Sorption linearity and reversibility are implicit in models for the environmental fate and transport of per- and polyfluoroalkyl substances (PFAS). However, in this study, we found that the sorption of cationic and zwitterionic PFAS in natural soils was highly nonlinear. The sorption nonlinearity was so severe that it led to a variation in sorption coefficients by several orders of magnitude over the experimental concentration range. This implies a considerable increase in sorption as concentration falls due to degradation or dilution of the liquid phase in the natural environment. Sorption of cationic PFAS correlated strongly with the soil organic matter (SOM) content and was reversible in all soils. Sorption of zwitterionic PFAS, on the other hand, displayed concentration-dependent hysteresis in soils with a low SOM content. The irreversibility, which was associated with neither SOM, micro- and mesopore deformation, nor surface complexation, was likely caused by the entrapment in microporous structures within inorganic components of soil aggregates. The maximum electrostatic potential of PFAS ions, computed using density functional theory, was found to be a useful predictor of the sorption of ionic PFAS with the same number of perfluorocarbons. Finally, some important consequences of sorption nonlinearity and irreversibility to the physical and biological availability of cationic/zwitterionic PFAS in the soil environment are discussed.

Sorption and desorption mechanisms of cationic and zwitterionic per- and polyfluoroalkyl substances in natural soils

2019 Fall National Meeting

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