This review article covers the processes affecting trace metals in deposited sediments. The sediment-water system can be divided in three parts: the oxic layer, the anoxic layer and the oxic-anoxic interface. Available data show that trace metals like Cu, Zn and Cd occur as sulphides in marine and estuarine anoxic sediments. Calculations show that organic complexation is unlikely and the dominant species are sulphide and bisulphide complexes. Chromium and arsenic are probably present as adsorbed species on the sediments; their concentrations in the pore waters, therefore depend on the concentrations in the sediments. The oxic-anoxic interface plays the major role in the potential flux of trace metals from the sediments, however this interface is not well studied at present. Changes from an anoxic to an oxic environment as occurs during dredging and land disposal of contaminanted sediments may cause a remobilization of some trace metals.

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