Geochemical Controls on Radon Mobility in Soils: Implications for Environmental Risk Assessments

Background: Radon-222 (²²²Rn) is a naturally occurring radioactive gas that poses a significant health hazard when it accumulates indoors. While traditional models emphasize uranium content, emerging evidence suggests that soil geochemistry plays a critical role in radon mobility. Objective: This review aims to clarify how specific geochemical properties influence radon behavior in soils and to highlight implications for risk assessment and mitigation strategies. Methods: Analysis of recent peer-reviewed studies was conducted, focusing on soils affected by contaminants such as arsenic, iron and lead. The review identifies dominant mechanistic pathways and synthesizes findings across diverse geographic and environmental contexts. Results: The findings indicate that soil radon flux is shaped by three principal mechanisms: (1) adsorption–desorption interactions involving iron oxides and organic matter; (2) changes in soil structure and permeability mediated by redox conditions; and (3) synergistic effects in multi-contaminant environments. Studies also highlight threshold responses to pH (particularly within the pH range of 4 to 8), organic matter content, and moisture saturation. In some cases, radon levels were elevated even when uranium concentrations were low, underscoring the influence of chemical modifiers. Conclusion: Radon risk assessment frameworks should move beyond uranium-focused models to incorporate geochemical complexity. Factoring in redox conditions, co-contaminants, and sorptive properties can improve hazard prediction and inform targeted remediation strategies.