Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a group of chemicals containing carbon chains with attached fluorine atoms instead of hydrogen atoms and one or more functional groups attached at the ends (Hamid et al. , 2018). They are widely used in the electronics industry, the oil mining industry, and in the production of fluorosurfactants and firefighting foams (Fiedler et al., 2010). The two main subcategories of PFAS are perfluoroalkyl carboxylic acids (PFCA) and perfluoroalkyl sulfonates (PFSA). According to the Organization for Economic Co-operation and Development (OECD) classification, PFAS are divided into short-chain PFAS and long-chain PFAS (Buck et al., 2011). PFSAs with chain lengths less than C6 and PFSAs with chain lengths less than C7 are defined as short-chain PFASs (Knutsen et al., 2019). perfluorobutanoic acid (PFBA), perfluorobutane sulfonate (PFBS), etc. (Gebink et al., 2017). Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two major long-chain PFAS.

Different PFAS classes exhibit different mobility, persistence, and bioaccumulation properties. Despite differences in the physical and chemical properties of various PFAS compounds, these contaminants are generally persistent and prone to bioconcentration, and some PFAS are highly mobile and have strong transport capabilities. (Cousins ​​et al., 2022; Whitehead et al., 2021). ∑PFAS total contamination level [11 PFCAs, 5 PFSAs, perfluoro-1-octanesulfonamide (FOSA), and N-Ethylperfluorooctane sulfonamidoacetic acid (N-EtFOSAA)] The concentrations in the groundwater of the Maozhu River area were 9.9–592.2 ng L.-1 (Lee et al., 2020a). 3 Contamination levels of long-chain PFAS [perfluoroheptanoic acid (PFHpA), PFOA and PFOS] and two short-chain PFAS. [perfluorohexane sulfonate (PFHxS), perfluorohexanoic acid (PFHxA)] PFHxA from 27 landfills was observed, with short-chain PFHxA predominating (on average 1700 ng L-1; range from 73 to 25,000 ng L-1) (Gallen et al., 2017). ∑PFAS contamination level [PFBA, perfluoropentanoic acid (PFPeA), PFHxA, PFHpA, PFOA, perfluorododecanoic acid (PFDoA), PFBS, PFOS, 2-N-methylperfluoro-1octanesulfonamido-ethanlo (N-MeFOSE), 2-N-ethylperfluoro-1octanesulfonamido-ethanlo (N-EtFOSE)] It has been observed in the soil in the hilly regions of central and eastern Nepal. Total PFAS concentrations ranged from 0 to 1.78 ng L .-1 Long-chain PFOA (0 to 0.26 ng L-1 dw) and short-chain PFBS (0–0.38 ng L-1 dw) were the main PFAS (Tan et al., 2014). Studies have now demonstrated that PFAS contamination levels are up to 25,000 ng L in some areas.-1. Total PFAS concentrations ranged from 88.0 to 973.0 ng L .-1 Groundwater at Australia's largest urban regeneration site. The concentrations of PFHxS, PFHxA, PFBA, PFPeA, PFOA, and PFBS ranged from 12.0 to 310.0 ng L .-19.0 to 240.0 ng L-18.0–71.0 ng L-18.0–120.0 ng L−17.0–66.0 ng L−1and 6.0–61.0 ng L−1, respectively (Currell et al., 2024). Total PFAS concentrations in the estuary were up to 17.3 μg L .-1the average concentration is 3.4 μg L−1 in the Kishon, Alexander and Lachish microestuaries located in the eastern Mediterranean Sea (Topaz et al., 2024). Given the widespread detection of PFAS in environmental media worldwide, there is an urgent need to develop effective technologies to remove or reduce PFAS contamination. Additionally, the transport of short-chain PFAS is faster and poses greater risks than long-chain PFAS, so it is necessary to clarify the differences in the relevant reaction mechanisms between long-chain and short-chain PFAS.

Long-chain PFAS are toxic and bioaccumulative and are listed in international and national regulations (Zhao et al., 2017). PFOS is a typical long-chain PFAS, and its salts are included in Annex B of the Stockholm Convention. In May 2009, PFOS was designated as a “restricted” persistent organic pollutant (UNEP, 2009). In 2012, PFOA was listed as a 2B carcinogen by the International Agency for Research on Cancer (Gallen et al., 2017). In 2016, the United States Environmental Protection Agency (USEPA) reset the lifetime drinking water health advisory levels to new values ​​of 300 to 7000 ng L.-1 For C4-C7 PFAS and 70 ng L-1 For combined or individual concentrations of C8 PFOA and PFOS (Verma et al., 2021). USEPA has published a draft toxicity assessment for short-chain PFBS and the substitute chemical perfluoro-2-propoxypropanoic acid (PFPrOPrA or “GenX”) (Crone et al., 2019). Additionally, in 2016, China launched a national implementation plan with a budget of $145.3 million to phase out the use of PFOS and its salts in key industrial activities (firefighting, electroplating, pesticides, etc.). (Xiang et al., 2018). In 2022, China's State Council promulgated the “Action Plan on Emerging Pollutants” to further promote environmental risk management of emerging pollutants (such as PFAS) and improve emerging pollutant treatment systems. In March 2023, the U.S. Environmental Protection Agency issued stricter standards, stipulating that his PFOA concentration in drinking water must be less than 4.0 ng L.-1 (USEPA, 2023). Perfluorohexane sulfonate (PFHxS) and perfluorononanoic acid (PFNA) have a hazard index of 1.0 (USEPA, 2023). In response to the current situation of PFAS contamination, this review summarized the differences in the remediation mechanisms of long-chain PFAS and short-chain PFAS, and provided new ideas for remediation research at various PFAS-contaminated sites. Additionally, this review also summarizes existing PFAS contamination remediation technologies, providing unique insights into the future development of PFAS remediation technologies.

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