Applying the Rayleigh Approach for Stable Isotope-Based Analysis of VOC Biodegradation in Diffusion-Dominated Systems,Environmental Science & Technology

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Applying the Rayleigh Approach for Stable Isotope-Based Analysis of VOC Biodegradation in Diffusion-Dominated Systems
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2018-07-05 , DOI: 10.1021/acs.est.8b01757
Ali M. Khan ₁ , Lukas Y. Wick ₁ , Martin Thullner ₁

Affiliation

Compound-specific stable isotope analysis (CSIA) has become an established tool for assessing biodegradation in the subsurface. Diffusion-dominated vapor phase transport thereby is often excluded from quantitative assessments due to the problem of diffusive mixing of concentrations with different isotopic signatures for CSIA interpretation. In soils and other unsaturated porous media volatile organic compounds (VOCs) however, are mainly transported via gas-phase diffusion and may thus prohibit a CSIA-based quantitative assessment of the fate of VOCs. The present study presents and verifies a concept for the assessment of biodegradation-induced stable isotope fractionation along a diffusive transport path of VOCs in unsaturated porous media. For this purpose data from batch and column toluene biodegradation experiments in unsaturated porous media were combined with numerical reactive transport simulations; both addressing changes of concentration and stable isotope fractionation of toluene. The numerical simulations are in good agreement with the experiment data, and our results show that the presented analytically derived assessment concept allows using the slope of the Rayleigh plot to obtain reasonable estimates of effective in situ fractionation factors in spite of diffusion-dominated transport. This enlarges the application range of CSIA and provides a mean for a better understanding of VOC fate in the unsaturated subsurface.

中文翻译：

基于瑞利方法的基于同位素的扩散控制系统中挥发性有机化合物生物降解的稳定分析

特定于化合物的稳定同位素分析（CSIA）已成为评估地下生物降解的成熟工具。因此，由于CSIA解释中具有不同同位素特征的浓度的扩散混合问题，经常将扩散为主的气相传输排除在定量评估之外。但是，在土壤和其他不饱和多孔介质中，挥发性有机化合物（VOC）主要是通过气相扩散运输的，因此可能会禁止基于CSIA的挥发性有机化合物的定量评估。本研究提出并验证了一种概念，用于评估不饱和多孔介质中VOC扩散传播路径上的生物降解诱导的稳定同位素分馏。为此，将不饱和多孔介质中间歇和塔柱甲苯生物降解实验的数据与数值反应输运模拟相结合。既解决了浓度的变化又解决了甲苯的稳定同位素分馏问题。数值模拟与实验数据非常吻合，我们的结果表明，尽管扩散占主导地位的运输，但所提出的分析得出的评估概念允许使用瑞利图的斜率获得有效的原位分馏因子的合理估计。这扩大了CSIA的应用范围，并为更好地理解非饱和地下VOC的命运提供了一种手段。数值模拟与实验数据非常吻合，我们的结果表明，尽管扩散占主导地位的运输，但所提出的分析得出的评估概念允许使用瑞利图的斜率获得有效的原位分馏因子的合理估计。这扩大了CSIA的应用范围，并为更好地理解非饱和地下VOC的命运提供了一种手段。数值模拟与实验数据非常吻合，我们的结果表明，尽管扩散占主导地位的运输，但所提出的分析得出的评估概念允许使用瑞利图的斜率获得有效的原位分馏因子的合理估计。这扩大了CSIA的应用范围，并为更好地了解不饱和地下中的VOC命运提供了一种手段。

更新日期：2018-07-08

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