Frontiers in Chemistry (Oct 2023)

A modified TOP assay to detect per- and polyfluoroalkyl substances in aqueous film-forming foams (AFFF) and soil

  • Md. Al Amin,
  • Md. Al Amin,
  • Yunlong Luo,
  • Yunlong Luo,
  • Feng Shi,
  • Feng Shi,
  • Linbo Yu,
  • Linbo Yu,
  • Yanju Liu,
  • Yanju Liu,
  • Annette Nolan,
  • Olalekan Simon Awoyemi,
  • Mallavarapu Megharaj,
  • Mallavarapu Megharaj,
  • Ravi Naidu,
  • Ravi Naidu,
  • Cheng Fang,
  • Cheng Fang

DOI
https://doi.org/10.3389/fchem.2023.1141182
Journal volume & issue
Vol. 11

Abstract

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Total oxidisable precursor (TOP) assay can oxidise some per- and polyfluoroalkyl substances (PFASs) and their precursors, most of which cannot be quantitatively detected so far, and convert them to detectable PFASs, such as perfluoroalkyl acids (PFAAs). However, the conversion is constrained by the complexity of the target samples, including co-existent organics, unknown PFAS precursors, and background. In this study, the TOP assay is modified to increase the oxidation and conversion efficiency by changing the initial concentration of target sample, increasing oxidising doses, time, temperature, etc. The modified TOP assay is applied to test several aqueous film-forming foams (AFFF) and a PFAS-contaminated soil extract. The sum concentrations of the detectable PFASs are increased by up to ∼534× in the AFFF samples and ∼7× in the PFAS-contaminated soil extract. The detectable fluorotelomer sulfonate (FTS, such as 6:2/8:2 FTS) is accounted as an oxidation indicator to monitor the oxidation and conversion progress of the oxidisable PFASs precursors to the detectable PFASs. Overall, the modified TOP assay could be an appropriate method for identifying missing PFASs mass in complex matrices by detecting the PFASs precursors effectively.

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