Measurement of Indoor Radon Levels, Natural Radioactivity and Lung Cancer Risks Estimation

Abstract

Sustained exposure of humans to a substantial concentration of indoor radon is a cause of lung cancer. Radon and its progenies are the main contributors of radiation exposure to humans from natural sources. Therefore, indoor radon measurements play a vital role in monitoring human health and safety in dwellings and workplaces. In this regard, systematic measurements were carried out in homes, schools and workplaces. As radon isotopes are produced by the radioactive decay of radium, and radium generated from uranium or thorium decay. Hence, besides measuring indoor radon, natural radioactivity in soil was also measured. Radon exhalation rate of building materials have been measured and compared with the published data. The studies were carried out in four districts of the Punjab province (namely, Rawalpindi, Jhelum, Attock and Chakwal), Islamabad Capital Territory and four districts of the Azad Kashmir using CR-39 based radon detectors. Radon concentration measurements were performed in four districts of the Punjab province in drawing rooms, bedrooms and kitchens throughout the year in four cycles to cover all the seasons. In Islamabad Capital Territory, the measurements were carried out in dwellings situated in the basements, on ground floor and first floor. Indoor radon concentrations in dwellings are found to vary from 15 ± 4 Bq m-3 to 176 ± 7 Bq m-3. The measured maximum indoor radon levels in workplaces are found to be 165 ± 8, 194 ± 11 and 293 ± 19 Bq m-3 in first floor, ground floor and basements, respectively. The studies regarding measurement of seasonal variation of indoor radon levels and calculation of the seasonal correction factors for four districts of the Azad Kashmir, Pakistan are performed. From the measured indoor radon concentrations, weighted average for living rooms and bedrooms is calculated. Measured indoor radon concentration levels in Azad Kashmir vary from 23 ± 9 to 398 ± 2 Bq m-3. Information regarding the indoor occupancy time was also gathered through interviewing the dwellers and workers during the installation and collection of the dosimeters. Based on these interviews, an average occupancy factor of 0.5 for dwellings and 0.3 for workplaces was estimated. From the measured indoor radon concentrations, seasonal correction factors were calculated. Correlations of radon activity concentrations in different seasons for different dwellings have also been included in this study. The mean annual effective dose received by the residents of the studied area found to be 0.87 ± 0.49 mSv in dwellings for four districts of Punjab province and 2.52 ± 1.20 mSv for Azad Kashmir. Assessment of lung cancer risk using measured indoor radon levels have been calculated using UNSCEAR, US-EPA risk factors and local occupancy factor. The estimated maximum risk for indoor radon induced excess lung cancer deaths is found to be 172 ± 73 in four districts of Punjab province and 174 ± 47 in Azad Kashmir. All the estimated effective doses are found to be less than the lower limit of the ICRP recommended action levels (3-10 mSv y-1). Naturally occurring and fallout radioactive elements in soil samples which were collected from four districts of Punjab province and Islamabad Capital Territory were measured. Radium equivalent activity, indoor and outdoor annual effective dose equivalent, dose rate, internal and external hazard indices are calculated from the measured activity. The mean radium equivalent activity, dose rate and indoor annual effective dose equivalent found to be 178.36 ± 11.93 Bq Kg-1, 84.63 ± 5.27 nGy h-1 and 0.42 ± 0.03 mSv respectively. The results obtained are within the recommended safety limits.