Thesis Title: Assessment of radiation levels and their hazards in agricultural and fallow soils in trans – nzoia county – Kenya 

Students Name: Wabomba jasper sifuna

Supervisors:

1. Dr Michael Nakitare Waswa
2. Dr Peter Nyongesa Khakina

ABSTRACT

Natural radioactivity levels and radiation risks due to fallow and agricultural soils of Trans- nzoia County was measured. Trans-nzoia County is one of the counties in Kenya known for large-scale maize farming. This study analyzed natural radioactivity and radionuclides distribution in fallow and agricultural soils in Trans-nzoia County. Limited research had been done to assess the radiation levels due to primordial and anthropogenic processes in Trans- Nzoia County. The activity concentration levels of natural radionuclides (²³²Th, ²³⁸U, and ⁴⁰K) in soil samples were analyzed using NaI (TI) gamma-ray spectrometry methods. The obtained activity concentrations were used to calculate the associated radiological parameters, including; external hazard index, radium equivalent activity, and dose rates. Twenty samples of soil were collected from several sample sites. The collected samples were dried in an oven at 110 , grounded and sieved through 0.5 mm diameter wire mesh, and packed in a sealed beaker to prevent radon leakage. The samples were preserved for a maximum of 28 days to achieve secular equilibrium between thorium, uranium, radium, potassium and their progenies. The NaI (TI) spectrometer was used to determine the activity concentration level for radium, thorium uranium, and potassium in soil samples. The results for average activity concentration in fallow soil for ²³⁸U, ²³²Th and ⁴⁰K was 0.5±0.02 Bq/kg, 144±7.44 Bq/kg and 839±40.56 Bq/kg respectively. The activity concentration in agricultural soil for ²³⁸U, ²³²Th and was 0.5±0.02 Bq/kg, 184±9.87 Bq/kg and 1273±63.86 Bq/kg respectively. The indoor annual effective dose rate of the fallow soil for the collected samples had an average of 0.3±0.01 mSv/y while the agricultural soil internal hazard index averaged at 0.2±0.01 mSv/y while the outdoor annual effective dose rate for the fallow and agricultural soil had an average 0.8±0.04 mSv/y and 0.5±0.02 mSv/y respectively.Fallow soil absorbed dose rate for the collected samples had an average of 125.8±6.09 nGy/h while the agricultural soil absorbed dose rate had an average of 169±8.68 nGy/h. Fallow soil radium equivalent for the collected samples averaged at 168±8.43 Bq/kg while the agricultural soil radium equivalent averaged at 327±16.86 Bq/kg. The internal hazard index of the fallow soil for the collected samples averaged at 0.4±0.02 mSv/y while the agricultural soil internal hazard index averaged at 1.1±0.05 mSv/y while the external hazard index for the fallow and agricultural soil had an average of 0.4±0.02 mSv/y and 1.1±0.05 mSv/y respectively. The values obtained were higher than the acceptable safe limit of 1 mSvy^-1 but lower than the action level limit of 100 mSv/y. The results revealed minimal radiological health hazards for locals in Trans-nzoia County and general public around the County. The results of this research provide useful information to policy makers in the agricultural sector and other organizations such as NEMA, KBS, NFP and MOH mandated with environmental monitoring and assessment.