Per‐ and Polyfluoroalkyl Substances (PFAS) in Subsurface Environments: Occurrence, Fate, Transport, and Research Prospect

Abstract

Per‐ and polyfluoroalkyl substances (PFASs), also known as “forever chemicals,” are manmade chemicals that have been increasingly detected in various geological settings since the early 2000s. The soil and subsurface environments are the geological media commonly affected by PFAS. We conducted a comprehensive review of peer‐reviewed articles published from 2010 through 2022 concerning the fate and transport of PFAS in subsurface environments. This review is organized into different subsections, covering the basics of PFAS properties and how they affect the occurrence, fate, and transport of PFAS, the fundamental processes affecting subsurface transport and fate of PFAS, and mathematical models for describing and predicting PFAS transport behaviors. Mechanisms governing PFAS transport in the subsurface environment, including the sorption of PFAS at the air‐water interface, solid‐water interface, and nonaqueous phase liquids‐water interface, were explored in detail. Challenges and future research priorities are identified to better mitigate the global challenges of PFAS contamination.

Role of Mineral–Organic Interactions in PFAS Retention by AFFF-Impacted Soil

“…The coordinates of the geometrically optimized AmPr-FHxSA-PrA and AmPr-FHxSA are provided in the SI (Tables S16 and S17). The computational predictions may explain why some zwitterionic PFAS may behave as "neutral" molecules with zero net charge 20 and why zwitterion mass retained was related to the largely aliphatic OC in this soil, whereas no such relationship was found for anionic C ≤ 7 PFAS.…”

“…35 In summary, most researchers conclude that no single soil or PFAS molecular property can fully capture PFAS retention in soil. 22,26,35,38,40,55,56 We took this situation as a call to reconcile and improve knowledge regarding the mechanistic connection between those chemical and physical sorbent (soil) and sorbate (PFAS) properties 20,57 that are relevant for retention and transport. 11,15,58 Accordingly, our overarching goal was to develop a generalizable model of PFAS retention in saturated soils of AFFF-impacted source zones.…”

“…We took this situation as a call to reconcile and improve knowledge regarding the mechanistic connection between those chemical and physical sorbent (soil) and sorbate (PFAS) properties , that are relevant for retention and transport. ,, …”

“…16−19 The various types of PFAS commonly found in AFFF complicate the long-term manage-ment of respective AFFF-impacted source zones since molecularly different PFAS cannot be expected to exhibit similar retention characteristics when confronted with variable sorbent (i.e., soil matrix) and solvent (e.g., electrolyte concentrations in H 2 O) properties (Figure 1). 20 To date, organic carbon (OC) 21−23 and the length of the fluorinated carbon chain (as a proxy for molecular hydrophobicity) are viewed as the primary features related to PFAS partitioning to soil, 24,25 especially for PFAS with more than six or seven fluorinated carbons. 26−28 However, recent analyses of published soil partitioning coefficients for anionic PFAS indicate that, in soils with less than 5% OC, the fluorinated tail−OC relationship is not a robust predictor of sorption, 22,29 with one study reporting little change in sorption with increasing OC content.…”

Polyfluoroalkyl substances requiring a renewed focus on groundwater‐surface water interactions

“…In Nevada, PFSAs were detected at higher concentrations ranging from 129.8 to 257 ng/g dw compared to PFCAs at 88.6 to 143.1 ng/g dw (Bai and Son 2021). The higher concentrations of PFSAs in sediments compared to PFCAs could be attributed to the former's higher hydrophobicity (Lyu et al 2022). Investigations into seasonal variations found that total PFAS levels during summer (53.5 ng/g dw) were much lower than winter concentrations (292.1 ng/g dw).…”