Determination of Methylmercury Levels in Mercury-Contaminated Soils from Oak Ridge TN by Cold Vapor Generation

Metals and Metals Speciation Analysis in Environmental Samples
Oral Presentation

Prepared by , I. Denmark, E. Begu, F. Han

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In early 1950s, elemental mercury (Hg) was used for manufacturing of various components nuclear weapons systems in the Y-12 Security Complex in Oak Ridge, TN. The Hg released to the environment contaminated the facilities, soil, sediment, surface water, and groundwater within the boundaries of the Y-12 Plant. Despite continuing remediation efforts, Hg levels in water at the Y-12 Complex boundary continue to exceed both the regulatory limit (51 ng/L) and the remediation goal (200 µg/L). Methylmercury (CH3Hg) is the most toxic form of mercury that bio-accumulates exponentially compared to other forms of mercury. Unlike many other Hg compounds, CH3Hg is found at very low levels in contaminated soils, yet it is water-soluble and contributes continuously to Hg-contamination in nearby freshwater ecosystems in Y-12 complex. The objective of this study was to develop analytical methods for selective determination of CH3Hg from mercury-contaminated soils that contain elevated levels of inorganic mercury, Hg(II). Studies were conducted to extract CH3Hg from predominantly Hg(II) contaminated sediments. Extractions with dilute HNO3 were more effective for selective separation of CH3Hg. Residual Hg(II) was removed via La(OH)3 + 0.1% (m/v) L-cysteine or HgS coprecipitation. Determinations were performed with cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS) The method was validated by determination of CH3Hg in sediment reference material (SQC1238) and an Estuarine sediment (ERM – CC580) containing trace levels of CH3Hg in Hg(II) matrix. The procedure was applied to selective determination of CH3Hg in Hg-contaminated floodplain top soils from Oak Ridge TN.