Three-dimensional spatial distribution of legacy and novel poly/perfluoroalkyl substances in the Tibetan Plateau soil: Implications for transport and sources

Driven by increasingly stringent regulations on the legacy poly/perfluoroalkyl (PFASs), a variety of fluorinated alternatives have emerged on the market. Tibetan Plateau (TP) plays an important role in accumulation of organic pollutants due to its high altitude and wet deposition. In this study, the occurrence, spatial distribution and sources of PFASs in the TP soils were investigated. The total concentrations of PFASs ranged from 0.814-4.51 ng/g in the TP soils, with the identification of a variety of novel PFASs, including fluorotelomer sulfonates (FTSs), chlorinated polyfluorinated ether sulfonic acid (Cl-PFESAs), and hexafluoropropylene oxide (HFPO) homologues. Generally, the PFAS concentrations exhibited an increase trend from the west to east, and gradually increased with the altitude increasing, suggesting the impacts of human activities and mountain cold-trapping. The PFASs decreased with the increase of soil depth, but at different extents, which were related to their occurrence time, interactions with organic matters, and microbial transformation in soil. Most of the PFASs were present as free fractions in soil, particularly for the short-chain perfluoroalkyl acids (PFAAs), implying that they were liable to be accumulated in organisms and transport to groundwater. Multiple source apportionment analyses indicated that PFASs in the soil of TP were not only derived from the local pollution, but also from the atmospheric migration influenced by Indian Monsoon and westerly winds.