Determination of 222Rn Concentration in Soils, Homes and Workplaces with its Radiological Impacts in Ondo State, Nigeria

Abstract

Soil and indoor radon concentrations were measured in 94 workplaces and 118 homes in selected cities/towns in Ondo state, south-western Nigeria with the aim of estimating the radiological effects on dwellers. The measurements were performed using CR-39 Solid-State Nuclear Track Detectors (SSNTDs). The soil radon level was measured by installing a detector at a depth of 50 cm in the soil with the aid of cylindrical PVC pipe in each of the selected workplaces and homes. A detector each was also suspended in four different apartments in each of the workplaces and homes at a height of about 1 m above the floor. The detectors were retrieved after 120 days of exposure, thereafter etched and the track counted. The geogenic maps for soil and indoor radon were drawn, to show the radon levels across the study area schematically. The results showed that the average values of soil radon levels were 2490.98 ±64.56 Bq m-3 and 2646.36 ±67.44 Bq m-3 for workplace and home respectively. The average indoor radon levels were 166.87 ±8.85 Bq m-3 and 175.09 ±9.0 Bq m-3 for workplace and home respectively. These values are within the limits of 100-300 Bq m-3 set by the World Health Organization for indoor radon. The radon reference levels for workplaces and homes are taken to be 300 Bq m-3 and 250 Bq m-3 respectively for the study area. The average annual effective dose due to exposure to radon (Eeff), equivalent dose to the lungs (Edl), the excess life-time cancer risk (ELCR) and the lung cancer cases (LCC) per year per million persons for workplace were 1.58 ±0.08 mSv y-1; 3.79 ± 0.20 mSv y-1; 4.76 ± 0.25; and 2.84x10-5 ±1.51x10-6 y-1 respectively, while those for home were 3.87 ±0.20 mSv y-1; 9.28 ± 0.48 mSv y-1; 11.7 ±0.61; and 6.96x10-5 ±3.61x10-6 y-1 respectively. The Eeff is within the limits of 3-10 mSv y-1 set by International Commission on Radiological Protection.