Spatial Distribution and Public Health Implications of Radon and Thoron in Groundwater: A Large-Scale Study in Largest Province of Iran - 2023

Introduction: Radon (222Rn) and thoron (220Rn) are radioactive gases that pose significant health risks, including lung cancer, when inhaled or ingested. This study aimed to assess the health risks associated with radon and thoron in groundwater across Kerman Province, the largest province in Iran. Materials and Methods: A total of 107 wells were sampled (2023), and radon/thoron concentrations were measured using a RAD7 detector. Data were analyzed using SPSS-26 and ArcMap 10.5, employing the Kruskal-Wallis test and ordinary kriging for spatial distribution mapping. Results: The annual effective dose of radon ranged from 10.00 ± 6.72 to 224.84 ± 28.40 μSv/yr for adults, while thoron doses ranged from 15.00 ± 10.07 to 337.26 ± 42.59 μSv/yr for adults. No significant correlation was found between radon concentration and environmental parameters (pH, temperature, and residual free chlorine). Seven sampling points exhibited a high respiratory risk, whereas the others posed a moderate risk. No association was observed between the radon/thoron levels and fault proximity. Conclusion: All measured radon concentrations were below Iran’s permissible limit (100 Bq/L). To mitigate health risks, high-concentration wells should be restricted or sealed, and aeration/storage tanks (≤ 4-day retention time) should be implemented to reduce radioactivity. These measures are crucial for minimizing public exposure to radioactive groundwater contamination.