals in sediment to benthic invertebrates.