Abiotic arsenic mobilization in Bangladesh groundwater aquifers?

孟加拉国地下水含水层中砷的非生物动员？在孟加拉国和其他受影响的南亚国家，数百万饮用地下水的人暴露在砷水平下，预计在未来几十年将导致死亡和疾病。尽管世界各地的科学家在过去几年中做出了巨大的努力，但导致这些地区地下水中砷浓度升高的步骤顺序仍然知之甚少。这是一个严重的问题，因为主要的政策决定取决于准确预测抽水灌溉对地下水浓度的影响。我们建议通过一系列简单的培养实验来探索砷在地下水中积累的新机制，这可能对孟加拉国浅层含水层对灌溉的响应具有重要意义。基于3H-3He测年和孟加拉国4个地点建立的地下水As剖面所限制的局部补给空间格局，我们提出原生矿物的风化作用是浅层含水层As动员的限速步骤。现有数据表明，该过程释放的砷在广泛的环境中具有相似的量级，对氧化还原条件相对不敏感，因此可能完全是非生物性质的。这意味着砷的分布主要是由局部补给对浅层含水层冲刷速率的空间变化决定的。这是对广泛持有的观点的直接挑战，即地下水中砷的分布主要由微生物介导的铁氢氧化物的还原性溶解控制。现有的现场数据表明，在很宽的设置范围内，砷的释放率相对一致，每年约20微克/升。因此，通过隔离新收集的含水层材料和定期取样地下水，可以直接探测到这种量级的通量。在这项试点研究中，我们建议在一个有充分记录的地点，用4个深度间隔的含水层材料进行厌氧培养18个月。微生物在As动员中的作用将分别通过添加抗生素和醋酸盐来测试。来自一个深度区间的含水层材料将受到额外的处理，例如好氧培养和用低砷地下水或池塘水替代原位地下水。除As浓度外，主要阳离子Na、Mg、K和Ca将作为化学风化的指标进行监测。氧化还原敏感溶质，如铁，锰，和水也将被测量。这些简单实验的结果可能会导致我们对地下水获取溶质的理解发生根本性的变化，比如在一个麻烦的成分，如as （NSF标准1）的情况下。从这项工作中获得的新认识可能影响影响南亚数百万人的生活和健康的政策（nsf标准2）。如果我们对砷积累的新解释成立，随着时间的推移，持续的灌溉实际上可能会降低浅层含水层中的砷浓度。这与最近孟加拉国地下水中砷含量升高归因于灌溉形成了对比。

Abiotic Mobilization of Arsenic in Bangladesh Groundwater Aquifers?AbstractMillions of people consuming groundwater in Bangladesh and other affected South Asiancountries are exposed to As levels that are predicted to cause death and disease in the comingdecades. The sequence of steps that leads to elevated groundwater As concentrations in theseregions remains poorly understood, despite intense efforts by scientists throughout the worldover the past several years. This is a serious problem because major policy decisions hinge onaccurate prediction of the impact of groundwater pumping for irrigation on groundwater Asconcentrations. We propose here to explore with a series of simple incubation experiments anew mechanism for As accumulation in groundwater that could have important implications forthe response of shallow Bangladesh aquifers to irrigation.On the basis of spatial patterns of local recharge constrained by 3H-3He dating andgroundwater As profiles established at four sites in Bangladesh, we propose that weathering ofprimary minerals is the rate-limiting step of As mobilization in shallow aquifers. The availabledata suggest that As release by this process is of similar magnitude across a wide range ofenvironments, relatively insensitive to redox conditions, and therefore possibly entirely abiotic innature. The implication is that the distribution of As is determined primarily by spatial variationsin the rate of flushing of shallow aquifers by local recharge. This is a direct challenge to thewidely-held view that the distribution of As in groundwater is controlled primarily bymicrobially-mediated reductive dissolution of Fe oxyhydroxides.The available field data indicate a relatively consistent rate of As release of ~20 ug/L peryear for a wide range of settings. A flux of this magnitude should therefore be detectabledirectly by isolating freshly collected aquifer material and sampling the groundwaterperiodically. In this pilot-study, we propose to conduct such incubations anaerobically for 18months with aquifer material from 4 depth intervals at a well-documented location. The role ofmicroorganisms in As mobilization will be tested by additions of an antibiotic and acetate,respectively. Aquifer material from one depth interval will be subjected to additional treatmentssuch as aerobic incubation and replacement of in situ groundwater with low-As groundwater orpond water. In addition to As concentrations, the major cations Na, Mg, K, and Ca will bemonitored as indicators of chemical weathering. Redox-sensitive solutes such as Fe, Mn, and Swill also be measured.Results from these simple experiments could lead to a radical change in ourunderstanding of the acquisition of solutes by groundwater in the case of a troublesomeconstituent such as As (NSF Criterion 1). The new understanding derived from this work couldinfluence policies that affect the lives and health of millions of people in South Asia (NSFCriterion 2). If our new explanation for As accumulation holds, continued irrigation mightactually reduce As concentrations in shallow aquifers over time. This contrasts with the recentattribution of elevated As levels in Bangladesh groundwater to irrigation.