The accumulation of per- and polyfluoroalkyl substances (PFAS) at the air-water interface: A systematic review

Per- and polyfluoroalkyl substances (PFAS) have attracted considerable attention due to their environmental persistence and the challenges of remediation. PFAS, typically composed of hydrophobic fluorocarbon chains linked to hydrophilic head groups, exhibit excellent surface activity, leading to their spontaneous accumulation/adsorption at the air-water interface (AWI). This review systematically summarizes the mechanisms of PFAS adsorption at the AWI, the methodologies for determining the AWI adsorption coefficient (K_aw), the factors influencing K_aw, the enrichment of PFAS across various environmental media, and the remediation technologies leveraging this adsorption mechanism. PFAS accumulation at the AWI occurs in various environmental compartments, including the surface microlayer (SML), natural foams, aerosols, and the vadose zone. The degree of PFAS enrichment generally follows the order: aerosols > natural foams > surface microlayer, which is closely associated with the differences in the specific surface area of these carriers. Sea spray aerosols (SSA) exhibit significant PFAS enrichment, serving as a key secondary emission source of PFAS in coastal areas. The vadose zone acts as a long-term reservoir, potentially releasing PFAS into groundwater for decades to centuries. Foam fractionation and aerosol separation are two promising technologies for remediation of PFAS-contaminated water. Future research should focus on elucidating the mechanistic impacts of diverse factors, developing unified fitting and predictive models, expanding investigations to emerging PFAS, and optimizing removal technologies to enhance remediation efficiency of short-chain PFAS.