¹³⁷Cs Distribution in Mulberry(Morus alba) after the Fukushima Dai-ichi Nuclear Power Plant Accident and Effect of Spray Application of a Liquid Potassium Fertilizer onto Trunk Surface

Abstract

After the Fukushima Dai‐ichi Nuclear Power Plant accident in March 2011, contamination of mulberry-leaf tea with over 100Bq kg^{－1 137}Cs was found. We therefore investigated ¹³⁷Cs distribution in mulberry trees(Morus alba) and soil in Nihonmatsu City from 2012. As a result, mulberry leaves near the end of branches(0 - 30cm), which are usually used as edible leaves, were shown to contain higher ¹³⁷Cs concentration than the others. Trunk showed highest ¹³⁷Cs concentration among the plant parts of mulberry investigated, while root ¹³⁷Cs concentration was relatively low. Autoradiographic studies for leaf, bark and cross-sectional trunk suggest that radioactive substances were deposited onto bark and leaf radioactive contamination could be due to translocation of ¹³⁷Cs from trunk. Spray application of 0.5% KH₂PO₄ solution onto trunk surface significantly reduced ¹³⁷Cs concentration in edible leaves emerged about one month after the application. However, the effect was limited and insufficient to solve the problem of radioactive contamination in edible mulberry leaves.