Radiological hazards associated with natural radioactivity in topsoil and subsoil from Osogbo, Nigeria

The present research used gamma-ray spectrometry to assess the amount of activity concentration for radionuclides (²²⁶Ra, ²³²Th and ⁴⁰K). That naturally exist in samples of topsoil and subsoil in Osogbo, Osun State, Nigeria, using a sodium-iodide detector and associated radiological risk factors were estimated. The activity levels of ²²⁶Ra, ²³²Th and ⁴⁰K are, respectively, ranges from 167.03 ± 4.37 to 1187.51 ± 178.68 Bqkg⁻¹, 18.21 ± 23.97 to 134.79 ± 60.00 Bqkg⁻¹ and 8.67 ± 4.80 to 188.65 ± 7.33 Bqkg⁻¹ for subsoil, and ranges from 263.64 ± 5.39 to 3303.33 ± 14.47 Bqkg⁻¹, 23.90 ± 32.28 to 191.05 ± 72.93 Bqkg⁻¹ and 9.90 ± 5.90 to 129.17 ± 8.94 Bqkg⁻¹for topsoil. According to the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the global average activity levels for these radionuclides are ²²⁶Ra (35 Bq/kg), ²³²Th (30 Bq/kg), and ⁴⁰K (400 Bq/kg). In the study area, the average activity levels of these radionuclides were found to be higher in subsoil compared to topsoil. The estimated average of radiological risk factors (radium activity, the absorbed dose rate, annual gonadal dose equivalent, excess lifetime cancer risk, and representative level index) are recorded, 166.52 Bq/kg, 78.62 nGy/h, 545.23 μSv/y, 0.38 and 1.21 For subsoil respectively, but for topsoil are recorded 184.39 Bq/kg, 90.39 nGy/h, 637.92 μSv/y, 0.44 and 1.40 respectively. All radiological risk factors are much greater than those reported by UNSCEAR (2000) magnitudes of 370 Bq/kg, 59 nGy/h, 300 μSv/y, 2.9 × 10-4, and 1, respectively. The results obtained reveal a high radioactivity level in the investigated area. Therefore, it is advised that the study region have regular radiation monitoring and ecological evaluations.