Transfer of Iodine and Cesium from the Surface of Leaf, Trunk or Fruit to the Interior ofApple Fruit
Hitoshi KAWABATA, Masumi YANAI, Yasuhiro TAKO
Yuichi TAKAKU, Shun'ichi HISAMATSU
Department of Radioecology
Abstract
When radionuclides are released into the atmosphere during nuclear fuel processing, some aredeposited on the surfaces of crop plants, followed by absorption and translocation to other parts of the plants.
Apples are one of the important agricultural products in Aomori Prefecture, where the first commercial
nuclear fuel reprocessing plant is undergoing final construction activities. Since the behavior of radiocesium
and radioiodine deposited on apple tree surfaces and their transfer to fruit are not well known, a research
project to determine them was launched in FY 2016. In FY 2018, we studied the absorption andtranslocation of stable Cs applied onto leaf or trunk surfaces. The Cs was applied as liquid droplets or solid
particles on these surfaces. Potted 2 year-old Plumleaf crab apple trees (Malus sp. cv. ALPS OTOME) wereused for our experiment since they are easy to grow and handle.
We cultivated the apple trees in artificial climate chambers and applied droplets of CsCl solution onto
the leaf or trunk surfaces of apple trees at early and late fruit development stages, corresponding to 87–92
and 118–119 days after flowering, respectively. Solid aerosols of NaCl containing CsCl were sprayed onto
the leaf or trunk surfaces of other apple tree groups before bearing fruit (35 to 43 d after flowering). The
whole apple trees were periodically collected after the application and separated into their parts. The
Cs-applied leaf and trunk samples were washed with solution containing detergent, followed by analyzing
the samples and the washed solution for Cs together with other plant part samples.
The washable proportion of Cs applied as liquid droplets on both of the leaf and trunk surfaces at theearly development stage, decreased in two steps, an initial rapid step and a later slow step, while that of Cs
applied at the late development stage rapidly decreased but was then followed by fairly constant values
without the later slowly decreasing step. Higher summed values of washable and un-washable proportions ofCs remaining until harvest in the applied trunk were found compared to those of Cs in the applied leaf. Thisshowed that the absorption/translocation rate from the leaf surface was higher than that from the trunksurface.
The washable Cs applied as particles on the leaf surfaces before bearing fruit also decreased in twosteps, while that on the trunk surfaces decreased in an initial rapid step followed by fairly constant values.
The washable proportions of particulate Cs in each applied part, leaf and trunk, were higher than those ofdissolved Cs applied as the droplets in the corresponding part (results in FY 2017) throughout the cultivation
period until harvest. This demonstrated the absorption rate of particulate Cs from the surfaces was lower
than the absorption rate of dissolved Cs. The summed values of washable and un-washable proportions ofparticulate Cs remaining until harvest in the applied leaf were found to be higher than those of dissolved Cs,
implying the absorption/translocation rate of particulate Cs was lower than that of dissolved Cs; however,those proportions of dissolved and particulate Cs in the applied trunk were similar to each other.

Some of the Cs applied on each surface was found in fruits in all experiments, demonstrating
absorption from the surfaces and translocation of Cs to fruits.

Remaining proportion

10.10.01●：Particle▲：Liquid0.001

020

40

60

80

100

120

140

Days after application of Cs （d）
Fig. 1 Change in remaining proportion of Cs after application of Cs. Remaining proportion of Cs wasdefined as the ratio of the amounts on leaf surfaces to that loaded initially on the leaf surfaces.
Vertical bars indicate a standard deviation of 2 or 3 samples. The lines show least squareapproximation by a function with two exponential terms of days after application of Cs.