Change in the chemical form of ~(137)Cs with age in needles of Japanese cedar

摘要

Radiocesium (Cs-137) derived from the accident of Fukushima Dai-ichi Nuclear Power Plant remains in forests. Although a large proportion of the Cs-137 in forests has been transferred to soils, the rates of transfer to soils depend on the chemical form of Cs-137, which determines the mobility of Cs-137 in plant tissues and subsequently during decomposition of leaf litter. In order to understand the dynamics of Cs-137 in Sugi (Japanese cedar, Cryptomeria japonica) forests, we identified the chemical forms, such as water soluble, ion-exchangeable, and residual of Cs-137, Cs-133, K, and Rb in needle-bearing Sugi branches of different ages across several years. Compared with the results for K and Rb, Cs (Cs-133 + Cs-137) tended to change from a water-soluble form to an immobilized form with aging of needle-bearing branch segments. In addition, it was observed that a larger proportion of the immobilized Cs were accumulated in the green outer portions of the stems through aging.