Targeted screening, characterization and sources of per- and polyfluoroalkyl substances in plateau lake Yangzonghai,...

Per- and polyfluoroalkyl substances (PFAS) have been detected in lake ecosystems globally, even in remote areas at high altitudes. Compared to plain lakes with short water change cycles and significant human influence, plateau lakes are primarily tectonic closed or semi-closed lakes with steep terrain. Their long water change cycles lead to an obvious cumulative effect on pollutants. In this study, a targeted screening method for 74 PFAS in aquatic environment was established. The contamination characteristics of PFAS in surface water samples (0.5 m below the water surface) and bottom samples (0.5 m above the lake bottom) of plateau Lake Yangzonghai were studied and compared to a reference site in Dianchi Lake which has been severely affected by anthropogenic sources. Results showed that 32 PFAS were detected in Lake Yangzonghai with the total concentration (∑₃₂PFAS) ranging from 14.95 to 26.42 ng L^-1. Among the 27 PFAS with available standards for accurate quantification, 22 PFAS were detected, with the concentration of ∑₂₂PFAS ranging from 13.27 to 20.17 ng L^-1. Significant differences (p < 0.05) in PFAS concentrations were observed between surface water (22.12 ng L^-1) and bottom water (18.18 ng L^-1), demonstrating a stratification phenomenon. The spatial differences in PFAS concentrations in surface water were minimal, indicating that the surface water was uniformly mixed with limited local disturbance from human pollution. The main PFAS monomers were perfluorooctanoic acid (PFOA), 8-3 fluorotelomer carboxylic acid (8-3 FTCA), perfluoroheptanoic acid (PFHpA) and 2H-perfluoro-2-decenoic acid (8-2 FTUCA), while PFBA was not detected. This distribution remarkably differed from many other plain lakes and the reference lake. Source apportionment analysis showed that PFAS primarily originated from atmospheric transport and precursor degradation. The results provide a background pollution level of PFAS in the plateau lake near the city and will benefit for formulating control policies.