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

Background: 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. Materials and Methods: 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. Results: 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 %). Conclusion: 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.