Transport and fate of radon: a critical review of mechanisms and environmental influences

Radon is a naturally occurring radioactive gas produced from the decay of uranium-238. It poses significant environmental health risks because it can migrate through soil, groundwater, and air before accumulating indoors. This review, based on a critical synthesis of 94 peer-reviewed publications (2009–2025), explores how radon moves and behaves, emphasising diffusion, advection, and dissolution, and the influence of soil properties, groundwater flow, building characteristics, and human activities. Indoor radon concentrations frequently exceed the WHO reference level of 100 Bq/m3 and may approach or exceed 300 Bq/m3 in radon-prone areas. Radon released from groundwater generally contributes less than 10% of indoor exposure, although it can contribute 5–15% where water has high radon concentrations and ventilation is limited. The review also highlights critical knowledge gaps, such as uncertainties in radon transport through heterogeneous geological media, potential effects of climate change, differences in urban versus rural exposure, and limitations of current transport models. Addressing these gaps will improve radon monitoring, risk assessment, and the development of effective mitigation strategies.