Advanced oxidation and reduction processes for PFAS treatment: Transformation products, toxicity risks, and detoxification challenge

Per- and polyfluoroalkyl substances (PFAS) are globally persistent and highly recalcitrant, necessitating destructive remediation approaches beyond conventional phase-transfer methods. Advanced oxidation/reduction processes (AOPs/ARPs) can achieve >90% degradation of terminal PFAAs and PFAS precursors, yet complete mineralization is uncommon. Treatment generates transformation products (TPs), including partially defluorinated organics, short-chain perfluoroalkyl acids (C4–C6 PFCAs/PFSAs), and inorganic fluoride. High-resolution mass spectrometry (HRMS)-based non-target screening shows that a single PFAS precursor may form 20–100 fluorinated species (polyfluoroethers, unsaturated acids, fluorotelomer olefinic acids). However, their toxicological significance remains poorly understood. Evidence indicates transient toxicity increases during AOP treatment, while QSAR studies suggest some short-chain TPs may exhibit toxicity comparable to or greater than the original PFAS compounds (e.g., PFOA, PFOS). Consequently, PFAS destruction does not necessarily correspond to toxicity reduction. Remediation outcomes depend on water matrix characteristics, defluorination extent, and operational conditions, highlighting the need to prioritize detoxification alongside degradation.