Yao Cong, Xue Jinping, Xie Qing, Chen Sha, Jiang Tao, Wang Juan, Wang Yongmin, Wang Dingyong
College of Resources and Environment, Southwest University, Chongqing, 400715, China.
Universite de Pau et des Pays de l'Adour, E2S UPPA, CNRS, Institut des Sciences Analytiques et des Physico-Chimie pour l'Environnement et les Matériaux (IPREM), Pau, 64000, France.
Environ Res. 2025 Jan 1;264(Pt 1):120332. doi: 10.1016/j.envres.2024.120332. Epub 2024 Nov 14.
Agricultural organic wastes can leach dissolved organic matter (DOM) into surrounding water bodies, establishing them as significant sources of aquatic DOM. Given the importance of DOM in biogeochemical cycling of mercury (Hg), this DOM may mediate divalent Hg (Hg(II)) reduction, a process that remains poorly understood. This study investigated Hg(II) reduction using DOM derived from six representative agricultural wastes, categorized into livestock manure (chicken, pig, cow) and crop straw (rice, corn, rapeseed), with systematic considerations of the kinetics of reduction processes and the involvement of key free radicals. Results revealed that photoreduction was the primary pathway for Hg(II) reduction, with pig manure DOM exhibiting the highest efficiency at 36%. Key DOM quality parameters, such as protein-like components, have been identified as critical determinants of Hg(II) photoreduction capacity. Furthermore, free radicals induced by DOM could either enhance or inhibit Hg(II) reduction capacities. Specifically, in livestock manure, the superoxide anion (O)·was identified as the primary radical promoting Hg(II) photoreduction of pig manure DOM. In crop straw, hydroxyl radicals (·OH) were found to inhibit Hg(II) photoreduction, whereas O promoted the Hg(II) photoreduction of rice straw DOM. These findings provide valuable insights into the role of agricultural organic wastes in biogeochemical cycling of Hg within aquatic ecosystems.
农业有机废物可将溶解有机物（DOM）淋溶到周围水体中，使其成为水生DOM的重要来源。鉴于DOM在汞（Hg）生物地球化学循环中的重要性，这种DOM可能介导二价汞（Hg(II)）的还原，而这一过程仍知之甚少。本研究使用源自六种代表性农业废物的DOM来研究Hg(II)的还原，这些废物分为畜禽粪便（鸡、猪、牛）和作物秸秆（水稻、玉米、油菜籽），并系统地考虑了还原过程的动力学以及关键自由基的参与情况。结果表明，光还原是Hg(II)还原的主要途径，猪粪DOM的光还原效率最高，为36%。已确定关键的DOM质量参数，如类蛋白成分，是Hg(II)光还原能力的关键决定因素。此外，DOM诱导产生的自由基既可以增强也可以抑制Hg(II)的还原能力。具体而言，在畜禽粪便中，超氧阴离子（O）·被确定为促进猪粪DOM中Hg(II)光还原的主要自由基。在作物秸秆中，发现羟基自由基（·OH）会抑制Hg(II)的光还原，而O则促进稻草DOM中Hg(II)的光还原。这些发现为农业有机废物在水生生态系统中Hg生物地球化学循环中的作用提供了有价值的见解。
