Investigation of per- and polyfluoroalkyl substances (PFAS) in soils and sewage sludges by fluorine K-edge XANES spectroscopy and combustion ion chromatography

Philipp Roesch,Philipp Wittwer,Thomas Huthwelker,Franz-Georg Simon,Christian Vogel

doi:10.1007/s11356-021-17838-z

Abstract

For the first time, fluorine K-edge X-ray absorption near-edge structure (XANES) spectroscopy was applied to detect per- and polyfluoroalkyl substances (PFAS) in various soil and sewage sludge samples. The method can be used to determine the speciation of inorganic and organic fluorides, without pre-treatment of solid samples. Therefore, XANES spectra of several inorganic fluorides as well as selected fluorinated organic compounds were recorded. While inorganic fluorides partially exhibit a variety of sharp spectral features in the XANES spectrum, almost all inspected organofluorine compounds show two distinct broad features at 688.5 and 692.0 eV. Moreover, the peak intensity ratio 688.5 eV/692.0 eV in the PFAS XANES spectrum can be inversely correlated to the chain length of the perfluoro sulfonic acid group. The detection of targeted PFAS by bulk-XANES spectroscopy in combination with linear combination fitting in soils and sewage sludges was not applicable due to the low organic fluorine to total fluorine ratio of the samples (0.01–1.84%). Nonetheless, direct analysis of pure PFAS revealed that analysis of organofluorine species might be achieved in higher concentrated samples. Furthermore, quantitative measurements by combustion ion chromatography (CIC) evaluated as sum parameters extractable organically bound fluorine (EOF) and total fluorine (TF) emphasize that besides soils, sewage sludges are a significant source of organic fluorine in agriculture (154–7209 µg/kg).

Highlights

Per- and polyfluoroalkyl substances (PFAS) have emerged over the course of the last 20 years as a global pollution issue (Giesy and Kannan 2001; Lindstrom et al 2011; De Silva et al 2021)
We could show that fluorine K-edge X-ray absorption near-edge structure (XANES) spectroscopy can be utilized to detect PFAS in high sample concentrations
The peak intensity ratio 688.5 eV/692.0 eV in the PFAS XANES spectrum can be inversely correlated to the chain length of the perfluorosulfonic acid group and might be applicable for perfluorocarboxylic acids

Summary

Introduction

Per- and polyfluoroalkyl substances (PFAS) have emerged over the course of the last 20 years as a global pollution issue (Giesy and Kannan 2001; Lindstrom et al 2011; De Silva et al 2021). There are currently more than 4700 known and partly characterized fluorinated compounds identified by the Organisation for Economic Co-operation and Development (OECD), most of them classified as toxic or dangerous for the environment (OECD 2018). Due to their highly stable C–F bond (D0 = 485 kJ/mol), most PFAS exhibit a chemically inert character, making them difficult for microorganisms to degrade and inaccessible for classical environmental degradation processes like oxidation (Liu and Mejia Avendano 2013; Roesch et al 2020). More than a decade later, fluorine sum parameters have been established as a useful supplement to classic target analytical approaches of PFAS (Nakayama et al 2019) and were implemented for the first time as a sum value “PFAS-total” in the recently revised Drinking Water Directive (2020/2184) by the European Commission

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