Effects of Dredging

BACKGROUND: Public laws regulating dredged material disposal (Section 404 of the Clean Water Act and Section 103 of the Ocean Dumping Act) require ecological evaluation prior to the permitting of operations. Assessment of the potential for bioaccumulation of chemical contaminants in sediment, including heavy metals, is required as part of the evaluation process. Metals can represent significant sediment contamination in the vicinity of industrial and commercial point sources. Mercury, in particular, enters the aquatic environment in various forms from chloralkali and instrumentation plants, paints, pulp and paper manufacture, agricultural sources, and other nonpoint sources such as atmospheric deposition (Khalid et al. 1977). Because sediment serves as a sink for mercury, dredging and disposal operations can affect the bioavailability of mercury to aquatic organisms. In general, metals in sediment have low bioavailability in reduced environments such as aquatic disposal sites, but may be highly bioavailable in upland disposal sites where the dredged material is subject to drying and oxidation.