Henry’s Law constants of 15 per- and polyfluoroalkyl substances determined by static headspace analysis

While it is thought that some per- and polyfluoroalkyl substances (PFAS) may volatilize from aqueous solutions, experimentally measured Henry’s Law constants (k_H, synonymous with air : water partition coefficient) are scarce. This leads to a lack of understanding of the partitioning of PFAS and an inability to predict concentrations above contaminated groundwater (e.g., vapor intrusion). We measured k_H for 27 PFAS via headspace analysis and manipulations of the gas to liquid phase ratio. Fifteen PFAS produced mass spectrometry signals suitable for k_H measurements. At 25 °C the experimentally measured dimensionless k_H were: 0.31 – 2.82 for four fluorotelomer alcohols (FTOHs), 0.09 – 0.18 for three fluorotelomer sulfonates (FTSs), 0.30 – 1.01 for three iodinated PFAS, 0.43 – 0.92 for two sulfonamides, 3.86 for 6:2 fluorotelomer olefin, 0.69 for 8:2 fluorotelomer carboxylic acid, and 0.32 for 8:2 fluorotelomer acrylate. Longer fluoroalkyl chain length resulted in increased k_H for FTOHs and FTSs, the only two groups in which chain length was studied. Perfluorinated sulfonates and carboxylates were generally not volatile enough to be measured, even at pH as low as 1, although fluorotelomers of both functional groups were measurably volatile. Temperature effects were well described by the van’t Hoff equation. k_H was not significantly different in various environmentally relevant matrices demonstrating the broad applicability of the produced constants.