Geospatial mapping of radon concentrations and uncertainties in radiological risk assessments using probabilistic...

Radon is a primary source of internal radiation exposure, occurring via inhalation and ingestion. This study investigates the distributions and radiological hazards of soil radon and groundwater radon in Ibadan, a major city in Nigeria. Radon concentrations were measured at 41 sites using a RAD7 detection system. The geospatial distribution was mapped using Surfer 10 software, and health risks were assessed via Monte Carlo simulations (MCS). Soil radon concentrations ranged from 1.75 to 47.24 kBq/m³ (mean: 22.30 ± 14.48 kBq/m³), while water radon concentrations ranged from 1.12 to 30.48 Bq/L (mean: 14.17 ± 8.80 Bq/L). The average soil radon level falls below the ICRP limit (40 kBq/m³), but the average water radon exceeded the EPA limit of 11.1 Bq/L. A strong Spearman rank correlation of 0.96 was observed between the two media. Geospatial analysis identified Class III hotspots (e.g., Pegba and Oranyan) as priority areas for local mitigation. The MCS quantified the probabilistic health burden, revealing a grand excess lifetime cancer risk ranging from 0.007 × 10⁻³ (found in the best-case scenario at Samonda and Molete) to 2.470 × 10⁻³ (found in the worst-case scenario at Oranyan) with an average mean of 0.605 × 10⁻³. Notably, the maximum probable risk in high-exposure hotspots remains below the ICRP reference level of 3.75 × 10⁻³, suggesting that while the risk is significant, it does not exceed the international threshold for emergency intervention. These findings underscore the necessity of targeted intervention to manage long-term radiological health implications for the population.