Influences of sediment geochemistry on metal bioavailability and effects on macroinvertebrate communities

In anoxic sediments, metal bioavailability is dominantly controlled by Acid Volatile Sulfides (AVS). AVS is the sulfide fraction which is operationally defined through extraction of wet sediment with hydrochloric acid (HCI). Metals which are associated and together extracted with AVS are called Simultaneously Extracted Metals (SEM). Since in the past decades contradictory results have been observed concerning the protective capacity of AVS and the importance of metal exposure routes (pore water vs. dietary metal), some important drawbacks need to be fully investigated, including the relation between AVS and bioaccumulation under environmentally realistic conditions, the importance of an organisms' feeding behavior and ecology, the metabolic availability of accumulated sulfide-bound metals and the impact of increasing oxygen levels on natural AVS concentrations.;The results of the current thesis clearly proved that benthic invertebrates can take up and accumulate metals from contaminated anoxic sediments to a large extent, and that this accumulation cannot be related to environmental AVS levels. Regarding the implications of this elevated tissue concentrations, we observed that accumulated sulfide-bound metals were primarily detoxified in the benthic oligochaete T. tubifex. Regarding species which are dominantly exposed through water, our results indicated that geochemical sediment conditions might influence metal accumulation if the species of concern does not feed on contaminated sediment particles or suspended matter. Nevertheless metal toxicity in the water-exposed waterflea D. magna could not be excluded when elevated AVS levels, compared to SEM, were measured in the superficial sediment layer. Furthermore our results demonstrated that increasing oxygen levels in the environment can break down metal-sulfide complexes and release metals into the sediment pore water, where they can become bioavailable to aquatic organisms.;Overall we can conclude that, although quantification of AVS levels provides a useful estimate of metal mobility in contaminated, anoxic sediments, results regarding the applicability of the AVS approach with respect to bioaccumulation and toxicity should always be carefully interpreted, taking into account the biology of the organism studied. Finally, our findings have important consequences regarding the risk assessment of anoxic, metal contaminated sediments, which are generally considered to be little harmful to the aquatic environment.