Unveiling the complex PFAS landscape in firefighting foams applied in the Yangtze River Delta of China: Comprehensive composition analysis and toxicity profiling.

Per- and polyfluoroalkyl substances (PFAS) in firefighting foams represent a persistent source of groundwater contamination due to their extreme environmental stability and toxicological properties. This study provides a comprehensive characterization of PFAS in eleven in-use firefighting foams collected from China's Yangtze River Delta, integrating non-targeted screening with total oxidizable precursor (TOP) assays. A total of 185 distinct PFAS compounds were identified, including 119 anionic, 100 cationic, and 34 zwitterionic species, representing the most diverse PFAS profile reported to date for firefighting foams in the Yangtze River Delta. Parallel analysis detected 139 hydrocarbon surfactants, underscoring the chemical complexity of real-world foam residues. QSAR-ToxPi modeling classified the identified PFAS into three tiers, with 95 compounds (51.4%) falling into the high-hazard category. TOP assays demonstrated that ostensibly PFAS-reduced formulations contained precursor reservoirs capable of generating terminal PFOA at concentrations up to 5198.4 mg/L, nearly 30-fold above initial measurements. These findings demonstrate that expanding water-quality monitoring programs to include PFAS precursors is essential to improve risk assessments for AFFF-impacted groundwater and drinking water sources.