Journal: Journal of Environmental Quality

Article Title: Bridging single‐species research and mixture reality: Emerging contaminants fate and transport in vadose zones

doi: 10.1002/jeq2.70177

Figure Lengend Snippet: Chemical breakthrough curves of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) as single species and mixtures under various conditions (i.e., source concentrations and water‐filled pore space percentage). Graphs are the fitted curves for measured data. Under saturated conditions, PFOA and PFOS display similar breakthrough patterns to each other when occurring in isolation (single solute) (A, left panel), whereas PFOS displays some competitive sorption against PFOA, when occurring as a mixture with PFOA arriving and ending slightly earlier as pointed out with the blue arrows (A, right panel). Measured bromide breakthrough curves are shown and used to represent non‐reactive, conservative transport in the soil (A). However, differential lag times emerge, and competitive sorption is evident in unsaturated conditions (50% water‐filled pore space) with chromatographic peaking in mixtures (i.e., C/C o > 1), which can occur with advancing displacement processes such as PFOS displacing sorbed PFOA (on both mineral‐water and air‐water interfaces) repeatedly as the solution advances through the soil (B). These competitive sorption processes of the mixture induce earlier breakthrough at higher concentrations than the source mixture for PFOA as compared to when present as a single solute (B). Similar to trends observed for mixtures in saturated soil, 10‐fold higher concentrations of the PFOA‐PFOS mixture induced nearly similar breakthrough curves with some slight patterns of competitive sorption (C, solid lines). However, notable differences in concentrations (including chromatographic peaking) and lag times occurred among PFOA and PFOS (panel C, dashed lines) when the source mixture was 10‐fold lower in concentrations as compared to panel B. All graphics in panels A, B, and C were recreated from data in Figures 4, 5, and 6, respectively, of Garza‐Rubalcava et al. ; used with permission from publisher.

Article Snippet: Following regulatory restrictions on long‐chain compounds, beginning with voluntary industry phase‐outs (2000; 3M Company), the USEPA PFOA Stewardship Program (2006–2015), and listing of PFOS (2009) and PFOA (2019) under the Stockholm Convention (ITRC, ), industry has shifted toward short‐chain PFAS containing fewer than seven perfluorinated carbons, as well as compounds with cationic, zwitterionic, and nonionic functional groups in addition to the traditional anionic carboxylate and sulfonate moieties (Nguyen et al., ; Post, ; USEPA, ; Xiao et al., ).

Techniques: Isolation