Binding and mobilization of heavy metals in contaminated sediments affected by pH and redox potential

Erik R. Christensen ... (eds.) Contaminated aquatic sediments : proceedings of the First International Specialized Conference, held in Milwaukee, WI, June 1993, pp. 223-35

In a contaminated sediment from Hamburg harbour, acid production, mobilization of Cu, Zn, Pb, and Cd at different redox- and pH-conditions, and the transfer and change of those particle bound metals are studied. During oxidation the pH value in the sediment suspension decreases from about 7 to 3.4 because of the low acid neutralization capacity (ANC). This leads to a mobilization of heavy metals whereby Cd and Zn as distinguished from Cu and Pb are strongly released. Also a change in particulate phase specific heavy metal binding forms is found. Generally the easily and moderately reducible fractions increase during oxidation while the sulfidic fraction decreases. Also great changes were found for the dissolved Zn- and Cd-concentrations which increased continuously. The results show that at identical pH values obviously more metals are mobilized in the oxidized sediment than in the reduced state. But although the pH value is the key factor - in particular if it sinks below 4.5 - the redox conditions may also control the mobilization of certain metals. Consequently, also in well buffered sediments a mobilization of metals during oxidation cannot be excluded.

Schlagworte

Heavy metal binding forms

periodical redox processes

acid producing capacity

buffer intensity

sediment quality

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Binding and mobilization of heavy metals in contaminated sediments affected by pH and redox potential