Kim H, Annable M D, Rao P S
Department of Environmental Science, Hallym University, South Korea.
Environ Sci Technol. 2001 Nov 15;35(22):4457-62. doi: 10.1021/es001965l.
Laboratory experiments were conducted employing gas chromatographic techniques to evaluate the gaseous transport of volatile organic chemicals (VOCs) in water-unsaturated soil columns as influenced by interfacial (air-water) adsorption and water partitioning. VOCs [methylene chloride, tetrachloroethene (PCE), 1,1,1-trichloroethane (TCA), ethyl-benzene, p-xylene, chlorobenzene] with different water-partitioning and interfacial adsorption coefficients (air-water) were used to evaluate the theoretical basis of using these coefficients to predict the retardation factors (Rt) observed during gaseous transport. A loamy sand from Dover Air Force Base, DE, and a commercial sand were used as the column packing material to assess the effect of grain size on the air-water interfacial area (ai) and retardation at different water saturations (Sw). The ai were measured using n-alkanes. At low Sw, interfacial adsorption contributed most to the retardation for all VOCs during gaseous transport in the Dover soil which has little sorption capacity for the VOCs. As Sw increased, the fraction of Rt attributed to interfacial adsorption decreased, while that due to water partitioning increased for all of the VOCs used for this study. For the sand, with a more uniform grain-size distribution than the Dover soil, the contribution of air-water interfacial adsorption to the Rt of a VOC (p-xylene) was not as significant as that for the Dover soil due to small ai. The fractions of Rt attributed to interfacial adsorption and water partitioning were quantified. The observed Rt for the VOCs agreed well with those predicted based on the sorption coefficients and the quantities of sorption domains (Sw, ai).
采用气相色谱技术进行了实验室实验，以评估挥发性有机化合物（VOCs）在水不饱和土壤柱中的气态传输，该传输受界面（气 - 水）吸附和水分配的影响。使用具有不同水分配系数和气 - 水界面吸附系数的VOCs [二氯甲烷、四氯乙烯（PCE）、1,1,1 - 三氯乙烷（TCA）、乙苯、对二甲苯、氯苯]来评估使用这些系数预测气态传输过程中观察到的阻滞因子（Rt）的理论基础。来自特拉华州多佛空军基地的一种壤质砂土和一种商业砂被用作柱填充材料，以评估粒径对不同水饱和度（Sw）下的气 - 水界面面积（ai）和阻滞作用的影响。使用正构烷烃测量ai。在低Sw时，对于多佛土壤中气态传输过程中的所有VOCs，界面吸附对阻滞作用的贡献最大，该土壤对VOCs的吸附能力很小。随着Sw的增加，归因于界面吸附的Rt分数降低，而对于本研究中使用的所有VOCs，归因于水分配的分数增加。对于砂，其粒径分布比多佛土壤更均匀，由于ai较小，气 - 水界面吸附对VOC（对二甲苯）的Rt的贡献不如多佛土壤显著。对归因于界面吸附和水分配的Rt分数进行了量化。观察到的VOCs的Rt与基于吸附系数和吸附域数量（Sw，ai）预测的结果非常吻合。
