Assessment of Extent of Radiological Exposures in Subsurface Dumpsite Sediments around the Residential Area of Oru-Ijebu South-West Nigeria

Abstract

Assessment of naturally occurring radionuclides was carried out from 20 sampling points in a dumpsite systematically collected from varying subsurface depth intervals of 0-0.2m, 0.2-0.4m, 0.4-0.6m, 0.6-0.8m and 0.8m-1.0m, while the control samples were taken from two sampling points located 200m away from the dumpsite. The samples were consequently analyzed in the laboratory for natural radioactive emission where each activity concentration measurements of the radionuclides were determined; the natural radionuclides identified were ²²⁶Ra, ²³⁸U, ²³²Th, ⁴⁰K utilizing gamma ray spectrometry with NaI (IT) detector. The mean activity concentrations recorded in Bqkg^-1 for  ²²⁶Ra, ²³⁸U, ²³²Th and  ⁴⁰K in the subsurface soil samples were respectively 2.53±0.60, 31.50±2.01, 27.20±1.63 and 340.39±19.48 in depth 0m−0.2m; 1.96±0.37, 28.2455±2.50, 23.84±3.07 and 320.59±24.07 respectively in depth 0.2m-0.4m; 1.24±0.41, 24.197±3.66, 19.86±2.46 and 290.71±28.99 respectively in depth 0.4m−0.6m; 0.80±0.34 Bqkg^-1, 20.10±4.133, 16.10±1.54, and 259.04±34.22 in depth 0.6m−0.8m and 0.68±0.25, 18.509±2.08, 14.50±0.91 and 247±30.13 for 0.8-1.0m. The levels of radioactivity were then used to assess public dose rates and radioactive contamination thereby predicting changes in environmental radioactivity caused by poor waste management, industrial activities, and other human activities. In all the investigated sampling point ⁴⁰K exhibited the highest activity concentration in 0-0.2m depth with the value of 383.45±19.4883 while Pr exhibited the lowest activity concentration with the value of 0.08±0.4252 in depth 0.8-1.0m.  The mean activity concentration of ²³⁸U, ²³²Th and ⁴⁰K, in the soil samples at the dumpsite were 20.80, 20.3 and 291.54 Bqkg^-1respectively for 0-0.2m depth. These results were lower than the world permissible standard stated by UNSCEAR. It was generally observed that the activity concentrations reduced with 0-0.2m having the highest concentration values for both the dumpsite and the control sites, while the mean activity concentrations of ²³⁸U, ²³²Th and⁴⁰K for the control sites were found to be 31.5045±2.0123, 13.145±1.4637 and 183.415±21.4465 respectively for 0-0.2m depth.