Transfer of Tellurium and Cesium from Nutrient Solution to Radish (Raphanus sativus var. sativus) and Their Distribution in the Plant

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1 Jpn. J. Health Phys. 50 () 89 9 (205) Report Transfer of Tellurium and Cesium from Nutrient Solution to Radish (Raphanus sativus var. sativus) and Their Distribution in the Plant Keiko FUJIWARA,* Tomoyuki TAKAHASHI,*, 2 Tadatoshi KINOUCHI,* Satoshi FUKUTANI,* Yuki HATTORI* 2 and Sentaro TAKAHASHI*, 2 Received on December, 20 Accepted on September, 205 Various radionuclides, including radioactive tellurium (Te), were released to the environment by the Fukushima nuclear power plant accident. The total amount of Te-2m released from the power plant was estimated to be. 5 q. The radioactive Te may have contributed to the internal radiation dose at the initial stage of the accident. However, data on the environmental behavior of radioactive Te are limited. In this study, therefore, the uptake of Te in plants was investigated. Radishes (Raphanus sativus var. sativus) were cultivated into a nutrient solution, grown for 200 days, and then their ne roots (taproots in the plant anatomy) and a part of eshy roots (hypocotyls in the plant anatomy) were immersed for two hours into nutrient solutions with different Te and Cs concentrations. After soaking, plants were returned to the initial Te- and Cs-free nutrient solution for further maturation. ICP-MS measurements were made to assess concentrations of Te and Cs in the plants leaves and eshy roots (the ne roots were removed). Resulting differences among the individual plants were large. The leaf/ eshy root ratios of the concentration of Te and Cs were and on a fresh-matter basis, respectively. oth Te and Cs were absorbed by the radishes through the ne roots. There was a general tendency for Te to be retained in the eshy roots, whereas Cs was mainly absorbed by the ne roots and then transferred to the leaves. KEY WORDS: transfer, tellurium, cesium, Fukushima nuclear power plant accident, transfer factor, radish. I INTRODUCTION Various radionuclides, including cesium, iodine, tritium, and noble gases, were released into the environment by the Fukushima nuclear power plant accident in 20. Regarding the resulting radioactive tellurium (Te) exposure, the Nuclear and Industrial Safety Agency estimated the total amount of Te- 2m released to be. 5 q. ) ecause of this signi cant amount of the released Te-2m and its relatively long halflife of 9 d, it possibly contributed to internal dose to people through foodstuff harvested in the area affected during the early stage of the accident. There is a plethora of experimental data available on the behavior of radionuclides in the environment, especially for such nuclides as Cs-, I- and Sr-90, which have been thought to be important for evaluating the human radiation doses caused by the nuclear accident. On the other hand, * Division of Radiation Safety and Control, Kyoto University Research Reactor Institute; 2, Asashironishi, Kumatoricho, Sennan-gun, Osaka 59009, Japan. fujiwara@rri.kyoto-u.ac.jp * 2 Graduate School of Agriculture, Kyoto University; Yoshida Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto , Japan. parameters of environmental behavior are still limited for some radionuclides including radioactive Te. Little is known about the behavior of Te in the environment. The transfer factor (TF) of a radionuclide can be a useful parameter for estimating internal radiation doses through foods. While only one value is given as the TF of Te in the IAEA technical report, 2) some researchers have noticed important behavior of Te in the environment after this accident. ) The range of TF for stable Te obtained by previous studies with eld observations under a variety of conditions is signi cantly wide. ) It is necessary to accumulate new experimental data on the behavior of radioactive Te because of the wide range from these eld data and the limited experimental data. In this study, the transfer and the distribution of Te through the root systems to other parts of a plant were determined experimentally in radishes (Raphanus sativus var. sativus) grown under hydroponic culture conditions that allowed rigorous constraint of parameters in uencing Te transfer within the limits of recognized nutrients in the solution. The radish plant was selected due to its easy cultivation and short harvest period. The behavior of Cs was also investigated using the same experimental protocols, and the results were compared with Te.

2 90 Keiko FUJIWARA, Tomoyuki TAKAHASHI, Tadatoshi KINOUCHI, Satoshi FUKUTANI, Yuki HATTORI and Sentaro TAKAHASHI II MATERIALS AND METHODS Seeds of radish cultivar (ATARIYA Co., Ltd) were placed on vermiculite immersed in deionized water to germinate. Through four experiment runs, total ten sets of ve individual germinated plants were moved to a nutrient solution (Fig. ) seven days after germination and continued to grow under 22.0 C, 60% relative humidity (RH), and long-day conditions (6h light, 8h dark) in an incubator (EYELA FLI-2000, TOKYO RIKAKIKAI Co., Ltd). The nutrient solution was composed of major nutrients ( mm Ca(NO ) 2, mm KCl, 0.5 mm mgso, 0.25 mm (NH ) 2 HPO, and 0.8 mm Fe(III)- EDTA) and micronutrients (6 M H O, 9 M MnCl 2, 0.8 M ZnSO, 0. M CuSO, and 0.08 M (NH ) 6 Mo O 2 ) in deionized water. One set of the plants was allocated for each experimental condition, i. e. Te and Cs concentrations in immersing solution and time interval from immersion to harvest. Twenty to thirty days after the start of the culture, the ne roots and a part of eshy roots of the plants were immersed for 2-hour immersion into a nutrient solution containing 0.5 or.0 mg/l Te and.0 mg/l Cs. After immersion, the ne and eshy roots were washed with nutrient solution including no Te nor Cs. Then the plants were returned to the Te- and Cs-free nutrient solution and continued to be cultured for lengths of one, three, seven, and ten additional days. The Te and Cs solutions were prepared from the commercial tellurium standard solution (Te 00, Wako) and CsCl (99.9%, Wako) at ph. The form of Te changes from HTeO 2 + to HTeO at ph 5.5 in the solution. ) A ph of was chosen in this initial study to investigate the behavior of HTeO 2+. As plants showed no growth inhibition for 2 hours at ph in preliminary experiments, contact time was set 2 hours for subsequent parts of the experiment. After harvest, plant bodies were divided into three portions of leaf including stem, eshy root (hypocotyls in the plant anatomy), and ne root (taproots in the plant anatomy). The eshy root and leaf including stem were used as the study sample (Fig. ). Radishes were then dried at 080 C (CD.5S, Isuzu Seisakusho Co. Ltd). The fresh and dry weights of samples were measured (Table ). After drying and powdering the samples, approximately 0 mg of each sample was dissolved by microwave-assisted pressure digestion (Topwave, Analytik Jena Japan Co. Ltd.) with 5 ml of 0% pure HNO (EL grade; Kanto Chemical Co. Inc.) and.2 ml of 0% pure H 2 O 2 (EL grade; Kanto Chemical Co. Inc.). When less than 0 mg of powdered sample was obtained, the entire sample Fi g. How to soak the plants (upper pane) and how to divide for samples (bottom pane). Five plants as one set were soaked in the nutrient solution. : Level of nutrient solution for hydroponic cultivation or the solution with Te and Cs. : Each radish plant body was settled in a circle hole of a supporting plate. : A sample was cut and divided into Leaf (I), Root (II) and ne root parts. II : Root sample (taproot in the plant anatomy) Table Fresh and dry weight of samples. Fresh Dry Experiment to harvest Part * 2 weight weight (g) * (g)* Root.2 ± ± 0. control Leaf. ± ± 0. Root.2 ± ± 0. Leaf 8.2 ± ± 0.2 Root.5 ± ± 0. Leaf 6.0 ± ± 0.2 Root 5.5 ±.0 0. ± 0. 2 Leaf 8. ± ± 0. Root 2.6 ± ± 0.2 Leaf 2.6 ± ± 0. Root.6 ± ± 0.0 Leaf.5 ±. 0. ± 0. Root.6 ± ± 0.0 Leaf. ±. 0. ± 0. Root. ± ± 0. Leaf 6.8 ± ± 0. Root.2 ± ± 0.2 Leaf.6 ±.6 0. ± 0. Root 2. ±.9 0. ± 0. Leaf. ±.2 0. ± 0.2 * Average weight ± standard deviation (n =5). * 2 Root.6 ±. 0.2 ± 0. Leaf 6. ± ± 0.2

3 Transfer of Tellurium and Cesium from Nutrient Solution to Radish (Raphanus sativus var. sativus) and Their Distribution in the Plant 9 was dissolved. The dissolved samples were then diluted with pure water and Te and Cs concentrations were quanti ed with a double-focusing sector eld ICP-MS (Element 2, Thermo Fisher Scienti c) or quadrupole ICP-MS (HP-500, Yokogawa, Japan). The experiments were then repeated under various other conditions. The detailed protocols of each experiment are shown in Table 2. III RESULTS AND DISCUSSIONS The concentrations of Te and Cs in eshy roots and leaves with stems are shown in Tables. The values are expressed as mean ± standard deviation (n = 5). There was a large variance among individual plants, especially for the concentration of Te in the eshy roots. The concentrations of Te in the eshy roots seven days or ten days after the immersion were higher than the concentrations measured on Table 2 Conditions of soak. Experiment Element Concentration (mg/l) to harvest ph ORP (mv) Te.0*. 2 2 Te + Cs 0.5,.0* 2,,.8 89 Te + Cs.0*,.2 0 Te + Cs.0*,,,. 5 * Each experiment is for 2-hour immersion. *.0 means.0 mg/l of Te and.0 mg/l of Cs. * 2 0.5,.0 means 0.5 mg/l of Te and.0 mg/l of Cs. the rst day. This nding may be explained by the involvement of ne root. The ne roots were discarded at harvest because they were entwined and it was dif cult to divide the ve plants in each set. ut, samples of entwined ne roots, which were day after immersion radishes experiment 2 and from and days after immersion radishes in experiment, were measured. The concentration of Te in the dry ne roots of day after immersion radishes was 629 mg/kg and that of Te in the dry ne roots of and days after immersion radishes were,28 and 880 mg/kg, respectively. The ne roots showed much higher Te concentrations than eshy root and leaf. This result may indicate signi cant absorption of Te in the ne roots or adsorption of large amount of Te on the ne roots. Some Te might be moved to nutrient solution or into eshy roots. Therefore, the eshy roots of radishes apparently continued to absorb Te even or days after immersion. The mechanisms related to the higher concentrations of Te in the ne roots are not readily apparent from the present experiment. It should be clari ed by the further investigations. There was no signi cant difference found in Te concentrations between plants immersed in Te-only solutions and Te and Cs solution. The leaf/ eshy root ratios of concentration (the Leaf/Root ratios, (mg/dry-kg)/(mg/dry-kg)) of Te and Cs were calculated and are shown in Table. The results show tendency of lower Leaf/Root ratio of Te than that of Cs in the corresponding sample. The Leaf/Root ratios of Te were almost less than.0. This shows that Te uptake from root is easy to stay in the eshy root of radish. On the other hand, the Leaf/Root ratios of Cs were up to 5. This result shows that Experiment to harvest 2 Table Te and Cs concentrations in dry samples and in fresh samples. Part* 2 Te/dry-sample* Cs/dry-sample* Te/fresh-sample* Cs/fresh-sample* (mg/kg) (mg/kg) (mg/kg) (mg/kg) Root.90 ± ± 0.25 Leaf 0. ± ± 0.0 Root 0.9 ±.26.9 ± ± ± 0. Leaf 0.0 ± ± ± ± 0.2 Root 2.50 ± ± ± ± 0.0 Leaf 0.86 ± 0..9 ± ± ± 0.0 Root.5 ±.2.5 ± ± ± 0.0 Leaf 0.6 ± ± ± ± 0. Root.52 ±..05 ± ± ± 0.0 Leaf 0.8 ± ± ± ± 0.02 Root. ± ± ± ± 0.02 Leaf 0. ± 0..2 ± ± ± 0. Root 6.96 ± ± ± ± 0.02 Leaf.2 ± 0..0 ± ± ± 0.0 Root.56 ± ± ± ± 0.0 Leaf.6 ± ± ± ± 0.0 Root.8 ± ± ± ± 0.0 Leaf. ± ± ± ± 0.05 Root 2.0 ± ± ± ± 0.0 Leaf 0.68 ± ± ± ± 0.00 * Average concentration ± standard deviation (n =5). * 2

4 92 Keiko FUJIWARA, Tomoyuki TAKAHASHI, Tadatoshi KINOUCHI, Satoshi FUKUTANI, Yuki HATTORI and Sentaro TAKAHASHI Table Leaf/Root ratios of Te and Cs in fresh and dry samples. Experiment to harvest Leaf/Root* ratio of Te* 2 Leaf/Root* ratio of Cs* 2 fresh samples dry samples fresh samples dry samples 0.29 ± ± ± ± ± 0.. ± ± ± ±.9.96 ± ± ± ± ± 0.5. ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±.6.9 ± ± ± 0.. ±.5.80 ± ± ± ±.9 2. ±.22 * * 2 Leaf/Root ratio of average concentration ± standard deviation (n =5). Cs uptake from root is easy to move from root to leaves. TF of selected radionuclides from some soils to radishes under continuous-exposure condition have been investigated in a previous study and the Leaf/Root ratios of Cs (from TFs on a fresh-matter basis) were found to be ) In this study, the Leaf/Root ratios of Cs were (mg/wet-kg)/(mg/wetkg). Under hydroponic and continuous-exposure condition, the shoot/root concentration ratios of Cs in Calendula alata, Amaranthus chlorostachys, and Chenopodium album have been reported as (mg/dry-kg)/(mg/dry-kg). 6) These values in the present study were (mg/dry-kg)/(mg/ dry-kg). It is very interesting that under different conditions (soil or nutrient solution, continuous uptake or one-time soaking) the Leaf/Root ratios of Cs indicate approximately the same level. In this study, the Leaf/Root ratio of Te was signi cantly lower than that of Cs in each experiment, indicating differences in the movement and metabolism of Te and Cs in the plants. The absorbed Te was mainly retained in the eshy roots, whereas Cs was initially absorbed by the ne roots and rapidly transferred to the leaves. These ndings partly con rm the previous study, which showed that Cs behaves similarly to K in plants and is retained mainly in leaves. 5) In previous studies on Cs uptake in hydroponically grown bean plants (Phaseolus vulgaris L.), ) Calendula alta, Amaranthus chlorostachys and Chenopodium album 6) and giant milkweed (Calotropis gigantea R. Br.), 8) the concentration ratios of Cs in a dried part of plants ( q/ g or mg/kg)/cs solution ( q/l or mg/l) were reported to be 8250, 20060, and 050, respectively. In this study, the concentration ratios of Cs in a dry part of plants (mg/kg) / Cs solution (mg/l) were , substantially lower than those of previous studies. We attribute this difference to the role of ph, set in our study at. Some data of Cs at ph 6.8 indicated greater Cs concentration ratios (from 68 to 58 in dry plants/cs solution). It is supposed that the abundance of H + in the soaking solution obstructed Cs + absorption into the plant. Much of the data of TF for Cs and the data for Te were given as the value from soil to plant ) (concentration of dry sample/ concentration of dry soil) including IAEA data. 2) Therefore, in the future experiments radish plants will be cultured with soil instead of liquid culture to determine the TF and to compare the ndings with previous results. Furthermore, it is necessary that an experiment also be conducted under various ph levels, because Te would be characteristically different under different ph conditions. Under new conditions there is a possibility that the concentration of Te in radish plants might change if the form of Te in the solution changes. V CONCLUSIONS Te and Cs were absorbed by radish plants. Te was absorbed and retained in the eshy roots, whereas Cs was absorbed by the ne roots and then primarily moved to the leaves. The averages Leaf/Root ratios of Cs ((mg/kg)/(mg/kg)) were and on fresh and dry-matter bases, respectively. The average ranges of Leaf/Root ratios of Te ((mg/kg)/(mg/ kg)) were and on fresh and dry-matters bases, respectively. ACKNOWLEDGEMENTS This work was supported by JSPS KAKENHI Grant Number 250. REFERENCES ) Ministry of Economy; Trade and Industry, Data on the amount of released radioactive materials. Available at: pdf, Accessed 2th November 20. 2) IAEA; Handbook of parameter values for the prediction of radionuclide transfer in terrestrial and freshwater environments, Technical Reports Series No. 2, IAEA (202). ) G. YANG, J. ZHENG, K. TAGAMI and S. UCHIDA; Soil-to-crop transfer factor of tellurium. Chemosphere,, (20). ) M. POURBAIX; Atlas of Electrochemical Equilibria in Aqueous Solutions. National Association of Corrosion

Transfer of Tellurium and Cesium from Nutrient Solution to Radish (Raphanus sativus var. sativus) and Their Distribution in the Plant 9 Engineers (9), Houston. 5) T. BAN-NAI and Y.

5 Transfer of Tellurium and Cesium from Nutrient Solution to Radish (Raphanus sativus var. sativus) and Their Distribution in the Plant 9 Engineers (9), Houston. 5) T. BAN-NAI and Y. MURAMATSU; Transfer factor of radioactive Cs, Sr, Mn, Co and Zn from Japanese soils to root and leaf of radish. J. Environ. Radioact., 6, 2526 (2002). 6) R. MOOGOUEI, M. BORGHEI and R. ARJMANDI; Phytoremediation of stable Cs from solutions by Calendula alta, Amaranthus chlorostachys and Chenopodium album. Ecotoxicol. Environ. Safety,, (20). ) J. F. CLINE and F. P. HUNGATE; Accumulation of potassium, cesium, andrubidium 86 in bean plants grown in nutrient solutions. Plant Physiol., 5, (960). 8) S. EAPEN, S. SINGH, V. THORAT, C. P. KAUSHIK, K. RAJ and S. F. D SOUZA; Phytoremediation of radiostrontium ( 90 Sr) and radiocesium ( Cs) using giant milky weed (Calotropis Chemoshere, 65, 2020 (2006) fujiwara@rri.kyoto-u.ac.jp

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