A comprehensive, generalized approach to predict the retention of per- and polyfluoroalkyl substances (PFAS) from aqueous film-forming foam (AFFF) by a soil matrix as a function of PFAS molecular and soil physiochemical properties was developed. An AFFF with 34 major PFAS (12 anions and 22 zwitterions) was added to uncontaminated soil in one-dimensional saturated column experiments and PFAS mass retained was measured. PFAS mass retention was described using an exhaustive statistical approach to generate a poly-parameter quantitative structure–property relationship (ppQSPR). The relevant predictive properties were PFAS molar mass, mass fluorine, number of nitrogens in the PFAS molecule, poorly crystalline Fe oxides, organic carbon, and specific (BET-N2) surface area. The retention of anionic PFAS was nearly independent of soil properties and largely a function of molecular hydrophobicity, with the size of the fluorinated side chain as the main predictor. Retention of nitrogen-containing zwitterionic PFAS was related to poorly crystalline metal oxides and organic carbon content. Knowledge of the extent to which a suite of PFAS may respond to variations in soil matrix properties, as developed here, paves the way for the development of reactive transport algorithms with the ability to capture PFAS dynamics in source zones over extended time frames.

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An electrical-matching, flow calorimeter was used to measure the enthalpies of ethylbenzene (349-551 K, 1.5-200 bar), Isooctane (358-520 K, 20-100 bar), and ethylcyclohexane (335-576 K, 20-100 bar). Water/steam calibration measurements show the apparatus capable of 0.1-0.2% precision with no detectable systematic bias.The present measurements are shown to be accurate to ±0.25% In enthalpy and ±2% in heat capacity.Literature vapor pressures, heats of vaporization, and perfect gas state enthalpies, consistent with the present hydrocarbon enthalpies, are used with our results to provide pressure/enthalpy diagrams for both the liquid and vapor states.

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