Non-Target Screening of Fluorinated Ionic Liquids and PFAS in European Wastewaters Using Supercritical Fluid Chromatography

Per- and polyfluoroalkyl substances (PFAS) and fluorinated ionic liquids are increasingly recognized as persistent environmental contaminants. In this study, municipal effluent samples from 30 wastewater treatment plants (WWTPs) across 15 European countries were analyzed using supercritical fluid chromatography–high-resolution mass spectrometry (SFC-HRMS) for non-target screening of fluorinated compounds. The bis-perfluoroalkyl sulfonimide (bis-FASI) class of ionic liquids was widely detected, including bis(trifluoromethanesulfonyl)imide (NTf₂⁻), two rarely reported homologues (±2 CF₂, namely FSI- and BETI-), and two previously unreported homologues (±1 CF₂, namely FTFSI- and FTNTf2-). Bis-FASIs were present in 85% of samples and were more abundant in effluents from larger WWTPs. The fluorinated anion PF₆⁻, commonly used in ionic liquids, was found in all samples at concentrations up to 3 µg/L. Hexafluoroarsenate (AsF₆⁻), reported here for the first time in municipal wastewater, was detected in 32% of samples in eight countries. PF₆⁻ and AsF₆⁻ concentrations (when present) exceeded those of traditional PFSAs and PFCAs in 97% of samples. Polyfluorinated compounds showed partial removal during treatment, while perfluorinated compounds, inorganic fluorinated anions, and low-fluorinated pharmaceuticals and pesticides showed no removal. Low-fluorinated substances exceeded 100 ng/L in 90% of samples, yet PF₆⁻ alone surpassed the combined concentration of all low-fluorinated substances in 27 out of 30 samples. These results reveal a significant contribution of unconventional fluorinated substances to the overall fluorine load in wastewater. The dominant contributor, PF₆⁻, falls outside current PFAS regulatory definitions, underscoring the urgent need to expand monitoring strategies beyond legacy PFAS to include both inorganic and low-fluorinated contaminants.