BINDING AND MOBILIZATION OF HEAVY-METALS IN CONTAMINATED SEDIMENTS AFFECTED BY PH AND REDOX POTENTIAL

In a contaminated sediment from Hamburg harbour, acid production, mobi lization 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 f rom about 7 to 3.4 because of the low acid neutralization capacity (AN C). 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 p articulate phase specific heavy metal binding forms is found. Generall y the easily and moderately reducible fractions increase during oxidat ion while the sulfidic fraction decreases. Also great changes were fou nd for the dissolved Zn- and Cd-concentrations which increased continu ously. The results show that at identical pH values obviously more met als are mobilized in the oxidized sediment than in the reduced state. But although the pH value is the key factor - in particular if it sink s below 4.5 - the redox conditions may also control the mobilization o f certain metals. Consequently, also in well buffered sediments a mobi lization of metals during oxidation cannot be excluded.