Li Yunyun, Jia Wen, Xu Bo, Lin Guoming, Wu Minghong
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.
College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, Fujian, China.
Water Res. 2025 Jul 11;286:124211. doi: 10.1016/j.watres.2025.124211.
Mercury (Hg) contamination in paddy systems poses severe environmental and public health threats due to the microbial transformation of inorganic Hg into highly toxic methylmercury (MeHg). Although biochar (BC) has been widely applied for heavy metal remediation, its limited capacity to immobilize Hg constrains its practical effectiveness. Here, we present a comprehensive study combining batch experiments and density functional theory (DFT) calculations to elucidate the molecular mechanisms by which iron-modified biochar (Fe-BC) enhances Hg stabilization and inhibits MeHg formation in paddy systems. Our results reveal that Fe modification induces the coordination of FeOOH clusters with oxygen-containing functional groups and aromatic domains on the BC surface, significantly enhancing its Hg-affinity. Notably, the structural stability and adsorption performance of Fe-BC are strongly size-dependent, with the FeOOH dimer (FeOOH) showing the most robust binding to BC and the highest capacity for Hg immobilization. Fe-BC application markedly reduces both MeHg production and bioavailability in the contaminated paddy by strengthening Hg adsorption through interactions with sub-nanometer FeOOH clusters, especially (FeOOH) anchored on the aromatic structures of BC. Furthermore, we demonstrate that coexisting soil ions modulate Hg adsorption: Na reduces Hg binding via electrostatic competition, whereas Cl and SO promote stable complex formation (Fe-BC-Hg-Cl and Fe-BC-Hg-SO), further enhancing Hg retention. These findings provide molecular-level insight into Fe-BC's stabilization mechanisms and highlight the importance of optimizing Fe cluster structures and ion interactions to maximize remediation efficiency. This study offers both theoretical and practical guidance for advancing Fe-BC-based strategies for sustainable Hg immobilization in contaminated paddy systems.
由于无机汞在微生物作用下转化为剧毒的甲基汞（MeHg），稻田系统中的汞（Hg）污染对环境和公众健康构成了严重威胁。尽管生物炭（BC）已被广泛应用于重金属修复，但其固定汞的能力有限，限制了其实际效果。在此，我们开展了一项综合研究，结合批量实验和密度泛函理论（DFT）计算，以阐明铁改性生物炭（Fe-BC）增强稻田系统中汞稳定性并抑制甲基汞形成的分子机制。我们的结果表明，铁改性促使FeOOH簇与生物炭表面的含氧官能团和芳香域配位，显著增强了其对汞的亲和力。值得注意的是，Fe-BC的结构稳定性和吸附性能强烈依赖于尺寸，FeOOH二聚体（FeOOH）与生物炭的结合最牢固，固定汞的能力最强。通过与亚纳米级FeOOH簇（尤其是锚定在生物炭芳香结构上的（FeOOH））相互作用加强汞吸附，施用Fe-BC显著降低了污染稻田中甲基汞的产生和生物有效性。此外，我们证明共存的土壤离子会调节汞的吸附：Na通过静电竞争降低汞的结合，而Cl和SO促进稳定络合物的形成（Fe-BC-Hg-Cl和Fe-BC-Hg-SO），进一步增强汞的保留。这些发现为Fe-BC的稳定机制提供了分子层面的见解，并突出了优化铁簇结构和离子相互作用以最大化修复效率的重要性。本研究为推进基于Fe-BC的策略以实现污染稻田系统中汞的可持续固定提供了理论和实践指导。
