Radiocesium accumulation properties of Chengiopanax sciadophylloides

Abstract

Through the assessments of radioactive contamination after the Fukushima Dai-ichi Nuclear Power Plant (F1NPP) accident, it has been reported that some sprouts of Chengiopanax sciadophylloides (Franch. et Sav.) at the site contained radiocesium (134,137Cs) at higher concentrations than the other plants. To assess the phytoremediation properties of C. sciadophylloides for 137Cs decontamination, we aimed to quantify the 137Cs accumulation in C. sciadophylloides. We measured the 137Cs concentrations in various organs of C. sciadophylloides collected from the forest in the town of Kawamata, Fukushima prefecture, together with the concentrations of other elements [potassium (K), rubidium, 133Cs, calcium, strontium, and manganese] present. In addition, we compared the foliar concentrations of these elements in C. sciadophylloides with those in four different deciduous tree species. The mean of foliar 137Cs concentration in C. sciadophylloides was 28.1 kBq kg−1 DW, one order of magnitude higher than that found in the other species. The 137Cs concentrations were in the order of leaves > bark > wood. The wood of the treetop, leaf scars, and roots contained higher amounts of 137Cs than that of the trunk. From the distribution of 137Cs in C. sciadophylloides, we confirmed that 137Cs tends to accumulate in the young growing parts. The difference in the distribution of 137Cs and 133Cs indicated that surface uptake of 137Cs occurs. A significant correlation between K and 137Cs concentrations in each organ was found, which suggested that 137Cs in the plant body is transferred through the same pathway as K. On the other hand, there was no correlation between foliar K and 137Cs concentrations, implying that the uptake ratio of K to 137Cs was different for each individual. To determine the factors driving specific 137Cs accumulation and/or the variability of the ratio between K and 137Cs, the distribution of 137Cs and the root in soil, the difference of the expression of transporter, and the existence of mycorrhizal fungi should be considered. However, further research is required.