Department of Civil, Environmental, and Geo- Engineering, University of Minnesota, 500 Pillsbury Drive SE, Minneapolis, Minnesota 55455-0116, United States.
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Chemistry, Überlandstrasse 133, CH-8600 Dübendorf , Switzerland.
Environ Sci Technol. 2020 May 5;54(9):5520-5531. doi: 10.1021/acs.est.9b07616. Epub 2020 Apr 22.
Ferrous iron-bearing minerals are important reductants in the contaminated subsurface, but their availability for the reduction of anthropogenic pollutants is often limited by competition with other electron acceptors including microorganisms and poor accessibility to Fe(II) in complex hydrogeologic settings. The supply of external electron donors through chemical reduction (ISCR) has been proposed as one remediation approach, but the quantification of pollutant transformation is complicated by the perturbations introduced to the subsurface by ISCR. Here, we evaluate the application of compound specific isotope analysis (CSIA) for monitoring the reduction of 2,4-dinitroanisole (DNAN), a component of insensitive munitions formulations, by mineral-bound Fe(II) generated through ISCR of subsurface material from two field sites. Electron balances from laboratory experiments in batch and column reactors showed that 3.6% to 11% of the total Fe in the sediments was available for the reduction of DNAN and its partially reduced intermediates after dithionite treatment. The extent of DNAN reduction was successfully quantified from its N isotope fractionation measured in the column effluent based on the derivation of a N isotope enrichment factor, ε, derived from a comprehensive series of isotope fractionation experiments with numerous Fe(II)-bearing minerals as well as dithionite-reduced subsurface materials. Our observations illustrate the utility of CSIA as a robust approach to evaluate the success of remediation through abiotic contaminant reduction.
含铁矿物是污染地下水中重要的还原剂，但由于与其他电子受体（包括微生物）的竞争以及在复杂水文地质条件下难以获得 Fe(II)，它们对人为污染物的还原作用往往受到限制。通过化学还原（ISCR）提供外部电子供体已被提议作为一种修复方法，但由于 ISCR 对地下环境的扰动，污染物转化的量化变得复杂。在这里，我们评估了化合物特异性同位素分析 (CSIA) 在监测两种现场地下物质通过 ISCR 生成的矿物结合的 Fe(II)还原 2,4-二硝基苯甲醚 (DNAN)（钝感弹药制剂的组成部分）的应用。批式和柱式反应器中的实验室实验的电子平衡表明，经过连二亚硫酸盐处理后，沉积物中总 Fe 的 3.6%至 11%可用于还原 DNAN 及其部分还原中间体。通过基于一系列广泛的同位素分馏实验推导的 N 同位素富集因子 ε，成功地从柱流出物中测量的 DNAN 的 N 同位素分馏定量了 DNAN 的还原程度，这些实验涉及许多含铁矿物以及连二亚硫酸盐还原的地下物质。我们的观察结果说明了 CSIA 作为一种评估通过非生物污染物还原进行修复成功的稳健方法的实用性。
