University of Neuchâtel, Centre for Hydrogeology & Geothermics (CHYN), Neuchâtel, Switzerland.
Swiss Center for Electronics and Microtechnology (CSEM), Systems Division, Neuchâtel, Switzerland.
PLoS One. 2018 Aug 22;13(8):e0202416. doi: 10.1371/journal.pone.0202416. eCollection 2018.
Predicting the fate of chloroethenes in groundwater is essential when evaluating remediation strategies. Such predictions are expected to be more accurate when incorporating isotopic parameters. Although secondary chlorine isotope effects have been observed during reductive dechlorination of chloroethenes, development of modelling frameworks and simulation has thus far been limited. We have developed a novel mathematical framework to simulate the C/Cl isotopic fractionation during reductive dechlorination of chloroethenes. This framework differs from the existing state of the art by incorporating secondary isotopic effects and considering both C and Cl isotopes simultaneously. A comprehensive general model (GM), which is expected to be the closest representation of reality thus far investigated, was implemented. A less computationally intensive simplified model (SM), with the potential for use in modelling of complex reactive transport scenarios, was subsequently validated based on its comparison to GM. The approach of GM considers all isotopocules (i.e. molecules differing in number and position of heavy and light isotopes) of each chloroethene as individual species, of which each is degraded at a different rate. Both models GM and SM simulated plausible C/Cl isotopic compositions of tetrachloroethene (PCE), trichloroethene (TCE) and cis-1,2-dichloroethene (cDCE) during sequential dechlorination when using experimentally relevant kinetic and isotopic parameters. The only major difference occurred in the case where different secondary isotopic effects occur at the different non-reacting positions when PCE is dechlorinated down to cDCE. This observed discrepancy stems from the unequal Cl isotope distribution in TCE that arises due to the occurrence of differential secondary Cl isotopic effects during transformation of PCE to TCE. Additionally, these models are shown to accurately reproduce experimental data obtained during reductive dechlorination by bacterial enrichments harbouring Sulfurospirillum spp. where secondary isotope effects are known to have occurred. These findings underscore a promising future for the development of reactive transport models that incorporate isotopic parameters.
预测地下水氯代烃的命运对于评估修复策略至关重要。当纳入同位素参数时，此类预测预计会更加准确。尽管在氯代烃的还原脱氯过程中已经观察到二次氯同位素效应，但建模框架和模拟的发展迄今为止仍然有限。我们开发了一种新的数学框架来模拟氯代烃还原脱氯过程中的 C/Cl 同位素分馏。该框架与现有的最先进技术不同，它纳入了二次同位素效应，并同时考虑了 C 和 Cl 同位素。实施了一个综合通用模型 (GM)，该模型有望成为迄今为止研究的最接近实际情况的模型。随后，根据其与 GM 的比较，验证了一种计算量较小的简化模型 (SM)，该模型具有在复杂反应性传输模拟中应用的潜力。GM 的方法考虑了每个氯代烃的所有同位质体（即分子在重同位素和轻同位素的数量和位置上有所不同）作为单个物种，其中每个物种以不同的速率降解。当使用实验相关的动力学和同位素参数时，GM 和 SM 两种模型都模拟了连续脱氯过程中四氯乙烯 (PCE)、三氯乙烯 (TCE) 和顺-1,2-二氯乙烯 (cDCE) 的合理 C/Cl 同位素组成。唯一的主要差异出现在 PCE 脱氯至 cDCE 时不同非反应位置发生不同的二次同位素效应的情况下。这种观察到的差异源于 PCE 转化为 TCE 过程中发生的差分二次 Cl 同位素效应导致的 TCE 中 Cl 同位素分布不均。此外，这些模型还准确地再现了在含有 Sulfurospirillum spp. 的细菌富集物中进行还原脱氯时获得的实验数据，其中已知发生了二次同位素效应。这些发现强调了开发纳入同位素参数的反应性传输模型的有前途的未来。
