放射線災害復興学報告書
コース名

放射能環境保全コース

氏

髙田 モモ名○放射線災害復興学に関して（放射線災害復興に関する考え，携わってきた経緯，研究経過等を記載）

Various radionuclides were released into the environment after the Fukushima Daiichi nuclear power plant(FDNPP) accident following the Great East Japan Earthquake in March 2011 (Endo et al., 2012; Yoshida andKanda, 2012). The accident was the most serious radiation disaster and caused the most widespreadcontamination since the Three Mile Island nuclear power plant accident in the USA in March 1979 and theChernobyl accident in the former Soviet Union (now Ukraine) in April 1986. Many other discharges ofradioactive material from nuclear facilities to the environment have occurred, including discharges from
Sellafield in the UK in the 1970s (Aarkrog et al., 1983), discharges in the Mayak area in South Ural in theformer Soviet Union (now Russia) in the late 1940s and the 1950s (Kryshev et al., 1998), and discharges at
the Savannah River site in the USA in the 1950s and 1960s (Carlton et al., 1994). The radioactive
contamination discharged during these events spread over natural ecosystems, such as forests, because mostnuclear facilities are in sparsely populated rural areas. Large areas of forest ecosystems were also
contaminated during the Chernobyl and Fukushima accidents (IAEA, 2006; Hashimoto et al., 2013).
Contamination in forest areas not only negatively affects the ecosystem and human lives but it can also be an
important and long-lasting source of contamination to residential areas. Studies of radionuclide dynamics(specifically, studies of 137Cs, which has a long half-life of 30.17 years) in forest ecosystems, including ofradionuclide cycling in the ecosystems and discharges to other systems, are therefore important because they
provide information that could be useful when recovering from a radiation accident. Such studies provide
evidence that is useful when developing plans for remediation activities in forest ecosystems and forprotecting the workers involved in the activities. Such studies are also required before forest resources (timberand non-timber products) will be used after an accident.
As I studied carbon cycle in a forest ecosystem in tropical region previously, I found that dynamics
of radioactive cesium in a forest ecosystem is closely related with carbon cycle in a forest, such as litterfall
and litter decomposition. In addition, through my field survey in the tropics, I understood that in so-called
developing countries, more people deeply relay on forest products compared to Japan. As several developingcountries have plans to build commercial nuclear facilities (World Nuclear Association fromhttp://www.world-nuclear.org/information-library/country-profiles/others/emerging-nuclear-energy-countries.
aspx), I thought that emergency preparedness for radiation disaster in forest ecosystems is very important forthe developing countries; prediction of dynamics of radioactive materials in a forest ecosystem, and creatingsocial systems that people stop using forest products immediately in an emergency situation. Many developingcountries that have plants to build commercial nuclear facilities are located in tropical regions. In this climate
zone, deposition of large amounts of radioactive materials in forest ecosystems has never occurred. Therefore,prediction of dynamics of radioactive materials needs to be studied thoroughly from the view of climaticparameters (e.g. carbon cycle) in such regions.
In my doctoral study, I conducted a quantitative study on dynamics of radioactive cesium in mixeddeciduous forests in Fukushima focusing on carbon cycle in the Fukushima forests.
Aarkrog, A., Dahlgaard, H., Hallstadius, L., Hansen, H., Holm, E. (1983) Radiocaesium from Sellafield
effluents in Greenland waters. Nature 304: 49–51.
Carlton, W.H., Murphy Jr., C.E., Evans, A.G. (1994) Cesium in the Savannah River Site Environment. Health
Physics 67: 233–244.
Endo, S., Kimura, S., Takatsuji, T., Nanasawa, K., Imanaka, T., Shizuma, K. (2012) Measurement of soil
contamination by radionuclides due to the Fukushima Dai-ichi Nuclear Power Plant accident andassociated estimated cumulative external dose estimation. Journal of Environmental Radioactivity 111:
18–27.
Hashimoto, S., Matsuura, T., Nanko, K., Linkov, I., Shaw, G., Kaneko, S. (2013) Predicted spatio-temporal
dynamics of radiocesium deposited onto forests following the Fukushima nuclear accident. Scientific
Reports 3: 2564.
IAEA (2006) Environmental Consequences of the Chernobyl Accident and their Remediation: Twenty Yearsof Experience. Report of the UN Chernobyl Forum Expert Group “Environment”, IAEA, Vienna.
Kryshev, I.I., Romanov, G.N., Sazykina, T.G., Isaeva, L.N., Trabalka, J.R., Blaylock, B.G. (1998)
Environmental Contamination and Assessment of Doses from Radiation Releases in the Southern Urals.
Health Physics 74: 687–697.
Yoshida, N., Kanda, J. (2012) Tracking the Fukushima radionuclides. Science 336: 1115–1116.
○学位論文題目
Spatio-temporal changes in 137Cs inventory in soils in neighboring mixed deciduous forests of Fukushima Daiichi
nuclear power plant○学位論文要旨（プログラムで修得した放射線災害復興学との関係性が判るように記載）
137Cs derived from the Fukushima Daiichi nuclear power plant (FDNPP) in 2011 is expected to contaminate

the surrounding forest environment for a long time. Precise studies of 137Cs dynamics in a forest ecosystem arerequired for developing remediation activities in forest areas, radiation protection for local residents andworkers, and resuming the use of the forest resources. I studied temporal changes in 137Cs dynamics in forest
ecosystems and environmental parameters influencing on the spatial heterogeneity of 137Cs after the FDNPP
accident from August 2013 (2.3 years after the accident) to November 2015 (4.7 years). The surveying 137Cs
contained in litter layers to soil 10 cm depth in mixed deciduous forests, approximately 40 km northeast fromFDNPP. I focused following three topics; (1) spatial variation of soil 137Cs in forest soils, (2) temporal changes

in vertical distribution of 137Cs, and (3) downward migration of dissolved 137Cs in forest soils. Based on themeasurements and analysis on the sampled 137Cs, I found that almost all 137Cs deposited on forest ecosystems
translocated to litter layers and surface soils (> 5 cm) via litterfall and precipitation by the beginning of thestudy, and they accounted for approximately 65% and 25%, respectively. Due to the translocation via
precipitation, spatial heterogeneity of soil 137Cs was predicted to be the largest during this period between theaccident to beginning of the study. By August 2014, 80% of 137Cs in litter layers in August 2013 migrated into
surface soil through litter decomposition process and leaching, and approximately 80% of 137Cs in the forest
ecosystems remained in the surface soils. The spatial heterogeneity in the surface soils became relatively
homogenous due to the migration. After August 2014, 137Cs activities in the litter layers, the surface soils andthe deeper soils (< 5 cm) did not change largely, suggesting that the so-called the “quasi-equilibrium” state(increase or decrease in 137Cs activity was not observed in any compartment in an ecosystem; IAEA, 2006)”
may have started in the forests. However, small amounts of dissolved 137Cs still migrated after August 2015.
The dissolved radioactive cesium shows high mobility and is biologically available although it was very smallamounts. Therefore, I suggested that the long term monitoring on dissolved 137Cs in forest soils should beconducted. In addition, I found that 137Cs dynamics from forest canopy to soils was largely affected by carbon
dynamics in a forest ecosystem. As similar trends of 137Cs dynamics were also reported in many studies onradioactive cesium derived from the Chernobyl accident in 1986 in the former Soviet Union (now Ukraine),
the temporal change in the present study was faster than the results shown in Chernobyl. The difference in twoareas (Fukushima and Chernobyl) may be attributed to the difference in rates of carbon dynamics in forest
ecosystems affected by such as annual temperature, forest type, and precipitation. As for the nuclear energy
development and preparedness, radioactive cesium dynamics needs to be studied thoroughly from the view ofclimatic parameters.
○その他学術雑誌に掲載された論文

１

著者名：Takada M, Yamada T, Ibrahim S, Okuda T
論文題目：Spatial variation in soil respiration in relation to a logging road in an upper tropical hill
forest in Peninsular Malaysia
雑誌名：Tropics（査読制度あり）
巻（号），頁，発行年：Vol. 24，（No. 1）1 頁-9 頁，2015

2

著者名：Takada M, Yamada T, Liang N, Ibrahim S, Okuda T
論文題目：Soil respiration change immediately after logging operations in an upper tropical hill forest,
peninsular Malaysia
雑誌名：HIKOBIA（査読制度あり）
巻，頁，発行年：Vol.17，3 頁-9 頁，2015

3

著者名：Takada M, Yamada T, Kadir WR, Okuda T
論文題目：Spatial and temporal variations in soil respiration hot spots in a lowland tropical rain forest,

Peninsular Malaysia
雑誌名：Tropics（査読制度あり）
巻（号），頁，発行年：Vol. 25，（No. 2）77 頁-83 頁，2016
4

著者名：Takada M, Yamada T, Takahara T, Okuda T
論文題目：Spatial variation in the 137Cs inventory in soils in a mixed deciduous forest in Fukushima,
Japan
雑誌名：Journal of Environmental Radioactivity（査読制度あり）
巻，頁，発行年：Vol. 161，35 頁-41 頁，2016