||Seasonal change of radiocesium and potassium concentrations in Someiyoshino cherry and Japanese chestnut trees observed after Fukushima nuclear accident
Tagami, KeikoUchida, Shigeo
Radiocesium and potassium-40 concentrations in two types of trees have been measured following the accident at Fukushima Daiichi Nuclear Power Plants (FDNPP) by collecting leaf samples several times a year from 2011 to 2014. We previously found that for herbaceous plants, K measurement could not be used as analogue of Cs although Cs is known to have a similar chemical reactivity to that o f K, because their distributions in plant tissues were different. However, it was not clear whether other higher plant species, such as trees, would similarly show different Cs and K fates or not.The sampling was carried out in Chiba, 220 km south of FDNPP. Two deciduous tree species, Someiyoshino cherry (Cerasus × yedoensis (Matsum.) A.V.Vassil. ‘Somei-yoshino’) and Japanese chestnut (Castanea crenata) were used in this study. Plant samples were washed with tap water to remove dust from the surface and then they were oven-dried to a constant weight at 80˚C in an electric oven for at least 2 d. Each sample was pulverized and mixed well, and transferred to a 100-mL plastic container.Radioactivity concentration in each sample was measured by a Ge detector system (Seiko EG&G). The Cs-137 concentration decreased with time for both tree leaves, while K concentration was almost constant. For the Japanese chestnut tree, both Cs-137 and K increase was observed every spring and then the concentration decreased when season changed. The results implied that Cs and K behaviors were different in different tree species.This work has been partially supported by the Agency for Natural Resources and Energy, the Ministry of Economy, Trade and Industry (METI), Japan.