Bindungsformen von Schwermetallen in Baggerschlämmen
For the assessment of the environmental compatability of dredged materials contaminated by heavy metals, a six-stage chemical leaching process was developed that avoids some inadequacies of earlier experiments. Investigations of dredged sludge from Rotterdam Harbour, from the Weser River Estuary and from the middle course of the Neckar River show that the cation exchangeable metal portion is significant only for cadmium and that the highest enrichment of metals occurs either in easily reducible or carbonate-associated forms (zinc and cadmium) or in moderately reducible phases (copper and lead). In contrast to the dredged material samples sewage sludge shows markedly higher contents of cadmium, copper and lead bound on organic phases. Generally the availability for short- and middle-term chemical processes or for biogenic uptake increases with intesity of anthropogenic metal input. However, this trend is superposed by effects that are specific to the element in question, the type of soil and the organism species. A uniform assessment model can therefore not yet be established on the basis of extraction chemical data.