State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of Environmental Science & Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
School of Environmental Studies, China University of Geosciences, Wuhan 430074, China.
Sci Total Environ. 2020 Mar 15;708:135162. doi: 10.1016/j.scitotenv.2019.135162. Epub 2019 Nov 21.
In East and Southeast Asia, the health of over 100 million people is threatened by the consumption of groundwater containing high concentrations of arsenic (>10 μg L), which is released from sediments through reductive dissolution of arsenic-bearing iron/manganese oxides. Dissolved organic matter (DOM) is known to play a crucial role in the process of arsenic mobilization in shallow aquifers, and its availability and reactivity are key factors controlling the variation of arsenic concentrations in groundwater. However, it is unclear how human activities influence the transport of DOM and how the transportation affects the DOM molecular properties in high arsenic groundwater. This study provides insights on the sources and molecular compositions of DOM in groundwater from the Jianghan Plain, central China, a newly discovered area with seasonal fluctuations in arsenic concentrations in shallow groundwater. Monitoring of water levels and stable carbon isotope compositions in groundwater from different depths and canal water over a year indicated that terrestrial DOM was the dominant source, accounting for 54.2%-85.5% of groundwater DOM. Electrospray ionization combined with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that canal water infiltration transferred aliphatic, tannin-like and leached aromatic DOM from sediments into groundwater. Therefore, groundwater recharge through irrigation using canal water not only inputs terrestrial DOM, but also accelerates the release of sedimentary DOM. Furthermore, carboxylic-rich alicyclic molecule (CRAM)-like DOM that is derived from biomolecules has the highest proportion (60.1%-65.5%) among the identified DOM structures. And, it might be reused in biochemical processes during arsenic mobilization, suggesting a third source of groundwater DOM in addition to canal water and sediments. The findings in this study advance the understanding on transport processes and molecular properties of DOM in high arsenic groundwater under extensive anthropogenic influences.
在东亚和东南亚地区，超过 1 亿人的健康受到地下水砷含量过高（>10μg/L）的威胁，这些地下水是通过含砷的铁/锰氧化物的还原溶解从沉积物中释放出来的。众所周知，溶解有机物质（DOM）在浅含水层中砷迁移的过程中起着至关重要的作用，其可用性和反应性是控制地下水砷浓度变化的关键因素。然而，人类活动如何影响 DOM 的迁移以及迁移如何影响高砷地下水中 DOM 的分子特性尚不清楚。本研究提供了中国中部江汉平原地下水 DOM 的来源和分子组成的见解，该地区是一个新发现的浅层地下水中砷浓度季节性波动的地区。对不同深度地下水和运河水水位和稳定碳同位素组成的监测表明，陆地 DOM 是主要来源，占地下水 DOM 的 54.2%-85.5%。电喷雾电离与超高效分辨率傅里叶变换离子回旋共振质谱联用表明，运河水的渗透将沉积物中的脂肪族、鞣质样和浸出芳香族 DOM 转移到地下水中。因此，通过灌溉使用运河水补给地下水不仅输入了陆地 DOM，而且还加速了沉积物 DOM 的释放。此外，源自生物分子的富羧酸脂环族分子（CRAM）样 DOM 占已鉴定 DOM 结构的比例最高（60.1%-65.5%）。并且，它可能在砷迁移过程中的生化过程中被再利用，这表明地下水 DOM 的第三个来源除了运河水和沉积物之外。本研究结果提高了在广泛人为影响下高砷地下水中 DOM 迁移过程和分子特性的认识。
