Differences in the distribution of radiocesium in deciduous and evergreen fruit trees: A case study

We investigated the distribution of radiocesium (¹³⁴Cs and ¹³⁷Cs) in three orchards in Tsukuba, 170 km southwest from the Tokyo Electric Power Company’s Fukushima Daiichi Nuclear Power Plant 9 months after the accident. The radiocesium was distributed mainly in the surface soil. The distribution of radiocesium differed between deciduous and evergreen plants. In deciduous blueberry (Vaccinium virgatum Aiton), the concentration was high in the old branches because the bushes had no leaves at the time of the accident. Therefore, the concentration per bush was greater in unpruned than in pruned bushes. More radiocesium was present in the trunk and rootstock of each bush, although the concentration was low. In evergreen Satsuma mandarin (Citrus unshiu Marcow), the concentration was high in the leaves, and it was higher in old leaves that expanded before the accident than in new leaves that expanded after the accident, because the old leaves were contaminated by direct deposition of the fallout. However, the total radiocesium was higher in the new leaves than in the old leaves because of the greater amount of new leaves. The radiocesium concentration in fruits was higher in trees with fewer fruits than in trees with many fruits, but the total radiocesium in fruits was higher in trees with many fruits.