Spatial distribution of gamma radiation dose rates from natural radionuclides and its radiological hazards in sediments along river Iju, Ogun state Nigeria

This study assessed the radioactivity level of Iju River sediments and its associated radiological risks exposure to human. Gamma absorbed dose rates were measured using a portable gamma spectrometer at an interval of 50 m between each point (Model No:RS-125 manufactured by Canadian Geophysical Institute). The measured absorbed gamma dose rates range from 22 to 59 nGy/h with the highest value noted in site 13. The mean activity concentrations of U-238, Th-232 and K-40 from Iju river sediments were 24.1 +/- 0.4 Bq/kg, 35.2 +/- 1.1 Bq/kg and 501.0 +/- 11.1 Bq/kg, which were lower than the world average values of 32 and 45 for U-238 and Th-232 by 25% and 21% and higher than 412 Bq/kg for K-40 by a factor of 0.22 (22%). This highest value of K-40 found in site 6 may be due to the presence of feldspartic minerals buried in the sediments. Consequently, the radiological hazard indices were below the permissible limits except the mean value of 28 x 10(-2) for excess lifetime cancer risk (ELCR) for the samples collected in site 6, which is higher than the average world value of 0.29 x 10(-3) by a factor of 0.03. The regression model indicates that Th-232 attributes more radioactivity impacts on the soil sediments than the contributions of U-232 and K-40, as such, presumed to be the radionuclide parameter controlling the depositional process in the region. (C) 2020 The Author(s). Published by Elsevier B.V.