Adsorption and Retardation of PFAs in Soils

Abstract

Per- and poly-fluorinated alkyl substances (PFAS) are contaminants of emerging concern (CECs) that are present in the subsurface at numerous military and industrial facilities. Knowledge of the retention behavior of these compounds in the subsurface environment is critical for effective risk characterization and remediation. The objective of this research is to investigate the role of adsorption at the air-water interface on PFAS retention in vadose-zone systems. Surface tensions were measured for select PFAS to determine interfacial adsorption coefficients. Column experiments were conducted to characterize retardation and transport under saturated and unsaturated flow conditions. The impact of solid-phase adsorption, and interfacial adsorption was investigated. The results shows that the PFOS and PFOA transport behavior in the unsaturated condition is regulated by both solid phase adsorption and air-water interfacial adsorption. PFOS has greater air-water interfacial adsorption, and greater retention was observed during the transport of PFOS in both the saturated and unsaturated conditions compared to PFOA. Air-water interfacial adsorption contributed approximately 77% of total retention for PFOS and PFOA transport in unsaturated conditions. The relative contribution of air-water interfacial adsorption to PFAS retardation will depend on input concentrations, water saturations, ionic strengths and perfluorinated chain length.