Investigating the Leaching and Transformation of PFAS in AFFF Encapsulated Concrete

Significance of the topic

The study addresses environmental and remediation challenges associated with per- and polyfluoroalkyl substances (PFAS) originating from aqueous film-forming foams (AFFF). AFFF-use at sites such as airports and refineries can lead to long-lived PFAS contamination in soils and construction materials. Concrete is a relevant sink and potential secondary source for PFAS because runoff or direct application can result in PFAS incorporation during curing. Understanding how an alkaline cementitious matrix influences PFAS persistence, transformation, and leaching is critical for risk assessment and designing effective encapsulation or remediation strategies.

Objectives and study overview

The work aimed to develop and demonstrate an untargeted high-resolution LC-QTOF workflow to characterize PFAS and transformation products present in concrete cast with a second-generation AFFF formulation. Main goals were to: (1) simulate AFFF incorporation into concrete via casting, (2) extract and profile PFAS-related features using untargeted QTOF analysis, and (3) compare spiked versus cured/encapsulated samples to identify potential transformation products formed during concrete curing.

Methods and sample preparation

Concrete cylinders were cast following ASTM C31 using a 0.3% (v/v) second-generation AFFF aqueous solution; PFAS-free water was used for controls. After curing, cylinders were sectioned and mechanically milled to aggregate powder (38–600 µm) using diamond tools and cleaned stainless-steel sieves. Powdered samples were extracted with 50:50 methanol:water. Analytical workflow included running solvent blanks in triplicate to create an exclusion list, employing a prior-ion list of 56 known PFAS with retention times from previous work, and exporting LCMS files to .mzML for downstream automated processing. Data processing combined FluoroMatch for PFAS annotation and LabSolutions Insight Profiler for feature alignment and multivariate analysis; results were visualized in a custom PowerBI environment.

Instrumental equipment used

• UHPLC: Shimadzu Nexera system with a PFAS delay column (Nexcol PFAS Delay) and Shim-pack Scepter C18-120 analytical column (2.1 × 100 mm, 3 µm).
• Mobile phases: A — 2 mmol/L ammonium acetate in water/acetonitrile (95/5); B — acetonitrile. Gradient ramped from 10% B to 95% B and returned to initial conditions over ~40 min. Column oven at 45 °C; flow 0.45 mL/min; injection 40 µL with multiple-draw co-injection steps and autosampler rinse (60/40 ACN/2-propanol).
• Mass spectrometer: Shimadzu LCMS-9030 QTOF operated in both negative and positive electrospray ionization modes. Data-dependent acquisition (DDA) covering MS (110–1300 m/z) and MS/MS (40–1300 m/z) with up to six dependent events, use of exclusion/prior-ion lists, and collision energy ~35 ± 22 eV.
• Software and processing: LabSolutions LCMS for acquisition and mzML export; FluoroMatch Flow for PFAS annotation (parameters tuned for MS1/MS2 thresholds and mass tolerances); LabSolutions Insight Profiler for PCA and feature exploration; results aggregated and reviewed in PowerBI.

Key results and discussion

• Feature richness: Untargeted processing detected thousands of features in AFFF-encapsulated concrete; Kendrick mass defect and retention time versus m/z plots revealed structured series consistent with fluorotelomer homologous series.
• Evidence of transformation: Extracted ion chromatograms showed substantially higher responses for oxidation products such as 6:2 FTSAm and 10:2 FTSAm in encapsulated samples versus spiked blanks. These FTSAm species are known oxidation derivatives of corresponding fluorotelomer amide-betaine precursors (FTAB), suggesting alkaline-driven transformation during the 28-day curing period.
• Multivariate separation: PCA of aligned features separated sample groups and highlighted features unique to cast/encapsulated concrete, supporting the presence of matrix-driven alteration pathways and distinct chemical signatures compared with spiked controls.
• Workflow performance: Combining exclusion/prior lists, high-resolution accurate-mass QTOF data, FluoroMatch annotation, and Insight Profiler reduced false positives while enabling discovery of lower-abundance transformation products beyond the dominant 6:2, 8:2, and 10:2 FTS species.

Benefits and practical applications of the method

• Comprehensive chemical profiling: The untargeted LC-QTOF approach captures both known PFAS and unknown transformation products, providing a fuller picture of PFAS fate in cementitious matrices.
• Remediation guidance: Identification of transformation products and their formation under concrete curing conditions informs risk assessments, selection of encapsulation strategies, and long-term management of PFAS-containing wastes.
• Analytical flexibility: The integrated workflow (acquisition, mzML export, FluoroMatch annotation, multivariate analysis) is adaptable for other complex matrices where PFAS undergo matrix-dependent transformations.

Future trends and potential uses

• Targeted follow-up: Prioritized suspects from untargeted datasets can guide targeted quantitation and targeted MS/MS method development to confirm structures and establish concentrations and mass balances.
• Leaching and mobility studies: Coupling the current approach with column leaching experiments or field-exposed concrete would clarify long-term release behavior under variable environmental conditions.
• Expanded annotation libraries: Growing MS/MS libraries and improved in-silico fragmentation models will enhance confident identification of novel PFAS transformation products in alkaline matrices.
• Remediation monitoring: The workflow can support evaluation of engineered remediation or stabilization treatments by tracking changes in dominant and emergent PFAS features over time.

Conclusion

The study demonstrates a practical untargeted LC-QTOF workflow capable of resolving complex PFAS chemistries in AFFF-impacted concrete. High-resolution data combined with FluoroMatch annotation and multivariate profiling revealed both expected fluorotelomer species and lower-abundance transformation products that appear to form under alkaline curing conditions. These findings underline the importance of considering matrix-induced transformations when assessing PFAS fate in construction materials and using such integrated analytical pipelines to inform remediation and management decisions.

References

• Interstate Technology & Regulatory Council. PFAS: Firefighting foams. ITRC guidance on PFAS in AFFF use and management.

Notes

• Data were generated for research use only and not for diagnostic purposes.
• Conflict of interest: some authors are affiliated with Shimadzu Corporation and RJ Lee Group as disclosed by the original study.