Migration of trace metals in interfaces of sea water and polluted surficial sediments

The migration of trace metals between the interface of seawater and polluted surficial sediments under different redox conditions was studied on three typically polluted nearshore surficial sediments. The experimental results obtained showed that under different sets of redox conditions over a period of 4-5 months of sediment/seawater contact time, three general trends could be observed; the released amount increased as the redox condition became progressively reducing(Fe and Mn), the released amount increased as the environment became more oxidizing (Cd, Cu, Ni, Pb, and Zn), and there was no significant change of concentration in interfacial water (Hg and Cr). An equilibrium model was set up to confirm the experimental results. After long-term incubation in a reducing environment, most of the trace metals analyzed closely followed the predictions from equilibrium calculations. Complex formation accounted mainly for the concentration levels analyzed. Under aerobic conditions after long-term incubation, most of the analyzed concentrations were either far below (Cd, Cu, Ni, and Pb) or far above (Fe and Mn) the equilibrium concentrations, probably due to the slowness in reaching the equilibrium condition or to the presence of unknown ligands.