Root-uptake of radioiodine by rice plants

Root-uptake of iodine by rice plants from two different soil types was studied using an 125I tracer. At harvest, the 125I concentration was 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 0.002. The ratio of the radioiodine concentrations between flag leaf (first leaf blade) and brown rice was about 400. Transfer factors in plants grown on Andosol were higher than those grown on Gray lowland soil. This may be related to the high 125I concentration in the Andosol soil solutions, particularly after the flowering period. The adsorption and desorption of iodine in the soil was effected by flooding with water and also by the cultivation of rice plants. The radioiodine concentration in the soil solutions first increased in the upper soil layer than in the lower layer. The desorption pattern of iodine was influenced by the soil types.