title: Estimation of absorbed radiation dose rates in wild rodents inhabiting a site severely contaminated by the Fukushima Dai-ichi nuclear power plant accident.
abstract: The dose rates of radiation absorbed by wild rodents inhabiting a site severely contaminated by the Fukushima Dai-ichi Nuclear Power Plant accident were estimated. The large Japanese field mouse (Apodemus speciosus), also called the wood mouse, was the major rodent species captured in the sampling area, although other species of rodents, such as small field mice (Apodemus argenteus) and Japanese grass voles (Microtus montebelli), were also collected. The external exposure of rodents calculated from the activity concentrations of radiocesium ((134)Cs and (137)Cs) in litter and soil samples using the ERICA (Environmental Risk from Ionizing Contaminants: Assessment and Management) tool under the assumption that radionuclides existed as the infinite plane isotropic source was almost the same as those measured directly with glass dosimeters embedded in rodent abdomens. Our findings suggest that the ERICA tool is useful for estimating external dose rates to small animals inhabiting forest floors; however, the estimated dose rates showed large standard deviations. This could be an indication of the inhomogeneous distribution of radionuclides in the sampled litter and soil. There was a 50-fold difference between minimum and maximum whole-body activity concentrations measured in rodents at the time of capture. The radionuclides retained in rodents after capture decreased exponentially over time. Regression equations indicated that the biological half-life of radiocesium after capture was 3.31 d. At the time of capture, the lowest activity concentration was measured in the lung and was approximately half of the highest concentration measured in the mixture of muscle and bone. The average internal absorbed dose rate was markedly smaller than the average external dose rate (<10% of the total absorbed dose rate). The average total absorbed dose rate to wild rodents inhabiting the sampling area was estimated to be approximately 52 μGy h(-1) (1.2 mGy d(-1)), even 3 years after the accident. This dose rate exceeds 0.1-1 mGy d(-1) derived consideration reference level for Reference rat proposed by the International Commission on Radiological Protection (ICRP).
authors: Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan. Electronic address: y_kubota@nirs.go.jp.
authors: Yoshihisa
authors: Y
authors: Kubota
authors: Tokyo Nuclear Services Co., Ltd., 1-3-5 Taito, Taito-ku, Tokyo 110-0016, Japan.
authors: Hiroyuki
authors: H
authors: Takahashi
authors: Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Yoshito
authors: Y
authors: Watanabe
authors: Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Shoichi
authors: S
authors: Fuma
authors: Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Isao
authors: I
authors: Kawaguchi
authors: Japan Wildlife Research Center, 3-3-7 Koutoubashi, Sumida-ku, Tokyo 130-8606, Japan.
authors: Masanari
authors: M
authors: Aoki
authors: Japan Wildlife Research Center, 3-3-7 Koutoubashi, Sumida-ku, Tokyo 130-8606, Japan.
authors: Masahide
authors: M
authors: Kubota
authors: Japan Wildlife Research Center, 3-3-7 Koutoubashi, Sumida-ku, Tokyo 130-8606, Japan.
authors: Yoshiaki
authors: Y
authors: Furuhata
authors: Japan NUS Co., Ltd., 7-5-25 Nishi-shinjyuku, Shinjyuku-ku, Tokyo 160-0023, Japan.
authors: Yusaku
authors: Y
authors: Shigemura
authors: Forestry and Forest Products Research Institute, 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
authors: Fumio
authors: F
authors: Yamada
authors: Department of Technical Support and Development, Research, Development and Support Centre, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Takahiro
authors: T
authors: Ishikawa
authors: Medical Radiation Exposure Project, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Satoshi
authors: S
authors: Obara
authors: Project for Environmental Dynamics and Radiation Effects, Fukushima Project Headquarters, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors: Satoshi
authors: S
authors: Yoshida
mesh_terms: D000818:Animals; D003411:Arvicolinae / Q000378:metabolism*; D002588:Cesium Radioisotopes / Q000378:metabolism*; D062406:Fukushima Nuclear Accident; D007564:Japan; D051189:Murinae / Q000378:metabolism*; D011829:Radiation Dosage; D000069079:Radiation Exposure; D011834:Radiation Monitoring; D012990:Soil Pollutants, Radioactive / Q000378:metabolism*
chemical_list: D002588:Cesium Radioisotopes; D012990:Soil Pollutants, Radioactive
keywords: Dosimeter; ERICA; Exposure; Half-life; Radiocesium; Small mammal