Solubility, mobility, and bioavailability of sediment-bound metals can be increased by four major facors: (1) Lowering of pH; (2) changing of redox conditions; (3) formation of organic complexes; and (4) increasing salinity. While the first two factors are particularly important for on-land deposition of dredged materials, the effect of salinity is particularly important for resuspended cadmium-rich sediments in estuaries. Chemical extraction studies, which were carried out under carefully controlled conditions on both fresh and freeze-dried samples, indicate that aeration of anoxic sediments (e.g., on-land disposal) may both increase and decrease the mobility of heavy metals. Transformation from sulfidic or carbonatic associations to oxidic phases will reduce mobility of manganese, wherease the respective changes from moderately reducible forms to carbonatic and easily reducible phases will enhance the reactivity of zinc during oxidation of dredged material.
