Department of Environmental Science and Technology, University of Maryland, College Park, Maryland 20742, United States.
Environ Sci Technol. 2010 Dec 15;44(24):9438-44. doi: 10.1021/es101859b. Epub 2010 Nov 24.
Oxidation of Cr(III) and reduction of Cr(VI) can occur simultaneously in aerobic soils, but the mechanisms involved are not well-understood, especially how electron shuttling by redox-active organic acids is involved. A and B soil horizons from three topohydrosequences from the Coastal Plain and Piedmont physiographic provinces of Maryland were chosen to investigate oxidation-reduction transformations of Cr under field moist conditions. Reduction of added Cr(VI) to Cr(III) was observed in all 18 samples, and 11 demonstrated enhanced reduction with added anthraquinone-2,6-disulfonate (AQDS) acting as an electron shuttle in 24 h quick tests under aerobic conditions. Oxidation of Cr(III) to Cr(VI) was observed in 12 samples, with 7 demonstrating diminished oxidation with AQDS added. Cr(VI) was undetectable after 11 d of incubation when lactic acid was added as a reductant for Cr(VI) to the Watchung soil A horizon. This reduction occurred in the presence of AQDS and a high salt background to suppress microbial growth, suggesting abiotic reduction was the dominant pathway. The results of this study demonstrate that in field-moist, aerobic soils, the electron shuttle, AQDS, enhanced Cr(VI) reduction and inhibited Cr(III) oxidation. This suggests redox-active organic C amendments and electron shuttles can be important in enhancing rates and extent of Cr(VI) reduction, while inhibiting Cr(III) oxidation in the in situ remediation of Cr(VI)-contaminated soils.
在有氧土壤中，Cr(III)的氧化和 Cr(VI)的还原可以同时发生，但涉及的机制尚未得到很好的理解，特别是氧化还原活性有机酸如何参与电子穿梭。本研究选择马里兰州沿海平原和皮埃蒙特地形省份的三个地形序列的 A 和 B 土壤层，在田间湿润条件下研究 Cr 的氧化还原转化。在所有 18 个样品中都观察到添加的 Cr(VI)还原为 Cr(III)，在有氧条件下的 24 小时快速试验中，11 个样品添加蒽醌-2,6-二磺酸钠（AQDS）作为电子穿梭剂，增强了还原作用。在 12 个样品中观察到 Cr(III)氧化为 Cr(VI)，其中 7 个样品添加 AQDS 后氧化作用减弱。当向 Watchung 土壤 A 层添加乳酸作为 Cr(VI)的还原剂时，Cr(VI)在 11 天的孵育期后无法检测到。在 AQDS 和高盐背景存在下抑制微生物生长的情况下发生了这种还原作用，这表明非生物还原是主要途径。本研究的结果表明，在田间湿润、有氧土壤中，电子穿梭剂 AQDS 增强了 Cr(VI)的还原，抑制了 Cr(III)的氧化。这表明氧化还原活性有机 C 添加剂和电子穿梭剂可以在原位修复 Cr(VI)污染土壤时，提高 Cr(VI)还原的速率和程度，同时抑制 Cr(III)的氧化。
