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Improving the understanding of per- & polyfluorinated substances (PFAS) transport in unsaturated porous media
Stults, John Forrest
Stults, John Forrest
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2022
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2023-05-04
Abstract
Per- and polyfluorinated alkyl substances (PFASs) are large class of anthropogenic compounds which are widespread emerging contaminants of concern in the environment. Colloquially referred to as forever chemicals, PFASs are most well known for their environmental persistence for decades after their initial releases. In addition to this environmental recalcitrance, some PFASs have a high level of human toxicity and are mobile in the environment. The widespread nature of PFAS contamination, their inherent environmental persistence, and high level of the toxicity led the Environmental Protection Agency (EPA) in 2016 to issue a lifetime health advisory limit of 70 parts per trillion (ng/L) for two PFASs, perfluorooctane sulfonate (PFOS) and perfluoroctanoate (PFOA) in drinking water. PFASs are most frequently introduced to terrestrial and aquatic systems through aerosol deposition, landfill leachate, and fire fighting aqueous film forming foams (AFFFs), and thus require transport through the vadose zone prior to contaminating groundwater sources. It has been observed that the vadose zone often serves as a long term source of PFASs, likely owing to PFASs sorption to the air water interface due to their surfactant properties.
The objective of this research is to better understand the subsurface transport properties of PFASs in the vadose zone, as their long¬ term residence in the vadose zone is poorly understood and not well explained by existing fate and transport models. Four research projects were conducted to better understand the fate and transport of PFASs in unsaturated porous media: an evaluation of conservative solute transport in unsaturated 1-D columns using X ray absorption spectroscopy and high temporal resolution sensor monitoring to fill in knowledge gaps of non Fickian transport in unsaturated porous media (Chapter 2); an assessment of PFOS transport in unsaturated 1-D column experiments under highly Fickian conditions (Chapter 3); the development of air water interfacial partitioning data for a broad suite of PFASs to enable creation of quantitative models to predict concentration and ionic strength air water dependent interfacial partitioning coefficients of PFASs (Chapter 4); and an examination of PFOS transport in unsaturated 1 D columns under highly non Fickian conditions (Chapter 5).
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