Indoor radon, external dose rate and assessment of lung cancer risk in dwellings: the case of Ebolowa town, Southern Cameroon

The present work reports indoor Radon-222 activity concentration measurements, external gamma dose rate measurements, and assessment of cancer risk in the different dwellings in Ebolowa town, southern Cameroon. The geological formations of this studied area are mainly granites. This studied area extends over the equatorial climatic zone. The mean temperature of the zone varies from 25 degrees C to 26 degrees C with two rainy and two dry seasons with a relative humidity of (70-80) % recorded throughout the year. The indoor radon activity concentrations were carried out using RADTRACK2 devices, which are the alpha track detectors made of CR-39 plastic ?lms contained in an antistatic black holder. Each device was hung in an inhabited room of each selected dwelling for an average period of three months. Radon concentrations in dwellings ranged between (23 +/- 10) Bq m(-3) and (2620 +/- 480) Bq m(-3) with an arithmetic mean of 135.6 Bq m(-3) and a geometric mean of 63 Bq m(-3). The estimated annual effective doses due to external gamma exposure ranged from (0.15 +/- 0.01) mSv y(-1) to (0.38 +/- 0.06) mSv y(-1) with an average value of 0.26 mSv y(-1). The estimated annual effective dose due to indoor radon ranged between 0.43 mSv y(-1) and 49.6 mSv y(-1) with an arithmetic mean of 2.6 mSv y(-1). This value was below the International Commission on Radiological Protection (ICRP) recommended action level. The Excess Lifetime Cancer Risk (ELCR) ranged from 1.39% to 158% with a mean value of 8.2%. According to these results, cancer risk due to inhalation of radon-222 must be further investigated in the population living in Ebolowa town.