Sadiq Muhammad, Eqani Syed Ali Musstjab Akber Shah, Podgorski Joel, Ilyas Shazia, Abbas Syed Sayyam, Shafqat Mustafa Nawaz, Nawaz Ismat, Berg Michael
Department of Biosciences, COMSATS University, Park Road, 44000 Islamabad, Pakistan; Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
Department of Biosciences, COMSATS University, Park Road, 44000 Islamabad, Pakistan.
Sci Total Environ. 2024 Jul 20;935:173452. doi: 10.1016/j.scitotenv.2024.173452. Epub 2024 May 21.
It is well known that groundwater arsenic (As) contamination affects million(s) of people throughout the Indus flood plain, Pakistan. In this study, groundwater (n = 96) and drilled borehole samples (n = 87 sediments of 12 boreholes) were collected to investigate geochemical proxy-indicators for As release into groundwater across floodplains of the Indus Basin. The mean dissolved (μg/L) and sedimentary As concentrations (mg/kg) showed significant association in all studied areas viz.; lower reaches of Indus flood plain area (71 and 12.7), upper flood plain areas (33.7 and 7.2), and Thal desert areas (5.3 and 4.7) and are indicative of Basin-scale geogenic As contamination. As contamination in aquifer sediments is dependent on various geochemical factors including particle size (3-4-fold higher As levels in fine clay particles than in fine-coarse sand), sediment types (3-fold higher As in Holocene sediments of floodplain areas vs Pleistocene/Quaternary sediments in the Thal desert) with varying proportion of Al-Fe-Mn oxides/hydroxides. The total organic carbon (TOC) of cored aquifer sediments yielded low TOC content (mean = 0.13 %), which indicates that organic carbon is not a major driver (with a few exceptions) of As mobilization in the Indus Basin. Alkaline pH, high dissolved sulfate and other water quality parameters indicate pH-induced As leaching and the dominance of oxidizing conditions in the aquifers of upper flood plain areas of Punjab, Pakistan while at the lower reaches of the Indus flood plain and alluvial pockets along the rivers with elevated flood-driven dissolved organic carbon (exhibiting high dissolved Mn and Fe and a wide range of redox conditions). Furthermore, we also identified that paired dissolved AsMn values (instead of AsFe) may serve as a geochemical marker of a range of redox conditions throughout Indus flood plains.
众所周知，巴基斯坦印度河泛滥平原的地下水砷污染影响着数百万人。在本研究中，采集了96份地下水样本和87份钻孔样本（来自12个钻孔的沉积物），以调查印度河流域泛滥平原地下水砷释放的地球化学替代指标。在所有研究区域，溶解态砷浓度（μg/L）均值与沉积物砷浓度（mg/kg）均值均呈现显著关联，具体如下：印度河泛滥平原下游地区（71和12.7）、泛滥平原上游地区（33.7和7.2）以及塔尔沙漠地区（5.3和4.7），这表明该流域存在地质成因的砷污染。含水层沉积物中的砷污染取决于多种地球化学因素，包括颗粒大小（细黏土颗粒中的砷含量比细粗砂高3 - 4倍）、沉积物类型（泛滥平原地区全新世沉积物中的砷含量是塔尔沙漠更新世/第四纪沉积物的3倍）以及不同比例的铝铁锰氧化物/氢氧化物。取芯含水层沉积物的总有机碳（TOC）含量较低（均值 = 0.13%），这表明在印度河流域，有机碳并非砷迁移的主要驱动因素（少数情况除外）。碱性pH值、高溶解态硫酸盐及其他水质参数表明，在巴基斯坦旁遮普省泛滥平原上游地区的含水层中，pH值引发了砷的淋滤作用，且氧化条件占主导地位；而在印度河泛滥平原下游以及河流沿岸的冲积区，洪水驱动的溶解有机碳含量升高（溶解态锰和铁含量较高，氧化还原条件范围较广）。此外，我们还发现，成对的溶解态砷锰值（而非砷铁值）可作为整个印度河泛滥平原一系列氧化还原条件的地球化学标志物。
