Soil-Air Exchange of Substituted Chlorobenzenes and Volatile PFAS at Contaminated Site: Impact of Environmental Factors and Development of a Fugacity-Based Model

Abstract

Substituted chlorobenzenes and volatile per- and polyfluoroalkyl substances (PFAS) are significant environmental contaminants that impact soil and air ecosystems. This study investigates the soil-air exchange behavior of these compounds and develops models to predict their exchange under varying environmental conditions. The soil-air partitioning coefficient (K_SA) was determined for substituted chlorobenzenes using a solid-phase fugacity meter under different temperatures, relative humidity, and soil organic carbon contents. The results indicate that temperature, relative humidity, and soil organic carbon content significantly influence K_SA values. Higher temperatures and humidity increase the volatilization of substituted chlorobenzenes from soil to air, while higher organic carbon content reduces volatility. A multiple linear regression (K_SA-MLR) model was developed to predict K_SA values, showing high accuracy (adjusted R² = 0.956). Additionally, a fugacity-based model (K_{SA-In situ}) was established to quantify the actual soil-air exchange of these compounds at contaminated sites or laboratory microenvironments. The K_{SA-In situ} model demonstrated better accuracy than the K_SA-MLR model in non-equilibrium conditions. This study provides insight into the soil-air behavior and fate of substituted chlorobenzenes and volatile PFAS at contaminated sites. It also offers a robust predictive framework for quantifying their soil-air exchange under varying environmental conditions. This enhances our understanding of their transport mechanisms and supports more effective environmental management and risk assessment.