Decontamination effects of bark washing with a high-pressure washer on peach [Prunus persica (L.) Batsch] and Japanese persimmon (Diospyros kaki Thunb.) contaminated with radiocaesium during dormancy

The effect of bark washing with a high-pressure washer on deciduous trees contaminated during dormancy by radiocaesium fallout derived from the Fukushima Daiichi Nuclear Power Plant accident was examined using peach [Prunus persica (L.) Batsch] and Japanese persimmon (Diospyros kaki Thunb.). Eighteen-year-old peach trees (‘Akatsuki’) were bark-washed twice with a high-pressure washer on July 5 and 27, 2011. Seven-year-old peach trees (‘Kawanakajima Hakuto’) were bark-washed on January 24, 2012, and thirty-year-old Japanese persimmon trees (‘Hachiya’) were bark-washed on December 21, 2011. For the peach trees, most of the bark was not removed by washing with a high-pressure washer. In contrast, the rough bark of Japanese persimmon was removed completely. No significant differences in the¹³⁷Cs concentration of ‘Akatsuki’ fruit were found between the treatments conducted in the summer of 2011. Upon the bark washing of peach ‘Akatsuki’ trees in summer, the possibility of secondary contamination of leaves via the leachate containing¹³⁷Cs was likely. The¹³⁷Cs concentrations in fruits and leaves of peach ‘Kawanakajima Hakuto’ collected in summer 2012 were decreased significantly by washing treatment conducted in winter 2011-2012. In the year after treatment, the¹³⁷Cs concentrations in fruits and leaves of Japanese persimmon were significantly decreased by the treatment. The effect of the bark washing on decreasing¹³⁷Cs contents in fruits and leaves was greater in Japanese persimmon than in peach. The results for ‘Kawanakajima Hakuto’ and ‘Hachiya’ demonstrated the possibility of additive contamination.