ROOT-UPTAKE OF RADIOIODINE BY RICE PLANTS

Root-uptake of iodine by rice plants from two different soil types was studied using an I-125 tracer. At harvest, the I-125 concentration wa s lowest in brown rice (hulled rice) followed by the rachis, stem and leaves. The transfer factors of iodine for brown rice grown on Andosol and Gray lowland soil (fine texture) respectively were 0.007 and 0.00 2. The ratio of the radioiodine concentrations between flag leaf (firs t leaf blade) and brown rice was about 400. Transfer factors in plants grown on Andosol were higher than those grown on Gray lowland soil. T his may be related to the high I-125 concentration in the Andosol soil solutions, particularly after the flowering period. The adsorption an d desorption of iodine in the soil was effected by flooding with water and also by the cultivation of rice plants. The radioiodine concentra tion in the soil solutions first increased in the upper soil layer the n in the lower layer. The desorption pattern of iodine was influenced by the soil types.