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.