Stability of Per- and Polyfluoroalkyl Substances in Solvents Relevant to Environmental and Toxicological Analysis

Per- and polyfluoroalkyl substances (PFASs) arewidely used anthropogenic chemicals. For environmental andtoxicological analysis, it is important to understand the stability ofPFASs, including novel per- and polyfluoroalkyl ether acids(PFEAs), in commonly used solvents. In this study, weinvestigated the effects of PFAS characteristics, solvent type,water-to-organic solvent ratio, and temperature on the stability of21 PFASs including 18 PFEAs. None of the studied PFASs showedmeasurable degradation in deionized water, methanol, or isopropylalcohol over 30 days; however, nine PFEAs degraded in the polaraprotic solvents acetonitrile, acetone, and dimethyl sulfoxide(DMSO). PFEA degradation followedfirst-order kinetics, andfirst-order rate constants increased with increasing temperature and with decreasing water-to-organic solvent ratio. Monoethers witha carboxylic acid functional group adjacent to a tertiary carbon (>CF-COOH) degraded more rapidly than multiethers in which thecarboxylic acid moiety was adjacent to repeating-CF2O-groups. In contrast, monoethers with a carboxylic acid moiety adjacent toa secondary carbon (-CF2-COOH) were stable in all tested solvents. Using high-resolution mass spectrometry, we determined thatPFEAs with a >CF-COOH group were stoichiometrically decarboxylated in aprotic solvents and formed products with a >CFHgroup; e.g., hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX), HFPO-trimer acid, and HFPO-tetramer acid werestoichiometrically converted to Fluoroethers E-1, E-2, and E-3, respectively. PFEA degradation results highlight the importance ofsolvent choice when preparing dosing solutions and performing extractions for environmental and toxicological assessments ofPFEAs.

Automated summary

This study investigated the stability of PFASs, including PFEAs, in different solvents. The results showed that PFEAs degraded in polar aprotic solvents, with degradation rate increasing with temperature and decreasing water-to-organic solvent ratio. Monoethers with a carboxylic acid functional group adjacent to a tertiary carbon degraded more rapidly than those adjacent to repeating-CF2O-groups. On the other hand, monoethers adjacent to a secondary carbon were stable in all tested solvents. High-resolution mass spectrometry revealed the stoichiometric decarboxylation of PFEAs in aprotic solvents, forming products with modified functional groups.