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 (R² = 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.