Landfill leachate as a global PFAS source reservoir: source-strength heterogeneity, compositional transition, and screening-level risk.

Landfill leachate is a pathway for PFAS release from end-of-life waste systems, but its source strength, mixture evolution, and risks remain poorly quantified. We compiled 1416 samples from 539 facilities in 76 cities across 22 countries, covering 150 legacy and emerging PFAS. ΣPFAS ranged from 1 to 5542,000 ng/L, with 93%/56% of sites exceeding 1000/10,000 ng/L, indicating high source strength. High-burden samples clustered in hotspot regions and landfill types rather than by continent. Industrial landfills showed the strongest signature, averaging 1141,345 ng/L, 56-101 times higher than other landfill types, and contributing 62% of the global burden. FOSA, PFOA, and PFBA accounted for over half of cumulative PFAS, while country-level fingerprints diverged into long-chain, short-chain, and precursor-enriched patterns, recording legacy use, replacement inputs, and precursor transformation. Higher PFAS concentrations were associated with organic matter, salts, and ammonium, especially TOC and COD (P < 0.001). Regional PLS-SEM explained only 22.4% of variance, highlighting facility-scale waste composition, receiving history, and operation. Risk screening showed long-chain PFAS dominated toxicity-weighted pressure, with SSD-derived PFOS HC5 values of 2.58-25.99 ng/L, over one order of magnitude lower than PFOA. Short and ultrashort PFAS created another pressure through mobility, persistence, and treatment resistance. Overall, landfill leachate is a dynamic PFAS source term controlled by high-risk waste inputs, delayed release, precursor transformation, and geochemistry. Management should shift from end-of-pipe control to fluorinated-waste identification, precursor reduction, mobile short-chain control, and residual management.