State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, No. 68 Jincheng Street, East Lake High-Tech Development Zone, Wuhan 430078, P. R. China.
Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, School of Environmental Studies, China University of Geosciences, No. 68 Jincheng Street, East Lake High-Tech Development Zone, Wuhan 430078, P.R. China.
Environ Sci Technol. 2022 Aug 16;56(16):11878-11887. doi: 10.1021/acs.est.2c02766. Epub 2022 Aug 7.
Dark formation of hydroxyl radicals (•OH) from soil/sediment oxygenation has been increasingly reported, and solid Fe(II) is considered as the main electron donor for O activation. However, the role of solid organic matter (SOM) in •OH production is not clear, although it represents an important electron pool in the subsurface. In this study, •OH production from oxygenation of reduced solid humic acid (HA) was investigated at pH 7.0. •OH production is linearly correlated with the electrons released from HA suspension. Solid HA transferred electrons rapidly to O via the surface-reduced moieties (hydroquinone groups), which was fueled by the slow electron transfer from the reduced moieties inside solid HA. Cycling of dissolved HA between oxidized and reduced states could mediate the electron transfer from solid HA to O for •OH production enhancement. Modeling results predicted that reduced SOM played an important or even dominant role in •OH production for the soils and sediments possessing high molar ratios of SOC/Fe(II) (e.g., >39). The significant contribution of SOM was further validated by the modeling results for oxygenation of 88 soils/sediments in the literature. Therefore, reduced SOM should be considered carefully to comprehensively understand •OH production in SOM-rich subsurface environments.
土壤/沉积物中氧的还原形成了大量的羟基自由基（•OH），而固态 Fe(II) 被认为是 O 激活的主要电子供体。然而，尽管固态有机物（SOM）是地下环境中重要的电子库，但它在•OH 产生中的作用尚不清楚。本研究在 pH 7.0 条件下，考察了还原态固态腐殖酸（HA）氧化过程中•OH 的生成。•OH 的生成与 HA 悬浮液中释放的电子呈线性相关。固态 HA 通过表面还原部分（对苯二酚基团）将电子快速转移给 O，这是由固态 HA 内部还原部分的缓慢电子转移提供动力。溶解态 HA 在氧化态和还原态之间的循环可以促进电子从固态 HA 转移到 O，从而增强•OH 的产生。模型预测结果表明，对于具有高 SOC/Fe(II) 摩尔比（例如，>39）的土壤和沉积物，还原态 SOM 在•OH 产生中起着重要甚至主导作用。通过对文献中 88 种土壤/沉积物氧化的模型预测结果，进一步验证了 SOM 的重要贡献。因此，在富含 SOM 的地下环境中，为了全面理解•OH 的产生，应该仔细考虑还原态 SOM。
