Measurement of radioactivity level of sand fraction of Nigerian oil sands for environmental impact assessment

Abstract

ABSTRACTThe radioactivity level of the sand fraction of Nigerian oil sands collected from four different locations, namely Ilubirin, Olowo-Irele, Loda, and Orisunbare, Ondo State, Nigeria, were identified and quantified with the view to assess its likely environmental and health impact of the exploration, exploitation, processing, and transportation of the fossil fuel. Soxhlet extractor was used to extract bitumen from the oil sand samples using toluene as extracting solvent. The sand fraction as left-over collected from the thimble after exhaustive extraction was dried in the oven at 70°C for 8 h to remove trace water and extracting solvent. A survey of radioactivity content and associated radiological risks was carried out on the sand fraction samples by means of a well-calibrated gamma-ray spectrometer containing Na-I (Tl) detector. The mean specific activities of 40K, 232Th, and 238U present in the analyzed sand fraction samples were 3131.17 ± 5.71, 147.90 ± 10.85, and 96.28 ± 2.59 Bq/kg, respectively. The results obtained for the absorbed dose rate (AD), annual effective dose rate (AEDR), internal hazard index (Hin), external hazard index (Hex), annual gonadal equivalent dose (AGED), and the representative levels index (Iγr) were 264.380 nGy/h, 0.324 mSv/year, 1.461 Bq/kg, 1.481 Bq/kg, 1903.073 µSvy–1, and 2.185, respectively. The AD values were higher than the population weighted average (60 nGy/h) recommended by UNSCEAR. The Hex and Hin values were above unity for the studied samples except from Ilubirin. The results follow similar trend for all the radiological parameters. The AGED values were higher than the world average (300 µSvy–1) set by UNSCEAR. The average lifetime cancer of mortality risk due to 40K, 232Th, and 238U was 2.09 × 10–3, 4.18 × 10–8, and 1.84 × 10–6, respectively, while that morbidity risks due to 40K, 232Th, and 238U were 3.07 × 10–3, 6.21 × 10–8, and 2.70 × 10–6, respectively. Radiological assessment however indicated that long-term exposure may pose an intrinsic health hazard.