EFFECT OF AERATION OF SEDIMENT ON CADMIUM BINDING

Acid-volatile sulfide (AVS) has been shown to be the dominant phase reacting with metals in anoxic sediments. The AVS in sediment decreases upon resuspension due to storms and dredging, and in winter when the rate of aeration processes exceeds that of the formation of sulfide. We conducted a series of lab aeration experiments in batch reactors to investigate the effects of aeration of sediment on the sulfide content of sediment and on the partitioning of cadmium, a model toxic metal, to the sediment. Aeration of sediment results in rapid decrease of the AVS. We studied the sediment characteristics for aeration periods of approximately a month. During this time, the concentrations of dissolved metals increased by 200 to 400% or more, relative to the concentrations present at the beginning of the test. The concentration of metal associated with AVS and with pyrite decreased. During the aeration, there are increases in the concentrations of hydrous iron and manganese oxides, and these materials become increasingly more important in the binding of cadmium. Following the aeration, >50% of the cadmium was associated with the extractable iron and manganese components of the sediment. Overall, the binding capacity of the sediments for cadmium decreased after aeration.