State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China; School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China.
State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Beijing 100083, China; School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, China.
Water Res. 2021 Jun 15;198:117140. doi: 10.1016/j.watres.2021.117140. Epub 2021 Apr 11.
Organic matter (OM) has been accepted as an important trigger fueling Fe(III) oxide reduction and arsenic release in the late Pleistocene-Holocene anoxic aquifers, whereas its fates and roles on arsenic mobility in the Pliocene aquifer are unclear. To fill this gap, groundwaters from a confined Pliocene aquifer (CG) and an unconfined Holocene aquifer (UG) were sampled in the Guide Basin, China, to monitor evolutions of groundwater geochemistry and OM molecular signatures along the groundwater flow path. The outcomes showed that groundwater pH, temperature, and arsenic concentrations in the CG samples generally increased along the groundwater flow path, which were much higher than those in the UG samples. The numbers and intensities of recalcitrant molecules (polycyclic aromatics and polyphenols) in the CG samples remarkably increased along the path, but relatively labile molecules (highly unsaturated and phenolic compounds and aliphatic compounds) showed the opposite trends. The arsenic-poor (<10 μg/L) UG samples contained more labile molecules than the arsenic-rich CG samples. High groundwater pH, temperature, and sediment age in the confined aquifers may be responsible for the selective mobilization of the unique polycyclic aromatics and polyphenols. The mobilized recalcitrant organic molecules may enhance arsenic release via electron shuttling, complexation, and competition. Furthermore, high temperature and pH may also facilitate arsenic desorption. The study provides molecular-scale evidences that the mobilization of recalcitrant organic molecules and arsenic were concurrent in the geothermal confined groundwater.
有机物质（OM）已被认为是在晚更新世-全新世缺氧含水层中推动 Fe(III)氧化物还原和砷释放的重要触发因素，而其在上新世含水层中对砷迁移的命运和作用尚不清楚。为了填补这一空白，在中国指南盆地采集了承压上新世含水层（CG）和无压全新世含水层（UG）的地下水样，以监测地下水地球化学和 OM 分子特征沿地下水流动路径的演变。结果表明，CG 水样的地下水 pH 值、温度和砷浓度沿地下水流动路径普遍升高，远高于 UG 水样。CG 水样中难降解分子（多环芳烃和多酚）的数量和强度沿路径显著增加，而相对不稳定的分子（高度不饱和和酚类化合物以及脂肪族化合物）则呈现相反的趋势。砷贫（<10μg/L）的 UG 水样比砷富的 CG 水样含有更多的易降解分子。承压含水层中高地下水 pH 值、温度和沉积物年龄可能是选择性迁移独特的多环芳烃和多酚的原因。迁移的难降解有机分子可能通过电子穿梭、络合和竞争来增强砷的释放。此外，高温和高 pH 值也可能促进砷的解吸。该研究提供了分子尺度的证据，表明在高温承压地下水中，难降解有机分子和砷的迁移是同时发生的。
