Sorption of Perfluorooctane Sulfonic Acid (PFOS) and Perfluorooctanoic Acid (PFOA) to Buried Valley Aquifer Sediments

Greater understanding of the sorption of poly- and perfluoroalkyl substances (PFAS) to aquifer materials, particularly buried valley aquifers, is of critical importance because many published PFAS sorption experiments have examined soils, surficial sediments, and manufactured homogeneous materials but not aquifer sediments. This study examined three sedimentary facies (i.e., sandy gravel, sand, and silty clay) collected from the Great Miami Buried Valley Aquifer at the Theis-Nash Environmental Monitoring and Modeling Site, OH. Solutions of five PFOS and PFOA concentrations ranging from 0.06 to 1.0 mg/L in synthetic groundwater were applied to prepared <2 mm sediment fractions for batch sorption experimentation. Sorption behavior in these sediments did not follow expected patterns based on their physical and chemical characteristics (e.g., grain size and organic matter, aluminum, and iron contents). The sandy gravel displayed the least amount of sorption, which was expected, but it did not align with differences in sediment composition (e.g., sandy gravel vs. sand). The silty clay would have been expected to display the highest sorption based on physical and chemical characteristics, but this was not the case, with sand having a higher KF value, albeit quite similar. Overall, PFOS was found to be more sorptive than PFOA.