Tahereh Moghtaderi¹, Dimitrios Ntarlagiannis¹, and Lee Slater^1,2

^[1] Rutgers University -Newark, Department of Earth and Environmental Sciences

^[2] Earth Systems Science Division of the Energy and Environment Directorate, Pacific Northwest National Laboratory

Contamination of subsurface environments by aqueous film-forming foams (AFFF) at former fire-training areas has raised significant environmental and health concerns due to the persistent and bioaccumulative nature of per- and polyfluoroalkyl substances (PFAS), which are key components of AFFF. These compounds pose substantial ecological risks and human health implications, highlighting the need for effective detection and remediation strategies. PFAS interact with soils in complex ways, necessitating more advanced monitoring techniques. Spectral induced polarization (SIP) has emerged as a promising tool for detecting PFAS contamination, owing to its sensitivity to changes in the soil’s interfacial properties, including electrochemical interactions that are influenced by contaminants such as PFAS.

This study aims to extend previous research by examining the sensitivity of SIP to a range of PFAS concentrations commonly found at contaminated sites. Specifically, the study focuses on evaluating SIP’s response to AFFF, zwitterionic, and anionic at concentrations that mimic the contamination levels observed in the field. To achieve this, synthetic soil samples were spiked with PFAS compounds at concentrations ranging from a 500-fold dilution (heavy) to a 1000-fold dilution (minimal), providing a broad spectrum of PFAS contamination levels. The synthetic soil mixture, which included fine sand and peat moss, was chosen because it reflects the characteristics of soils at contaminated sites. Sand was selected for its high permeability, while peat moss was incorporated for its ability to enhance PFAS sorption, thus providing an ideal substrate to study the mobility and retention of PFAS in soils.

The results of the study reveal distinct adsorption and polarization behaviors for the different types of PFAS. AFFF components were found to reduce the mobility of counterions and neutralize surface charges in the soil, leading to a decrease in polarization and a measurable reduction in imaginary conductivity (σ′′), as surfactant adsorption limits ion movement within the soil. Zwitterionic, in contrast, exhibited stronger electrostatic interactions with the soil surface and concentration-dependent sorption, resulting in increased conductivity and a shift in polarization peaks over time, which reflects their higher sorption capacity. Anionic PFAS demonstrated weak sorption behavior primarily driven by hydrophobic partitioning rather than electrostatic interactions, leading to minimal changes in σ′′ and stable SIP responses throughout the experimental period. While AFFF and zwitterionic significantly altered the soil's electrical properties, anionic PFAS remained highly mobile with weak sorptive interactions, resulting in weak polarization effects and minimal variation in SIP measurements.

These findings emphasize the complex nature of PFAS-soil interactions and the varying impacts of different PFAS types on soil electrical properties. By elucidating the distinct behaviors of AFFF, zwitterionic, and anionic in soils, the study enhances the understanding of PFAS detection through SIP, providing valuable insights for refining contamination assessments and improving remediation strategies for PFAS-impacted environments.