RADIOISOTOPES

We evaluated the effects of pruning on the concentration and total amount of radiocaesium in Japanese chestnut trees (Castanea crenata Sieb. et Zucc. ‘Porotan’) after radionuclide deposition from the nuclear accident at the Fukushima Daiichi Nuclear Power Plant. In March 2013 (2 years after the accident), trees grown in Ibaraki Prefecture were subjected to heavy or conventional pruning, or no pruning as a control. Over the next 2 years, pruning significantly decreased the yield of fruits, but did not significantly affect the concentration of radiocaesium in new organs including fruits. Two years after the treatments, the total amount of radiocaesium in a tree was reduced by 13％ by conventional pruning and by 36％ by heavy pruning in comparison with that in control. Furthermore, the distribution of radiocaesium in a tree two years after the treatment suggested that, unlike radioactive postasium, radiocaesium in new organs was not derived from the soil through root uptake but was translocated from old branches and trunks which exposed at the time of radionuclide deposition.