ASSESSMENT OF NATURAL RADIOACTIVITY AND SOIL-TOTUBER TRANSFER FACTOR IN TUBER CROPS FROM EKITI STATE, SOUTH WEST, NIGERIA

Abstract

Activity concentrations of some natural radionuclides (40K, 232Th and 238U ) in tuber crops and soil samples collected from eight(8) different towns of Ekiti State have been measured. The activity concentrations of 40K, 232Th and 238U in tuber crops (cassava, cocoyam and yam) and their soils from the spot of where they were planted in strategic areas of Ekiti State have been measured using Gamma Ray Spectrometer Hyper Pure Germanium Detector. The mean activity concentrations of 40K, 232Th and 238U for the tubers were found to be 31.970 ± 4.308, 2.409 ± 0.389 and 1.381 ± 0.241 in Bqkg-1 (dry weight). The mean activity concentrations of natural radionuclides and standard deviation of 40K, 232Th and 238U in the soils where they were planted are 225.887 ± 9.932, 14.894 ± 1.98, 7.670 ± 1.174 and 108.601 ± 34.980, 6.590 ± 1.998, 4.096 ± 1.200, in Bqkg-1 respectively. The soil-to-tuber transfer factor(TF) of 40K, 232Th, and 238U for cassava, cocoyam and yam, were measured and 238U (TF) values from soil-to- cocoyam were found to be higher than those of yam and cassava. The transfer factors (TF) for 40K from soil to yam were found to be higher than those of cassava and cocoyam. The mean absorbed dose rate, annual effective dose, annual gonadal dose equivalent for the soils from the locations were estimated to be 24.202 nGyh-1, 0.0297 mSv y-1 and 0.172 mSv y-1 respectively. Results of external and internal radiation hazard indices were obtained and found to be less than unity. The excess lifetime cancer risk was calculated to be 9.0 using the risk factors of International Commission on Radiological Protection and Biological Effects of Ionizing Radiation. All measured natural radioactivity, doses, hazard indices, transfer factor and excess lifetime cancer risk were all found to be within the recommended limits. This work provides a good baseline data of natural radioactive element for tubers and soils of Ekiti State and its radiological impacts. It implies that consumers of tuber crops in Ekiti State are not at health risk.