Abstract
The radiocesium concentrations in acorns and leaves of Shirakashi (Quercus myrsinifolia) were studied in order to clarify their contamination levels and the transfer pathways of cesium radionuclides following the accident at the Fukushima Daiichi Nuclear Power Plant. The results obtained showed that the contamination level of radiocesium measured in old leaves (grown before 2010) which existed before the accident were still very high, i.e., higher than 12,000 Bq・kg-1 (sum of 134Cs and 137Cs concentrations on a fresh weight basis). However, the radiocesium concentrations in young leaves (grown 2012) were less than 300 Bq・kg-1. The concentration of radiocesium in acorns was a maximum of 305 ± 8 Bq・kg-1 in 2012. The contamination did not appear to be surface deposition because there was no difference in the concentrations between unwashed and washed acorns or between the husk and acorn nut (seed). A correlation was found in the radiocesium concentrations between old and young leaves, and also between acorns and young leaves. The ratio between acorns and young leaves was approximately 0.85. A relationship was observed between the radiocesium contamination of acorns and the area of the exposed root zone not covered with concrete on the pavement. This suggests that the root-uptake pathway should also be considered in addition to translocation from the contaminated canopy to acorns and young leaves of the trees.
