Quantifying PFAS contamination and environmental risk in municipal solid waste landfill refuse: Implications for...

Per- and polyfluoroalkyl substances (PFAS) are frequently detected at elevated levels in municipal solid waste (MSW) landfill leachate, which is recognized as an important source of environmental PFAS contamination. Yet, PFAS presence in MSW landfill refuse remains largely unexplored, despite the growing interest in landfill refuse utilization and the potential for subsequent PFAS emissions into the environment. This study aimed to quantify PFAS contamination in landfill refuse collected from a closed, typical MSW landfill, by analyzing 24 PFAS (including 18 perfluoroalkyl acids (PFAAs) and 6 PFAA precursors) through target analysis and further capturing unknown precursors using a direct total oxidizable precursor (d-TOP) assay. Our findings revealed that perfluorooctanoic acid (PFOA) was the dominant PFAS in landfill refuse, with a median concentration exceeding 10 μg/kg. The comparison of PFAS in refuse and leachate based on detection and mass level clearly reflected that large amount of PFAS, particularly long-chain perfluoroalkyl carboxylic acids (PFCAs) and PFAA precursors, was still retained in refuse compared to leachate even after more than ten years' leaching. Moreover, significant levels of unknown precursors were identified through the d-TOP assay, highlight that neglecting these unknown precursors could lead to an underestimation of PFAS contamination by a factor of 4 to 18. A probabilistic risk assessment indicated a 25 % likelihood that PFAS in landfill refuse pose moderate to high environmental risk, if excavated refuse is sieved and used as greening soil. To our knowledge, this study marks the first report on PFAS distribution between landfill refuse and leachate, as well as the contribution of unknown precursors in refuse, which underscores the need to consider potential PFAS emission when MSW landfill refuse faces utilization.