Adsorption behavior of per- and polyfluoralkyl substances (PFASs) to 44 inorganic and organic sorbents and use of dyes as proxies for PFAS sorption

Per- and polyfluoralkyl substances (PFASs) are a major concern in pollution of drinking water sources and aquatic environments. This study investigated the sorption behavior of 17 PFASs of varying chain lengths and functional groups to 44 conventional and novel inorganic and organic sorbents with potential in treatment of PFAS-contaminated water or soil. For the first time, a large number of sorbents were tested for a wide variety of PFASs in batch sorption experiments under controlled experimental set-up. Also, the sorption behavior of four different dyes (methylene blue, crystal violet, indigo carmine, rose bengal) was also determined, to assess whether dyes can be used as a proxy for PFAS sorption. Of the 44 sorbents tested, PFASs sorbed best (mean > 99.9 %) to activated carbons (granulated and pulverized (n = 5)). Sorption of PFASs to magnesium chloride-fortified biochar, Moringa seed, and pyrolytic carbon waste was 17- to 25-fold higher than to sand. Sorption generally increased with increasing perfluorocarbon chain length and based as follows on functional group: fluorotelomer sulfonic acids (FTSAs) < perfluoroalkyl carboxylates (PFCAs) < perfluoroalkane sulfonates (PFSAs) < perfluorooctanesulfonamide (FOSA). Principal component analysis revealed that electrostatic sorption dominated for shorter-chained PFASs and that hydrophobic sorption dominated for longer-chained PFASs. All four dyes tested proved suitable as proxies for sorption of PFASs. In particular, methylene blue correlated best to short-chain PFASs (e.g., perfluorohexanoate (PFHxA)) and rose bengal to longer homologues (i.e., per-fluorooctanesulfonate (PFOS)).