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

摘要浅层地下水天然砷污染在世界许多地区对人类健康构成重大威胁。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成问题的，因为它们的局部砷含量很高，而且因为它们被发展中国家数千万到数亿人用于饮用。最近的研究支持了这一概念，即砷是通过在洪泛区含水层中含砷的含水氧化铁（HFO）的还原性溶解释放的。我们最近提出As- hfo假说实际上是一个更大的大陆As输运现象的一部分，我们称之为砷地、生物、水（GBH）输运过程。GBH过程的本质是典型的地质、水文和微生物过程相互联系并导致河流泛滥平原含水层中的砷污染。GBH过程始于更新世冰川事件期间冰川的机械作用对山脉的风化作用，然后在全新世期间，气候变暖导致含有少量砷的冰川沉积物和基岩的快速化学风化，并将其释放到水圈。河流沉积物中的砷被HFO从河水中吸收，河流沉积物最终与河流洪泛区的有机质一起沉积。这反过来又导致厌氧地下水的发展，厌氧铁还原细菌（FeRB）溶解含砷的HFO，产生富铁和富砷的浅层地下水。我们最近的研究首次获得了as -地下水循环过程的现场微生物学数据（来自美国），并确定了FeRB和硫酸盐还原细菌（SRB）的属。我们的研究表明，导致河漫滩水化学反应的条件是普遍存在的，但只有在发展中国家才会成为一个严重的问题，因为这些国家的水被开发用于人类消费。这项拟议研究的主题将扩展和检验我们从美国三个实地地区得出的假设和结论，并将其推广到世界上一个受严重影响的地区。这将是对我们关于对这类天然砷污染进行生物地球化学控制的普遍性假设的最终检验。此外，我们之前的研究也证明了SRB在去除地下水中砷方面发挥的重要作用。我们将通过刺激原生SRB来研究原位硫酸盐还原条件下砷的地球化学，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较高（例如，排除形成重要的As-thio络合物），砷可能会被SRB从地下水中去除。拟在孟加拉国进行的实地研究将包括：1)在从达卡大学以前的研究中选择的实地地点钻探和安装新井（包括一些多端口监测井），并收集固体含水层材料；2)收集现有井和新井的现场地球化学数据；3)通过过滤地下水收集细菌样本进行DNA测序，并从固体含水层样本中提取；4)收集假设的自生碳酸盐和硫化物矿物相，评价其对砷迁移和地下水地球化学的控制作用；5)研究了人工诱导硫酸盐还原条件下砷的田间行为。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。建议的研究包括研究生和博士后的教育和研究活动。拟议的研究有重要的技术转让因素，在研究过程中，我们也将必要地与当地科学家和政府官员合作，我们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，我们在孟加拉国吸取的教训应该适用于许多其他国家。这个拟议的项目几乎属于所有五个“优先研究”主题领域，但在2002年1月28日至31日于孟加拉国拉金德拉普尔举行的恒河-布拉马普特拉河-梅克纳河三角洲美国-孟加拉国研讨会上，被确定为“合作研究领域”的主题领域IV更受重视。该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.