Measurement of (40K, 238U and 232Th) and Associated Dose Rates in Soil and Commonly Consumed Foods (Vegetables and Tubers) at Okitipupa, Ondo State, Southwestern Nigeria

The aim of this present study is to collect soil samples and some commonly consumed food materials in Ondo State, Nigeria such as tubers (cassava, Manihot esculent and yam, Dioscorea alata) samples and vegetables (waterleaf, Talinium triangulare and bitter leaf, Vernonia amygdalina) samples at some selected locations in Okitipupa, Ondo state, Southwestern, Nigeria in order to determine the following natural radionuclides (40K, 238U and 232Th) levels using a well calibrated NaI(TI) which is well shielded with a detector coupled to a computer resident quantum MCA2100R Multichannel. The transfer factors, annual absorbed dose rate and the annual effective dose in the samples collected were estimated.

The results showed that the measured natural radionuclides were present in the mean concentrations of 323.79 ± 12.45 Bqkg-1, 81.87 ± 45.30 Bqkg-1 and 57.62 ± 18.04 Bqkg-1 for 40K; 11.76 ± 36.03 Bqkg-1, 4.67 ± 10.12 Bqkg-1 and 3.45 ± 2.10 Bqkg-1 for 238U and 9.66 ± 0.89 Bqkg-1, 3.07 ± 2.45 Bqkg-1 and 2.45 ± 0.92 Bqkg-1 for 232Th for soil, yam and cassava samples respectively. The results also showed that the radionuclides were present in the concentrations of 11.76 ± 36.03 Bqkg-1 and 9.66 ± 0.89 Bqkg-1 for 40K; 9.67 ± 8.53 Bqkg-1 and 7.87 ± 1.89 Bqkg-1 for 238U and 8.63 ± 6.08 Bqkg-1 and 6.58 ± 0.76 Bqkg-1 for 232Th for waterleaf and bitter leaf samples respectively. The soil-to-yam transfer factors were found to be 0.26, 0.40 and 0.32 for 40K, 238U and 232Th and soil-to-cassava yam transfer factors were found to be 0.18, 0.29 and 0.25 for 40K, 238U and 232Th respectively. The soil-to-waterleaf transfer factors were found to be 0.37, 0.82 and 0.82 for 40K, 238U and 232Th while the soil-to-bitter leaf transfer factors were found to be 0.32, 0.74 and 0.68 for 40K, 238U and 232Th respectively.

The mean absorbed dose rate was 25.08 ± 0.57 and the mean annual outdoor effective dose was 46.17 . The annual effective dose reported for this present study area represents 65.95% of the world average value of 70.00 and 47.11% of Nigeria value of 98.00 mSvy-1