Transfer pathways of 54Mn, 57Co, 85Sr, 103Ru and 134Cs in rice and radish plants directly contaminated at different growth stages

In order to study radionuclide transfer pathways related to direct contamination of plants, the above-ground parts of rice and radish plants were sprayed with a solution containing 54Mn, 57Co, 85Sr, 103Ru and 134Cs in a greenhouse at 5 or 6 different times. Showing little difference among radionuclides, the interception factor increased as plants grew to maturity. Its highest observed value was 0.94 in rice and 0.83 in radish. Weathering losses of the intercepted activity by harvest were 32–89% in rice and 32–85% in radish depending on application time and radionuclide. Half lives for weathering loss were estimated to be longer on the whole for earlier applications. The translocation factor varied with application time by factors of 6–110 for hulled rice seeds and 2–23 for radish roots depending on the radionuclide. It varied with radionuclides by factors of 6–800 depending on application time and plant species. It was highest in the plants sprayed during active seed growth for rice and during early plant growth for radish. In general, 134Cs and 57Co had the highest translocation factors followed by 54Mn, 85Sr and 103Ru. Based on the experimental results, radionuclide concentrations in the edible parts of mature plants were predicted for unit deposition.