Spatial distribution and radiological hazards assessment of naturally occurring radionuclide materials in soil from quarry sites in Ogun State, Nigeria

Abstract

Workers and dwellers around quarrying sites are exposed to naturally occurring radioactive materials (NORMs) during various activities done on the rock and earth crust. This study investigated the spatial distribution and radiological health effects of quarrying activities in ten quarry sites in three districts (Odeda, Ajebo, and Ijebu Ode) around Ogun State, Nigeria. The NORMs (⁴⁰K, ²³⁸U, ²³²Th) were assessed using a gamma spectrometer with a NaI(Tl) detector. The radiological hazards of NORMs were assessed and statistically analyzed. The activity concentration of NORMs (Bq/kg) ranged from ⁴⁰K (76.8 ± 44.8–2647.9 ± 179.4), ²³⁸U (3.2 ± 1.8–55.4 ± 24.9), and ²³²Th (5.2 ± 3.9–244.4 ± 89.8) revealing 70% of all samples above the world average limit 420(⁴⁰K), 33(²³⁸U), and 45 (²³²Th). The activity concentration of NORMs in all the sites followed in the order ²³⁸U < ²³²Th < ⁴⁰K. The radiological and health parameter ranges for the adsorbed dose rate (D_R) 3.0–339.92 (nGy/h), radium equivalent (Ra_eq) 5.88–739.4 (Bq/kg), annual effective dose equivalent outdoor (AEDEout) 3.72–417.16(µSvy⁻¹), excess lifetime cancer risk (ELCR × 10⁻³) 0.01–1.46, and exposure rate (ER) 13.10–1531.47(µRh⁻¹). The radiological hazard parameters are 2–3 times higher than their world averages in most of the samples thus discouraging the usage of the soil for building and ecological activities. This study showed that radionuclides are priority pollutants with high impact and with high exposure risk tendencies in all the quarry sites investigated and therefore unsuitable for ecological and building activities.