Indoor Radon and Thoron Concentrations in Dwellings of Chandigarh, India: Seasonal Variability, Exhalation Characteristics and Radiological Dose Assessment

Abstract

Radon (^222Rn) and thoron (^220Rn) are naturally occurring radioactive noble gases generated in the uranium-238 and thorium-232 decay series, respectively. Because they are chemically inert gases, they can migrate from soil and building materials into indoor environments, where their short-lived radioactive progeny may attach to aerosols and contribute to human inhalation exposure. Indoor exposure to radon is an important component of natural radiation exposure and has consequently received considerable attention in environmental radioactivity research. Thoron has a much shorter half-life than radon, but its progeny can nevertheless make a significant contribution to radiation dose under certain building and ventilation conditions. Chandigarh provides an important setting for studying these gases because of its distinctive urban development, variation in dwelling characteristics, soil conditions, construction materials and seasonal meteorology. The present paper reviews and synthesizes published measurements of indoor radon and thoron in dwellings of the Union Territory of Chandigarh and evaluates their radiological significance. Published investigations have reported indoor radon concentrations ranging from approximately 7.9 to 62.1 Bq m^-3 and thoron concentrations from approximately 0.15 to 99.2 Bq m^-3 across different measurement campaigns and dwelling groups. One Chandigarh investigation reported a mean radon concentration of 23.3 Bq m^-3 and a mean thoron concentration of 10.7 Bq m^-3, whereas another investigation using pin-hole based radon-thoron dosimeters reported mean concentrations of 39.9 Bq m^-3 for radon and 31.1 Bq m^-3 for thoron. Annual effective doses reported in these investigations were generally within the range associated with normal environmental exposure, although considerable dwelling-to-dwelling variability was observed. Soil and construction materials were identified as important sources of indoor radon, while ventilation, building characteristics and the spatial distribution of radioactive elements influenced indoor concentrations. The review demonstrates that Chandigarh generally exhibits relatively moderate indoor radon levels, but isolated dwellings can show substantially higher thoron concentrations. The findings emphasize the importance of measuring radon and thoron separately, because detectors that do not discriminate between the two gases may overestimate radon concentrations or obscure the contribution of thoron. Continued long-term monitoring, systematic seasonal measurements, characterization of building materials and development of a Chandigarh-specific indoor radon-thoron database are recommended.

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1. 1. Mehta, V., Kumar, A., Singh, S. P., Chauhan, R. P., & Mudahar, G. S. (2015). Measurement of indoor radon, thoron and their progeny levels in dwellings of Union Territory Chandigarh, India: Correlation with radon exhalation rates. Indoor and Built Environment, 24(6), 833–842. DOI: 10.1177/1420326X14535792.
2. 2. Shikha, D., Mehta, V., Chauhan, R. P., & Mudahar, G. S. (2018). Measurement of variation of radon-thoron and their progeny concentrations in dwellings using pin hole based dosimeters. Aerosol and Air Quality Research, 18, 811–819.
3. 3. UNSCEAR. (2006). Sources-to-Effects Assessment for Radon in Homes and Workplaces. United Nations Scientific Committee on the Effects of Atomic Radiation.
4. 4. UNSCEAR. (2019). Sources and Effects of Ionizing Radiation: UNSCEAR 2019 Report. United Nations Scientific Committee on the Effects of Atomic Radiation.
5. 5. Eappen, K. P., Mayya, Y. S., et al. Nationwide indoor ^222Rn and ^220Rn mapping studies in India using solid-state nuclear track detector techniques. The national review reports ^222Rn concentrations ranging from 4.6 to 147.3 Bq m^-3 across surveyed locations.
6. 6. Published Chandigarh SSNTD measurements have additionally reported individual-dwelling radon values of approximately 14.9–34.2 Bq m^-3 in one dataset, illustrating the variability observed between homes.

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