Influences of Chemical Properties, Soil Properties, and Solution pH on Soil–Water Partitioning Coefficients of Per- and Polyfluoroalkyl Substances (PFASs)

Abstract

The aim of this study was to assess the soil–water partitioning behavior of a wider range of per- and polyfluoroalkyl substances (PFASs) onto soils covering diverse soil properties. The PFASs studied include perfluoroalkyl carboxylates (PFCAs), perfluoroalkane sulfonates (PFSAs), fluorotelomer sulfonates (FTSs), nonionic perfluoroalkane sulfonamides (FASAs), cyclic PFAS (PFEtCHxS), per- and polyfluoroalkyl ether acids (GenX, ADONA, 9Cl-PF3ONS), and three aqueous film-forming foam (AFFF)-related zwitterionic PFASs (AmPr-FHxSA, TAmPr-FHxSA, 6:2 FTSA-PrB). Soil–water partitioning coefficients (log K d values) of the PFASs ranged from less than zero to approximately three, were chain-length-dependent, and were significantly linearly related to molecular weight (MW) for PFASs with MW > 350 g/mol (R 2 = 0.94, p < 0.0001). Across all soils, the K d values of all short-chain PFASs (≤5 −CF2– moieties) were similar and varied less (<0.5 log units) compared to long-chain PFASs (>0.5 to 1.5 log units) and zwitterions AmPr- and TAmPr-FHxSA (∼1.5 to 2 log units). Multiple soil properties described sorption of PFASs better than any single property. The effects of soil properties on sorption were different for anionic, nonionic, and zwitterionic PFASs. Solution pH could change both PFAS speciation and soil chemistry affecting surface complexation and electrostatic processes. The K d values of all PFASs increased when solution pH decreased from approximately eight to three. Short-chain PFASs were less sensitive to solution pH than long-chain PFASs. The results indicate the complex interactions of PFASs with soil surfaces and the need to consider both PFAS type and soil properties to describe mobility in the environment.

Granular activated carbon‐based treatment and mobility of per‐ and polyfluoroalkyl substances in potable reuse for aquifer recharge

“…It has been well documented that short‐chain PFAS are typically transported through groundwater aquifers at higher velocities than long‐chain PFAS (Gellrich et al, 2012; Guelfo & Higgins, 2013; Higgins & Luthy, 2006; Li et al, 2020; Nguyen et al, 2020). There is not currently enough data to support or refute this hypothesis in the Potomac Aquifer.…”

“…It has been documented that PFBA, a short‐chain PFAS, has similar sorption behavior to its long‐chain congener PFOA, as evidenced by similar log K oc values for these two compounds (Guelfo & Higgins, 2013). However, more recent work found that a suite of soil and sediment properties (carbon content, pH, texture, cation exchange capacity, and soil micropore volume) did a better job of describing subsurface mobility of a variety of PFAS with different chain lengths and charge distributions (Nguyen et al, 2020). Using multiple linear regression analysis, the authors found that long‐chain PFAA sorption was positively related to higher organic carbon content in the soil, negatively related to soil micropore volume, and positively related to silt plus clay content in the soil (Nguyen et al, 2020).…”

“…However, more recent work found that a suite of soil and sediment properties (carbon content, pH, texture, cation exchange capacity, and soil micropore volume) did a better job of describing subsurface mobility of a variety of PFAS with different chain lengths and charge distributions (Nguyen et al, 2020). Using multiple linear regression analysis, the authors found that long‐chain PFAA sorption was positively related to higher organic carbon content in the soil, negatively related to soil micropore volume, and positively related to silt plus clay content in the soil (Nguyen et al, 2020). Short‐chain PFAA sorption was not related to soil micropore volume and was more strongly linked to silt plus clay content when compared to the long‐chain PFAAs.…”

“…Short‐chain PFAA sorption was not related to soil micropore volume and was more strongly linked to silt plus clay content when compared to the long‐chain PFAAs. Organic carbon content was positively related to short‐chain PFAA sorption, but to a lesser extent as compared to the long‐chain PFAAs (Nguyen et al, 2020).…”

Modified clays reduce leaching of per‐ and polyfluoroalkyl substances from AFFF‐contaminated soils

“…The difference in PFAS leachability suggests that soil textural class may play a role and the sandy soils tend to leach out most of the PFAS (65%–99%) they retain. Whether such a trend can be generalized to other soils needs caution, as soil properties could greatly influence the desorption of nonanionic PFAS from soils (Nguyen et al, 2020; Schaefer et al, 2021; Xiao et al, 2019).…”