Fujian Provincial Key Laboratory of Ecology-Toxicological Effects & Control for Emerging Contaminants, Key Laboratory of Ecological Environment and Information Atlas, College of Environmental and Biological Engineering, Putian University, Putian 351100, China; Department of Environmental Science, Zhejiang University, Hangzhou 310058, China.
School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310024, China.
J Hazard Mater. 2023 Aug 5;455:131602. doi: 10.1016/j.jhazmat.2023.131602. Epub 2023 May 9.
Sulfur has a high affinity for mercury (Hg) and can serve as effective treating agent for Hg pollution. However, conflict effects between reducing Hg mobility and promoting Hg methylation by sulfur were found in recent studies, and there is a gap in understanding the potential mechanism of MeHg production under different sulfur-treated species and doses. Here, we investigated and compared the MeHg production in Hg-contaminated paddy soil and its accumulation in rice under elemental sulfur or sulfate treatment at a relatively low (500 mg·kg) or high (1000 mg·kg) level. The associated potential molecular mechanisms are also discussed with the help of density functional theory (DFT) calculation. Pot experiments demonstrate that both elemental sulfur and sulfate at high exposure levels increased MeHg production in soil (244.63-571.72 %) and its accumulation in raw rice (268.73-443.50 %). Coupling the reduction of sulfate or elemental sulfur and decrease of soil redox potential leads to the detachment of Hg-polysulfide complexes from the surface of HgS which can be explained by DFT calculations. Enhancement of free Hg and Fe release through reducing Fe(III) oxyhydroxides further promotes soil MeHg production. The results provide clues for understanding the mechanism by which exogenous sulfur promotes MeHg production in paddies and paddy-like environments and give new insights for decreasing Hg mobility by regulating soil conditions.
硫对汞（Hg）具有高亲和力，可用作 Hg 污染的有效处理剂。然而，最近的研究发现，硫在降低 Hg 迁移性和促进 Hg 甲基化方面存在冲突效应，并且对于不同硫处理物种和剂量下 MeHg 生成的潜在机制存在理解上的差距。在这里，我们研究并比较了在相对较低（500mg·kg）或较高（1000mg·kg）水平下单质硫或硫酸盐处理对 Hg 污染稻田中 MeHg 生成及其在水稻中的积累的影响。还借助密度泛函理论（DFT）计算讨论了相关的潜在分子机制。盆栽实验表明，单质硫和硫酸盐在高暴露水平下均增加了土壤中 MeHg 的生成（244.63-571.72%）和糙米中的积累（268.73-443.50%）。耦合硫酸盐或单质硫的还原和土壤氧化还原电位的降低导致 Hg-多硫化物复合物从 HgS 表面脱附，这可以通过 DFT 计算来解释。通过还原 Fe（III）氢氧化物释放更多自由 Hg 和 Fe 进一步促进了土壤中 MeHg 的生成。该结果为理解外源硫促进稻田和类似稻田环境中 MeHg 生成的机制提供了线索，并为通过调节土壤条件降低 Hg 迁移性提供了新的见解。
