Trace Metals in Open Water Disposal of Dredged Material

Upon addition of sediment/seawater mixture to the seawater column, most trace metals were found to display a pattern of immediate release. These released metals were subsequently removed. The removal is gradually under reducing environments and almost immediately under oxidizing environments. The degree of release was significant for Fe, Mn, and Ni. The Cr, Cu, Pb, and Zn were moderately released. The release of Ag, Cd, and Hg was negligible. After resedimentation, the migration of trace metals between the sediment/seawater interface were found to be influenced by the redox conditions of the overlying water. In general, three patterns of metal behavior were observed: (1)The release amount increases as the redox conditions become more reducing (Fe and Mn); (2)the release amount increases as the environment becomes more oxidizing (Cd, Cu, Ni, Pb, and Zn); and (3)no significant release (Cr and Hg). The soluble metal concentrations during and after open water disposal of dredged materials were found to be in the range of sub-ppb to ppb with the exception of Fe, under reducing condition.