“Short Facts”: PFAS Composition, Precursors and Biodegradation in AFFF
Aqueous film-forming foams (AFFFs) are used extensively for fire suppression but are a major source of PFAS contamination. Two main chemistries dominate AFFF formulations: electrochemical fluorination (ECF) and fluorotelomerization (FT). ECF-based foams, historically produced by 3M, are rich in PFOS and PFHxS, while FT-based foams contain a variety of 6:2 fluorotelomer compounds such as FTSAS, FTAB, and DPOSA. Analytical methods like non-target analysis (NTA), suspect screening analysis (SSA), and the Total Oxidizable Precursor (TOP) assay are essential for identifying both known and hidden PFAS. Despite improvements, targeted analyses often capture only a small fraction of total PFAS, necessitating broader characterization to understand environmental behavior.
Biodegradation studies show that PFAS in AFFFs degrade slowly and incompletely. FT-based compounds degrade under aerobic conditions, often yielding less than 10% terminal products like PFHxA or PFPeA over 100 days. Betaine structures, such as FTBs, are particularly persistent. ECF-based PFAS show a wide range of degradation behaviors, with quaternary ammonium and betaine structures being the most resistant. Structural features—especially nitrogen head groups and chain length—strongly influence degradation rates. While some transformation occurs, many PFAS may persist for decades, emphasizing the need to identify stable structures to predict long-term environmental impacts.
Understanding AFFF composition and biodegradation is critical for soil risk assessment. Soils impacted by AFFF use contain both terminal PFAS and a wide range of precursors that can degrade over time, potentially contaminating groundwater. The TOP assay and suspect screening help reveal hidden precursors and transformation products, enabling more accurate mass balance and source attribution. Studies of contaminated soils show high levels of PFOS as well as FT based substances such as FTAB. The latter group may impose precursor degradation, contributing significantly to PFCA formation. These findings highlight the importance of comprehensive PFAS profiling to inform remediation strategies and long-term risk evaluation.
These topics are explored in a new “Short Facts” review authored by Patrick van Hees at the Eurofins European PFAS Competence Centre and Örebro University. The review summarizes key findings on AFFF composition, PFAS precursor transformation, and environmental persistence. It also highlights recent insights from studies on highly polluted soils, including AFFF constituents and precursor occurrence and levels. This concise overview aims to support understanding of PFAS chemistry in the context of AFFF pollution to assist risk assessment and remediation strategies for PFAS-impacted sites.
The ”Short Facts” review can be downloaded here
Questions about PFAS can be answered by our analytical advisory service, which can be reached via the customer support, 010-490 8110 or e-mail: sh-analys.miljo.se@etn.eurofins.com