Chemical elements > Metals > Heavy metals > Cadmium Chemical elements > Metals > Heavy metals > Lead Chemical elements > Metals > Transition elements > Heavy metals > Iron Chemical elements > Metals > Transition elements > Heavy metals > Manganese Chemical reactions Chemistry > Geochemistry > Sediment chemistry Pollution > Sediment pollution Pollution > Water pollution > Marine pollution Properties > Physicochemical properties Sedimentary structures > Mud flats Sediments Water bodies > Coastal waters > Coastal landforms > Coastal inlets > Estuaries ANE, Nederland, Westerschelde, Ballastplaat [Marine Regions] Marien/Kust; Brak water
The Ballasplaat intertidal mud flat in the Scheldt estuary has been polluted by Cd and Pb and also high amounts of organic matter as a result of suspended matter deposition. The degree of pollution is, however, not uniform over the mud flat due to varying physico-chemical conditions (essentially variable redox profiles). Measurements of the redox profile, and the metal concentrations in the pore water, the total sediment and the fraction <63 µm combined with sequential extraction results and enrichment factors can explain the behaviour of Cd, Pb, Fe and Mn in the sediments. In a strong anoxic sediment, where sulphate reducing bacteria are active, the heavy metals are trapped as poorly soluble metal complexes while in an oxic or suboxic sediment metals tend to be redissolved due to the oxidation of organic matter, and the reduction of particulate Fe and Mn oxyhydroxides. The transportation of heavy metals across the sediment water interface is very much depending upon the physiochemical conditions of the sediment.
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