Assessment of Human Exposure to Natural Source of Radiation on the Soil in Tongaren Constituency of Bungoma County, Kenya
Musamali, Enock Wanjala
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Radionuclides are unstable nuclei with high ratio of proton to neutron. Natural activities like volcanic eruption and anthropogenic activities expose originally concealed radioactive elements in the rocks within the earth crust. Poor agricultural practices such as excessive use of fertilizers add radioactive elements in the soil. Transport agents like run-off water and rivers, spreads these radionuclides within the soil in Tongaren Constituency. The radionuclides disintegrate to form lighter atoms by emitting radiations like alpha, beta and gamma rays. Gamma rays penetrate in to human tissue causing cancer, tumor, fibroites and lens opacification. The greatest effect of radiations was felt during Nagasaki and Hiroshima bomb where more than 40,000 people lost life in 1945 (Murray et al., 2000). Tongaren constituency is situated between latitude 000 34’ 00’’ N and longitude 340 34’ 00’’ E. The increasing cases of cancer has been an issue of global concern and with little information on the level of radionuclides in Tongaren constituency this research is conducted out to find out whether the soil is safe for human being. Agriculture being a major source of income in Tongaren the use of inorganic fertilizers containing radioactive elements, in maize production may lead to gradual accumulation of radionuclides. When radionuclides accumulate beyond the threshold level they pose danger to health of human being. This study determined the concentration levels of radionuclides in Tongaren constituency of Bungoma county. Twenty samples of soil were collected from maize plantation areas. 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 wire mesh of diameter 0.5mm 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, potassium, radium and their progeny. The activity concentration level for 226Ra, 232Th, 238U and 40K in soil samples were determined using gamma ray spectrometer with NaI (Tl). The average activity concentration for 232Th, 238U and 40K was found to be 85.0±4.3 BqKg-1 within the range (13.1-212.4), 260.3±13.0BqKg-1 within the range (34.6-484.8) and 981.5±49.1 BgKg-1 within the range (9.7-2178.5) respectively. The average radium equivalent activity was found to be 456.4±22.8 BqKg-1 while external and internal hazard indices were found to be 1.24±0.06 and1.94±0.10 respectively. According to European commission, (1999), values of index He≤ 2 corresponds to a dose rate criterion of 0.3 mSvy-1, whereas 2≤ He ≤ 6 correspond to 1.0 mSvy-1 and hence the hazard values are insignificant. The average dose rate was found to be 206.4±10 nGyh-1 within the range 36.4±1.8 nGyh-1 to 360.7±18 nGyh-1 which was below the hazard limit of 1500 nGyh-1. The annual effective dose rate was found to be 0.63±0.03 mSvy-1 within the range 0.11±0.01 mSvy-1 to 1.11±0.06 mSvy-1. These health hazard parameters were below the safe limit of 1.0 mSvy-1 since the maximum limit for annual effective dose rate is 1.0 mSvy-1 (UNSCEAR, 2001). These results reveal no significant radiological health hazards for inhabitance within the study areas.