Partitioning of Per- and Polyfluoroalkyl Substances to Weathered Light Non-Aqueous Phase Liquid

Per- and polyfluoroalkyl substances (PFAS) and weathered petroleum hydrocarbons can be co-contaminants at sites where aqueous film-forming foam (AFFF) was used to extinguish high-temperature petroleum fires. Here, we report on the partitioning of six PFAS between water and a weathered diesel and gasoline range hydrocarbon light non-aqueous phase liquid (LNAPL) collected from the subsurface of a decommissioned refinery. Results showed that both the structural features of PFAS and the characteristics of LNAPL exhibited significant impacts on the magnitude of PFAS partitioned to the LNAPL. The LNAPL–water partition coefficients (K_l) of PFOA and PFOS to the weathered LNAPL measured in this work were nearly or more than 10 times greater than K_l values calculated by others for partitioning to single-component, unweathered NAPLs, indicating that laboratory studies evaluating LNAPL–water partitioning studies using single component NAPLs can largely underestimate the K_l expected to be encountered at contaminated AFFF sites. Interactions with LNAPL can be important controllers of PFAS fate and transport, and the K_l values estimated in this work suggest that LNAPL could be a significant transport sink for PFAS in the field. Results from this work suggest that PFAS partitioning to weathered LNAPL is an important process to be considered when designing remedial strategies, particularly those incorporating monitored natural attenuation or natural source zone depletion.