Isomer-specific sediment-water partitioning and bioaccumulation of perfluoroalkyl sulfonyl fluorides

Perfluoroalkyl sulfonyl fluorides (PFASFs) have long been used as crucial synthetic intermediates in the production of various perfluoroalkyl substances. While, knowledge on the environmental occurrence and behaviors of PFASFs in the aquatic environment is still very limited, especially at the isomer-specific level. In this study, surface water, sediment, and fish samples were collected from the water environment near a wastewater treatment plant outlet, and analyzed them for five PFASFs. The highest mean water concentration was observed for linear perfluorobutyl sulfonyl fluoride (l-PFBSF; 122 ng/L, 10-457 ng/L). While, linear perfluorooctane sulfonyl fluoride (l-PFOSF) displayed the highest mean concentration in collected sediment (108 ng/g dw, 78-271 ng/g dw) and fish (113 ng/g ww, 48-244 ng/g ww). For detected PFASFs, their branched isomers accounted for mean 16-29 %, 8.2-11 %, and 16-25 % of total PFASFs (sum of linear and branched isomers) in water, sediment, and fish samples, respectively. Calculated log-transformed sediment-water partitioning coefficients (log K_oc) of linear PFASFs linearly increased with the increasing carbon chain length, with the mean values ranging from 2.1 ± 0.36 (l-PFBSF) to 3.9 ± 0.18 (l-PFOSF). Calculated log-transformed bioaccumulation factors (log BAF) of linear PFASFs increased from 1.7 ± 0.34 (l-PFBSF) to 3.0 ± 0.27 (l-PFOSF) with the carbon chain length. Branched isomers of detected PFASFs displayed lower log K_oc and log BAF values than their respective linear isomers. To our knowledge, this study provides the first evidence on isomer-specific environmental behaviors of PFASFs, which is crucial for assessing the ecological risks these compounds may pose.