Chromium transformations in natural environments: The role of biological and abiological. processes in chromium(VI) reduction
Chromium transformations in natural environments: The role of biological and abiological. processes in chromium(VI) reduction
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DOI：
10.1080/00206810009465107
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发表时间：
2000-08-01
影响因子：
2.6
通讯作者：
Hansel, CM
中科院分区：
文献类型：
--
作者：
Fendorf, S;Wielinga, BW;Hansel, CM
铬是一种氧化还原动力学元素，具有许多工业用途。因此，它往往通过人类活动以较高的水平进入地表环境。此外，超镁铁质岩石如蛇纹岩通常富含铬，因此也可导致土壤和沃茨中铬元素的含量可观。在三价状态下，它对生物活性几乎没有危害，但不幸的是，在六价状态下，它对生物体毒性很大。因此，必须评估给定系统中Cr的氧化态，并确定价态之间转化的可能性。综述了自然环境中Cr（VI）还原反应的研究进展，并提出了新的见解。一些好氧和厌氧细菌表现出将Cr（VI）还原为Cr（III）的酶促能力;两个物种甚至可以使用Cr（VI）作为呼吸中的末端电子受体来生长。然而，减少铬的能力本身并不能证明该过程将在自然环境中以可观的水平发生。还原材料，如亚铁或硫化氢可能会与生物途径竞争还原铬（VI）。在测得的反应速率和推导出的速率表达式的基础上，我们表明，生物途径不太可能有助于减少铬酸盐在厌氧系统中。在pH值大于5.5时，亚铁将主导铬酸盐的还原，而在pH值低于5.5时，硫化氢将主导铬酸盐的还原。相比之下，细菌可能是在有氧环境中将Cr（VI）转化为Cr（III）的主要手段。因此，Cr（VI）还原的过程将主要取决于系统的通气状态，其次取决于pH和特定还原相的浓度。
Chromium is a redox-dynamic element that has many industrial uses. As a consequence, it is often introduced at elevated levels into the surface environment through human activity. Additionally, ultramafic rocks such as serpentinite are commonly enriched in chromium, and thus can also lead to appreciable levels of this element within soils and waters. In the trivalent state, it poses little hazard to biological activity, but, unfortunately, in the hexavalent state it is very toxic, to living matter. One must;therefore assess the oxidation state of Cr in a given system and determine the potential for transformation between valence states. The objective of this paper to is review and provide new insight on reduction reactions of Cr(VI) within natural environments. A number of aerobic and anaerobic bacteria demonstrate the enzymatic ability to reduce Cr(VI) to Cr(III); two species can even grow using Cr(VI) as the terminal electron acceptor in respiration. The ability to reduce chromium in itself is not evidence that the process will take place at appreciable levels in natural environments, however. Reduced materials such as ferrous iron or hydrogen sulfide may compete with biological pathways in the reduction of Cr(VI). On the basis of measured reaction rates and derived rate expressions, we demonstrate that biological pathways are not likely to contribute to the reduction of chromate in anaerobic systems. Ferrous iron will dominate the reduction of chromate at pH values greater than similar to 5.5, whereas hydrogen sulfide will dominate at pH values below this value. In contrast, bacteria may be the principal means by which Cr(VI) is converted to Cr(III) in aerobic environments. Thus, the process by which Cr(VI) is reduced will depend primarily on the aeration status of the system, and secondarily on pH and the concentrations of specific reduced phases.