Baseline Radiation Survey of Osun State

ABSTRACT The radionuclides present in soil, water and selected foodstuffs taken from all the thirty local government areas of Osun State have been identified and their activity concentrations measured in order to calculate, the absorbed dose, collective effective dose equivalent and committed effective dose for the estimation of the potential biological risk/damage of naturally occurring radionuclides in the State. One hundred and twenty six samples each of soil, water, yam flour, cassava flour, maize, vegetables and eighty four samples each of meat and fish were collected from all the local governments in a way that ensured coverage of the entire State. The soil and water samples were collected from the chosen locations, while the yam flour, cassava four, maize, meat, fish and vegetable samples were bought from the local markets. Gamma ray spectrometry using high purity germanium detector was used in radionuclide identification and activity concentration determination. The radionuclides identified in the soil, water, meat, fish, vegetable and foodstuff are 238U, 232Th and 40K, as well as the man-made radionuclide 137Cs. The mean activity concentration of 238U, 232Th and 40K, in the soil were 17.5 ± 2.3 Bqkg-1 , 24.6 ± 3.1 Bqkg-1 and 216.7 ± 21.6 Bqkg-1 respectively. 137 Cs was detected in seven out of sixty three locations investigated with a mean value of 0.99 ± 0.03 Bqkg-1 . The mean specific activities for water were 3.43 ± 0.64 BqL-1 and 3.46 ± 0.72 BqL-1 for 238U and232Th respectively. The mean activity concentration of 238U, 232Th and 40K for yam were 1.72 ± 0.10 Bqkg-1 , 2.24 ± 0.21 Bqkg-1 and 37.84 ± 2.40 Bqkg-1 respectively. The content of the radionuclides in maize gave a mean value of 2.49 ± 0.48 Bqkg-1 for 238U, 2.12 ± 0.06 Bqkg-1 for 232Th and for 40K, the mean value is 30.92 ± 2.15 Bqkg-1 . The average activity concentrations of238U, 232Th and 40K radionuclides in beef samples were 2.98 ± 0.48 Bqkg-1 , 2.16 ± 0.12 Bqkg-1 and 274.44 ± 18.26 vi Bqkg-1 respectively. The mean specific activities of the radionuclides in fish were 1.95 ± 0.23 Bqkg-1 for 238U; 1.46 ± 0.11 Bqkg-1 for 232Th and 170.75 ± 9.42 Bqkg-1 for 40K. The mean specific activities of 238U, 232Th and 40K for African spinach (green) were 2.28 ± 0.11 Bqkg1 ,1.82 ± 0.32 Bqkg-1 and 48.19 ± 3.42 Bqkg-1 respectively. The total absorbed dose rate in air for Osun State ranged between 17.1 nGyh-1 and 45.4 nGyh-1 with an average value of 32.97 nGyh-1 . The committed effective doses were 0.66 µSvy-1 for the consumption of yam flour, 0.54 µSvy-1 for maize, 0.24 µSvy-1 for beef, 0.16 µSvy-1 for fish and 0.10 µSvy-1 for amaranth (green). The values obtained in this work show that there is no radiological contamination of foodstuffs consumed in Osun State. The mean annual effective dose rate for the towns and villages is 41.9 µSvy-1 and the collective effective dose equivalent for Osun state is 2.14 x 102 man-Svy-1 . This means that 214 people in Osun State (or 0.004% of the population) are at risk of incurring radiation induced diseases due to terrestrial gamma radiations from 238U, 232Th and 40K in the soil. Since the uranium and thorium specific activities fall within the earth crustal mean for normal environmental, no uranium or thorium deposit could be said to be in Osun State.