Graduate Student Derek Bussan will Present “Mercury Methylation Potentials in Wetland Sediments Using Species-Specific Isotope Dilution-GC-ICP-MS” to the Department.
Mercury (Hg) is a global pollutant that can affect both human and ecological systems. Recognizing this, >100 nations, including the U.S., signed the Minamata Treaty in 2013 to reduce Hg emissions. Hg is dispersed globally through the atmosphere and deposits to terrestrial and aquatic ecosystems, where it can be converted to methylmercury (MeHg).1 Wetland sediments are of particular interest because they are known to be “hot-spots” for Hg methylation. Humans are exposed to MeHg through consumption of fish and shellfish. MeHg is capable of crossing the blood brain- and placental- barriers, and exposure in-utero has been linked to subtle developmental deficits.2 In the present study we used species-specific enriched isotope tracers to, for the first time, to investigate Hg transformations in an old growth cypress wetland located at Sky Lake in the Mississippi Delta. Methylation rates increased with temperature from ~1% day-1 in the winter to ~5% day-1 in the summer. Methylation rates generally were higher in open water areas compared to the swamp. We also developed a novel analytical technique for the direct analysis of Hg in environmental solids by ICP-MS.3 This method utilized a direct mercury analyzer (DMA) based on sample combustion, preconcentration by amalgamation with gold, and atomic absorption spectrophotometry to introduce Hg to a sector field ICP-MS. The combined system (DMA-ICP-MS) was optimized and evaluated for the determination of Hg in environmental samples using both external calibration and isotope dilution for quantitation. The method was validated using certified reference materials, including sediment, leaves, and fish-muscle tissue. The limit of detection was ~0.37 pg, about two orders of magnitude lower than the DMA system alone. Precision was generally <7% relative standard deviation, and total analyses time per sample was <8 min. The DMA-ICP-MS system has several advantages over both the DMA alone and conventional cold-vapor AAS for the determination of mercury, including increased sensitivity, lower detection limits, decreased potential for sample contamination, and applicability to Hg stable isotope tracer studies. Finally, the effects of biochar and activated carbon on Hg methylation rates were evaluated.
- N. Pirrone, et al., Atmospheric Chemistry and Physics, 2010, 10, 5951-5964.
- L. E. Davis, et al., Annals of neurology, 1994, 35, 680-688.
- D. Bussan, R. Sessums, J. Cizdziel, Journal of Analytical Atomic Spectroscopy, 2015, DOI: 10.1039/C5JA00087D