Evaluation of radon exhalation rate and excessive lifetime cancer risk in Dumpsites in Ondo city Southwestern Nigeria

Ondo city in Ondo State Nigeria includes Ondo East and West could be described as a research city due to antecedent number of research institutes. Dose due to radioactivity content of soil samples from sixteen waste dump sites in Ondo, Southwestern Nigeria was determined using gamma-ray spectrometer in order to evaluate the radiation hazard health profile and excess lifetime cancer risk ELCR. The weighted average value of radon emanation coefficient, mass exhalation rate, concentration in soil gas and surface exhalation rate were 10.5%, 15.2 µBq kg-1 s-1, 2.2 kBq m-3 and 18.8 mBq m-1s-1. The weighted mean concentrations obtained were 354 ± 53, 58±14 and 23 ± 2Bq kg-1 for 40K, 226Ra and 232Th respectively. Radium equivalent activity (119.11Bq kg-1), Outdoor external dose (54.26 nGy h-1), Indoor external dose (107.04 nGy h-1), and total average annual effective dose (0.59 mSv y-1) were obtained. From the measured γ-rays spectra, elemental concentrations were determined for 232Th (mean 5.8ppm), 226Ra (mean 4.8ppm) and 40K (mean 1.1 %). Thorium was lower than world average 7.4ppm by a factor of 1.3; radium was higher than the world average (2.8 ppm) by factor 1.7 while potassium was relatively equal to world average (1.3 %). The total excess lifetime cancer risk ELCR was found to be 1.95 x 10-3 which was slightly higher than the world average. In addition, a good correlation was found between the radium concentration and radon exhalation rate in the area.