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

摘要浅层地下水中的天然砷污染对世界许多地区的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)河流泛滥平原含水层问题最大，因为它们在当地的砷含量很高，而且在发展中国家，数千万到数亿人利用它们来饮用。最近的研究支持这样一个概念，即洪泛平原含水层中含砷的水合氧化铁(HFO)是通过还原溶解释放出来的。我们最近提出，As-HFO假说实际上是一个更大的大陆As迁移现象的一部分，我们称之为砷的地质、生物、水力(GBH)迁移过程。GBH过程的本质是典型的地质、水文和微生物过程相互关联，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的机械效应对山脉的风化，然后在全新世，气候变暖导致含有少量As的冰川沉积物和基岩迅速化学风化，并将其释放到水圈。水系沉积物中的砷被HFO从河流水体中吸收，最终与河流泛滥平原中的有机物一起沉积。这进而导致厌氧地下水的发育和厌氧铁还原细菌(FERB)溶解含砷的HFO，产生富含铁和砷的浅层地下水。我们最近的研究已经为AS-地下水循环过程产生了第一个现场微生物学数据(来自美国)，并确定了FeB和硫酸盐还原细菌(SRB)的属。我们的研究表明，在河流泛滥平原导致这种水化学的条件是普遍的，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用来供人类消费。这项拟议研究的主题将把我们从美国三个领域得出的假设和结论扩展到世界上受AS严重影响的地区，并对其进行检验。这将是对我们关于生物地球化学控制这类自然砷污染的普遍性的假设的最终检验。此外，我们之前的研究也证明了SRB在自然界中在去除地下水中的砷方面发挥了重要作用。我们将像我们在美国的生物修复研究中所做的那样，通过刺激本土SRB来研究原位硫酸盐还原条件下As的地球化学，该研究表明，如果溶解铁浓度保持较高水平(例如，阻止形成重要的As-thio络合物)，SRB可以从地下水中去除As。拟议在孟加拉国进行的实地研究将包括：1)在达卡大学以前的研究工作中选定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)收集实地现有和新井的地球化学数据；3)通过过滤地下水收集细菌样本，用于DNA测序并从固体含水层样本中提取；4)收集假想的自生碳酸盐和硫化物矿物相，以评估它们在控制地下水流动性和地下水地球化学方面的作用；5)调查AS在外地人工诱导硫酸盐还原条件下的行为。总而言之，我们的研究团队拥有以前从未在砷污染地区部署过的独特技能和背景，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，以及一个潜在的补救工具。拟议的研究包括针对研究生和博士后的教育和研究活动。拟议的研究中有重要的技术转让因素，在研究过程中，我们还必须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经验教训应该适用于许多其他国家。这一拟议项目属于几乎所有五个“优先研究”专题领域，尤其是在美国-孟加拉国恒河-雅鲁藏布江-梅格纳三角洲研讨会(2002年1月28日至31日，孟加拉国拉金德拉普尔)上确定的专题领域IV下的“合作研究领域”。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.