Sediment water (interface) mobility of metal(loid)s and nutrients under undisturbed conditions and during resuspension

The contribution of the release from sediments to the overall river Trave budget was evaluated with respect to 16 metal(loid)s, three non-metals and the ions PO₄^3- and NH₄⁺. To consider undisturbed conditions and sediment resuspension in-situ dialyses-based and ex-situ suction-based pore water sampling was complemented by sequential extraction and suspension reactor experiments. In the investigated sediments, representative for the study area, metal(loid) partitioning between the different geochemical fractions was very similar despite some higher contaminated spots. Pore water investigations emphasis that profiling and peeper based analyses are comparable and deliver an indication that sediment dwelling organisms are exposed to elevated metal(loid) concentrations. However, higher toxicity of the contaminated sediments compared to the sediment treated as background reference was not revealed. During resuspension only few metal(loid)s exceeded specified guideline values. The maximum amounts released, were only between 10^-5 and 10^-1% of the average daily load of the river Trave per ton of suspended sediment. Overall the "most pristine sediments" and not the potentially hazardous materials in the study area are found to be from highest concern. The results support requests to better include fractionation and speciation demands in legal assessments of sediments.