Occurrence of per- and polyfluoroalkyl substances (PFAS) in soil: Sources, fate, and remediation

Abstract

Per- and polyfluoroalkyl substances (PFAS) are being widely investigated for their distribution and remediation in the environment. It is crucial to consider the interactions of PFAS between soil and the other media in the ecosystem, including air, water, and plants, when studying their fate and transport in soil, while few studies have taken such an integrative approach. This review examined the potential input of PFAS to soil from air, water, and landfill by analyzing both the PFAS concentration in each source and the mechanisms by which a soil is impacted by PFAS from these sources. It was found that PFAS in air (on average 10¹⁻² ​pg/m³) and landfill leachates (on average 10^0-2 ​ng/L) are the main sources of PFAS in soil. Many factors, such as solution pH and cations, influence sorption and desorption of PFAS in the water-soil interface, but no single factor is deterministic. The migration of PFAS from soil to plant through root uptake was found in many plant species, including wheat and maize, and the effects vary with different PFAS and plant species. PFAS levels in soil were associated with land-use type. They were the highest in the primary exposure sites (10⁻¹-10² ​ng/g), followed by secondary exposure sites (10⁻¹-10¹ ​ng/g), and background sites (10⁻²-10¹ ​ng/g), with legacy PFAS- PFOA (10^0-1 ​ng/g) and PFOS (10^0-2 ​ng/g) as the most predominant. There are a few promising destructive technologies targeted at PFAS in soil, such as thermal treatment and ultrasound, but still need to overcome low efficiency and high cost to scale up. In the meantime, PFAS may either be immobilized in soil or be removed for ex-situ treatment.