Evolution of element release during oxidation and its relevance towards the management of contaminated sediments

The understanding of the behaviour and fate of contaminants in soils, sediments and dredged materials is essential to deal with their management. In the present study, heavy-metal contaminated anoxic sediments originating from different locations in Flanders (Belgium) were exposed to oxidizing conditions during 20 weeks in order obtain a better insight in the release of elements during oxidation. Heavy metal release during oxidation was in accordance with theevolution of porewater pH, which was on its turn determined by the cidneutralizing capacity (ANC) of the sediments. Three categories of sediments could be distinguished based on the evolution of sediment and porewater composition during oxidation. Clay content was an important factor in determining the ANC, whereas the total metal load was not indicative for the potential release of heavy metals. Moreover, the precipitation of Fe-(hydr)oxides or the formation of secondary minerals influenced heavy metal concentrations released into the porewater, pointing to the importance of mineralogical sediment characterisation in the environmental impact assessment.