Transformation of PFAS precursors in Tetradesmus Obliquus: insights from LC-HRMS analysis

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous, highly persistent compoundsTheir exceptional chemical and thermal stability is attributed to the presence of strong carbon-fluorine (C-F) bonds, which make them resistant to natural degradation over time. This persistence enables PFAS to (bio)accumulate in ecosystems[2]. Once released into the environment, PFAS can be absorbed and bioaccumu-lated by wildlife and humans, potentially reaching toxic concentrations and causing adverse effects. Indirect exposure may occur via the environmental release and degradation of PFAS precursors, which can transform into more stable and even restricted PFAS, further contributing to their persistence[3]. Understanding the fate of these precursors is therefore crucial. This study investigates the degradation and meta-bolization of two PFAS precursors, which include perfluorooctanesul-fonamide (PFOSA) and 6:2 fluorotelomer sulfonate (6:2 FTS), by the green microalga Tetradesmus obliquus, as an in vitro model system, providing complementary insights to in silico metabolite predictions. T. obliquus is a robust microalgaknown for its ability to remove carbon and nutrients in wastewater treatment and its potential for pollutant transformation in aquatic environments[4]. In this experiment, T. obliquus was individually incubated with PFOSA and 6:2 FTS for seven days (16 h light: 8 h dark, 100 r.p.m), with daily measurements of chlorophyll a content and biovolume to assess algal growth and biomass. In silico tools (QSAR Toolbox, Biotransformer) and literature searches were used to predict potential metabolite formation. After the seven-day incubation period, samples were analyzed using ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS). Data processing employed both target and suspect screening approaches. The results revealed distinct behaviours for the two PFAS precursors. While 6:2 FTS showed no observable effects on T. obliquus growth or biomass, PFOSA significantly reduced biomass growth. 6:2 FTS remained stable with no decrease in concentration. In contrast, PFOSA concentration decreased over time, with detected transformation products such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), indicating potential biotransformation by T. obliquus. These findings highlight the different environmental fate of two PFAS precursors and their possible ecotoxicological implications. The transformation of PFOSA into more persistent, bioaccumulative and toxic perfluoroalkyl acids raises concerns, emphasizing the need for further research into PFAS precursor degradation in aquatic ecosystems. Ongoing research focuses on the PFOSA experimental batch to identify lower-concentration transformation products and assess potential stress and toxicity markers.