Verification of radiocesium decontamination from farmlands by plants in Fukushima

Daisuke Kobayashi, Toshiyasu Okouchi, Mutsumi Yamagami, Takuro Shinano

The purpose of this study was to verify radiocesium decontamination from Fukushima farmland by plants and to screen plants useful for phytoremediation. Thirteen species from three families (Asteraceae, Fabaceae, and Poaceae) of crops were grown in shallow and deeply cultivated fields (0-8 and 0-15 cm plowing, respectively). To change plowing depth was expected to make different contacting zone between root system and radiocesium in soil. The radioactivity values of the plants due to the radiocesium ¹³⁴Cs and ¹³⁷Cs were 22-179 and 29-225 Bq kg dry weight⁻¹, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the shallow field ranged from 0.021 to 0.12 and fro 0.019 to 0.13, respectively, with the geometric means of 0.051 and 0.057, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the deep field ranged from 0.019 to 0.13 and from 0.022 to 0.13, respectively, with the geometric means of 0.045 and 0.063, respectively. Although a reducing ratio was calculated to evaluate the decrease in radiocesium from contaminated soil during cultivation (i.e., phytoremediation ability), no plant species resulted in a remarkable decrease in radiocesium in soil among the tested crops. These results should be followed up for several years and further analyses are required to evaluate whether the phytoremediation technique is applicable to radioactively contaminated farmlands.