32 Air Monitoring
QUANTIFICATION OF PER- AND POLYFLUOROALKYL COMPOUNDS (PFAS) IN FLUE GASSES: EXPERIENCES FROM THE BELGIAN FRONTLINE
“What are PFAS?”
PFAS comprise a huge family (>10 000) of man-made chemicals consisting of poly- (partially) and per- (fully) fl uorinated alkyl compounds (PFAS), produced since 1940 (EEA, 2019, EPA, 2020, Abunada et al., 2020, OECD, 2018). Most well-known chemicals include PFOA, PFOS and GenX. Thanks to their unique water- and grease-repellent properties and thermal, biological and chemical inertness, PFAS are applied in a wide range of industrial applications and consumer products resulting in the widespread prevalence and bioaccumulation of these compounds in consumer products, food chains and our environment (Groffen et al., 2023, Winchell et al., 2021, Abunada et al., 2020, Rauert et al., 2018, Giesy and Kannan, 2001, Buck et al., 2011, Brunn et al., 2023). Past research and legislation focused primarily on food, soil and water prevalence of PFAS, resulting in strategic roadmaps and legislative actions, but the air compartment can today still be considered as a black box in terms of PFAS composition, concentration ranges and exposure routes (D’Ambro et al., 2023, D’Ambro et al., 2021, Lin et al., 2020, Brunn et al., 2023).
“PFAS in air?”
To date, there is no reference methodology available to characterize PFAS in the air or emissions, nor advisory guideline values or limit values for air. In response to fi ndings of elevated PFAS levels in different environmental media, the Flemish Institute for Technological research (VITO) and reference laboratory in Flanders, Belgium, was asked by the government in 2021 to develop methods for the quantifi cation of PFAS in ambient air, depositions and emissions. With regard to PFAS emissions, VITO gained experience with the OTM-45 methodology, published by US EPA (EPA, 2021), in combination with the existing compendium method for the quantifi cation of PFAS via LC-MS/MS in water (WAC/IV/A/025 (VITO, 2022). VITO conducted stack emission monitoring for initially 38 and later 50 individual PFAS compounds on various stacks and industries in Flanders and gained experience on prevailing concentration levels of PFAS, compositional fi ngerprints and potential impacts from fl ue gas treatment technologies. In collaboration with commercial laboratories in Flanders, VITO adapted the OTM-45 methodology and validated the proposed compendium method in order to arrive at a scientifi cally sound and supported methodology for the quantifi cation of PFAS (>C4, boiling point >100°C) in ducted gas streams.
This knowledge resulted in the development of a Belgian compendium method for the sampling and quantifi cation of per- and polyfl uoroalkyl substances (PFAS) in a fl ue gasses (LUC/ VI/003), and provided valuable insights in prevailing emission
concentration levels and PFAS fi ngerprints of a variety of stacks and industries in Flanders, Belgium.
“How to measure PFAS?”
The broad chemical diversity of PFAS challenges both the sampling and analytical procedures required to collect and characterize PFAS, their intermediates and breakdown products in different environmental media (Brunn et al., 2023, Smith et al., 2024). The scope of our study was on the quantitative characterization of a set of well-know semi-volatile and particle bound PFAS (C4-18, boiling point>100°C). In order to gain practical experience with the OTM-45 methodology and evaluate the reproducibility of the technique, a dedicated monitoring campaign with repeated sampling was set up at a rotary kiln of Indaver, a waste treatment plant located in Antwerp, Belgium. Indaver processes approximately 750 000 tons of hazardous and industrial waste per year, of which 150 000 tons by means of high-temperature incineration in rotary kilns guaranteeing thermal destruction of hazardous waste under high temperature (>950°C), long residence times (30 min to 1 hour) and proper turbulence (rotating drum) of the material. A dedicated fl ue gas treatment includes an electrostatic precipitator (dust removal), a four-step wet gas washing with various chemical fl ows (gaseous compounds), and an active carbon fi lter (organic compounds like dioxins and furans) before fl ue gasses are released to the atmosphere via a chimney.
A PFAS emission measurement includes 3 hours (~2Nm³) of isokinetic sampling from the stack by means of a heated sampling
probe. The fl ue gas is guided over a fi berglass fi lter, cooled in a condenser and guided over a primary adsorbent (XAD-2) module. The adsorbent module is followed by a condensate fl ask, impinger train and a secondary (breakthrough) adsorbent module to evaluate potential breakthrough of the PFAS sampling train (EPA, 2021). Chimney emissions were sampled on 13 different days between December, 2021, and May, 2023, using a sampling train setup as described by OTM-45 and LUC/VI/003 (Figure 1). The procedure considers several QA/QC steps and controls for potential contamination by means of medium, fi eld and post-rinse blanks.
The collected fi eld samples are aggregated in 6 analytical fractions, extracted and subsequently analyzed via Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) in the Multiple Reaction Monitoring (MRM) detection mode. The fi rst chimney measurements (December 2021) aimed at evaluating the practical feasibility of the OTM-45 method. After testing the practical feasibility, further incremental improvements and simplifi cations of the monitoring setup and analytical procedure were tested. Indaver collaborated in this effort by opening up their facilities for development and optimization purposes of the compendium method.
Validation of the fi nal LUC/VI/003 OTM-45 sampling train for 50 individual PFAS compounds was conducted in 2023, by means of 3 hour sampling of ambient air at a background location by means of 3 spiked sampling trains (50 native compounds spiked in fi lter, XAD-2 and water) evaluating native spike recovery and measurement uncertainty based on the observed bias of the 3 measurements (Figure 2). In February 2024, an interlaboratory
Figure 1: Schematic representation of OTM-45 sampling train1
. 1https://refl
abos.vito.be/2024/LUC_VI_003_ENG.pdf IET ANNUAL BUYERS’ GUIDE 2024/25
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