Evaluation of radiocesium concentrations in new leaves of wild plants two years after the Fukushima Dai-ichi Nuclear Power Plant accident

Radiocesium (137Cs) transfer to plants immediately after the Fukushima Dai-ichi Nuclear Power Plant accident was investigated by collecting newly emerged leaf and soil samples between May 2011 and November 2012 from 20 sites in the Fukushima prefecture. Radiocesium concentrations in leaf and soil samples were measured to calculate concentration ratios (CR). Woody plants exhibited high CR values because 137Cs deposited on stems and/or leaves were transferred to newly emerging tissues. The CR values in 2012 declined as compared to that in 2011. Exchangeable 137Cs rates in soil (extraction rate) samples were measured at five sites. These rates decreased at four sites in 2012 and depended on environmental conditions and soil type. Both CR values and extraction rates decreased in 2012. However, CR values reflected the changes in extraction rates and characteristics of each species. Amaranthaceae, Chenopodiaceae, and Polygonaceae, which had been identified as Cs accumulators, presented no clear 137Cs accumulation ability. In 2012, the perennial plant Houttuynia cordata and deciduous trees Chengiopanax sciadophylloides and Acer crataegifolium displayed high CR values, indicating that these species are 137Cs accumulators and may be considered as potential species for phytoremediation.