QSPR-based prediction of air-water interfacial adsorption coefficients for nonionic PFAS with large headgroups.

Air-water interfacial adsorption has been demonstrated to be an important process affecting the retention and distribution of PFAS in soil, surface waters, and the atmosphere, as well as being central to certain remediation methods. Measured or estimated air-water interfacial adsorption coefficients are needed for quantifying and modeling the interfacial adsorption of PFAS. A single-descriptor QSPR model developed in prior work for predicting air-water interfacial adsorption coefficients of PFAS was demonstrated to successfully represent more than 60 different PFAS, comprising all headgroup types and a wide variety of tail structures. However, the model overpredicted values for nonionic PFAS with very large headgroups. A revised QSPR model was developed in the present study to predict air-water interfacial adsorption coefficients for nonionic PFAS with large headgroups. A two-descriptor QSPR model employing molar volume and headgroup-to-tail molar-volume ratio successfully represented measured data for both nonionic PFAS and nonionic hydrocarbon surfactants. This new model provides a means to produce estimates of air-water interfacial adsorption coefficients for nonionic PFAS for which measured values are typically not available.