Accurate detection and high throughput profiling of unknown PFAS transformation products for elucidating degradation pathways.

The accurate detection of unknown per- and polyfluoroalkyl substances (PFAS) transformation products (TPs) is essential for elucidating degradation pathways and advancing remediation strategies. Herein, we developed a workflow that combined Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with a paired mass distance (PMD) network. This study achieved high throughput profiling of PFAS TPs with mDa resolving power and sub-ppm mass error. UV treatment revealed chain-shortening pathways, while plasma treatment uncovered competing mechanisms of chain shortening and lengthening, generating oxygen-rich TPs with increased hydrophilicity. Specifically, UV treatment of a 15-PFAS mixture and contaminated natural water showed disappearance of 7 unknown PFAS homologues and the emergence of 12 unknown PFAS homologues. Despite PFAS persistence under UV exposure, previously undetected low-abundance PFAS species were identified, indicating non-negligible photochemical transformation. Under plasma treatment of isolated PFOS, 39 unknown PFAS homologues including 142 suspect and 34 unknown PFAS TPs were identified, highlighting the extensive transformation of emerging and persistent PFAS. Overall, our approach enabled accurate and high-throughput profiling of unknown PFAS TPs and their degradation pathways, providing new insights into persistent unknown PFAS.