Assessing the bioavailability of metals in natural sediments by DGT passive sampling and bioaccumulation

Introduction: Worldwide, high metal concentrations from recent and historic sediment contamination form a widespread problem in aquatic ecosystems and are of major concern for water system managers due to their impact on the surrounding water quality and resident biota. Sediment related metals can be present in a range of different physicochemical forms, some of which may be unavailable, non-toxic and therefore not-harmful to organisms so that the interplay between chemical speciation and biological effects can be very site specific and hard to predict [1]. Total sediment concentrations are therefore often found to be poor predictors of the actual risk and a measure of bio-availability should be considered in risk assessment procedures [2]. In this regard however, the established techniques of measuring the level of bioaccumulation in exposed organisms has been experienced to be highly disruptive, time consuming and limited in comparability as its results are strongly dependent on the analysed organisms themselves. Therefore, an increasing need for less disruptive, more reliable and standardized methods exists. Recently, passive samplers have been tested to estimate the bioavailable contaminant fraction as well as the contaminant flux over sediment-water interface over time. Diffusive Gradient in Thin film samplers (DGTs) have been indicated to provide reliable predictions of metal bioavailability and toxic potential for single (benthic) invertebrate species under (semi-) controlled conditions, by allowing weakly bound metals to selectively accumulate onto a Chelexembedded hydrogel layer [3]. In this study, the use of DGT passive sampler as indicators for the bioavailability of metals for (benthic) macroinvertebrates should be evaluated and the robustness of the results from laboratory studies under field conditions be tested. The results are expected to increase the insights in the applicability of passive sampler for future sediment risk assessment and to be useful for the development of more standardized and integrated approaches.