Transfer of radiocesium released in the 2011 Fukushima Daiichi Nuclear Power Station accident to Eleutherococcus sciadophylloides, a wild tree that produces edible sprouts

Radiocesium (sup(137)Cs) migration from the environment to wild tree species that produce edible sprouts was examined following the accident at the Tokyo Electric Power Company's Fukushima Daiichi Nuclear Power Station in March 2011. Compared to available data on edible herbaceous species, little is known about edible tree sprouts. The sup(137)Cs released into the environment following the accident has not yet reached equilibrium in the ecosystem, unlike naturally occurring cesium 133 (sup(133)Cs), and its distribution is still changing. The current distribution of sup(137)Cs in the ecosystem, including that in plants, is thought to be approaching that of sup(133)Cs. By clarifying the present distribution and metabolic characteristics of sup(133)Cs, the future state of sup(137)Cs can be estimated. Therefore, in 2015-2017, the current status of radioactive sup(133)Cs and sup(137)Cs in Eleutherococcus sciadophylloides and its environment were examined in six municipalities in Fukushima Prefecture. The average sup(133)Cs concentration in current-year shoots (leaves and branches) was not correlated with sup(133)Cs concentrations in litter (P = 0.425) or soil (P = 0.751) but was negatively correlated with soil Ksup(+) concentration (R**2 = 0.2756, P = 0.025) and deposition (R**2 = 0.3390, P = 0.011). The sup(137)Cs current-year shoot concentration/litter deposition ratio (Tsub(ag)) was positively correlated with sup(133)Cs Tsub(ag) (R**2 = 0.5748, P <0.001). Thus, sup(137)Cs transfer appeared to accompany sup(133)Cs transfer. Comparing organ-specific concentrations in trees, the current sup(137)Cs/sup(133)Cs concentration ratios were occasionally smaller in leaves and roots than in other organs, e.g., bark and wood. Concentrations in the former will rise to those of the latter as sup(137)Cs approaches equilibrium in the ecosystem. In addition, sup(137)Cs concentrations in sprouts may decline in forestland with high soil Ksup(+) concentrations and increase in forestland with low soil Ksup(+) concentrations. Further studies of edible wild tree sprouts are required to verify the findings and assumptions of this study.