Distribution dynamics and descriptive statistical analysis of radionuclides in the farmland soils near mining areas in Southwestern Nigeria

Abstract

Human exposure to ionizing radiation in the environment is mainly due to naturally occurring radionuclides in the soils, building materials and rocks, but the level may vary depending on the anthropogenic activities prevalent in each location. Presently, in Nigeria, there are concerns due to environmental health implications of all sorts of mineral mining and processing spreading across the southwestern states of the country. This work determines the activity concentrations of naturally occurring radionuclide materials (NORMs) in the farmland soil with the aim of evaluating the radiation hazards. A total of 200 composite soil samples were taken from five states in the southwest of Nigeria, close to active mining sites at the root (0.2 m) and at deep planting zones (0.5 m) for analysis by gamma-ray spectrometry using NaI(Tl) detector. The activity concentrations of natural radionuclides in the composite soil samples were determined to vary in the order of ⁴⁰ K > ²³²Th > ²²⁶Ra/²³⁸U for all locations. In contrast to the other locations, Olode and Igbokoda had average radium equivalent activities (Ra_eq) to be 1.6 and 1.8 times, respectively, higher than the reference limit of 370 Bqkg^-1. The estimated excess life cancer risk values were lower than the 0.29 × 10^-3 global average value for soil by United Nations on Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and International Commission on Radiological Protection (ICRP). Negative and low skewness values of 0.61 and 1.20 were obtained for ⁴⁰ K in Itagunmodi, and also 0.47 and 0.66 for ²³²Th were obtained in Sagamu. The kurtosis analysis of the activity concentrations was low and negative for soil at Itagunmodi for ⁴⁰ K and ²²⁶Ra/²³⁸U; Olode for ⁴⁰ K and ²³²Th; and Igbokoda for ²²⁶Ra/²³⁸U and ²³²Th where mining activities are commonly practiced. The variation in the results has been attributed to different agriculture practices and artisanal mining operations in each location.

Keywords: Cancer risks; Farmland soil; Mining areas; Radiation hazard; Radionuclides distribution; Southwestern Nigeria.