From PFOS to a Sum of 25 PFASs: Regulatory and Effect-Based Risk Assessment in the River Ruhr

Regulatory assessment of per- and polyfluoroalkyl substances (PFASs) in European surface waters is shifting from a single-compound environmental quality standard (EQS) for perfluorooctane sulfonic acid (PFOS) toward a potency-weighted sum of 25 PFASs criterion under the revised Water Framework Directive (WFD). This environmental survey investigated how this regulatory change affects screening-level assessment of PFAS contamination and whether chemical classifications are consistent with an effect-based endpoint. Fourteen surface-water samples from the river Ruhr and its tributary, the Möhne (Germany), were enriched by weak anion-exchange solid-phase extraction and analyzed by targeted liquid chromatography-electrospray ionization-mass spectrometry, combustion ion chromatography for extractable organic fluorine (EOF), and the TTR-TRβ chemical activated luciferase gene expression bioassay (referred to as PFAS CALUX). Thirteen PFAS were quantified. At every location with valid target-PFAS data except site A, both the former PFOS annual average EQS of 0.65 ng L^-1 and the revised water-column criterion of 4.4 ng PFOA-equivalents L^-1 for the sum of 25 PFASs were exceeded when the latter was calculated from the WFD-listed PFASs covered by the analytical method. Because trifluoroacetic acid and perfluor (((5-methoxy-1,3-dioxolan-4-yl)oxy)acetic acid) were not measured, this represents a lower-bound estimate of the revised metric. In contrast, the PFAS CALUX bioassay exceeded the pragmatic effect-based trigger value in 10 of 14 samples and produced discordant classifications at several sites. Target PFASs explained <5% of EOF and generally <3% of the observed bioassay response. Thus, in this river dataset, expansion from PFOS alone to a potency-weighted PFAS mixture did not materially change the chemical screening classification, whereas effect-based assessment revealed a different spatial pattern. EOF provides complementary evidence of a substantial uncharacterized organofluorine burden. However, compared to other studies, it did not provide any insights into PFAS hotspots.