Mercury Methylation Rates for Geochemically Relevant HgII Species in Sediments

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• 作者：Sofi Jonsson ; Ulf Skyllberg ; Mats B. Nilsson ; Per-Olof Westlund ; Andrey Shchukarev ; Erik Lundberg ; Erik Bj枚rn
• 刊名：Environmental Science & Technology (ES&T)
• 出版年：2012
• 出版时间：November 6, 2012
• 年：2012
• 卷：46
• 期：21
• 页码：11653-11659
• 全文大小：310K
• 年卷期：v.46,no.21(November 6, 2012)
• ISSN：1520-5851

文摘

Monomethylmercury (MeHg) in fish from freshwater, estuarine, and marine environments is a major global environmental issue. Mercury levels in biota are mainly controlled by the methylation of inorganic mercuric mercury (Hg^II) to MeHg in water, sediments, and soils. There is, however, a knowledge gap concerning the mechanisms and rates of methylation of specific geochemical Hg^II species. Such information is crucial for a better understanding of variations in MeHg concentrations among ecosystems and, in particular, for predicting the outcome of currently proposed measures to mitigate mercury emissions and reduce MeHg concentrations in fish. To fill this knowledge gap we propose an experimental approach using Hg^II isotope tracers, with defined and geochemically important adsorbed and solid Hg^II forms in sediments, to study MeHg formation. We report Hg^II methylation rate constants, k_m, in estuarine sediments which span over 2 orders of magnitude depending on chemical form of added tracer: metacinnabar (尾-²⁰¹HgS(s)) < cinnabar (伪-¹⁹⁹HgS(s)) < Hg^II reacted with mackinawite (鈮eS-²⁰²Hg^II) < Hg^II bonded to natural organic matter (NOM-¹⁹⁶Hg^II) < a typical aqueous tracer (¹⁹⁸Hg(NO₃)₂(aq)). We conclude that a combination of thermodynamic and kinetic effects of Hg^II solid-phase dissolution and surface desorption control the Hg^II methylation rate in sediments and cause the large observed differences in k_m-values. The selection of relevant solid-phase and surface-adsorbed Hg^II tracers will therefore be crucial to achieving biogeochemically accurate estimates of ambient Hg^II methylation rates.