Per- and polyfluoroalkyl substances (PFAS) profiles in primary and secondary landfill leachates: Indications of transformation, liner interactions, and other PFAS sources.

Per- and polyfluoroalkyl substances (PFAS) are a growing concern due to their persistence, bioaccumulation potential, and continued widespread use in consumer products. PFAS disposed of in landfills are emitted to the environment via leachate, which drives a need to better understand PFAS behavior in landfills and landfill liner systems. This study examines PFAS concentrations in primary and secondary leachate from three municipal solid waste landfills utilizing double HDPE geomembrane liner systems. Samples were also analyzed for physical-chemical constituents such as chloride, ammonia, chemical oxygen demand, and metals. On average, physical-chemical parameter concentrations were significantly lower in the secondary compared to the primary leachate, although PFAS concentrations were not significantly different between leachate sources. Concentrations of chloride in groundwater and primary leachate were used to calculate expected PFAS concentrations in the secondary leachate. PFAS concentrations in secondary leachate were often higher than expected, with PFAAs more likely to exceed expected levels. Of the 92 PFAS analyzed, 50 were quantified in primary leachates and 48 in secondary leachates. The ∑PFAS concentrations in primary leachate ranged from 3200-81,000 ngL, and secondary leachate ranged from 3300-96,000 ngL. Possible explanations for the disproportionately high PFAS concentrations in secondary leachates, including residence time, transformation, liner sorption, and other PFAS sources (e.g., landfill gas) are explored. While liner systems are highly effective, PFAS migration through landfill liners and potential groundwater impacts remain a concern. This study underscores the importance of continued research into PFAS migration mechanisms and the potential environmental impacts of unidentified precursor PFAS in landfills.