Mobilization and scavenging of heavy metals following resuspension of anoxic sediments from the Elbe River

Resuspension of sediments from the Elbe River can significantly decrease pH values due to high acid-producting potential and low neutralizing capacity. Metals can be released into the dissolved phase, but may subsequently be readsorbed or precipitated in part to solid phases. To evaluate the potential for metal release and scavenging on a regional and long-term scale, experiments were undertaken at stable neutral-pH values. Rates of total metal release and metal scavenging were extrapolated from time series of netrelease values measured over 630 hours. The order of total release from the sediment was Cd (5%) > Zn (1.5%) > Cu (1%) > Pb (0.7%). The scavenging of released metals was in the reverse order: Pb (86%) > Cu (53%) > Zn (34%) > Cd (30%). Dominant processes are adsorption on organic substances, adsorption/coprecipitation by fresh Fe-Mn oxides and precipitation of metal phosphates originating from the decomposition of organic matter. Based on our experimental results and relevant published data, a four-stage interaction model is developed for metals in anoxic sediments. This model describes the behavior of heavy metals in the system subsequent to oxidation