Environmental Geochemistry Laboratory, Faculty of Biological Sciences, Department of Environmental Sciences, Quaid-i-Azam University, Islamabad, Pakistan.
Isotope Application Division, Pakistan Institute of Nuclear Science and Technology (PINSTECH), Nilore, Islamabad, Pakistan.
Chemosphere. 2020 Jul;251:126374. doi: 10.1016/j.chemosphere.2020.126374. Epub 2020 Mar 3.
Biogeochemical mobilization of arsenic in groundwater depends on the presence of dissolved organic matter (DOM) that likely promotes the As release, i.e., reductive dissolution, complexation, competition, and electron shuttling. We investigated the role of DOM in As release, along with its complete characterization, in the Indus plain of Pakistan, one of the worst arsenic impacted zones in the South Asian region. In total, 60 groundwater and 15 soil samples, collected at six sites from north to south within the flood plain of the Ravi River, Lahore, Pakistan were investigated. Arsenic concentration ranged from 9.61 μg/L to 386 μg/L in the groundwater samples (high As observed in areas close to the river). Dissolved organic carbon (DOC) in 29 groundwater samples ranged between 0 and 10.1 mg-C/L. A moderately positive correlation of As with DOC and Fe in the northern part of the study area suggest the reductive dissolution of FeOOH associated with dissolved organic matter (DOM). The reductive dissolution plays an essential role for As enrichment in the area evidenced by the lower concentrations of SO, NO, and POand a non-correlative pattern with As. In contrast, a positive correlation of As with PO, DOC, and HCO in the southern part indicate competitive desorption behind the As release. Fluorescence excitation-emission matrix intensity data of DOM indicate the maximum presence of humic-like substances in the northern part that gradually shifts to aromatic, fulvic and protein type towards the southern part. Specific ultraviolet absorbance and fluorescence index display aromatic and terrestrial (allochthonous) sources of DOM near the riverbank and mixed (both allochthonous and autochthonous) source away from the river. The positive correlations of As with DOC and fluorescence intensity also attest that DOM played a vital role in the As mobilization in groundwater of the study area.
地下水砷的生物地球化学迁移取决于溶解有机质 (DOM) 的存在，DOM 可能促进砷的释放，即还原溶解、络合、竞争和电子穿梭。我们研究了 DOM 在砷释放中的作用及其在巴基斯坦印度河流域平原的完全特征，该地区是南亚受砷影响最严重的地区之一。总共调查了巴基斯坦拉合尔市拉维河泛滥平原从北到南的六个地点的 60 个地下水和 15 个土壤样本。地下水样本中的砷浓度范围为 9.61μg/L 至 386μg/L（靠近河流的地区观察到高砷）。29 个地下水样本中的溶解有机碳 (DOC) 介于 0 至 10.1mg-C/L 之间。研究区北部砷与 DOC 和 Fe 的中度正相关表明与溶解有机质（DOM）相关的 FeOOH 的还原溶解。还原性溶解对该地区砷富集起着至关重要的作用，这从 SO、NO 和 PO 的浓度较低且与砷无相关性得到证明。相比之下，南部地区砷与 PO、DOC 和 HCO 的正相关表明砷释放背后存在竞争性解吸。DOM 的荧光激发-发射矩阵强度数据表明，北部地区腐殖质样物质的存在最多，然后逐渐向南部地区的芳香、富里酸和蛋白质类型转变。特定紫外吸光度和荧光指数显示，靠近河岸的 DOM 具有芳香和陆地（异源）来源，远离河流的 DOM 具有混合（异源和同源）来源。砷与 DOC 和荧光强度的正相关也证明了 DOM 在研究区地下水砷迁移中的重要作用。
