Migration of Per- and Polyfluoroalkyl Substances in Soil Under Rainfall Simulation

Abstract

Understanding the migration of per- and polyfluoroalkyl substances (PFAS) in soil via groundwater and surface water is vital for managing PFAS. PFAS transport via surface runoff during rainfall is less known than leaching. This study investigated PFAS migration under simulated rainfall in soils with varying contamination levels, examining multiple pathways to assess the factors affecting PFAS migration. Rainfall simulations were conducted over 15 days with wetting and drying cycles. Results indicate that leaching is likely the dominant pathway for PFAS transport, accounting for the largest proportion (on average 72%) of PFAS mass in the released fractions. Runoff was also an important pathway for long-chain PFAS, whereas short-chain PFAS were not detected in runoff. Both PFAS concentration and the wetting-drying cycles influenced PFAS distribution. Leaching was negligible when PFAS concentrations exceeded 30 mg/kg perfluorooctane sulfonic acid (PFOS), potentially due to reduction in soil hydraulic conductivity. PFAS concentrations in runoff increased following extended drying periods, suggesting accumulation of PFAS in the upper soil. This pattern of evapoconcentration, likely driven by capillary water movement and subsequent evaporation, is consistent with the resurgence of concentration in surface soils. Overall results highlight that surface runoff is an important pathway for PFAS transport, particularly for long chain PFAS. Wetting and drying cycles may promote accumulation in the upper soil layers, increasing the potential for mobilization via runoff. By considering both leaching and runoff, this study contributes to a better understanding of PFAS transport in soils and can help inform management strategies to reduce contaminant spread to surface waters.