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Predicting Secular Changes in Arsenic Hazard in Circum-Himalyan Groundwaters

预测环喜马拉雅地下水砷危害的长期变化

基本信息

批准号：
NE/J023833/1
负责人：
David Polya
金额：
$ 64.19万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FJ023833%2F1
关键词：
Predicting Secular Changes Arsenic Hazard

项目摘要

Over 100 million people drink groundwaters containing naturally occurring arsenic (As) higher than the WHO guide value (10 ppb). In Bangladesh alone, 20% of all deaths in impacted areas are attributable to such exposure (ARGOS, 2010) - this corresponds to about 30,000 premature deaths every year.Studies provide evidence for both in-aquifer and near-surface sediment As sources. ISLAM (2004) demonstrated that As release occurs from within the aquifer sediments & highlighted the importance of organic matter (OM) in this process. BENNER (2008) & POLIZZOTTO (2008) have suggested, instead, that As release mostly occur in near-surface sediments BEFORE entering the aquifer. Determining the relative importance and controls of As release from the near surface sediments (typically 5 m - 15 m depth) from that which occurs within the aquifer, as well as assessing the various controls on As once in solution, are critical if we are to develop the required process oriented understanding of As mobility in drinking water supplies.Identifying study areas that reveal these processes is hard. For example, massive groundwater abstraction in the densely populated areas of West Bengal and Bangladesh has resulted in a complex subsurface hydrological environment which makes tracking As release mechanisms almost impossible. However, the absence of such extensive abstraction in As-rich aquifers of Cambodia means that this subsurface hydrological environment remains largely unaltered. Recent work by project partners (Stanford) means that a representative high As area has been identified and the hydrogeology established - but not on a scale or with the geochemical techniques required to establish a full understanding.We will drill 77 new and relatively inexpensive boreholes at the Cambodian site after using geophysics (supplied by our BGS partner) to determine the best locations. These new wells will allow us to collect samples across established As hotspots at a scale over which the As release process must be operating. Three well nests will sample an oxbow lake overlying an As contaminated aquifer, a sand 'window' through the overlying clay sediments and a control through the clay sediment overlying the As contaminated main aquifer. Two further well sequences will allow sampling of the main aquifer along its flow path. A 5-20m tube-well separation represents ~5-250 years of aquifer chemical evolution. Our Cambodian partners at RUPP & RDI will give local logistic support.We have been working closely our NERC Radiocarbon Lab partner. We show within our proposal that 14-C dating of organic matter in sediments and of dissolved inorganic and organic carbon in groundwaters provides a profound technique for identifying organic matter sources, central to resolving As release mechanisms. Similarly, pilot work withour NERC stable isotope facility partner has shown the utility of applying delta-18O and delta-D data to quantify surface water input into the main aquifer. Both of these approaches, combined with Manchester anion, cation and inorganic assay of sediments as well as tritium and 4-He techniques to date any young water input or ancient fluid contribution, will provide a fully comprehensive geochemical approach. With the high spatial resolution of sampling we expect this approach to make a major contribution in: i) quantifying the flux of As on a spatial scale alongside secular changes in As hazard from these two potential As sources; ii) identifying the dominant source of OM responsible for driving As release from these locations; and iii) identifying the controlling processes and mechanisms responsible for As release in these profiles. Together this understanding will enable the development of a quantitative model with predictive capacity that will inform governmental agencies responsible for drinking water and irrigation supplies to assess how continuation of, or changing, water use practice will impact future water supply As risks.

超过 1 亿人饮用的地下水中天然存在的砷 (As) 含量高于世界卫生组织指导值 (10 ppb)。仅在孟加拉国，受影响地区所有死亡的 20% 归因于此类暴露（ARGOS，2010 年）——这相当于每年约 30,000 人过早死亡。研究为含水层内和近地表沉积物作为来源提供了证据。 ISLAM（2004）证明砷的释放是从含水层沉积物内部发生的，并强调了有机物（OM）在此过程中的重要性。相反，BENNER (2008) 和 POLIZZOTTO (2008) 提出，砷的释放主要发生在进入含水层之前的近地表沉积物中。如果我们要发展对饮用水供应中砷迁移率所需的面向过程的理解，那么确定近地表沉积物（通常为 5 m - 15 m 深度）砷释放与含水层内砷释放的相对重要性和控制，以及评估溶解后砷的各种控制，至关重要。确定揭示这些过程的研究领域是困难的。例如，西孟加拉邦和孟加拉国人口稠密地区的大规模地下水抽取导致了复杂的地下水文环境，使得追踪砷释放机制几乎不可能。然而，柬埔寨富含砷的含水层缺乏如此广泛的抽取，这意味着这种地下水文环境基本上保持不变。项目合作伙伴（斯坦福大学）最近的工作意味着已经确定了一个具有代表性的高砷区域并建立了水文地质，但尚未达到一定规模，也没有建立充分了解所需的地球化学技术。在使用地球物理学（由我们的 BGS 合作伙伴提供）确定最佳位置后，我们将在柬埔寨现场钻 77 个相对便宜的新钻孔。这些新井将使我们能够在砷释放过程必须运行的范围内收集已建立的砷热点样品。三个井巢将对砷污染的含水层上的牛弓湖进行采样，通过覆盖的粘土沉积物进行沙“窗口”采样，并对砷污染的主含水层上的粘土沉积物进行控制采样。另外两个井序列将允许沿其流动路径对主要含水层进行采样。 5-20m 的管井间隔代表约 5-250 年的含水层化学演化。我们在 RUPP 和 RDI 的柬埔寨合作伙伴将提供当地后勤支持。我们一直与 NERC 放射性碳实验室合作伙伴密切合作。我们在提案中表明，沉积物中的有机物以及地下水中溶解的无机和有机碳的 14-C 测年为识别有机物来源提供了一种深刻的技术，这对于解决砷释放机制至关重要。同样，与我们的 NERC 稳定同位素设施合作伙伴的试点工作也显示了应用 delta-18O 和 delta-D 数据来量化流入主要含水层的地表水的效用。这两种方法，结合曼彻斯特阴离子、阳离子和沉积物无机测定，以及氚和 4-He 技术来测定任何年轻水输入或古代流体贡献，将提供全面的地球化学方法。凭借采样的高空间分辨率，我们预计这种方法将在以下方面做出重大贡献：i) 量化空间尺度上的砷通量以及这两个潜在砷源的砷危害的长期变化； ii) 确定负责推动这些地点砷释放的 OM 的主要来源； iii) 确定负责这些概况中砷释放的控制过程和机制。总之，这种理解将有助于开发具有预测能力的定量模型，该模型将告知负责饮用水和灌溉供应的政府机构，以评估用水实践的继续或变化将如何影响未来的供水风险。