Fate and Persistence of Bisphenol AF (BPAF) in Agricultural Soils: Role of Nonextractable Residues

Bisphenol AF (BPAF), a polyfluorinated compound and widely used substitute for bisphenol A, is ubiquitous in the environment. However, the fate of BPAF in soil is still obscure. Here, we used [ring-U-14C]-labeled BPAF to investigate its fate in three agricultural soils for 240 days, based on a four-compartment fate model. BPAF dissipated in the soils with a half-life of 35-110 days, accompanied by low mineralization (8.5-11.3% of the initial radioactivity). The main fate of BPAF in the soils was formation of nonextractable residues (NERs) (44.2-65.3%), mostly (>90%) via physicochemical sequestration (31.2-42.7%) and ester bonds (10.0-22.6%). Notably, the sequestered free BPAF in the NERs increased the half-life by 1.4-2.5 times. Six transformation products (TPs) were identified, including BPAF mono- and dimethyl ethers, monosulfate ester, and three single-ring monophenolic compounds. BPAF monomethyl ether was the predominant extractable TP, while the polar TPs were the predominant physico-chemically sequestered and ester-linked TPs in the NERs. Three transformation pathways for BPAF in the soils are proposed, including type II ipso-substitution, O-methylation, and sulfate conjugation. Our study provides the first quantitative information on the fate of BPAF in soil, and highlights the importance of NERs in determining the persistence of BPAF.