Transfer factor of radionuclides from soil-to-palm oil produced from Elere palm tree plantation near Ibadan Oyo state, Nigeria

Abstract

The migration of contaminants including radionuclides from soil-to-plant system is usually predicted by mathematical models commonly employed in a soil-to-plant transfer factor for activity concentration. Local palm trees found mostly in Nigeria are very tall and their fruits are used for production of red palm oil. Ibadan and its environs including Elere are underlain by crystalline basement complex which is known to be rich in natural radionuclides. Hence enhanced radioactivity and soil-toplant transfer factor influenced by physical-chemical form of the radionuclides in the soil and types of plant could be obtained. The study is aimed at determining the radioactivity levels of 40K, 238U and 232Th in the soil and palm oil; and calculating the soil to palm oil transfer factor. A total number of 20 palm trees were randomly selected in the study areas. From each palm tree, bunches of palm fruits were collected to prepare palm oil and the soil samples at the spot of the tree were also collected. The activity concentration of the natural radionuclides were determined using a single crystal 0.51cm x 0.51cmNaI (Tl) detector coupled through a Hamamatsa (R1306NSV3068) photomultiplier tube to a Multichannel Analyser, MCA (2100R:01). The activity concentrations of 40K, 238U and 232Th in palm oil ranged from 50.48 Bqkg^-1 to 112.16 Bqkg^-1; 6.35 Bqkg^-1to 12.80 Bqkg^-1and 6.08 Bqkg^-1to 10.13 Bqkg^-1 respectively. The activity concentrations of 40K, 232U and 232Th in the soil samples ranged from 412.43 Bqkg-1to 672.16 Bqkg^-1; 10.25 Bqkg^-1to17.43 Bqkg^-1and 8.12 Bqkg^-1to 12.48 Bqkg^-1respectively. The mean transfer factors were 0.17±0.02, 0.27±0.06 and 0.28±0.02 for ⁴⁰K, ²³⁸U and ²³²Th respectively. The ⁴⁰K, ²³⁸U and ²³²Th radioactivity levels in the soil are comparable to the world average values of 420Bqkg^-1, 32 Bqkg^-1and 40 Bqkg^-1respectively. The transfer factors indicated that about 17%, 27% and 28% of ⁴⁰K, ²³⁸U and ²³²Th respectively are transferred from soil to the palm.

Keywords: radionuclide, transfer factor, mathematical model, palm oil, Ibadan