Sulfur and biochar are two important agents for remediating heavy metal-polluted soils. Nevertheless, the double-edged sword effect of sulfur and the relatively limited efficacy of biochar in addressing soil mercury (Hg) contamination have constrained its practical use in Hg-polluted areas. This study developed an optimized strategy involving the combined application of biochar and sulfate to reduce soil methylmercury (MeHg) production and grain MeHg accumulation and revealed the underlying molecular mechanisms governing the interactions among sulfate, biochar, and Hg, based on both batch experiments and density functional theory calculations. Our findings demonstrate that the combined use of biochar and sulfate at optimal proportions can effectively promote rice crop growth while mitigating grain MeHg accumulation. This positive effect is attributed to the strong adsorption capacity of carboxylic and phenolic hydroxyl groups in biochar for soil Hg. Sulfate can further enhance the stability of adsorbed Hg(II), forming a highly stable biochar-Hg(–SO₄)–Cl structure in soil, thereby mitigating MeHg production. Meanwhile, the suppression of Hg methylator activity, coupled with alterations in soil pH, and the chemical speciation of Fe and Mn upon biochar addition, indirectly counteracts sulfate-stimulated microbial Hg-methylation in paddy soils. This research highlights the effectiveness of a combined biochar and sulfate application strategy in Hg sequestration and reduction of MeHg accumulation in grains. By unveiling the molecular mechanisms underlying the interactions among sulfate, biochar, and Hg in soil, our study offers fresh insights for designing more efficient and safe strategies aimed at enhancing rice yields while mitigating the risks associated with soil Hg pollution.

中文翻译：

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硫酸盐和生物炭联合应用策略对汞封存的分子见解污染处理

硫磺和生物炭是修复重金属污染土壤的两种重要药剂。然而，硫的双刃剑效应和生物炭在解决土壤汞（Hg）污染方面相对有限的功效限制了其在汞污染地区的实际应用。本研究制定了一种优化策略，涉及生物炭和硫酸盐的联合应用，以减少土壤甲基汞（MeHg）的产生和谷物甲基汞的积累，并基于批量实验和密度揭示了控制硫酸盐、生物炭和汞之间相互作用的潜在分子机制。泛函理论计算。我们的研究结果表明，以最佳比例联合使用生物炭和硫酸盐可以有效促进水稻作物生长，同时减少谷物中甲基汞的积累。这种积极作用归因于生物炭中羧基和酚羟基对土壤汞的强大吸附能力。硫酸盐可以进一步增强吸附Hg(II)的稳定性，在土壤中形成高度稳定的生物炭-Hg(–SO ₄ )–Cl结构，从而减少MeHg的产生。同时，汞甲基化活性的抑制，加上土壤 pH 值的变化，以及添加生物炭后铁和锰化学形态的变化，间接抵消了稻田土壤中硫酸盐刺激的微生物汞甲基化。这项研究强调了生物炭和硫酸盐联合应用策略在汞封存和减少谷物中甲基汞积累方面的有效性。通过揭示土壤中硫酸盐、生物炭和汞之间相互作用的分子机制，我们的研究为设计更有效、更安全的策略提供了新的见解，旨在提高水稻产量，同时减轻与土壤汞污染相关的风险。