Avoiding Regrettable Replacements: Can the Introduction of Novel Functional Groups Move PFAS from Recalcitrant to Reactive?

Abstract

Per- and polyfluoroalkyl substances (PFASs) are present in a range of commercial and consumer products. These chemicals are often high-performance surfactants or nonstick/water-repellant coatings due to their chemical stability; however, this stability leads to select PFAS being environmentally persistent. To facilitate degradation, new fluorosurfactant building blocks (F₇C₃-O-CHF-CF₂-S-CH₂-CH₂-OH (FESOH), F₃C-O-CHF-CF₂-S-CH₂-CH₂-OH (MeFESOH), F₇C₃-O-CHF-CF₂-O-CH₂-CH₂-OH (ProFdiEOH), F₇C₃-O-CHF-CF₂-CH₂-OH (ProFEOH), and F₃C-O-CHF-CF₂-O-CH₂-CH₂-OH (MeFdiEOH)) have been systematically developed with heteroatom linkages such as ethers, thioethers, and polyfluorinated carbons. The room temperature, gas-phase OH oxidation rate constants, and products of these chemicals were monitored in an atmospheric chamber to investigate their fate in the atmosphere. Analysis was performed using online high-resolution chemical ionization mass spectrometry (CIMS) using the iodide reagent ion and via offline UPLC-MS/MS. FESOH and MeFESOH, the thioether congeners, were observed to have the largest rate constants of k_FESOH = 2.82 (±0.33) and k_MeFESOH = 2.17 (±0.17) (×10^-12 cm³ molecules^-1 s^-1, respectively). First-, second-, and third-generation products of OH oxidation were observed as a function of time, while product quantification yielded ultrashort perfluoropropionic acid (PFPrA) and short polyfluoroether acid species as the terminal products for FESOH and ProFdiEOH. There was evidence for MeFESOH being fully mineralized, demonstrating the potential benign chemical architecture.

Keywords: HFE; PFAS atmospheric degradation; PFAS replacement; hydrofluorothioether; polyfluorinated.