Wastewater treatment plants as sinks and sources of PFASs: A global comparative review of occurrence, removal, and risks.

Per- and polyfluoroalkyl substances (PFASs) are increasingly recognized as persistent and hazardous pollutants, yet their occurrence and removal in wastewater treatment plants (WWTPs) remain poorly understood on a global scale. Here, we compiled data from 402 WWTPs across 17 countries covering 45 PFASs (22 legacy and 23 emerging compounds) to evaluate their occurrence, removal pathways, and ecological risks. Influent and effluent concentrations varied widely (non-detection (n.d.)-4220 ng/L and n.d.-4310 ng/L, respectively), with most PFASs showing low or even negative calculated removal efficiencies (-2703 % to 100 %). Long-chain PFASs generally exhibited higher removal than short-chain analogues, while many emerging PFASs were detected at substantial levels in Chinese WWTPs, reflecting region-specific usage patterns. Predicted removals based on adsorption coefficients (Kd) were consistently higher than observed values, indicating the overvalued adsorption and overlooked transformation. Risk quotient analysis revealed that several PFASs, including PFOS, PFOA, PFBS, PFPeA, PFDA, HFPO-DA (GenX) and 6:2 Cl-PFAES, pose high ecological risks in effluents, highlighting the unintended consequences of substituting legacy with emerging PFASs. This work provides the first global comparative assessment of PFAS fate in WWTPs, demonstrating their dual role as sinks and sources of PFASs and identifying management priorities for mitigating ecological risks.