Bouchard Daniel, Hunkeler Daniel, Marchesi Massimo, Aravena Ramon, Buscheck Tim
GHD, 4600 Boul Cote Vertu, Montreal, QC, Canada; Centre for Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Rue Emile Argand 11, Neuchâtel CH-2000, Switzerland.
Centre for Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Rue Emile Argand 11, Neuchâtel CH-2000, Switzerland.
J Contam Hydrol. 2024 Mar;262:104310. doi: 10.1016/j.jconhyd.2024.104310. Epub 2024 Feb 1.
The solvent-based sampling method for collecting gas-phase volatile organic compounds (VOCs) and conducting compound-specific isotope analysis (CSIA) was deployed during a controlled field study. The solvent-based method used methanol as a sink to accumulate petroleum hydrocarbons during the sampling of soil air and effluent gas. For each gaseous sample collected, carbon isotope analysis (δC) was conducted for a selection of five VOCs (benzene, toluene, o-xylene, cyclopentane and octane) emitted by a synthetic hydrocarbon source emplaced in the subsurface. The δC values obtained for gaseous VOCs (collected from soil gas and effluent gas) were compared to measurements obtained for the same VOCs present in the source material (none aqueous phase liquid - NAPL) and dissolved in groundwater to evaluate the reliability of the solvent-based sampling method in providing accurate isotope measurements. Since the NAPL source was composed of only 12 VOCs, potential bias related to the analytical procedure (such as co-elution) were avoided, hence emphasizing on field-related bias. This field evaluation demonstrated the capacity of the solvent-based method to produce precise and accurate δC measurements. The isotopic discrepancies between the gaseous and the NAPL values were < 1 ‰ for 39 out of the 41 comparison points, thus deemed not statistically different based on a common isotopic uncertainty error of ±0.5 ‰. Moreover, the current field study is the first field study to report δC measurements for up to five gas-phase VOCs obtained from the same sample, which appears to be of interest for VOC fate or forensic studies. The possibility to use several VOC isotopic measurements enabled by the sampling method would contribute to strengthen the connection assessment between gaseous VOCs and the suspected emitting source. Accordingly, the field results presented herein support the application of this sampling methodology to conduct CSIA assessment in the frame of VOC vapor studies.
在一项受控的现场研究中，采用了基于溶剂的采样方法来收集气相挥发性有机化合物（VOCs）并进行化合物特异性同位素分析（CSIA）。基于溶剂的方法使用甲醇作为吸收剂，在土壤空气和废气采样过程中积累石油烃。对于每个采集的气态样品，对地下放置的合成烃源排放的五种VOC（苯、甲苯、邻二甲苯、环戊烷和辛烷）进行碳同位素分析（δC）。将气态VOC（从土壤气体和废气中收集）获得的δC值与源材料（非水相液体 - NAPL）中存在并溶解于地下水中的相同VOC的测量值进行比较，以评估基于溶剂的采样方法提供准确同位素测量的可靠性。由于NAPL源仅由12种VOC组成，避免了与分析程序相关的潜在偏差（如共洗脱），因此重点关注与现场相关的偏差。该现场评估证明了基于溶剂的方法能够产生精确和准确的δC测量值。在41个比较点中的39个点，气态和NAPL值之间的同位素差异<1‰，因此基于±0.5‰的常见同位素不确定误差，认为在统计学上没有差异。此外，当前的现场研究是第一项报告从同一样品中获得的多达五种气相VOC的δC测量值的现场研究，这似乎对VOC归宿或法医研究具有重要意义。采样方法实现的使用多种VOC同位素测量的可能性将有助于加强气态VOC与疑似排放源之间的关联评估。因此，本文给出的现场结果支持在VOC蒸汽研究框架内应用这种采样方法进行CSIA评估。
