University of Wuppertal, School of Architecture and Civil Engineering, Institute of Foundation Engineering, Water and Waste Management, Laboratory of Soil and Groundwater Management, Pauluskirchstraße 7, 42285 Wuppertal, Germany.
US Department of Agriculture, Coastal Plains Soil, Water, Plant Research Center, 2611 West Lucas Street, Florence, SC, USA.
J Hazard Mater. 2024 Jul 5;472:134446. doi: 10.1016/j.jhazmat.2024.134446. Epub 2024 Apr 27.
Mercury (Hg) contaminated paddy soils are hot spots for methylmercury (MeHg) which can enter the food chain via rice plants causing high risks for human health. Biochar can immobilize Hg and reduce plant uptake of MeHg. However, the effects of biochar on the microbial community and Hg (de)methylation under dynamic redox conditions in paddy soils are unclear. Therefore, we determined the microbial community in an Hg contaminated paddy soil non-treated and treated with rice hull biochar under controlled redox conditions (< 0 mV to 600 mV) using a biogeochemical microcosm system. Hg methylation exceeded demethylation in the biochar-treated soil. The aromatic hydrocarbon degraders Phenylobacterium and Novosphingobium provided electron donors stimulating Hg methylation. MeHg demethylation exceeded methylation in the non-treated soil and was associated with lower available organic matter. Actinobacteria were involved in MeHg demethylation and interlinked with nitrifying bacteria and nitrogen-fixing genus Hyphomicrobium. Microbial assemblages seem more important than single species in Hg transformation. For future directions, the demethylation potential of Hyphomicrobium assemblages and other nitrogen-fixing bacteria should be elucidated. Additionally, different organic matter inputs on paddy soils under constant and dynamic redox conditions could unravel the relationship between Hg (de)methylation, microbial carbon utilization and nitrogen cycling.
受汞（Hg）污染的稻田土壤是甲基汞（MeHg）的热点区域，它可以通过水稻植物进入食物链，对人类健康造成高风险。生物炭可以固定 Hg 并减少植物对 MeHg 的吸收。然而，生物炭对稻田土壤中动态氧化还原条件下微生物群落和 Hg（去）甲基化的影响尚不清楚。因此，我们使用生物地球化学微宇宙系统，在受控氧化还原条件（<0 mV 至 600 mV）下，确定了未经处理和用稻壳生物炭处理的受 Hg 污染稻田土壤中的微生物群落。在生物炭处理的土壤中，Hg 甲基化超过了去甲基化。芳香烃降解菌 Phenylobacterium 和 Novosphingobium 提供电子供体，刺激 Hg 甲基化。在未经处理的土壤中，MeHg 的去甲基化超过了甲基化，并且与可用有机物含量较低有关。放线菌参与 MeHg 的去甲基化，并与硝化细菌和固氮属 Hyphomicrobium 相互关联。微生物组合似乎比单个物种在 Hg 转化中更为重要。未来的研究方向应该阐明 Hyphomicrobium 组合和其他固氮细菌的去甲基化潜力。此外，在恒温和动态氧化还原条件下，不同的有机物质输入到稻田土壤中，可以揭示 Hg（去）甲基化、微生物碳利用和氮循环之间的关系。
