Soil-to-cassava plant transfer factor of natural radionuclides on a mining impacted soil in a tropical ecosystem of Nigeria

Abstract

The transfer factors (TFs) of naturally occurring radionuclides, 238U and 232Th from soil to different cassava plant compartments were calculated. Cassava is widely cultivated in Nigeria and contributes significantly to the food supply of the nation. There is sparsity of data on the TFs in Nigeria, and no TF data from any African country were included in the International Atomic Energy Agency's compilation of TFs for the tropical ecosystem. Samples of tin tailings and soil samples from virgin land were used to formulate three soil groups; group-A (soil from virgin land only), group-B (tailings only) and group-C (equal dry mass combination of tailings and soil from virgin land). Pot experiments were set up to determine the TFs of 238U and 232Th. The activity concentrations of 238U and 232Th in the dried samples of the soil and plant compartments were determined using a sodium iodide detector. The TF of 238U ranged from below detection limit (BDL) to 0.01 in the tuber samples, BDL to 0.23 in the stem samples and BDL to 0.90 in the leaf samples, while the TF of 232Th ranged between 0.006 and 0.49 for tuber samples, 0.03 and 0.65 in stem samples and 0.03 and 1.54 in the leaf samples. There were significant difference in the TF of 238U and 232Th between the soil groups. The leaf compartment generally had most of the highest TF values while the tuber samples had most of the lowest TF values for both radionuclides.