Radon and Thoron Concentrations in Dwellings of Kanpur City, Uttar Pradesh: Assessment, Influencing Factors and Radiological Significance

Abstract

Radon (^222Rn) and thoron (^220Rn) are naturally occurring radioactive noble gases generated in the uranium-238 and thorium-232 decay series, respectively. Because both gases can accumulate indoors, their short-lived radioactive progeny may contribute appreciably to radiation exposure of occupants. The present research paper reviews and evaluates the available evidence concerning indoor radon and thoron concentrations in residential dwellings of Kanpur City, Uttar Pradesh, with particular emphasis on measured radon concentrations, building characteristics, ventilation, floor level, dwelling type, equilibrium factors, and associated radiation-dose considerations. An important earlier investigation involving 120 dwellings in Kanpur reported mean radon concentrations of approximately 40 ± 10 Bq m^-3 in living rooms, 46 ± 6 Bq m^-3 in bedrooms, and 70 ± 5 Bq m^-3 in kitchens. The corresponding geometric means were approximately 25.3, 36.2 and 40 Bq m^-3, respectively. The study also reported an average radon equilibrium factor of 0.38 ± 0.26 and an estimated annual effective dose equivalent of approximately 1.0 mSv y^-1 for living-room exposure. Poorly ventilated dwellings showed substantially greater radon concentrations than well-ventilated dwellings, demonstrating the importance of indoor air exchange. Although thoron is increasingly recognized as an important component of indoor natural radiation exposure, the published Kanpur-specific study cited here primarily quantified ^222Rn rather than providing a complete modern ^220Rn dataset. Therefore, thoron values reported for Central Uttar Pradesh should not be incorrectly presented as direct Kanpur measurements. The available regional evidence nevertheless establishes the scientific importance of simultaneous radon–thoron monitoring in Uttar Pradesh. Contemporary international guidance recommends that residential radon concentrations be kept as low as reasonably achievable, with WHO proposing a reference level of 100 Bq m^-3 where feasible and indicating that the selected national reference level should not exceed 300 Bq m^-3 when 100 Bq m^-3 cannot reasonably be achieved. The present review demonstrates that the historical Kanpur radon measurements were below these reference values, while still indicating measurable exposure and considerable variation between rooms and building conditions. A systematic city-wide survey using radon–thoron discriminating passive detectors, seasonal measurements and detailed building questionnaires would provide an updated exposure map for Kanpur.

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References

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1. 1. Khan, A. J. (2000). A study of indoor radon levels in Indian dwellings, influencing factors and lung cancer risks. Radiation Measurements, 32(2), 87–92. The study included 120 dwellings in Kanpur and 180 in Lucknow and evaluated indoor radon, ventilation, floor level and dwelling characteristics.
2. 2. World Health Organization (WHO). Radon and Health. WHO. The WHO identifies radon as an important environmental risk factor and recommends national programmes for reducing residential exposure.
3. 3. World Health Organization. WHO Handbook on Indoor Radon: A Public Health Perspective. WHO/NCBI Bookshelf. The handbook discusses residential reference levels and recommends 100 Bq m^-3 as a preferred reference level where achievable, with 300 Bq m^-3 as an upper value where lower levels cannot reasonably be implemented.
4. 4. WHO Global Health Observatory. Radon reference level for dwellings. WHO. The database identifies 300 Bq m^-3 as the maximum residential reference level provided in the IAEA GSR Part 3 framework.
5. 5. UNSCEAR. UNSCEAR 2017 Report. United Nations Scientific Committee on the Effects of Atomic Radiation. The report includes Indian data on effective doses associated with indoor radon and thoron progeny.
6. 6. UNSCEAR. UNSCEAR 2024 Report, Volume II. The report estimates a global mean indoor radon concentration of approximately 50 Bq m^-3 and describes the worldwide distribution of residential radon concentrations.
7. 7. Srivastava, A., et al. (2005). An overview of an indoor radon study carried out in dwellings in India and Bangladesh during the last decade using solid state nuclear track detectors. Journal of Environmental Radioactivity, 78(1), 113–121.
8. 8. Nationwide indoor ^222Rn and ^220Rn mapping studies of India. These investigations demonstrate substantial geographical variation in indoor radon and thoron concentrations and emphasize geological and building-related controls.
9. 9. Environmental Monitoring of Indoor Radon, Thoron and Their Progeny in Dwellings of Uttar Pradesh, India. The Central Uttar Pradesh study reported mean radon and thoron concentrations of approximately 27.90 and 16.75 Bq m^-3, respectively.
10. 10. Rani, S., Kansal, S., et al. (2026). Seasonal Variations and Dose Estimation of Indoor Radon (^222Rn), Thoron (^220Rn), and Their Progenies in Malwa Region, Punjab, India. CLEAN – Soil, Air, Water, 54(5), e70183.

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