Poly- and perfluoroalkyl substances (PFAS) often present at higher concentrations than the permissible levels in soil and groundwater, are emerging as a pernicious challenge to safe water supplies. One approach uses amendments to immobilize the pollutants in situ delaying the movement toward ground/surface water. This study investigated the role of activated carbon and compost as two different amendments in immobilizing perfluorooctanoic acid, PFOS (C8HF15O2), in two different soils. The soil samples are from calcareous Florida topsoil, and Ringold Formation sediment collected at DOE’s Hanford site, WA, an iron-rich silicon oxide containing sediment. The soils were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier Transform Infrared Spectroscopy. PFOS concentration was measured by LC-HRMS (Orbitrap). Detailed kinetic adsorption studies showed that adsorption equilibrium occurred within 24 hours following a pseudo-second order model for amended and native soils. PFOS removal was ~57 % for both native soils. The adsorption of PFOS on native Ringold sediment and compost amended Ringold sediment was the same indicating that Total Organic Carbon (TOC) from the amendment was not a significant factor in the adsorption of PFOS onto sediment. Perhaps aluminum and iron oxides play the primary roles on the adsorption of PFOS onto the Ringold sediment. Since the surface of both iron and aluminum oxides were positively charged, the electrostatic attraction with negatively charged PFOS should play an important role during the adsorption process. The effect of activated carbon amendment for both soils was found to be significantly higher than in native soil. Overall, the efficiency of the amendment on perfluoroalkyl substances immobilization was demonstrated to be highly impacted by soil type.

Effect of compost and activated carbon amendments on immobilization of perfluorooctanoic acid (PFOS) in two soils with contrasting texture

ACS Spring 2022

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