Reducing Transferability of Radionuclides from Soil to Crops
Akira TAKEDA, Mutsumi YAMAGAMI, Yusuke UNNO
Yuichi TAKAKU, Shun’ichi HISAMATSU
Department of Radioecology
Abstract
Countermeasures for reducing radiocesium transfer from soil to crops have been investigatedintensively after the 2011 accident at the Tokyo Electric Power Company Fukushima Dai-ichi Nuclear PowerStation, and their effectivenesses were found to depend on many factors including types of crop and soil. Theaims of this study are to establish the countermeasures suitable for reducing radiocesium transfer from soil tograss and its translocation from rice shoot to brown rice. In FY 2017, we investigated: 1) soil factors
controlling the radiocesium transfer to grass from soil in the Kamikita region, Aomori; 2) trials of various
methods to reduce the transfer; and 3) the effect of a transpiration inhibitor on cesium translocation to brownrice.
Soil-to-grass (Dactylis glomerata L.) transfer factor (TF) of 137Cs was obtained by the small-scale
short-term cultivation experiment, which was established in FY 2016, using soils spiked with 137Cs tracer inan artificial climate chamber. The TFs of 137Cs in soils from the Kamikita region were generally higher thanthose in soils from other regions outside of the prefecture. Correlation analysis between the TFs and varioussoil factors, such as exchangeable 137Cs concentration and radiocesium interception factor, showed that thepotassium concentration extractable by boiling in 1 M nitric acid was the best independent variable toexplain the variation of TFs, suggesting that the potassium supplying ability in grassland soils in theKamikita region controls their TFs.
The reducing abilities of various soil fertilizers and additives were tested by the cultivation method
mentioned above for two groups of soil that were selected from the experimental results in FY 2016: soils
with low potassium-supply ability and soils with low 137Cs-retention ability. For the first group, all of thepotassium fertilizers and materials tested showed the reducing effect of TF, with the highest by potassium
chloride, which is a fast-acting fertilizer. For the second group, some zeolite and vermiculite materials, whichwere additives for fixing 137Cs, showed the highest effect, and that effect might be strengthened by theirpotassium-supply ability.
Rice plants (Oryza sativa subsp. japonica) were cultivated in sand-filled pots, installed in a rain shelter,with cultivation solution containing 0.01 μM Cs. A transpiration inhibitor (0.7% wax concentration) was
sprayed on the whole rice plant, twice a week during three developing stages: 1) late vegetative growth, 2)
the young panicle formation - blooming and 3) the blooming – harvest stages. The rice plants sprayed with
the inhibitor during 1)-3) stages and the control with water spraying were also prepared. The Cs
concentration in brown rice decreased 25% more than the control by spraying during 1)-3) stages, while
decreases of 20%, 15% and 0% were found for the spraying during 1), 2) and 3) stages, respectively.

Fig. 1 Relationship between transfer factor of 137Cs from soil to grass and potassium
concentration extractable with boiling 1 M nitric acid in soil.
Blue circles indicate soils from grassland in Kamikita region in Aomori.
Orange circles indicate soils from other regions outside the prefecture
including Iwate, Miyagi, Fukushima and Tochigi.