Noémie Janot*, Sarrah M. Dunham-Cheatham, Juan S. Lezama Pacheco, José M. Cerrato, Daniel S. Alessi, Vincent Noël, Eunmin Lee, Don Q. Pham, Elena Suvorova, Rizlan Bernier-Latmani, Kenneth H. Williams, Philip E. Long and John R. Bargar,
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引用次数: 0
摘要
本研究介绍了在科罗拉多州里弗尔受污染含水层中进行的现场实验,以确定原位生物还原过程中铀在沉积物中的种类和积累情况。我们应用同步辐射 X 射线光谱和成像技术以及水化学测量方法,确定了电子供体添加后最初几天水和沉积物中铀的种类变化。在整个研究过程中,观察到的铀固体形态变化有限,在所有获得的样本中都发现了非结晶铀(IV)。然而,在原位生物还原过程中,当主要微生物体系从铁还原条件过渡到硫酸盐还原条件时,铀的积累率急剧上升。结果表明,铀在铁还原过程中被酶还原,这是预料之中的。在硫酸盐还原过程中新形成的矿物晶粒表层是还原热点,众多还原剂可在此充当电子供体(铁(II)、硫(II)和微生物胞外聚合物物质),与铀结合并将其还原。这项研究的结果为了解沉积物中铀的积累机制提供了更多的见解,有助于完善描述洪泛区含水层氧化还原过程和污染物动态的定量模型。
Reducing Conditions Influence U(IV) Accumulation in Sediments during In Situ Bioremediation
This study presents field experiments conducted in a contaminated aquifer in Rifle, CO, to determine the speciation and accumulation of uranium in sediments during in situ bioreduction. We applied synchrotron-based X-ray spectroscopy and imaging techniques as well as aqueous chemistry measurements to identify changes in U speciation in water and sediment in the first days follwing electron donor amendment. Limited changes in U solid speciation were observed throughout the duration of this study, and non-crystalline U(IV) was identified in all samples obtained. However, U accumulation rates strongly increased during in situ bioreduction, when the dominant microbial regime transitioned from iron- to sulfate-reducing conditions. Results suggest that uranium is enzymatically reduced during Fe reduction, as expected. Mineral grain coatings newly formed during sulfate reduction act as reduction hotspots, where numerous reductants can act as electron donors [Fe(II), S(II), and microbial extracellular polymeric substances] that bind and reduce U. The results have implications for identifying how changes in the dominant reducing mechanism, such as Fe versus sulfate reduction, affect trace metal speciation and accumulation. The outcomes from this study provide additional insights into uranium accumulation mechanisms in sediments that could be useful for the refinement of quantitative models describing redox processes and contaminant dynamics in floodplain aquifers.
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.