Black carbon plays an essential role in controlling the fate and transport of per- and polyfluoroalkyl substances (PFAS) in soils and sediments. The results of conventional batch sorption experiments offer limited information on the thermodynamic parameters to describe the sorption processes of PFAS by black carbon from water, whereas the thermodynamics are crucial to a comprehensive understanding of sorption mechanism and accurate prediction of the distribution of PFAS between black carbon and water which is commonly presented as partition coefficient (KBC). Isothermal titration calorimetry (ITC) offers precise and direct measurements of the partition coefficients and associated thermodynamics simultaneously and avoids the delicate measurement of PFAS by LCMS/MS. The polyparameter linear free energy relationships (ppLFER) are the most robust and widely used methods currently available to describe the partition of organic compounds in various environmental and engineering systems. This proof-of-concept project aims to understand the black carbon-water partition of PFAS and develop a predictive tool for estimating KBC using the structures of PFAS.

Three specific objectives are:

1. To develop and validate a robust isothermal titration calorimetry method for quantifying black carbon-water KBC of PFAS and thermodynamics associated with this process;
2. To elucidate the underlying intermolecular interactions governing the partition process;
3. To develop ppLFER models to predict the KBC of various PFAS in soil and sediment at different temperatures.

 

The project team will first develop and optimize an ITC method to determine the sorption kinetics, isotherms, and thermodynamics (ΔH, ΔS, and ΔG) of two model PFAS compounds N-ethyl perfluorooctanesulfonamidoethanol and N-ethylperfluorooctanesulfonamide by two model black carbon (National Institute of Standards and Technology Standard Reference Material 2975 and United Kingdom Biochar Research Centre SWP550). Then, batch sorption experiments will be carried out in a refrigerated shaker to validate the results obtained by ITC. After that, the validated ITC method will be applied to PFAS with diverse functional groups to obtain the KBC and associated thermodynamics. Finally, the project team will apply activity-dependent ppLFER to characterize the intermolecular interactions that control the partition process. The established ppLFER will be used to predict the KBC of PFAS at different temperatures.

The results from this project will 1) improve the fundamental understanding of the environmental distribution of PFAS, 2) develop a robust method to measure the partitioning of PFAS and the thermodynamics associated with this process, and 3) provide a tool to accurately predict the black carbon-water partition coefficients (K_BC) of PFAS, especially at temperatures other than 25°C. These outcomes will support assessments and management of PFAS in environmental systems, ultimately contributing to the Department of Defense's operational capabilities and securing warfighters preparedness. (Anticipated Project Completion - 2026)