Soil-water distribution coefficients (K_d) of PFAS in field-collected contaminated soils from Lyon, France

The distribution coefficients (log K_d) of per- and polyfluoroalkyl substances (PFAS) were investigated in 84 soils from around Lyon, France. This area is located adjacent to an industrial facility that uses various PFAS in its production processes and that has been known to emit PFAS. A total of 77 target PFAS were analyzed in soil leachates using ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-Orbitrap Q Exactive). While total PFAS concentrations in soil ranged from 3.8 to 175 μg kg^-1 dry weight, the corresponding concentrations transferred to the aqueous phase ranged from 3.0 to 1215 ng L^-1. A clear predominance of perfluoroalkyl carboxylic acids (PFCAs), including PFHxA, PFHpA, PFNA, PFPeA, and PFOA, was observed in the aqueous phase following soil-water equilibration across all soil types. The data were used to determine solid-liquid partitioning coefficients that can be used to model downward mobility of the PFAS. The resulting log K_d for the PFCAs (C3-C11) varied from 0.08 to 3.41 mL g^-1, while values for PFSAs (specifically PFBS (C4), PFHxS (C6), and PFOS (C8)) varied between 0.80 and 4.94 mL g^-1. Spearman's rank correlations between K_d values and soil properties (pH and SOC) for the 14 detected PFAS revealed that soil pH is a primary factor influencing PFAS partitioning, with statistically significant negative correlations for PFHxA and PFDA and highly significant negative correlations for PFBA, PFNA, PFUnDA, and PFHxS. In contrast, SOC (%) generally showed no significant influence on PFAS partitioning, except for PFBS and PFOA, which exhibited a strong, highly significant positive correlation.