Post-commissioning Radiological Assessment of Soil and Water Around Dangote Refinery, Lagos, Nigeria

Abstract

A post-commissioning radiological assessment was conducted to evaluate the radiological status of soil and water in three host communities, Idaso, Ilege, and Mobido, located around the Dangote Petroleum Refinery in Ibeju-Lekki, Lagos, Nigeria. Seven composite soil samples and three composite water samples were collected and analysed by gamma-ray spectrometry using a 3″ × 3″ NaI(Tl) detector. The activity concentrations of naturally occurring Potassium – 40 (40K), Uranium -238 (238U) and Thorium -232 (232Th) were determined, and selected radiological parameters, including absorbed dose rate, annual effective dose, radium equivalent activity, external hazard index and annual ingestion dose, were evaluated. Mean soil activity concentrations (Bq/kg) were 191.29 ± 11.74, 16.17 ± 5.13 and 14.53 ± 3.78 for 40K, 238U and 232Th, respectively, all below the corresponding UNSCEAR reference values. In water, mean activity concentrations (Bq/L) were 71.73 ± 14.76, 4.45 ± 3.53 and 2.04 ± 0.97 for 40K, 238U and 232Th, respectively. The mean absorbed dose rate for soil and the corresponding mean annual effective dose were 24.22 nGyh-1 and 0.030 mSvy-1, respectively. The mean radium equivalent activity in soil was 51.68 Bq/kg and the mean external hazard index was 0.140, indicating a low external gamma-radiation hazard. However, the total annual ingestion dose due to water intake from 238U and 232Th ranged from 0.277 to 0.770 mSvy-1, with a mean of 0.489 mSvy-1, exceeding the 0.1 mSvy-1 reference criterion. The findings indicate that the post-commissioning radiological status of the study area is generally within the evaluated reference levels for external exposure, but the elevated ingestion dose estimates warrant continued monitoring and further assessment of radionuclide contributions in water.