Bioaccumulation of methylmercury in the aquatic food web is governed in part by the methylation of inorganic divalent mercury (Hg(II)) by anaerobic microorganisms. In sulfidic settings, a small fraction of total Hg(II) is typically bioavailable to methylating microorganisms. Quantification of this fraction is difficult due to uncertainties in the speciation of Hg(II) and the mechanisms of uptake by methylating microbes. However, recent studies have shown that the bioavailable fraction is likely to include a portion of Hg(II) associated with solid phases, that is, nanostructured mercuric sulfides. Moreover, addition of thiols to suspensions of methylating cultures coincides with increased uptake into cells and methylmercury production. Here, we present a thiol-based selective extraction assay to provide information on the bioavailable Hg fraction in sediments. In the procedure, sediment samples were exposed to a nitrogen-purged solution of glutathione (GSH) for 30 min and the amount of GSH-leachable mercury was quantified. In nine sediment samples from a marine location, the relative GSH-leachable mercury concentration was strongly correlated to the relative amount of methylmercury in the sediments (r2=0.91, p<0.0001) across an order of magnitude of methylmercury concentration values. The approach was further applied to anaerobic sediment slurry microcosm experiments in which sediments were cultured under the same microbial growth conditions but were amended with multiple forms of Hg with a known spectrum of bioavailability. GSH-leachable Hg concentrations increased with observed methylmercury concentrations in the microcosms, matching the trend of species bioavailability in our previous work. Results suggest that a thiol-based selective leaching approach is an improvement compared with other proposed methods to assess Hg bioavailability in sediment and that this approach could provide a basis for comparison of sites where Hg methylation is a concern.

中文翻译：

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基于硫醇的选择性提取分析比较评估沉积物中生物可利用的汞

甲基汞在水生食物网中的生物积累部分受厌氧微生物对无机二价汞 (Hg(II)) 的甲基化控制。在硫化环境中，总 Hg(II) 的一小部分通常可被甲基化微生物生物利用。由于 Hg(II) 的形态和甲基化微生物吸收机制的不确定性，很难对这一部分进行量化。然而，最近的研究表明，生物可利用部分可能包括一部分与固相相关的 Hg(II)，即纳米结构的硫化汞。此外，将硫醇添加到甲基化培养物的悬浮液中与细胞吸收和甲基汞产量的增加相吻合。这里，我们提出了一种基于硫醇的选择性提取试验，以提供有关沉积物中生物可利用 Hg 分数的信息。在此过程中，将沉积物样品暴露在经过氮气净化的谷胱甘肽 (GSH) 溶液中 30 分钟，并量化 GSH 可浸出的汞含量。在来自海洋位置的九个沉积物样本中，相对 GSH 可浸出的汞浓度与沉积物中甲基汞的相对量（r2=0.91，p<0.0001）在一个数量级的甲基汞浓度值之间密切相关。该方法进一步应用于厌氧沉积泥浆微观实验，其中沉积物在相同的微生物生长条件下培养，但用具有已知生物利用度谱的多种形式的汞进行修正。GSH 可浸出的汞浓度随微观世界中观察到的甲基汞浓度而增加，这与我们之前工作中物种生物利用度的趋势相匹配。结果表明，与其他提议的评估沉积物中汞生物利用度的方法相比，基于硫醇的选择性浸出方法是一种改进，并且这种方法可以为比较关注汞甲基化的位点提供基础。