Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland.
Chemosphere. 2011 Oct;85(5):774-81. doi: 10.1016/j.chemosphere.2011.06.063. Epub 2011 Jul 7.
The evaluation of biotransformation of chlorinated ethenes (CEs) in contaminated aquifers is challenging when variable redox conditions and groundwater flow regime are limiting factors. By using compound-specific stable carbon isotope analysis (C-CSIA) and ³H-³He based groundwater dating, we assessed three CE-contaminated field sites that differed in groundwater flow velocities, redox conditions, and level of contamination. CE isotopic signatures and carbon isotopic mass balances were applied to quantify CE transformation, whereas groundwater dating allowed determining degradation timescales and assessing hydrodynamic regimes. The combination of these techniques enabled at all field sites to indicate zones within the aquifers where CE dechlorination preferably occurred, sometimes even to metabolites of no toxic concern. However, the natural transformation processes were insufficient to mitigate the entire CE contamination at the studied sites. Such situations of limited transformation are worldwide far more common than sites where optimal natural (mainly redox) conditions are enabling complete CEs degradation. Despite such constraints for natural transformation, this study showed that even under non-favorable biogeochemical CEs degradation, the combination of CSIA and groundwater dating provide valuable information to the understanding of the fate of the CEs, thus, being an important contribution in the definition of efficient remediation measures at any given biogeochemical conditions.
在地下水流动和氧化还原条件受到限制的情况下，评估污染含水层中氯代烯烃（CEs）的生物转化是具有挑战性的。通过使用特定于化合物的稳定碳同位素分析（C-CSIA）和基于 ³H-³He 的地下水定年，我们评估了三个在地下水流动速度、氧化还原条件和污染程度方面存在差异的 CE 污染现场。CE 同位素特征和碳同位素质量平衡被用于量化 CE 的转化，而地下水定年则允许确定降解时间尺度并评估水动力状况。这些技术的结合使得在所有现场都能够指示含水层中 CE 脱氯优先发生的区域，有时甚至可以达到无毒性关注的代谢物。然而，自然转化过程不足以减轻研究地点的整个 CE 污染。在全世界范围内，这种转化有限的情况远比那些能够使所有 CE 完全降解的最佳自然（主要是氧化还原）条件下的情况更为常见。尽管存在这些自然转化的限制，但本研究表明，即使在不利于生物地球化学 CE 降解的情况下，CSIA 和地下水定年的结合也提供了有关 CE 命运的有价值信息，因此，在定义任何给定的生物地球化学条件下的有效修复措施方面具有重要意义。
