Reciprocal influence of per- and polyfluoroalkyl substances (PFAS) and soil organic matter on their fate in soils.

The global accumulation of per- and polyfluoroalkyl substances (PFAS) in soils raises concerns about soil quality. While PFAS sorption may depend on the quality of soil organic matter (SOM), their unique properties may also affect SOM dynamics in complex and poorly understood ways, impacting long-term soil quality. Literature provides vague conclusions about how SOM, particularly its quality, influences PFAS-soil interactions and whether PFAS can modify SOM characteristics. The present study aims to enhance both the qualitative and quantitative understanding of the reciprocal impact that PFAS and SOM have on each other's environmental fate. Sorption of three PFAS molecules and simultaneous mobilization of dissolved organic matter (DOM) in three distinct soils were studied. PFOS had the highest sorption by ranging 61-98% followed by PFOA and PFBA. 13C NMR analysis indicated that PFAS sorption is driven by hydrophobic components of SOM. The highest PFAS sorption was observed in soils containing polycyclic aromatic hydrocarbons (PAHs), while the lowest was recorded in soils with less hydrophobic SOM. Conversely, the presence of PFAS increased the release of DOM in soils with less hydrophobic SOM. The changes in DOM release induced by PFAS were directly influenced by the chemical properties of the soil components. Additionally, 1H NMR revealed notable structural changes in the chemical composition of DOM caused by PFAS, characterized by an increase in hydrophobic constituents and a decrease in hydrophilic components. The results indicated that PFAS can affect both the quantity and quality of SOM, potentially compromising long-term SOM stability and carbon sequestration in contaminated soils.