Abstract

Knowledge on the photocatalytic degradability of the emerging poly- and perfluorinated alkyl substances (PFAS) in water, specifically GenX, is limited. GenX has been detected globally in river water and is considered potentially more toxic than legacy PFAS. In this study, we compared the photocatalytic degradability of GenX with the legacy compounds perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) using Fe-zeolite photocatalysts. After 7 h of irradiation, GenX showed lower removal (79%) and defluorination (33%) as compared to PFOA (100% removal and 69% defluorination) and PFOS (100% removal and 51% defluorination). The quasi-first-order degradation rate of GenX (1.5 h1) was 12 and 1.2 times lower than PFOA (18.4 h−1) and PFOS (1.8 h−1), respectively. Additionally, PFOA's defluorination rate (0.9 h−1) was approximately 2.6 and 9 times higher than GenX (0.35 h−1) and PFOS (0.1 h−1), respectively. These outcomes correlate with GenX's lower hydrophobicity, leading to reduced adsorption (40%) compared to PFOA (99%) and PFOS (87%). Based on identified transformation products, we proposed a GenX degradation pathway, resulting in ultra-short-chain PFASs with a chain length of 2 and 3 carbon atoms, while PFOA and PFOS degraded stepwise, losing 1 carbon-fluorine bond at a time, leading to gradually shorter chain lengths (from 7 to 2 carbon atoms). In conclusion, GenX is more challenging to remove and degrade due to its lower adsorption on the photocatalyst, potential steric hindrance, and higher production of persistent ultra-short-chain transformation products through photocatalysis.

Keywords

Defluorination; Degradation pathway; Fe-zeolite; Hexafluoropropylene oxide dimer acid; Photocatalysis; Poly- and perfluorinated alkyl substances

Published in

Chemosphere
2023, Volume: 344, article number: 140344
Publisher: Elsevier Ltd

SLU Authors

• Lundqvist, Johan

  • Department of Animal Biosciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Environmental Sciences


Publication identifier

DOI: https://doi.org/10.1016/j.chemosphere.2023.140344

Permanent link to this page (URI)

https://res.slu.se/id/publ/129566