ELEMENTAL AND RADIOACTIVITY ANALYSES OF ROCK AND SOIL SAMPLES FROM SOME SELECTED SITES IN ONDO AND EKITI STATES, NIGERIA

Abstract

The activity concentrations of natural radionuclides and the elemental compositions in soils and rocks of some selected sites in Ondo and Ekiti states have been determined. The activity concentrations of 238U, 232Th and 40K were determined using high purity germanium (HPGe) detector. The neutron activation analysis (NAA) method was used to determine the elemental compositions of the rock and soil samples. The results showed that the activity concentrations of 238U, 232Th and 40K in the rock samples ranged from 12.11 ± 1.82 to 42.63 ± 6.40 Bq kg-1, 39.74 ± 5.96 Bq kg-1 to 90.67 ± 13.60 Bq kg-1, 401.49 ± 60.22 Bq kg-1 to 749.38 ± 112.41 Bq kg-1 respectively, while those of the soil samples varied from 4.84 ± 0.73 Bq kg-1 to 17.05 ±2.56 Bq kg-1, 10.11 ± 1.52 Bq kg-1 to 29.58 ± 4.44 Bq kg-1, 64.24 ± 9.64 Bq kg-1 to 293.64 ± 44.05 Bq kg-1 respectively. The rocks of the study area showed elevated levels of natural radionuclides compared to the soils of the area. The mean concentrations of the major and minor elements in the rock and soil samples followed the order Al ˃ Ca ˃ Na ˃ K > Mg ˃ Fe ˃ Ti and Mn ˃ Ba ˃ V ˃ As ˃ Cr ˃ Ni ˃ Zn ˃ Cu respectively. The results of the statistical analysis carried out using SPSS software showed varying trends of linear relationships between the natural radionuclides and the elemental compositions of the rocks and soils. The radiation hazard indices were calculated in order to assess the radiological effect of ionizing radiation emitted by the rocks and soils of the study area. For the rock samples, the mean values of the absorbed dose rate in air (D), indoor and outdoor annual effective dose equivalent (AEDE), radium equivalent activity (Raeq), annual gonadal equivalent dose (AGED), external hazard index (Hex), internal hazard index (Hex), representative gamma index (Iγ), outdoor and indoor excess lifetime cancer risk (ECLR) are 71.82 nGy h-1, 88.08 μSv y-1, 352.34 μSv y-1, 155.61 Bq kg-1, 508.40 mSv y-1, 0.42, 0.49, 1.15, 0.31, 1.23 respectively, while the mean values for soil are 20.64 nGy h-1, 25.31 μSv y-1, 101.25 μSv y- 1, 44.79 Bq kg-1, 145.80 mSv y-1, 0.12, 0.14, 0.33, 0.09, 0.35respectively. All the radiation hazard indices for the rocks and soils of the study area were lower than the maximum permissible limit of 1 mSv y-1, 370 Bq kg-1, 300 mSv y-1 for AEDE, Raeq, AGED, and 1 for Hex, Hin, Iγ and ECLR with the only exception of AGED, Iγ and ECLR (indoor) for the rocks which had higher mean values than their respective maximum permissible limits. The results of the geo-accumulation index calculated to determine the contamination level of heavy metals in the soils of the study area indicate that the soil of Akure, Idanre, Oke-Igbo, Ilawe, Aramoko, and Efon-Alaye are uncontaminated with the heavy metals measured while Ado-Ekiti, Ikere and Igbara-Odo soils are moderately contaminated with Arsenic (As). The macro and micronutrients measured are sufficient for plant growth except potassium, which is deficient. However, addition of fertilizer to the soil would increase plant yield, but could increase the natural radioactivity levels in the soils of the study area.