Assessment of natural radioactivity and its radiological risks in the soil of local government areas (Asa, Ilorin East, Ilorin South, Irepodun, Moro, and Oyun) in Kwara State, Nigeria

Abstract

An extensive investigation was undertaken in Kwara State, Nigeria, to evaluate the radioactivity levels in soils across six local government areas, specifically, Asa, Ilorin East, Ilorin South, Irepodun, Moro, and Oyun. Within mining sites in these regions, soil samples (n = 24) were gathered, and ²³⁸U, ²³²Th, and ⁴⁰K's specific activities were quantified via a NaI(Tl) scintillation detector. The data revealed ²³⁸U's specific activity to be in the 4.43–20.06 Bq kg⁻¹ range (average: 10.64 Bq kg⁻¹), and thus below 35 Bq kg⁻¹ as the international recommended threshold. ²³²Th's specific activity was found to be in the 1.44–12.60 Bq kg⁻¹ range (average: 6.61 Bq kg⁻¹), and thus again below the international recommended threshold of 30 Bq kg⁻¹. However, ⁴⁰K's specific activity was in the 325.96–1855.23 Bq kg⁻¹ range (average: 711.26 Bq kg⁻¹), exceeding 400 Bq kg⁻¹ as the recommended threshold. Radiological risk parameters such as Ra_eq were evaluated, with values at the studied sites being less than the UNSCEAR threshold of 370 Bq kg⁻¹. The values of the measured absorbed dose rate were in the 35.02–55.67 nGy h⁻¹ range, and thus below 57 nGy h⁻¹ as the worldwide mean. Statistical analyzes including correlation analysis and principal components analysis were also performed, where the correlation analysis showed a strong association between ⁴⁰K and radiation risk criteria, indicating that an increase in ⁴⁰K levels is associated with an increase in radiation risk. 84.3 % of the variance in the data was explained by the first principal component (PC1) through principal components analysis, which indicates the presence of strong relationships between the studied variables. These results reflect the impact of increasing mining activities on soil pollution in the region, necessitating the need for continuous monitoring to maintain environmental safety and public health.