Collaborative Research: Bacterial Controls on Mineral Dissolution and Precipitation and Aqueous Geochemistry of Natural Arsenic-Contaminated Groundwater, Bangladesh

摘要在世界许多地方，浅层地下水的天然砷污染对人类健康构成了重大威胁。 我们和其他人的研究表明，年轻的（全新世）河流洪泛区含水层是最有问题的，因为它们的局部高砷含量，因为它们被开发用于饮用的数千万到数亿人在发展中国家。 最近的研究支持的概念，砷释放的含砷的水合氧化铁（HFO）在河漫滩含水层的还原溶解。我们最近提出，作为HFO假说实际上是一个更大的大陆作为运输现象，我们称之为砷的地质，生物，水（GBH）运输过程的一部分。 GBH过程的本质是典型的地质、水文和微生物过程相互联系，导致河流漫滩含水层中的砷污染。 GBH过程开始于更新世冰川事件期间冰的机械作用对山脉的风化，然后在全新世期间，温暖的气候导致含有少量As的冰川沉积物和基岩的快速化学风化，并将其释放到水圈。 河流沃茨中的砷被HFO吸附到河流沉积物中，最终与河流漫滩中的有机质一起沉积。 这反过来又导致厌氧地下水的发展和厌氧铁还原菌（FeRB）溶解含砷的HFO，产生富铁和富砷的浅层地下水。 我们最近的研究已经产生了第一个现场微生物数据（来自美国）作为地下水循环过程，并确定了铁RB和硫酸盐还原菌（SRB）的属。我们的研究表明，导致河流洪泛区这种水化学的条件是普遍的，但只有在开发这种水供人类消费的发展中国家才成为严重问题。 这项研究的主题将扩展和测试我们的假设和结论，从我们在美国的三个领域，以一个严重的影响地区的世界。 这将是对我们关于地球化学控制对这种类型的天然砷污染的普遍性的假设的最终检验。 此外，我们以前的研究也证明了SRB在自然界中对去除地下水中的砷起着重要作用。 我们将研究As在原位硫酸盐还原条件下的地球化学，方法是刺激本地SRB，就像我们在美国的生物修复研究中所做的那样，这表明如果溶解铁浓度保持升高（例如，排除了显着As-硫代复合物的形成）。 拟在孟加拉国进行的实地研究将包括：1）钻探和安装新威尔斯井（包括一些多口监测井）在从以前的达卡大学的研究中选择的实地地点，并收集固体含水层材料; 2）从现有和新的威尔斯收集实地地球化学数据; 3）通过过滤地下水收集细菌样品用于DNA测序，以及从固体含水层样品中提取; 4）收集假设的自生碳酸盐和硫化物矿物相，以评价它们在控制As活动性和地下水地球化学中的作用;（5）人工诱导硫酸盐还原条件下As的行为研究。 总之，我们的研究团队拥有独特的技能和背景，以前从未在砷污染地区部署过，因此这项研究提供了一个无与伦比的机会来记录砷问题的原因，以及潜在的补救工具。 拟议的研究包括研究生和博士后的教育和研究活动。拟议的研究具有重要的技术转让要素，在研究过程中，我们还将与当地科学家和政府官员合作，并计划在孟加拉国举办技术研讨会。 由于砷污染是发展中国家的一个紧迫问题，我们在孟加拉国学到的教训应该适用于许多其他国家。这个拟议的项目几乎福尔斯所有五个“优先研究”专题领域，但特别是在专题领域IV下，该专题领域IV在孟加拉国拉金德拉布尔举行的美国-孟加拉国恒河-布拉马普特拉河-梅克纳河三角洲讲习班上被确定为“合作研究领域”（2002年1月28日至31日）。研讨会由美国国家科学基金会和孟加拉国政府赞助。

AbstractNatural arsenic contamination of shallow groundwater poses a major human health threat in many parts of the world. Research by us and others indicates that young (Holocene) river floodplain aquifers are most problematic due to their locally high arsenic levels and because they are exploited for drinking by tens to hundreds of millions of people in developing nations. Recent research supports the concept that As is released by reductive dissolution of the As-bearing hydrous ferric oxides (HFO) in the floodplain aquifers. We have recently proposed that the As-HFO hypothesis is actually part of a much larger continental As transport phenomena, which we have called the arsenic geo-, bio-, hydro- (GBH) transport process. The essence of the GBH process is that typical geologic, hydrologic, and microbial processes are linked and lead to arsenic contamination in river floodplain aquifers. The GBH process starts with weathering of mountain ranges by mechanical effects of ice during the Pleistocene glacial events, and then during the Holocene, warmer climates leads to rapid chemical weathering of glacial deposits and bedrock containing minor amounts of As, and its release to the hydrosphere. Arsenic is sorbed from river waters by HFO in stream sediments, and stream sediments ultimately are deposited with organic matter in river floodplains. This in turn causes anaerobic groundwater to develop and anaerobic iron-reducing bacteria (FeRB) to dissolve As-bearing HFO, producing Fe- and As-riched shallow groundwater. Our recent research has generated the first field microbiologic data (from USA) for the As-groundwater cycling processes and has identified genera of FeRB and sulfate-reducing bacteria (SRB). Our research indicates that the conditions that lead to this water chemistry in river floodplains is universal, but only rises to a serious problem in the developing nations where this water is exploited for human consumption. The subject of this proposed research will extend and test our hypotheses and conclusions drawn from our three field areas in USA to a seriously As-affected region of the world. This will be the ultimate test of our hypothesis regarding the universality of biogeochemical controls on this type of natural arsenic contamination. Further, our previous research has also demonstrated an important role that SRB play in nature in removing As from groundwater. We will investigate the geochemistry of As under in situ sulfate-reducing conditions by stimulating indigenous SRB as we have done in our bioremediation research in the USA, which suggests that As may be removed from groundwater by SRB if dissolved iron concentrations remain elevated (e.g., precludes formation of significant As-thio complexes). The proposed field research in Bangladesh will include: 1) drilling and installation of new wells (including some multiport monitoring well) at field sites selected from previous Dhaka University research, and also collection of solid aquifer materials; 2) collection of geochemical data in the field from existing and new wells; 3) collection of bacteria samples by filtering of groundwater for DNA sequencing and also extraction from solid aquifer samples; 4) collection of hypothesized authigenic carbonate and sulfide mineral phases to evaluate their role in controlling As mobility and groundwater geochemistry; and 5) an investigation of the behavior of As under artificially induced sulfate-reducing conditions in the field. In summary, our research team has unique skills and backgrounds that have never been deployed in As-contaminated areas before, and thus this research offers an unparalleled opportunity to document the cause of the arsenic problem, as well as a potential remediation tool. The proposed research includes educational and research activities for graduate students and post-docs. The proposed research has significant technology transfer elements in it, during the progress of the study, we will also by necessity be cooperating with local scientists and government officials, and we plan on presenting technical seminars in Bangladesh. Because As-contamination is a pressing problem in the developing world, lessons we learn in Bangladesh should be applicable to many other countries. This proposed project falls under almost all five "priority research" thematic areas, but particularly more under thematic area IV as identified as "collaborative research areas" at the US-Bangladesh Workshop on the Ganges-Brahmaputra-Meghna Delta, held in Rajendrapur, Bangladesh (January 28-31, 2002). The workshop was sponsored by the US National Science Foundation and the Government of Bangladesh.