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The biological availability and geochemical fate of toxic metals in materials disposed of in the marine environment are dependent in part on the chemical forms in which the metals are present. In order to characterize the associations of trace metals with particulate matter in polluted marine sediments, samples of dredged materials removed from Black Rock Harbor, CT and sediments from the disposal site in Long Island Sound collected subsequent to disposal have been sequentially extracted with a series of solutions. The solutions correspond to a range of conditions under which different sediment phases can be solubilized, and operationally define four sediment fractions: exchangeable, weak acid soluble, oxidizable, and strong acid soluble.
In the dredge material, cadmium, copper, and chromium are all predominantly associated with the oxidizable fraction, that is, with sulfides and organic matter, while lead is found primarily in the residual, strong acid soluble fraction. Data from sediment samples collected at the disposal site indicate oxidation of the surface sediments during the warmer months and result in the redistribution of cadmium and, to a lesser extent, copper to the more labile exchangeable and weak acid soluble fractions. Chromium and lead show little evidence of alterations in the binding of those metals to sediments.
trace metals, sediments, selective extraction, ferric oxides, manganese oxides
Associate chemist, Science Applications International Corporation, Narragansett, RI