Iron cycling in the environment: new insights from the micro to the macro-scale

了解环境中的铁循环至关重要，因为氧化铁在吸附可溶性污染物（如有毒金属）方面非常有效。乍一看，铁循环似乎相当直接，即，二价铁的微生物和/或化学氧化和随后的铁氧化物沉淀以及三价铁氧化物的非生物和/或生物还原和随后的氧化物还原溶解。然而，最近的研究表明，铁的循环比我们想象的要复杂得多，铁在环境中的行为与其他溶质的存在密切相关，如砷、铝、氮、硅、硫、磷酸盐，因此，本提案旨在研究天然和合成生物氧化铁（BIOS）中的铁循环在已知影响铁转化和/或稳定性的几种溶质的存在下。本提案的3个目标是：1）化学变化如何影响天然BIOS矿物学和微生物多样性？2)哪些化学因素控制着BIOS的减少？ 有机物是否稳定BIOS并防止矿物学转变？将从渥太华附近的几个淡水地点（原始和金属污染）收集天然BIOS，而人工BIOS将在实验室合成。首要目标是使“环境”，即，BIOS，到实验室，并通过改变广泛的物理化学参数（即，pH、氧化还原等）为了区分其他溶质（Al、As、N、S、Si等）的作用，在铁循环在微观尺度上使用原位传感器和批量分析。BIOS的氧化还原稳定性也将使用环境相关条件来确定。为了阐明铁和其他溶质之间的复杂关系，合成BIOS也将被合成并用于受到与天然BIOS相同操作的良好控制的系统中，以分离特定的化学和微生物转化。将分析各种系统的水（使用原位微剖面仪和微电极）和固相地球化学，沿着微生物活动和多样性。本研究项目将培养几名HQP（7名B.Sc.，2名硕士和3名博士）他们将接触到地球化学和地球微生物学领域的最先进技术，并获得进入劳动力市场的宝贵技能。该提案的结果将使我们能够更好地预测有毒金属在因季节变化而发生氧化还原和化学波动的环境中的命运。

Understanding the iron cycle in the environment is of prime importance because iron oxides are highly efficient at sorbing soluble contaminants, such as toxic metals. At first glance, iron cycling appears rather straight forward, i.e., microbial and/or chemical oxidation of ferrous iron and subsequent precipitation of iron oxides and abiotic and/or biotic reduction of ferric iron oxides and subsequent reductive dissolution of the oxides. Recent studies have however shown that the iron cycle is far more complex than we thought and that iron behavior in the environment is closely linked to the presence of other solutes, such as arsenic, aluminum, nitrogen, silicon, sulfur, phosphate, etc. The present proposal therefore aims at investigating iron cycling in natural and synthetic biogenic iron oxides (BIOS) in the presence of several solutes known to affect iron transformation and/or stability. The 3 objectives of this proposal are 1) How do chemical changes affect natural BIOS mineralogy and microbial diversity?, 2) Which chemical factors control the reduction of BIOS? and 3) Does organic matter stabilize BIOS and prevent mineralogical transformation over time? Natural BIOS will be collected from several freshwater sites near Ottawa (pristine and metal contaminated), whereas artificial BIOS will be synthesized in the laboratory. The overarching goal is to bring the “environment”, i.e., BIOS, to the laboratory and modify it by changing a wide range of physico-chemical parameters (i.e., pH, redox, etc.) in order to tease apart the role of other solutes (Al, As, N, S, Si, etc.) in iron cycling at the micro scale using in situ sensors and bulk analyses. The redox stability of BIOS will also be determined using environmentally relevant conditions. In order to elucidate the intricate relationship between iron and other solutes, synthetic BIOS will also be synthesized and used in well controlled systems submitted to the same manipulations as natural BIOS in order to isolate specific chemical and microbial transformations. The various systems will be analyzed for aqueous (using an in situ micro-profiler and micro-electrodes) and solid phase geochemistry, along with microbial activity and diversity. This research project will train several HQPs (7 B.Sc., 2 M.Sc. and 3 Ph.D.) who will be exposed to state-of-the-art techniques in the field of geochemistry and geomicrobiology and gain valuable skills to enter the work force. Results from this proposal will enable us to better predict the fate of toxic metals in the environment where redox and chemical fluctuations occur due to seasonal changes.