Soil-to-maize Transfer Factor of Natural Radionuclides in a Tropical Ecosystem of Nigeria

Abstract

Soil-to-plant transfer factor (TF) is a parameter utilized in predicting the accumulation of radionuclides in the plant system. Virgin soil from an uncultivated area and tailings from an abandoned tin mining site were used to formulate three soil groups. Group A (virgin soil only), group B (tailings only) and group C (equal mixture by mass of the virgin soil and tailings). Pot experiments were performed using the soil groups to determine the transfer factors of 40K, 238U and 232Th in maize (Zea mays L.) plants for the tropical ecosystem of Nigeria. The activity concentrations of 40K, 238U and 232Th in the soil groups and the maize plant compartments (seed, stem, leaf and root) were determined using NaI(Tl) gamma-detector. The geometric mean (GM) of the TF values for 40K, 238U and 232Th respectively ranged from 0.02 to 0.27, below detectable limit (BDL) to 0.008 and 0.01 to 0.09 in the in the seeds; 0.04 to 1.74, BDL to BDL and 0.01 to 0.29 in the stems; 0.03 to 0.93, BDL to 0.33 and 0.02 to 0.08 in the leaves and 0.03 to 1.29, 0.05 to 0.38 and 0.08 to 0.41 in the roots.. Potassium-40 had the highest TF values and exhibited the plant accumulation strategy for all the plant compartments. The stem samples had the highest TF for 40K and BDL values for 238U for all the soil groups. Significance differences were observed only in the accumulation of 40K and 232Th across the soil group.

Keywords: Radioactivity, potassium, mining, Gamma-ray detectors, calibration