The transfer of radiocesium released in the 2011 Fukushima Daiichi Nuclear Power Station accident to bracken (Pteridium aquilinum subsp. japonicum)

Abstract

The transition pattern of radiocesium released from the 2011 TEPCO Fukushima Daiichi Nuclear Power Station accident from the environment to edible wild plants varies across species. We investigated the relationship between radiocesium in bracken (Pteridium aquilinum subsp. japonicum) and habitat conditions of bracken, such as the radiocesium mass and slope position, in four bracken communities at Iwaki (IO), Iitate (IM and IU), and Katsurao (KM) in 2017. In the bracken communities on land that was formerly pasture (IO, IM, and IU), there was no significant (P = 0.499) difference in ¹³⁷Cs concentrations between the young leaves, adult leaves, and belowground organs of bracken, while there was a difference among the research sites (P = 0.049). The exchangeable potassium (K) concentrations in soil were 0.42–1.11 cmol_c kg^-1, and there was no relationship between exchangeable K concentrations and the ¹³⁷Cs aggregated transfer factor (T_ag) from litter layer and soil to bracken leaves. Young-leaf ¹³⁷Cs concentrations were more closely related to ¹³⁷Cs mass values in soil (R² = 0.7844) than to those in the litter layer (R² = 0.4669). A strong indirect correlation (r = 0.757) was found between air dose rates (ADRs) and the concentrations of young-leaf ¹³⁷Cs via the ¹³⁷Cs mass in soil. At KM, which did not have a grazing history, the concentrations of young-leaf ¹³⁷Cs were lower than those estimated from ADRs, implying the influence of other conditions, such as more roots in deeper soil with lower ¹³⁷Cs values.