Contaminants in sediments: remobilisation and demobilisation.

In this study, the contaminated anoxic sediment of the Mulde reservoir (Saxony, Germany) was investigated. Several sediment cores were analysed for heavy metals and organic chemicals such as chlorobenzenes and DDTs. The comparison between anoxic and oxidised sediment cores showed the potential danger for heavy metal (Zn and Cd) remobilisation from sediment due to bioturbation or resuspension by flooding. Chemical sequential extraction was used to describe partitioning of heavy metals among different mineralogical components in the sediments. Results showed remobilisation of Zn and Cd from the sediments. The stable fraction (organic/sulfidic-bound) of Zn and Cd decreased from 10 to 3%, and from 35 to 5%, respectively. Simultaneously, the carbonate fraction increased from 3 to 12% for Cd and from 10 to 22% for Zn. Furthermore, the simulation of the diffusion of organic pollutants showed remobilisation of 1,4-dichlorobenzene. The results confirmed the necessity of sediment remediation in the reservoir. Capping seems to be a promising approach for a low-cost remediation.