Zhang Yufan, Wang Xiangqin, Yang Yang, Huang Yingmei, Li Xiaomin, Hu Shiwen, Liu Kexue, Pang Yan, Liu Tongxu, Li Fangbai
SCNU Environmental Research Institute, Guangdong Provincial Key Laboratory of Chemical Pollution and Environmental Safety & MOE Key Laboratory of Theoretical Chemistry of Environment, South China Normal University, Guangzhou, 510006, China; School of Environment, South China Normal University, Guangzhou, 510006, China; National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou, 510650, China.
National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou, 510650, China.
Environ Pollut. 2023 Apr 15;323:121335. doi: 10.1016/j.envpol.2023.121335. Epub 2023 Feb 22.
To estimate the risks and developing remediation strategies for the mercury (Hg)-contaminated soils, it is crucial to understand the mechanisms of Hg transformation and migration in the redox-changing paddy fields. In present study, a Hg-spiked acidic paddy soil (pH 4.52) was incubated under anoxic conditions for 40 d and then under oxic conditions for 20 d. During anoxic incubation, the water-soluble, exchangeable, specifically adsorbed, and fulvic acid-complexed Hg decreased sharply, whereas the humic acid-complexed Hg, organic, and sulfide-bound Hg gradually increased, which were mainly ascribed to the enhanced adsorption on the surface of soil minerals with an increase in soil pH, complexation by organic matters, precipitation as HgS, and absorption by soil colloids triggered by reductive dissolution of Fe(III) oxides. By contrast, after oxygen was introduced into the system, a gradual increase in available Hg occurred with decreasing soil pH, decomposition of organic matters and formation of Fe(III) oxides. A kinetic model was established based on the key elementary reactions to quantitatively estimate transformation processes of Hg fractions. The model matched well with the modified Tessier sequential extraction data, and suggested that large molecular organic matter and humic acid dominated Hg complexation and immobilization in acidic paddy soils. The content of methylmercury increased and reached its peak on anoxic 20 d. Sulfate-reducing bacteria Desulfovibrio and Desulfomicrobium were the major Hg methylating bacteria in the anoxic stage whereas demethylating microorganisms Clostridium_sensu_stricto_1 and Clostridium_sensu_stricto_12 began to grow after oxygen was introduced. These new dynamic results provided new insights into the exogenous Hg transformation processes and the model could be used to predict Hg availability in periodically flooded acidic paddy fields.
为评估汞（Hg）污染土壤的风险并制定修复策略，了解Hg在氧化还原变化的稻田中的转化和迁移机制至关重要。在本研究中，向酸性稻田土壤（pH 4.52）中添加Hg后，先在缺氧条件下培养40天，然后在有氧条件下培养20天。在缺氧培养期间，水溶性、可交换性、特异性吸附性和富里酸络合态Hg急剧下降，而腐殖酸络合态Hg、有机态和硫化物结合态Hg逐渐增加，这主要归因于随着土壤pH值升高，土壤矿物表面吸附增强、有机物络合、HgS沉淀以及Fe（III）氧化物还原溶解引发的土壤胶体吸附。相比之下，向系统中引入氧气后，随着土壤pH值降低、有机物分解和Fe（III）氧化物形成，有效Hg逐渐增加。基于关键的基本反应建立了动力学模型，以定量估算Hg形态的转化过程。该模型与改进的Tessier连续提取数据匹配良好，表明大分子有机物和腐殖酸在酸性稻田土壤中主导Hg的络合和固定。甲基汞含量增加，并在缺氧20天时达到峰值。硫酸盐还原菌脱硫弧菌属和脱硫微菌属是缺氧阶段主要的Hg甲基化细菌，而脱甲基微生物严格梭菌1和严格梭菌12在引入氧气后开始生长。这些新的动态结果为外源Hg转化过程提供了新的见解，该模型可用于预测周期性淹水酸性稻田中Hg的有效性。
