Seasonal variation of indoor radon–thoron levels in dwellings of four districts of Haryana, India

Abstract

In the present work, seasonal (winter, rainy, summer) variation of indoor radon and thoron was measured for 120 days from 91 dwellings in different villages and towns in four districts (Rohtak, Sonipat, Panipat, and Jind) of Haryana using single-entry pinhole-based radon–thoron-discriminating dosimeters. The present study is imperative because a thermal power plant is present in Panipat district, and the Yamuna River passes through the Sonipat and Rohtak districts, and a high-heat-producing granite (HHPG) region is in the vicinity of the study area. Annual effective dose due to radon and thoron has been calculated by using an equilibrium factor as determined by other studies in the neighboring region. Concentrations for one year were estimated (March 2015–February 2016) from data collected for 4 months. The result shows that the annual indoor radon levels vary from 9.12 ± 1.14 to 94.23 ± 9.94 Bq/m3 with an average value of 21.66 ± 3.08 Bq/m3. The annual indoor thoron levels vary from 15.18 ± 2.85 to 105.35 ± 15.17 Bq/m3 with an average value of 52.82 ± 7.15 Bq/m3. The annual effective dose varies from 0.85 to 4.73 mSv with an average value of 2.41 mSv. The average value of annual indoor radon and thoron is lower than the limits of 100 Bq/m3 as recommended by the World Health Organization and the thoron value is higher than the worldwide average value of 40 Bq/m3. Indoor radon and thoron concentrations are highest in the winter and lowest in the summer. Concentrations of these gases in the rainy season are higher compared to the summer season. When we compare the rainy and winter seasons, concentrations of these gases are higher in the winter season. The differences in average concentrations of radon and thoron values are presented by the ratio of average radon and thoron concentrations in three seasons. Hence, the winter–summer ratio, winter–rainy season ratio, and rainy season–summer ratio of average radon concentrations in the study region are 1.72, 1.41, and 1.50, respectively. For the thoron concentration, winter–summer ratio, winter–rainy season ratio, and rainy season–summer ratio are 1.38, 1.05, and 1.38, respectively. This study area is safe from radiological effects of radon and thoron gases in confined spaces because the annual effective dose is lower than established safe limits.