State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, 430074, Wuhan, China.
State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, 430074, Wuhan, China.
Environ Pollut. 2020 Jul;262:114305. doi: 10.1016/j.envpol.2020.114305. Epub 2020 Mar 2.
Organic matter (OM) acts as a source of carbon and is strongly implicated in biogeochemical processes, such as metal complexation and redox reactions. To illustrate the effects of OM on As mobilization in aquifers, this study characterized fluorescence features and hydrochemical properties of OM in sediments and groundwater from an As-affected field site located in the Datong Basin. Fluorescence analysis showed sediment and groundwater OM are dominated by oxidized and reduced quinone-like compounds; shorter emission wavelengths observed in groundwater indicated more labile and protein-like organic substances than in sediments. Dissolved As concentrations were positively correlated with dissolved Fe and HCO concentrations in middle and deep groundwater, suggesting labile OM degradation promotes the release of As and Fe from sediments into the groundwater. This result also demonstrated more bioavailable OM occurs in groundwater and that labile OM degradation promotes As release. Grain size distribution results indicated sedimentary As, Fe and OM are associated with fine-grained fractions. Sedimentary As content was significantly and positively correlated with FeO and OM content, suggesting the potential existence of As-Fe-OM ternary complexation; this was further supported by the results of Fourier-transform infrared (FTIR) spectra and extraction experiments. In addition, the ratio of dissolved reduced quinone-like compounds to oxidized quinone-like compounds was positively correlated with both dissolved As and HCO concentrations, implying quinone-like compounds participate in the complexation and influence As mobilization. In the reducing environment, labile OM served as the electron donor to maintain microbial respiration and mediated reductive dissolution of Fe minerals. As-Fe-OM ternary complexation in sediments and microbial reduction have a potentially strong impact on As enrichment in groundwater, and therefore are important considerations for regulating As contamination.
有机物质 (OM) 是碳的来源，并强烈参与生物地球化学过程，如金属络合和氧化还原反应。为了说明 OM 对含水层中 As 迁移的影响，本研究对大同盆地受 As 影响的田间场地的沉积物和地下水中的 OM 的荧光特征和水文化学性质进行了表征。荧光分析表明，沉积物和地下水中的 OM 主要由氧化和还原醌类化合物组成；在地下水中观察到较短的发射波长，表明比沉积物中更不稳定且具有蛋白质样的有机物质。中间和深部地下水中溶解 As 的浓度与溶解 Fe 和 HCO 的浓度呈正相关，表明不稳定的 OM 降解促进了 As 和 Fe 从沉积物中释放到地下水中。这一结果还表明，更多具有生物利用性的 OM 存在于地下水中，并且不稳定的 OM 降解促进了 As 的释放。粒度分布结果表明，沉积物中的 As、Fe 和 OM 与细颗粒分数有关。沉积物中 As 的含量与 FeO 和 OM 的含量呈显著正相关，表明存在 As-Fe-OM 三元络合作用；傅里叶变换红外（FTIR）光谱和提取实验的结果进一步支持了这一点。此外，溶解还原型醌类化合物与氧化型醌类化合物的比值与溶解 As 和 HCO 的浓度均呈正相关，这意味着醌类化合物参与了络合作用并影响了 As 的迁移。在还原环境中，不稳定的 OM 作为电子供体，维持微生物呼吸并介导 Fe 矿物的还原溶解。沉积物中 As-Fe-OM 三元络合物和微生物还原对地下水中 As 的富集有潜在的强烈影响，因此是调节 As 污染的重要考虑因素。
