Metal solubility as a function of pH in a contaminated, dredged sediment affected by oxidation.

The solubility as a function of pH for metals in a reduced dredged sediment, subjected to different redox conditions, was studied in a laboratory experiment. The redox conditions imposed simulated (i) the undisturbed sediment (flooded), (ii) a dredged material stored in a confined pond (aerated once and then flooded), (iii) an upland stored dredged material (drained and dried), and (iv) an upland stored sediment subjected to tillage (drained, dried and mixed). Minor differences in the solubility as a function of pH were observed between the treatments after two weeks. After three months, the solubility of Cd, Cu, Pb and Zn increased strongly in the oxidized sediments. Leachability of Fe decreased, while Mn, Ni and Co were mostly unaffected. Both short- and long-term mobility of metals (except Fe) is expected to be lowest when a reduced sediment remains in reduced conditions. Studying the solubility as a function of pH may provide additional information on the chemical association of metals in sediments.