Per- and polyfluoroalkyl substances (PFAS) in surface sediments: Occurrence, patterns, spatial distribution and contribution of unattributed precursors in French aquatic environments

While perfluoroalkyl sulfonic acids (PFSAs) and perfluoroalkyl carboxylic acids (PFCAs) are ubiquitous in aquatic en-vironments, non-targeted methods have recently revealed the presence of numerous unidentified per-and polyfluoroalkyl substances (PFAS). Besides those methods, the total oxidizable precursor (TOP) assay has proved use-ful to estimate the contribution of unattributed perfluoroalkyl acids precursors (pre-PFAAs). In this study, an optimized extraction method was developed to examine the spatial distribution of 36 targeted PFAS in surface sediments col-lected at French nationwide scale (n = 43), including neutral, anionic and zwitterionic molecules. In addition, a TOP assay procedure was implemented to estimate the contribution of unattributed pre-PFAAs in these samples. Con-version yields of targeted pre-PFAAs were determined for the first time under realistic conditions and led to differences in oxidation profiles compared to the common spiked ultra-pure water method. PFAS were detected in 86 % of samples and n-ary sumation PFAStargetedwas in the range < Limit of Detection - 23 ng g-1 dry weight (dw) (median: 1.3 ng g-1 dw), with n-ary sumation pre-PFAAstargetedrepresenting on average 29 +/- 26 % of n-ary sumation PFAS. Among pre-PFAAs, compounds of emerging interest such as the fluorotelomer sulfonamidoalkyl betaines 6:2 FTAB and 8:2 FTAB were respectively detected in 38 % and 24 % of samples, with levels similar to those of L-PFOS (<0.36-2.2, <0.50-6.8 and < 0.08-5.1 ng g-1 dw, respec-tively). A hierarchical cluster analysis coupled with a geographic information system-based approach revealed similar-ities between groups of sampling sites. For instance, elevated contribution of FTABs were associated with the proximity to airport activities where betaine-based aqueous film-forming foam (AFFFs) might have been used. In addition, unattributed pre-PFAAs were strongly correlated with n-ary sumation PFAStargetedand they accounted for 58 % of n-ary sumation PFAS (median value); they were generally found in larger quantity near industrial and urban areas where the highest n-ary sumation PFAStargeted were also observed.

Automated summary

Unidentified per- and polyfluoroalkyl substances (PFAS) are commonly found in aquatic environments, and this study aimed to estimate their contribution using the total oxidizable precursor (TOP) assay. An optimized extraction method was developed to examine the distribution of targeted PFAS in French surface sediments, and the results showed that unattributed PFAS were more abundant in industrial and urban areas, with strong correlations to targeted compounds.