Anomalous Adsorption Of Pfas At The Air–Water Interface Of Thin Water Films In Water-Unsaturated Porous Media
Presenter: Wenqian Zhang1
Co-Author(s): -
Advisor(s): Dr. Bo Guo
1Department of Hydrology and Atmospheric Sciences, University of Arizona
PFAS are emerging contaminants that tend to adsorb at the air–water interface (AWI). Due to the abundance of AWIs in water-unsaturated soils, this interfacially-active property complicates the transport of PFAS in the vadose zone. The AWIs in water-unsaturated soils include two types: one is associated with the pendular rings between soil grains (i.e., bulk AWI) and the other arises from the thin water films covering the soil grains. To date, the two types of AWIs have been treated the same when modeling PFAS fate and transport. However, the adsorption of PFAS at the AWI of thin water films can significantly deviate from that at the bulk AWI, due to the electrical double layers at soil grain surfaces. Given that the thin water films contribute to over 90% of AWIs in the vadose zone, it is critical to quantify the potential anomalous adsorption of PFAS at the AWIs of thin water films. We develop the first thermodynamics-based model to represent and quantify this anomalous adsorption. Our analysis suggests that PFAS air–water adsorption at thin water films can be up to 80% smaller than that at the bulk AWI. The deviation becomes greater for thinner water film and higher solid charge density. These results highlight the importance of accounting for anomalous adsorption of PFAS at the AWI of thin water films when modeling PFAS fate and transport in the vadose zone.