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Analytical Challenges for PFAS in Environmental Samples - Methods, Approaches and Applicability
(2022)
Per- and polyfluoroalkyl substances (PFAS) are anionic, cationic and zwitterionic synthetic products, in which the hydrogen atoms on the carbon skeleton of at least one carbon atom have been completely replaced by fluorine atoms and which include up to 1.7 M compounds, depending on the definition. As a result of continuous and prolific use, mainly in aviation firefighting foams, thousands of industrial and military installations have been found to contain contaminated soil, groundwater and surface water. Furthermore, because of the continuous contamination through PFAS containing commercial products, effluents and sewage sludge from WWTPs have been shown to be an important source of PFAS discharge into the aquatic environment. In the last few years, legacy PFAS (≥C4) have been found in various environments, including soil, water and wastewater, and their environmental pathways have been partly described.
Several long-chain PFAS species, and their respective salts are considered as persistent organic pollutants by the United Nations Stockholm Convention. These pollutants have been linked to altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer. A significant shift in the chemical industry towards production of short (C4-C7) and ultrashort (C1-C3) alternatives was observed in response to recently intensified regulations and restrictions on the use of long-chain (≥C8) PFAS. PFAS analysis in environmental samples is currently mainly done by liquid chromatography tandem mass spectrometry (LC-MS/MS). This efficient method is conducted in a targeted fashion analyzing a small subset of PFAS. The US EPA method for analysis of PFAS using LC-MS/MS for example currently lists 40 PFAS (≥C4). However, to get a better overview of the amount of “total PFAS,” sum parameter methods like total oxidizable precursor (TOP) assay and methods based on combustion ion chromatography (CIC) are in development. CIC results in data regarding the sum of absorbable organic fluorine (AOF) or extractable organic fluorine (EOF), which can also quantify other organically bound fluorine compounds such as fluorinated pesticides and pharmaceutical. Moreover, non-target and suspect screening mass spectrometry can be used to identify novel emerging PFAS and partly unknown fluorinated compounds in environmental samples. Furthermore, to analyze ultrashort PFAS (C1-C3), supercritical fluid chromatography (SFC), hydrophilic interaction chromatography (HILIC) and gas chromatography-mass spectrometry (GC-MS) are available, but further research is needed to develop reliable and accurate methods to quantify several ultrashort PFAS in environmental samples.
Additionally, for research purpose several spectroscopical methods like X-ray photoelectron spectroscopy (XPS), fluorine K-edge X-ray absorption near-edge structure (XANES)spectroscopy, particular induced gamma-ray emission (PIGE) spectroscopy and 19F nuclear magnetic resonance (NMR) spectroscopy are available.
Per- and polyfluoroalkyl substances (PFAS) are anionic, cationic and zwitterionic synthetic products, in which the hydrogen atoms on the carbon skeleton of at least one carbon atom have been completely replaced by fluorine atoms (see Figure 1) and which include more than 4730 compounds, depending on the definition. As a result of continuous and prolific use, mainly in aviation firefighting foams, thousands of industrial and military installations have been found to contain contaminated soil, groundwater and surface water. Furthermore, because of the continuous contamination through PFAS containing commercial products, effluents and sewage sludge from WWTPs have been shown to be an important source of PFAS discharge into the aquatic environment. In the last few years, legacy PFAS (≥C4) have been found in various environments, including soil, water and wastewater, and their environmental pathways have been partly described. To get a better
overview of the amount of “total PFAS,” sum parameter methods like total oxidizable precursor (TOP) assay and methods based on combustion ion chromatography (CIC) are in development. CIC results in data regarding the sum of absorbable organic fluorine (AOF) or extractable
organic fluorine (EOF), which can also quantify other organically bound fluorine compounds such as fluorinated pesticides and pharmaceutical. Additionally, for research purpose several spectroscopical methods like X-ray photoelectron spectroscopy (XPS), fluorine K-edge X-ray absorption near-edge structure (XANES) spectroscopy, particular induced gamma-ray emission (PIGE) spectroscopy and 19F nuclear magnetic resonance (NMR) spectroscopy are available. Therefore, an overview is given on various analytical techniques for PFAS in environmental samples and their application possibilities discussed for different kind of PFAS compounds
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).
Per- and polyfluoralkyl surfactants (PFAS) are industrially produced surface chemicals used in daily applications that have gained public and political attention due their unnaturally high appearance in drinking water, nourishments and soils.[1] Their chemical structures exhibit both lipophilic and hydrophilic properties, leading to a highly inert and persistent character.[2] Various PFAS have shown to be bioaccumulative in plants and animals, and some have been characterized as highly toxic when ingested.[3] When exposed to the environment, PFAS slowly get mobilized by natural water resources, leading to contamination of large areas of soil and natural water sources.[4] While PFAS contamination of drinking water has been investigated intensively, perfluoralkyl contamination of soils has been rarely examined as of yet. At the same time, an increasing amount of PFAS contamination sites are being discovered worldwide, calling for a sophisticated strategy towards analytical characterization.[5] Since the number of known PFAS already exceeds 4700, the established sum parameters like extractable organic fluorine (EOF) and adsorbable organic fluorine (AOF) are key elements to fully survey the impact of exposure.[6] Simultaneously, innovative soil remediation strategies are required to contain environmental destruction and to minimize further spreading of contaminants.[7] Addressing these challenges requires suitable analytical devices that are capable of mobilizing PFAS in the solid as well as in the liquid phase. The use of combustion ion chromatography (CIC) enables analysis of both immobile and volatile PFAS and allows the detection of both total fluorine (TF) and EOF or AOF of a given soil or aqueous sample. Based on preliminary results, the clean-up of a PFAS contaminated matrix is monitored via EOF detection over time. Additionally, we tested the effectiveness of urea (CH₄N₂O) as fluoride scavenger with the aim to improve the separation of inorganic and organic fluorine and therefore, to improve AOF accuracy. The presented findings can be contributive with regard to future AOF/EOF sum parameter development and application.
Per- and polyfluoroalkyl substances (PFAS) have been used extensively in the past because of their inert chemical character and resistance to degradation by environmental influences. Since the beginning of their commercial use, PFAS have been widely exposed to the environment by application of PFAS in consumer products or as foaming agent in firefighting foams, thus several cases of contaminated soils sites have been reported. Since the number of known PFAS already exceeds 4700, their characterization and direct analysis is challenging given the current available techniques. Here, we introduce the novel fluorine (F) K-edge X-ray absorption near-edge structure (XANES) spectroscopy as a tool to analyze PFAS and inorganic fluorine compounds in contaminated soils and sewage sludges. While F K-edge bulk-XANES spectroscopy provide us information on the overall fluorine bonding in a sample micro X-ray fluorescence (XRF) in combination with F K-edge micro-XANES spectroscopy can also detect minor fluorine compounds and PFAS hotspots in investigated soils and sludges. Additionally, we used the combustion ion chromatography (CIC) to analyze the total amount of all PFAS as a sum parameter (extractable organic fluoride: EOF) in soils and sewage sludges. During combustion in the CIC, the PFAS in the sample get destroyed at temperatures of approx. 1000 °C and converted in inorganic fluorides that subsequently gets quantified by ion chromatography. Thus, for the first time we successfully combined F K-edge XANES spectroscopy and CIC as analytical tools to detect and quantify PFAS contaminants in soils and sewage sludges.
Per- and polyfluoralkyl surfactants (PFASs) are industrially produced surface chemicals used in daily applications that have gained public and political attention due their unnaturally high appearance in drinking water, nourishments and soils. Their chemical structures exhibit both lipophilic and hydrophilic properties, leading to a highly inert and persistent character. Various PFASs have shown to be bioaccumulative in plants and animals, and some have been characterized as highly toxic when ingested. When exposed to the environment, PFASs slowly get mobilized by natural water resources, leading to contamination of large areas of soil and natural water sources. While PFASs contamination of drinking water has been investigated intensively, perfluoralkyl contamination of soils has been rarely examined as of yet. At the same time, an increasing amount of PFASs contamination sites are being discovered worldwide, calling for a sophisticated strategy towards analytical characterization. Since the number of known PFASs already exceeds 4700, the established sum parameters like extractable organic fluorine (EOF) and adsorbable organic fluorine (AOF) are key elements to fully survey the impact of exposure. Simultaneously, innovative soil remediation strategies are required to contain environmental destruction and to minimize further
spreading of contaminants. Addressing these challenges requires suitable analytical devices that are capable of mobilizing PFASs in the solid as well as in the liquid phase. The use of combustion ion
chromatography (CIC) enables analysis of both immobile and volatile PFASs and allows the detection of both total fluorine (TF) and EOF or AOF of a given soil or aqueous sample. Based on preliminary results, the clean-up of a PFAS contaminated solid matrix is monitored via EOF detection over time.
Additionally, we demonstrate the pH dependency of hydrogen fluoride absorption on active carbon (AC) and found a simple organic additive to be an effective fluoride scavenger. The presented findings can be contributive with regard to future AOF/EOF sum parameter development and application.