Transformation of polyfluoroalkyl precursors in AFFT-contaminated concrete

Abstract

The contamination of concrete by per- and polyfluoroalkyl substances (PFAS) derived from aqueous film-forming foams (AFFFs) at impacted sites is a newly recognized issue, but the behavior and transformation of PFAS within concrete and in its vicinity remain largely unexplored. In this study, we discovered amide-based precursors from an electrochemical fluorination (ECF) AFFF, specifically, N-(3-(dimethylamino)propyl)-perfluoroalkylamides (PFAAAm or AmPr-FAAd), can transform into perfluoroalkyl carboxylates (PFCAs) when AFFF solutions or individual PFAS were exposed to concrete. This transformation was attributed to alkaline hydrolysis driven by leaching of Ca(OH)2 from concrete, which raises the solution pH. In the same experiments, the generation of perfluoroalkyl sulfonamides (FASAs) was also observed, but their precursors remained unidentified. Meanwhile, during the validation of PFAS extraction methods from AFFF-contaminated concrete powder, PFCAs and FASAs were similarly generated during the pre-equilibration step, further confirming the occurrence of hydrolysis. Further investigations using four sulfonamide-based precursors suggested that their rapid decrease in aqueous concentration was likely due to low solubility and sorption to container walls and concrete powder, rather than chemical transformation, which suggests the relatively high stability of these perfluoroalkyl sulfonamide precursors. The exact precursors to FASAs remain unresolved, highlighting the need for research into PFAS behavior in concrete.