Abstract
Radiocesium (137Cs) 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 137Cs released into the environment following the accident has not yet reached equilibrium in the ecosystem, unlike naturally occurring cesium 133 (133Cs), and its distribution is still changing. The current distribution of 137Cs in the ecosystem, including that in plants, is thought to be approaching that of 133Cs. By clarifying the present distribution and metabolic characteristics of 133Cs, the future state of 137Cs can be estimated. Therefore, in 2015–2017, the current status of radioactive 133Cs and 137Cs in Eleutherococcus sciadophylloides and its environment were examined in six municipalities in Fukushima Prefecture. The average 133Cs concentration in current-year shoots (leaves and branches) was not correlated with 133Cs concentrations in litter (P = 0.425) or soil (P = 0.751) but was negatively correlated with soil K+ concentration (R2 = 0.2756, P = 0.025) and deposition (R2 = 0.3390, P = 0.011). The 137Cs current-year shoot concentration/litter deposition ratio (Tag) was positively correlated with 133Cs Tag (R2 = 0.5748, P < 0.001). Thus, 137Cs transfer appeared to accompany 133Cs transfer. Comparing organ-specific concentrations in trees, the current 137Cs/133Cs 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 137Cs approaches equilibrium in the ecosystem. In addition, 137Cs concentrations in sprouts may decline in forestland with high soil K+ concentrations and increase in forestland with low soil K+ concentrations. Further studies of edible wild tree sprouts are required to verify the findings and assumptions of this study.
