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PT07 Contaminated Harbor and River Sediment
(PT131) Methylmercury formation in dredged sediments in confined disposal facilities.
King, J.1, Saunders, F. 2, 1 Applied Technology & Management Inc., Savannah, Georgia, USA2 Georgia Institute of Technology, Atlanta, Georgia, USA
ABSTRACT- Strict requirements exist for characterization of dredge materials placed in confined disposal facilities (CDF), as well as associated effluent waters from CDFs. Although current regulations address total mercury concentrations as the endpoint of concern, historical data specific to bioaccumulation of mercury suggest that methylmercury concentrations found in sediments, water, and biota may require additional regulatory limits. Our research on formation of methylmercury in sediments indicates that dredging of mercury-containing sediments results in an increased availability of inorganic mercury for methylation by sulfate-reducing bacteria. Model results will be presented to confirm the potential for, and rate of, methyl-mercury production. Prior to dredging, undisturbed sediments contain inorganic mercury complexed to sulfide in insoluble, unavailable forms. However, hydraulic and clamshell dredging can result in oxidation of sediments and remobilization of mercury-sulfide species, thus potentially increasing mercury methylation. Once sediments are disposed in a CDF, sulfate-reducing bacteria profiles are re-established vertically in dredge spoils and methylmercury synthesis can readily occur. Models based on sulfate-reducing bacterial profiles, sulfate-reduction rates, and inorganic mercury concentrations have been developed in order to predict the potential bacterial methylation of mercury prior to the start of dredging activities. Moreover, these models may also prove beneficial in predicting dredge spoil-derived, methylmercury concentrations in waters discharged from CDFs. Future studies will focus on the use of this model as an indicator of benefits associated with the capping measures utilized to reduce the bioavailability of mercury in contaminated dredge spoils.
Key words: methylation, mercury, sediments, cofined disposal facility
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