Environmental Occurrence, Source Identification, and Health Hazards of Ultrashort-Chain PFAS in the Yangtze River Delta

Ultrashort-chain per- and polyfluoroalkyl substances (USC-PFAS), defined by three or fewer carbon atoms in their backbone, represent an emerging class of environmental contaminants whose prevalence and hazards remain inadequately characterized. This study conducted a comprehensive survey of seven USC-PFAS and 37 other PFAS compounds in aquatic environments within the Integrated Demonstration Zone of the Yangtze River Delta, a region undergoing continued industrialization. Results showed that USC-PFAS overwhelmingly dominated PFAS profiles, with trifluoroacetic acid (TFA) representing the most abundant species. Mean concentrations of TFA reached 8.7 × 10 4 ng/L in surface water, 8.0 × 10 4 ng/L in source water, and 6.9 × 10 4 ng/L in tap water, constituting 90.1% to 99.6% of total ∑ 44 PFAS across matrices. When TFA was excluded, the remaining ∑ 6 USC-PFAS contributed 44.0% to 58.8% of the total PFAS burden. Trifluoromethanesulfonic acid (TFMS) was the second most abundant in surface and source waters, while trifluoromethane sulfonimide (Ntf2) ranked second in tap water. Source apportionment analyses implicated battery electrolyte formulations as major contributors of TFMS and Ntf2. Hazard prioritization based on persistence, mobility, bioaccumulation, and toxicity (PMBT) metrics, alongside measured environmental levels, identified TFA, TFMS, perfluoro-2-(perfluoromethoxy)propanoic acid (PMPA), and perfluorooctanoic acid (PFOA) as high-hazard compounds. These findings suggest that USC-PFAS constitute a pervasive and underregulated class of pollutants, whose high mobility and recalcitrance challenge current assumptions regarding their environmental safety and call for urgent regulatory reevaluation.