Identification, Quantification, and Characterization of Per- and Polyfluoroalkyl Substances (PFAS) in Soil and Groundwater by High-Resolution Mass Spectrometry and Oxidative Transformation

Abstract

The uncontrolled release of aqueous film-forming foam (AFFF) during a major fire in Reilingen, Germany, in 2008 resulted in significant contamination of soil and groundwater with per- and polyfluoroalkyl substances (PFAS). Due to the proprietary nature of AFFF formulations, the identity and environmental behavior of these fluorochemical surfactants remain largely obscured, highlighting the need for comprehensive site-specific characterization. This dissertation presents a systematic, multi-faceted analytical approach to elucidate the composition, abundance, and transformation of PFAS at this contaminated site. Using an optimized extraction protocol combined with liquid chromatography high-resolution quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS), a total of 124 PFAS from 42 subclasses were identified, spanning anionic, cationic, and zwitterionic compounds with perfluoroalkyl chains ranging from 3 to 14 carbon atoms. Notably, one previously unreported PFAS subclass was discovered, and nine additional PFAS subclasses were detected in soil for the first time. These findings highlight the complexity of AFFF contamination and the presence of both primary and secondary precursors, including numerous by-products and intermediates formed under environmental conditions. To overcome limitations associated with the lack of analytical standards, a novel semiquantification approach for non-target screening (NTS) was developed, combining matrix-matched calibration and ionization class-specific average calibration curves. This method enabled the (semi)quantification of 96 tentatively identified PFAS in addition to 28 target compounds, revealing that semiquantified PFAS concentrations exceeded those of conventional target analytes. Validation against extractable organofluorine (EOF) demonstrated a closed mass balance (102%), confirming the robustness and applicability of the approach for complex environmental matrices. Furthermore, the PhotoTOP assay was applied for the first time to both AFFF standards and contaminated soil, facilitating photocatalytic oxidation of PFAS precursors into quantifiable perfluoroalkyl carboxylic acids. Target and non-target analyses identified numerous novel intermediates of the PhotoTOP, including perfluoroalkyl sulfonamide- and fluorotelomer sulfonamide-based compounds, dimers, fluorotelomer betaines, and unsaturated perfluoroalkyl sulfonic acids. Semiquantitative mass balance analysis indicated near-complete conversion of precursors, while kinetic investigations provided insight into transformation rates and persistence, giving information on potential environmental fate and long-term PFAS release from soils. Overall, this dissertation demonstrates the power of combining non-target screening, semiquantification, and oxidative conversion approaches to provide a detailed, validated characterization of the AFFF-related PFAS contamination. The findings have broad implications for environmental monitoring, remediation planning, regulatory compliance, and risk assessment, while also establishing a methodological approach that can be adapted to other complex matrices such as wastewater, sediments, and consumer products.