Reducing Transferability of Radionuclides from Soil to Crops
Mutsumi YAMAGAMI, Akira TAKEDA, 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 clarify factors controlling transferability of radiocesium from soil to crops, and toestablish the countermeasures suitable for agricultural products in Aomori. A type of grass and rice wereselected as our target products, and two things were done in FY 2016: 1) the establishment of anexperimental method to study reduction of radiocesium transfer from soil to grass, and 2) the investigation of
the effect of a transpiration inhibitor on cesium transfer to brown rice.
We established methods of soil analyses for evaluating the retention capacity of radiocesium in soil,
making chemical speciation of potassium and radiocesium in soil, and measuring microbial activities in soil
to study soil characteristics relating to radiocesium transfer from soil to grass. A small-scale cultivation
experiment system using soils spiked with 137Cs tracer was developed for the measurement of transfer of137

Cs from soil to one type of grass (Dactylis glomerata L.). Twenty-nine soil samples were collected from

Aomori, Miyagi, Fukushima and Tochigi Prefectures and used for the preliminary experiment by theestablished methods. Higher soil-grass transfer of 137Cs was found in soils with low ability for potassium
supply and radiocesium retention.
Two commercial transpiration inhibitors containing wax or paraffin were selected to test the effect on
the transfer of stable Cs absorbed from the cultivation solution to brown rice. Rice plants (Oryza sativa subsp.
japonica) were cultivated in a rain shelter, in sand-filled pots and cultivation solution. The transpiration
inhibitor (2% or 0.7% wax concentration, or 1.8% or 0.7% paraffin concentration) was sprayed on the whole
rice plant, twice a week from the vegetative growth stage until harvest. The cultivation solution, which waschanged every two weeks, had Cs concentration of 0.05 μM from the vegetative growth stage until harvest.
The Cs concentration in brown rice decreased 25%-35% by spraying the transpiration inhibitor compared tothe control with water spraying. Dry weight of the above-ground part and yield components, such as numberof spikelets per plant and percentage of ripened grains, were not affected by the spraying of transpiration
inhibitors in comparison to the control. Similar decreasing effects of Cs concentration were observed for rice
plants grown using cultivation solution with 0.01, 0.05 or 0.1μM Cs and spraying 0.7% wax transpiration
inhibitor in the same manner as mentioned above. When we sprayed 0.7% wax transpiration inhibitor onto
the whole plant from the vegetative growth stage to the blooming stage, then sprayed the inhibitor onto oneof the ears, leaves/stem, and whole plant until harvest, the decreasing level of Cs concentration in brown rice,which was cultivated with 0.05 μM Cs cultivation solution, was not affected by the different plant parts being
sprayed.

Cesium concentration (ng mg-1 Dw)
Fig. 1. Small scale plant cultivation systemdeveloped for evaluating transfer factor ofradiocesium from soil to a type of grass
during 3 d – 24 d after seeding.

Fig. 2. Effect of transpiration inhibitor on cesium
concentration in brown rice of rice plant.