Natural radioactivity levels in agricultural soils in trans Nzoia county, Kenya

Samples of soil were collected from the selected regions of agricultural activities in Trans – Nzoia county, Kenya. Three adjacent soil samples were mixed up from each sampling point to get twenty representative (composite) soil samples. The soil samples were dried at 1100C, grounded and sieved through a wire mesh of diameter 0.5 mm and packed in plastic beaker that were sealed to prevent leakage of radon. The soil samples were kept for 28 days for secular equilibrium to be reached between the activity of uranium, thorium and potassium, radium and their progeny. The activity concentration level for 232Th, 238U and 40K in soil samples were determined using gamma ray spectrometer with NaI (TI). The average activity concentration for 232Th, 238U and 40K was found to be 171±8.56 BqKg-1 with the range of 32±1.6 – 414 ± 20.73, 0.5±0.02 BqKg-1 with the range of 0.3±0.01-1.7±0.08 and 1059±52.96 BqKg-1 with the range of 301±15.07-1541±77.07 respectively. The average radium equivalent activity was found to be 326±16.3 BqKg-1 while external and internal hazard indices were found to be 0.8±0.04 and 0.8±0.04 respectively. These results reveal minimal significant radiological health hazards for inhabitants within the selected study areas.