GHD inc., 4600 Blvd Côte Vertu, Montreal, H4S 1C7, Canada; Centre for Hydrogeology and Geothermics (CHYN)University of Neuchâtel, Rue Emile Argand 11 CH-2000 Neuchâtel, Switzerland.
Aix Marseille University - CNRS, UMR 7376, Laboratory of Environmental Chemistry, 3 Place Victor Hugo, F-13331 Marseille, France.
Chemosphere. 2022 Dec;308(Pt 2):136209. doi: 10.1016/j.chemosphere.2022.136209. Epub 2022 Aug 27.
Several types of laboratory experiments were conducted to evaluate isotope fractionation caused by phase transfer process for a selection of common environmental contaminants. Carbon and hydrogen isotope fractionation caused by vaporization of non-aqueous phase liquid (NAPL), by volatilization from water and by dissolution into an organic solvent (tetraethylene glycol dimethylether or TGDE) under equilibrium conditions was investigated with closed system experimental setups to isolate the air-liquid partitioning process. A selection of aromatic, aliphatic and chlorinated compounds along with one fuel oxygenate (methyl tert-butyl ether or MTBE) were evaluated to determine isotope enrichment factor related to respective phase transfer process. During NAPL vaporization, the residual mass of aromatic compounds, aliphatic compounds and MTBE became progressively depleted in heavy carbon and hydrogen isotopes. In contrast, during volatilization from water, the residual mass of aromatic compounds and MTBE dissolved in the water became progressively enriched in heavy hydrogen isotopes, whereas no significant change in carbon isotope was observed, except for MTBE showing a significant depletion. For the air-TGDE partitioning process, most of the aromatic compounds tested led to no significant carbon (except ethylbenzene) or hydrogen (except toluene and o-xylene) isotope fractionation. In contrast, significant carbon isotope fractionation was observed for aliphatic and chlorinated compounds and hydrogen isotope fractionation for aliphatic compounds, and are comparable to progressive NAPL vaporization in direction and magnitude. The isotope fractionation factors determined in this study are key for interpreting the change in isotope ratios when assessing the fate of gas-phase VOCs present in the soil air or when gas-phase VOCs are sampled using TGDE as the sink matrix. The results of this study contribute to expand the list of common environmental contaminants that can be assessed by the compound-specific isotope analysis (CSIA) method deployed in the frame of gas-phase studies.
进行了几种类型的实验室实验，以评估选择的常见环境污染物的相转移过程引起的同位素分馏。通过封闭系统实验装置研究了非水相液体（NAPL）蒸发、从水中挥发以及在平衡条件下溶解到有机溶剂（四乙二醇二甲醚或 TGDE）引起的碳和氢同位素分馏，以隔离气液分配过程。评估了一系列芳香族、脂肪族和氯化化合物以及一种燃料含氧物（甲基叔丁基醚或 MTBE），以确定与各自相转移过程相关的同位素富集因子。在 NAPL 蒸发过程中，芳香族化合物、脂肪族化合物和 MTBE 的残余质量逐渐耗尽重碳和氢同位素。相比之下，在从水中挥发时，溶解在水中的芳香族化合物和 MTBE 的残余质量逐渐富含重氢同位素，而碳同位素没有明显变化，除了 MTBE 表现出明显的耗尽。对于空气-TGDE 分配过程，大多数测试的芳香族化合物没有导致显著的碳（除乙苯外）或氢（除甲苯和邻二甲苯外）同位素分馏。相比之下，观察到脂肪族和氯化化合物的显著碳同位素分馏以及脂肪族化合物的氢同位素分馏，其方向和幅度与渐进 NAPL 蒸发相当。本研究确定的同位素分馏因子是解释土壤空气中存在的气相 VOCs 或使用 TGDE 作为汇矩阵采样时气相 VOCs 同位素比值变化的关键。本研究的结果有助于扩大可以通过部署在气相研究框架内的化合物特异性同位素分析（CSIA）方法评估的常见环境污染物的清单。
