Degradation and mechanism of hexafluoropropylene oxide dimer acid by thermally activated persulfate in aqueous solutions

Hexafluoropropylene oxide dimer acid (HFPO-DA), an alternative of perfluorooctanoic acid (PFOA), has been detected frequently in environmental media worldwide. It has been reported that HFPO-DA is equal to or more toxic than PFOA, as well as more recalcitrant to degradation. In this study, the efficient degradation of HFPO-DA was achieved by the thermally activated persulfate (TAP) system, but the influence of co-contaminants in the field can be significant. The degradation pathways of HFPO-DA were proposed through an integrated approach of experiment and density functional theory (DFT) calculations. CF3CF2COO- and CF3COO-, were the stable intermediates identified by ultra-performance liquid chromatography-quadrupole-time-of-flight-mass spectrometry (UPLC-Q-TOF-MS). Electron transfer, decarboxylation, H abstraction, HF elimination using H2O as a catalyst and hydrolysis occurred in different steps of HFPO-DA degradation process, with -COO- as the initial oxidative site attacked by SO4 center dot-. In addition, the acute toxicity assessment for HFPO-DA degradation in the TAP system performed by Escherichia coli suggested that HFPO-DA was degraded to a level having no adverse effect on the growth of E. coli, and no more toxic intermediates were formed. Overall, this work provides insights for the degradation of HFPO-DA contamination by the TAP system.

Automated summary

The study successfully degraded HFPO-DA using the TAP system, but the influence of co-contaminants in the field can be significant. The degradation pathways of HFPO-DA were proposed through an integrated approach of experiment and DFT calculations, with stable intermediates identified by UPLC-Q-TOF-MS. Acute toxicity assessment showed that the degradation of HFPO-DA had no adverse effect on the growth of Escherichia coli.