Effect of Chemical Form of Mercury on the Performance of Dosed Soils in Standard Leaching Protocols: EP and TCLP

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Abstract
Application of the EP (Extraction Procedure) and TCLP (Toxicity Characteristic Leaching Procedure) to a variety of mercury-contaminated soils and solid wastes from U.S. Department of Energy facilities in Oak Ridge, Tennessee, has not shown any consistent relationship between test results and total mercury concentrations. To determine the effects of the chemical form of mercury on leaching results, samples of uncontaminated soil were dosed with four different forms of mercury (Hg0, HgS, HgO, Hg2O) at three concentrations (100, 1000, 10000 μg/g) and then subjected to headspace mercury vapor analysis and application of the two leaching protocols. None of the leaching protocol results for soil dosed with Hg0 or HgS exceeded the Resource Conservation and Recovery Act (RCRA) limit (200 μg/L) even at the highest dosing level (10000 μg/g). For both mercury oxide forms only the higher soil concentrations (1000 and 10000 μg/g) yielded leachate concentrations exceeding the RCRA limit. In general, the TCLP yielded higher leachate concentrations of mercury than the EP. This study verified that, where the chemical form of mercury is unknown, total mercury concentrations in the soil or waste provide no clue as to the performance of a soil in the leaching protocols. Results of sample headspace analysis, in addition to TCLP results and analysis for total mercury, are recommended to fully evaluate the hazards of mercury-contaminated waste and soil.

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