A mathematical model for the transport of multi-component PFAS in unsaturated porous media

Hassan Saleem1, Bo Guo1, and Hoshin Gupta1
1Department of Hydrology and Atmospheric Sciences, University of Arizona

In the past 80 years, per- and polyfluoroalkyl substances (PFAS) have been widely used in many industrial and consumer products and other manufacturing applications, including nonstick coating, textiles, paper products, and firefighting foams. Large-scale manufacturing and use of PFAS have resulted in their wide presence in the environment especially in the vadose zone. Many PFAS are surfactants that are surface active, and as a result, they tend to accumulate at the solid surfaces and air-water interfaces in soils and may be retained in the vadose zone for long periods of time. Moreover, the presence of multiple PFAS components (commonly found in the vadose zone) introduces additional complexities to their fate and transport due to competitive interactions. Here, we develop a mathematical model that represents transient variably saturated flow, nonlinear solid-phase and air-water interfacial adsorption, and competitive interactions among the PFAS components. We illustrate the impact of the competitive interactions among multiple PFAS components on their transport and retention in soils via a series of numerical experiments that cover a wide range of physical conditions.

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