Evaluation of radiological hazards due to natural radioactivity in bituminous soils from tar-sand belt of southwest Nigeria using HpGe-Detector

Oil exploration is known to have great impact on the environment due the presence of natural radionuclides in crude oil and bitumen. In this study, high purity germanium (HpGe) detector was used to determine the activity concentrations of 40K, 226Ra and 232Th in bituminous soil and viscous bitumen samples collected from 5 different locations within the tar-sand belt of southwest Nigeria. Soil samples were collected also from a non tar-sand area to serve as control. The average concentrations of 40K, 226Ra and 232Th in the bituminous-soil samples were 139.32, 28.21 and 27.13 Bq kg-1, respectively for Agbabu, 16.09, 18.71 and 17.99 Bq kg-1, respectively for Ilubirin, 33.98, 38.90 and 29.82 Bq kg-1, respectively for Iju Oke, 35.01, 30.06 and 21.52 Bq kg-1, respectively for Ode Aye, 7.99, 4.77 and 4.08 Bq kg-1, respectively for Ode Irele. Their respective values were 306.82, 23.52 and 23.14 Bq kg-1 for the non bituminous-soil. The natural radioactivity levels of 40K, 226Ra and 232Th in the viscous bitumen samples ranged from below detection level (BDL)-30.74, 2.02-36.33 and 3.38-33.71 Bq kg-1, respectively. The estimated gamma dose rate was higher in the non-bituminous soil than that of bituminous soil. All the radiation hazard indices estimated in this study are lower than the acceptable limits. It can therefore be concluded that the soil and bitumen samples are safe for use as materials for building and road constructions.