Estimation of transfer factor from soil to cassava in Ethiope East, Delta State, Nigeria

Abstract

Cassava is a very important staple food crop in Delta state. The aim of this research is to assess the activity concentration level and determine the transfer factor of radionuclide from soil to cassava in Ethiope Local Government Area of Delta state, Nigeria. The activity concentration of ⁴⁰K, ²³⁸U and ²³²Th in soil and cassava samples collected from the study area were analysed using gamma spectrometry. A lead-shielded 3 x 3 inch coaxial type Sodium Iodide Thallium [NaI(TI)] doped detector crystal (Model No. 802 series, Canberra Inc.) coupled to a Canberra series multichannel Analyzer (MCA) (Model N0.1104) through a preamplifier was used. The results of the activity concentration in soil samples indicate that, 40K has the highest mean activity concentration ((38.66 ± 3.69) BqKg⁻¹) with the highest value ((62.47 ± 5.67) BqKg⁻¹) recorded at E2. The mean activity concentrations of 238U and 232Th are 3.65 ± 0.90 BqKg⁻¹ and 0.46 ± 0.05 BqKg−1respectively. The peak values of ²³⁸U and ²³²Th are 5.07 ± 1.17 BqKg⁻¹ and 0.98 ± 0.11 BqKg⁻¹. From cassava, 40K varies from 75.06 to 200.08 BqKg⁻¹ with the highest mean activity concentration of 99.62 ± 8.32 BqKg⁻¹ and 200.08 ± 14.90 BqKg⁻¹ as the highest value noted at C5. The mean activity concentrations of 238U and 232Th are 3.89 ± 0.93 BqKg⁻¹ and 0.81 ± 0.09 BqKg⁻¹ respectively. The maximum values of ²³⁸U and ²³²Th determined from the computation from cassava samples are 11.10 ± 2.48 BqKg⁻¹ and 1.70 ± 0.18 BqKg⁻¹. The results of this study show that the activity concentration of ⁴⁰K, ²³⁸U and ²³²Th in the study area are lower than world average values of 420, 30 and 35 BqKg^-1 in soil and cassava respectively, and it is therefore not harmful if consumed. The mean transfer factor of ⁴⁰K, ²³⁸U and 232Th from soil to cassava are 3.12 ± 0.44, 0.95 ± 0.31 and 2.96 ± 0.91 respectively. The range of values of ⁴⁰K, ²³⁸U and 232Th varied as 1.41 to 5.82, BDL to 2.98 and 0.21 to 9.35 correspondingly. Peak values of the TF were noted as 5.82 for ⁴⁰K at E8, C8, 2.98 for ²³⁸U at at E9, C9 and 9.35 for 232Th at E9, C9. The high value of TR is accredited to the richness of the organic matter in the soil. The quick recycling of natural radionuclides through the soil-cassava suggests the presence of an internal cycling that help the build-up of the natural radionuclides.