A study of technetium 99 uptake by irrigated rice (Oryza sativa L.)

The absorption of technetium 99 (an important fission product which can be released in the environment at different steps of the nuclear fuel cycle) by rice (Oryza sativa L.) was studied in nutrient solutions and in flooded soils with contaminated water. The absorption kinetics established in water culture (continuous flowing system) for 99Tc concentrations ranging from 0.017 to 17 μCi.I-1 revealed two phases: the former corresponds to the diffusion in the apparent free spaces and the second, which is linear, represents the transfer of 99Tc from the external medium into the root cells as well as its translocation to the leaves. The study of the desorption mechanism confirmed the existence of these compartments, the second one containing more than 95% of the total activity of the plant. The biological half-life of 99Tc of the second compartment is so high that decontamination of the plant may not be expected. In soils, toxicity symptoms were observed for a 99Tc water concentration of 17 μCi.I-1. The transfer factors calculated in irrigated soils are very high (>103 for the leafy shoots) and the distribution of 99Tc between the different organs waries with the concentration used. More than 90% of 99Tc is found in the leafy shoots meanwhile 1% of the plant total activity is only found in the caryopses