Transfer of Radionuclides from the Atmosphere to Agricultural Products
Shogo IMADA, Ryuji ARAI, Hitoshi KAWABATA, Yasuhiro TAKO, Takashi TANI,Masumi YANAI, Yuichi TAKAKU
Department of Radioecology
Abstract
314While radionuclides ( H, C,129I etc.) are released into the atmosphere from the first commercial nuclear

fuel reprocessing plant in Aomori Prefecture, the transfer of such radionuclides to commercially important
agricultural products grown in the prefecture, such as fruit trees (especially, apple) and Chinese yam plants
has not been adequately understood. In addition, under some abnormal situations, it is probable that thereprocessing plant will discharge radiocesium. The first purpose of this research project is to obtain empiricalparameters for the transfer of 14C to apples and Chinese yams and for the transfer of radioiodine andradiocesium to apples by conducting tracer experiments using stable isotopes. The second purpose is tocontribute to realistic dose assessment in the future through the accuracy improvement of the advanced
environmental transfer and dose assessment model (AdvETDAM).
In FY 2020, the data for the transfer of stable carbon isotope (13C) to each plant organ after 13CO2 exposure
experiments and for the growth of the plant organs were obtained in mature apple trees. These data are neededfor extending the model developed for young apple trees to mature apple trees. Furthermore, the method forcarrying out cultivation experiments of Chinese yam in growth chambers was developed and the data related
to growth in each plant organ were obtained. In addition, the parameters for the transfer and accumulation ofiodine (I) and cesium (Cs) applied on the surface of each plant organ of apple and for the weathering of theelements from the surface were obtained.
For the research on 14C transfer to crop plants, an in-situ exposure chamber system was developed for 16year old ‘Fuji’ apple (Malus domestica) trees grafted on JM. 1 rootstock. 13CO2 exposure experiments to matureapple trees were conducted three times from September to October and the data for the concentrations of photoassimilated 13C in each plant organ were obtained over time. For two mature apple trees, the size of each plantorgan on 12 branches in each of the trees was nondestructively measured over time and the biomass of eachplant organ at a whole-tree level and corresponding C content were determined in mid-November, so that
temporal variations in the C mass of each plant organ at a whole-tree level were estimated. Temporal variations
in plant organ biomass of Chinese yam (Dioscorea opposita ‘nagaimo’) were also determined under fieldconditions. In addition, Chinese yam plants were cultivated from propagules in growth chambers to check theeffect of pot size on plant growth, and growth patterns of leaf and rhizophore in the field were reproduced
using pots of 30 to 40 cm in depth and 15 to 25 cm in inner diameter.
For the research on weathering and transfer of I and Cs, three subjects were investigated with two typesof apples: 1) the effect of rainfall on the weathering of I applied onto fruit surfaces of ‘Fuji’ apple trees (M.
domestica) as dry aerosol; 2) the effect of rainfall on the weathering of Cs applied onto bark surfaces of ‘Fuji’
apple trees as dry aerosol; and 3) the absorption and translocation of stable I- applied onto leaf surfaces of‘Alps Otome’ apple (M. domestica) trees as liquid droplets. More I was removed from the fruit surfaces as therainfall intensity increased and as the rainfall duration increased. Cs applied onto the bark surface was removed

slightly, but rainfall intensity and duration had little effect. I applied on the leaf surface was absorbed throughthe surface and accumulated inside the leaf, but the transfer of absorbed I to the fruit was negligible.

Fig. 1 A photo during the 13CO2 exposure experiment using a mature apple tree in an orchard.

(Mean ± S.D., N = 3)0.02

13C/(13C + 12C)

0.018
LeavesCurrent branches
Fruits

0.016
0.014
0.012
0.01
9/16

Fig. 2

9/26

10/6

10/16

10/26

11/5

Temporal variations in 13C/(13C + 12C) in theleaves, current branches, and fruits of mature apple
trees exposed on September 17, October 6, andOctober 21. Data were collected at 0, 24, 48, 72,
and 144 h after the exposure finished.

250

C mass (mol C)

200
150
10050
00Fig. 350100150
Days after bud break (DAB)

200

250

Temporal variations in the C mass of the leaves(BL(t), FL(t)), current branches (BB(t)), and fruits ofa mature apple tree (BF(t)).