The objective of this research was to investigate the retention and transport behavior of GenX in five natural porous media with similar median grain diameters but different geochemical properties. Surface tensions were measured to characterize surface activity. Miscible-displacement experiments were conducted under saturated conditions to characterize the magnitude of solid-phase adsorption, while unsaturated-flow experiments were conducted to examine the impact of air–water interfacial adsorption on retention and transport. The results from surface-tension measurements showed that the impact of solution composition is greater for the ammonium form of GenX than for the acid form, due to the presence of the NH₄ counterion. The breakthrough curves for the experiments conducted under saturated conditions were asymmetrical, and a solute-transport model employing a two-domain representation of nonlinear, rate-limited sorption provided reasonable simulations of the measured data. The magnitudes of solid-phase adsorption were relatively small, with the highest adsorption associated with the medium containing the greatest amount of metal oxides. The breakthrough curves for the experiments conducted under unsaturated conditions exhibited greater retardation due to the impact of adsorption at the air–water interface. The contributions of air–water interfacial adsorption to GenX retention ranged from ∼24% to ∼100%. The overall magnitudes of retardation were relatively low, with retardation factors < ∼3, indicating that GenX has significant migration potential in soil and the vadose zone. To our knowledge, the results presented herein represent the first reported data for solid–water and air–water interfacial adsorption of GenX by soil. These data should prove useful for assessing the transport and fate behavior of GenX in soil and groundwater.

中文翻译：

---

GenX 在饱和和不饱和多孔介质中的传输

本研究的目的是研究 GenX 在具有相似中值粒径但不同地球化学性质的五种天然多孔介质中的保留和传输行为。测量表面张力以表征表面活性。在饱和条件下进行混相置换实验以表征固相吸附的大小，而进行不饱和流动实验以检查空气-水界面吸附对保留和传输的影响。表面张力测量结果表明，由于 NH ₄的存在，溶液组成对 GenX 铵形式的影响大于酸形式反离子。在饱和条件下进行的实验的穿透曲线是不对称的，采用非线性、限速吸附的双域表示的溶质传输模型提供了对测量数据的合理模拟。固相吸附量相对较小，最高吸附量与含有最多金属氧化物的介质有关。由于空气-水界面吸附的影响，在不饱和条件下进行的实验的穿透曲线表现出更大的延迟。空气-水界面吸附对 GenX 保留率的贡献范围从~24% 到~100%。延迟的整体幅度相对较低，延迟因子<~3，表明 GenX 在土壤和包气带中具有显着的迁移潜力。据我们所知，本文提供的结果代表了土壤对 GenX 的固-水和空气-水界面吸附的首次报道数据。这些数据对于评估 GenX 在土壤和地下水中的运输和归宿行为应该是有用的。