Reducing Transferability of Radionuclides from Soil to Crops
Yusuke UNNO, Akira TAKEDA, Mutsumi YAMAGAMI,
Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
Countermeasures for reducing radiocesium transfer from soil to crops have been investigatedextensively after the 2011 accident at the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear
Power Station, and their effectivenesses were found to depend on many factors including types of crop andsoil. The aim of this study is to establish the countermeasures suitable for reducing radiocesium transfer fromsoil to grass and its translocation from rice shoot to brown rice. In FY 2018, we investigated: 1) soil factors
controlling the radiocesium transfer to grass from soil in the Shimokita region, Aomori; 2) the effect ofvarious methods to reduce the transfer for the selected soils in the Kamikita region, Aomori; and 3) the effectof a growth regulators on Cs translocation to brown rice.
Soil-to-grass (Dactylis glomerata L.) transfer factor (TF) of 137Cs was obtained by the small-scale
short-term cultivation experiment using soils spiked with 137Cs tracer in an artificial climate chamber.
Correlation analysis between the TFs and various soil factors, showed that the K concentration extractable byboiling in 1 M nitric acid was the best independent variable to explain the variation of TFs, suggesting that
the K supplying ability in grassland soils in the Shimokita region controls their TFs.
The reducing abilities of various soil fertilizers and additives were tested by the cultivation method
mentioned above for two soils in Kamikita region selected from the experimental results in FY 2017: bothsoils had low abilities for supplying K and retaining 137Cs. The effectiveness of the target substances wasevaluated from the viewpoint of not only reduction of 137Cs concentration but also increase of K
concentration in the grass, because too high K concentration has a harmful effect on bovines. For the firstsoil, zeolite materials showed the highest effect, which may arise from their abilities of retaining 137Cs andsupplying K. For the second soil, K and P fertilization were effective, especially from the viewpoint of K
concentration in the grass. In addition, for soil with high organic matter content, it was found that an organic
matter decomposition accelerator possibly reduced the transfer.
Two varieties of rice (Oryza sativa subsp. japonica Nipponbare and Masshigura) were grown in agreenhouse with a culture solution containing 0.01 μM Cs. The effect of spraying the plant with growth
regulators on the brown rice Cs concentration were investigated. When gibberellins (GA) was sprayed toripening stage ears after flowering of the rice plants, the Cs concentration in brown rice tended to decreaseby ~10% for both varieties. In addition, when kinetin was sprayed to the leaves of the late vegetative growthstage, the Cs concentration in brown rice tended to decrease.

Fig. 1The effect of various fertilizers and additives for transfer factor of 137Cs in two soil samples
from the Kamikita region to grass, and the shoot potassium concentration of grass plant. Redline: Feeding management using grass with K concentration lower than 20 mg/g isrecommended for dairy cattle during dry periods.