Uncovering PFAS emissions in wastewater treatment plants through comprehensive assessment of targets, precursors, and unexplained organofluorine.

Abstract

A national sampling campaign across 21 Swiss wastewater treatment plants (WWTPs) assessed the occurrence and fate of per- and polyfluoroalkyl substances (PFASs). A tiered analytical framework combined 66 ultrashort-chain and conventional target analytes, the total oxidizable precursor (TOP) assay, extractable organic fluorine (EOF) analysis, and high-resolution mass spectrometry screening of 6:2 fluorotelomer precursors. Besides trifluoroacetic acid (TFA), zwitterionic 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB; median influent 74.9 ng/L, sludge 47.8 ng/g) dominated PFAS profiles, indicating widespread upstream use. WWTPs receiving high industrial fractions had elevated TFA (up to 1260 µg/L) and inorganic tetrafluoroborate (BF4-). Co-occurrence of bistriflimide (bisFMeSI) and elevated inorganic hexafluorophosphate (PF6-) suggested battery-related inputs at some sites. Conventional biological treatment yielded negligible target removal, whereas powdered activated carbon advanced treatment (n = 2 WWTPs) removed > 50% of 6:2 FTAB and PFOS from influent to effluent. Effluent concentrations exceeded EU surface water quality standards 2.5- to 330-fold. Median effluent mass loads were ≤ 4.4 µg/day/person for most conventional PFASs. Historical sludge trends (2011-2024) indicate an order-of-magnitude decline in PFOS but increased abundances of fluorotelomer compounds. The TOP assay revealed large untargeted precursor fractions (median 56% influent; 91% sludge) with prominent 6:2 fluorotelomer signatures, partially explained by suspect screening detections of aqueous film-forming foam components (6:2 FTNO, 6:2 FTAA, 6:2 FTSA-HOPrS, and 6:2 FtTAoS). EOF revealed extensive fluorine mass gaps; targets and oxidizable precursors accounted for < 27% of median EOF in influent and sludge. These findings highlight the need to expand the scope of WWTP monitoring to capture uncharacterized PFAS burdens and manage emerging upstream sources.

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