Duke University , Department of Civil and Environmental Engineering, 121 Hudson Hall, Durham, North Carolina 27708 United States.
Environ Sci Technol. 2014 Aug 19;48(16):9133-41. doi: 10.1021/es500336j. Epub 2014 Jul 23.
The production of methylmercury (MeHg) by anaerobic microorganisms depends in part on the speciation and bioavailability of inorganic mercury to these organisms. Our previous work with pure cultures of methylating bacteria has demonstrated that the methylation potential of mercury decreased during the aging of mercuric sulfides (from dissolved to nanoparticulate and microcrystalline HgS). The objective of this study was to understand the relationship between mercury sulfide speciation and methylation potential in experiments that more closely simulate the complexity of sediment settings. The study involved sediment slurry microcosms that represented a spectrum of salinities in an estuary and were each amended with different forms of mercuric sulfides: dissolved Hg and sulfide, nanoparticulate HgS (3-4 nm in diameter), and microparticulate HgS (>500 nm). The results indicated that net MeHg production was influenced by both the activity of sulfate-reducing microorganisms (roughly represented by the rate of sulfate loss) and the bioavailability of mercury. In the presence of abundant sulfate and carbon sources (supporting relatively high microbial activity), net MeHg production in the slurries amended with dissolved Hg was greater than in slurries amended with nano-HgS, similar to previous experiments with pure bacterial cultures. In microcosms with minimal microbial activity (indicated by low rates of sulfate loss), the addition of either dissolved Hg or nano-HgS resulted in similar amounts of net MeHg production. For all slurries receiving micro-HgS, MeHg production did not exceed abiotic controls. In slurries amended with dissolved and nano-HgS, mercury was mainly partitioned to bulk-scale mineral particles and colloids, indicating that Hg bioavailability was not simply related to dissolved Hg concentration or speciation. Overall, the results suggest that models for mercury methylation potential in the environment will need to balance the relative contributions of mercury speciation and activity of methylating microorganisms.
甲基汞（MeHg）的生成取决于部分厌氧微生物，这些微生物对无机汞的形态和生物可利用性具有依赖性。我们之前的研究工作主要集中在纯培养的甲基化细菌，研究结果表明汞的甲基化潜能会随着硫化汞（从溶解态到纳米颗粒态和微晶态 HgS）的老化而降低。本研究的目的是在更接近沉积物环境复杂性的实验中，理解硫化汞形态与甲基化潜能之间的关系。研究涉及沉积物悬浮液微宇宙，这些微宇宙代表了河口盐度范围，并分别添加了不同形式的硫化汞：溶解态的 Hg 和硫化物、纳米态 HgS（直径为 3-4nm）和微粒子态 HgS（>500nm）。结果表明，净甲基汞生成受到硫酸盐还原微生物活性（大致由硫酸盐损失率表示）和汞生物可利用性的影响。在有丰富硫酸盐和碳源存在的情况下（支持相对较高的微生物活性），添加溶解态 Hg 的悬浮液中的净甲基汞生成量大于添加纳米态 HgS 的悬浮液，这与之前用纯细菌培养物进行的实验结果相似。在微生物活性较低（硫酸盐损失率较低）的微宇宙中，添加溶解态 Hg 或纳米态 HgS 都会导致相似量的净甲基汞生成。对于所有接收微粒子态 HgS 的悬浮液，甲基汞生成量均未超过非生物对照。在添加溶解态和纳米态 HgS 的悬浮液中，汞主要分配到大规模矿物颗粒和胶体中，这表明汞的生物可利用性与溶解态汞浓度或形态无关。总的来说，这些结果表明，环境中汞甲基化潜能的模型将需要平衡汞形态和甲基化微生物活性的相对贡献。
