Whaley-Martin K J, Mailloux B J, van Geen A, Bostick B C, Ahmed K M, Choudhury I, Slater G F
School of Geography and Earth Sciences, McMaster University, ON, Canada.
Environmental Sciences Department, Barnard College, NY, NY 10027, USA.
Sci Total Environ. 2017 Oct 1;595:63-71. doi: 10.1016/j.scitotenv.2017.03.234. Epub 2017 Apr 4.
Recent studies have demonstrated that the supply of relatively young organic carbon stimulates the release of arsenic to groundwater in Bangladesh. This study explores the potential role of human and livestock waste as a significant source of this carbon in a densely populated rural area with limited sanitation. Profiles of aquifer sediment samples were analyzed for phytosterols and coprostanol to assess the relative contributions of plant-derived and human/livestock waste-derived organic carbon at two well-characterized sites in Araihazar. Coprostanol concentrations increased with depth from non-detection (<10m at Site B and <23m at Site F) to maxima of 1.3 and 0.5ng/g in aquifer sands recovered from 17m (Site B) and 26m (Site F), respectively. The commonly used sewage contamination index ([5β-coprostanol]/([5α-cholestanol]+[5β-coprostanol])) exceeds 0.7 between 12 and 19m at Site B and between 24 and 26m at Site F, indicating input of human/livestock waste to these depths. Urine/fecal input within the same depth range is supported by groundwater Cl/Br mass ratios >1000 compared to Cl/Br <500 at depths >50m. Installed tube wells in the area's study sites may act as a conduit for DOC and specifically human/livestock waste into the aquifer during flood events. The depth range of maximum input of human/livestock waste indicated by these independent markers coincides with the highest dissolved Fe (10-20mg/L) and As (200-400μg/L) concentrations in groundwater at both sites. The new findings suggest that the oxidation of human/livestock waste coupled to the reductive dissolution of iron-(oxy)-hydroxides and/or arsenate may enhance groundwater contamination with As.
最近的研究表明，相对年轻的有机碳供应会刺激孟加拉国地下水中砷的释放。本研究探讨了在卫生设施有限的人口密集农村地区，人类和牲畜粪便作为这种碳的重要来源的潜在作用。分析了含水层沉积物样本的甾醇和粪甾烷醇，以评估在阿拉伊扎尔两个特征明确的地点，植物源有机碳和人类/牲畜粪便源有机碳的相对贡献。粪甾烷醇浓度随深度增加，从未检测到（B 站点<10 米，F 站点<23 米）增加到从 17 米（B 站点）和 26 米（F 站点）回收的含水层砂中分别达到最大值 1.3 和 0.5 纳克/克。常用的污水污染指数（[5β-粪甾烷醇]/（[5α-胆甾烷醇]+[5β-粪甾烷醇]））在 B 站点 12 至 19 米之间以及 F 站点 24 至 26 米之间超过 0.7，表明人类/牲畜粪便输入到这些深度。与深度>50 米处 Cl/Br<500 相比，同一深度范围内尿液/粪便输入得到地下水 Cl/Br 质量比>1000 的支持。该地区研究站点安装的管井可能在洪水事件期间作为溶解有机碳特别是人类/牲畜粪便进入含水层的管道。这些独立指标表明的人类/牲畜粪便最大输入深度范围与两个站点地下水中最高溶解铁（10 - 20 毫克/升）和砷（200 - 400 微克/升）浓度一致。新发现表明，人类/牲畜粪便的氧化与铁（氧）氢氧化物和/或砷酸盐的还原溶解相结合，可能会加剧地下水砷污染。
