Optimization of extraction methods for comprehensive profiling of perfluoroalkyl and polyfluoroalkyl substances in firefighting foam impacted soils

Abstract

The comprehensive analysis of aqueous film forming foam (AFFF) formulations has led in recent years to the discovery of novel classes of perfluoroalkyl and polyfluoroalkyl substances (PFASs). Whether the pre-existing analytical methods for historically monitored PFASs, including perfluorooctane sulfonate (PFOS), could be transferable to a large breadth of newly identified PFASs remains, however, an open question. Data from various lines of evidence indicate that current extraction procedures previously validated with anionic and neutral PFASs may seriously underperform for many cationic and zwitterionic PFASs. The extraction efficiency and instrumental response could be strongly matrix-dependent, which may preclude a robust analysis. The present study sought to investigate a suitable sample preparation procedure for the analysis of anionic, cationic, and zwitterionic PFASs in soil samples. In total, 86 PFASs, representing 24 chemical classes previously discovered in AFFF formulations or at AFFF-impacted sites, were evaluated. The merits and limitations of various extraction media were examined using an AFFF-impacted field-weathered loam soil, as well as a background loam soil amended with AFFFs in-house. Methanol with hydrochloric acid provided excellent recoveries for most cationic and zwitterionic PFASs, including fluorotelomer sulfonamidoalkyl betaines (e.g., 6:2 FTAB) and fluorotelomer betaines (e.g., 9:1:2 FTB), yet performed less satisfactorily for certain anionic PFASs, and may also cause conversion of some PFASs. Sequential extractions using methanol with ammonium acetate exhibited limited matrix effects and suitable recoveries of PFASs from soils of diverse textural classes and organic matter content. The newly-developed extraction method presented the best option for future in-depth characterization of PFASs at AFFF-impacted sites.