title: Individual external doses below the lowest reference level of 1 mSv per year five years after the 2011 Fukushima nuclear accident among all children in Soma City, Fukushima: A retrospective observational study.
abstract: After the 2011 Fukushima Daiichi nuclear power plant accident, little information has been available on individual doses from external exposure among residents living in radioactively contaminated areas near the nuclear plant; in the present study we evaluated yearly changes in the doses from external exposure after the accident and the effects of decontamination on external exposure. This study considered all children less than 16 years of age in Soma City, Fukushima who participated in annual voluntary external exposure screening programs during the five years after the accident (n = 5,363). In total, 14,405 screening results were collected. The median participant age was eight years. The geometric mean levels of annual additional doses from external exposure attributable to the Fukushima accident, decreased each year: 0.60 mSv (range: not detectable (ND)-4.29 mSv), 0.37 mSv (range: ND-3.61 mSv), 0.22 mSv (range: ND-1.44 mSv), 0.20 mSv (range: ND-1.87 mSv), and 0.17 mSv (range: ND-0.85 mSv) in 2011, 2012, 2013, 2014, and 2015, respectively. The proportion of residents with annual additional doses from external exposure of more than 1 mSv dropped from 15.6% in 2011 to zero in 2015. Doses from external exposure decreased more rapidly than those estimated from only physical decay, even in areas without decontamination (which were halved in 395 days from November 15, 2011), presumably due to the weathering effects. While the ratios of geometric mean doses immediately after decontamination to before were slightly lower than those during the same time in areas without decontamination, annual additional doses reduced by decontamination were small (0.04-0.24 mSv in the year of immediately after decontamination was completed). The results of this study showed that the levels of external exposure among Soma residents less than 16 years of age decreased during the five years after the Fukushima Daiichi nuclear power plant accident. Decontamination had only limited and temporal effects on reducing individual external doses.
authors.affiliation: Department of Radiation Protection, Soma Central Hospital, Soma, Fukushima, Japan.
authors.forename: Masaharu
authors.identifier: http://orcid.org/0000-0001-8027-202X
authors.initials: M
authors.lastname: Tsubokura
authors.affiliation: Department of Health Risk Communication, Fukushima Medical University School of Medicine, Fukushima, Fukushima, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Murakami
authors.affiliation: Department of Global Health Policy, Graduate School of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, Japan.|Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, Norfolk Place, London, United Kingdom.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Nomura
authors.affiliation: Department of Internal Medicine, Soma Central Hospital, Soma, Fukushima, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Morita
authors.affiliation: Department of Health Informatics, School of Public Health, Kyoto University, Kyoto, Kyoto, Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nishikawa
authors.affiliation: Global Public Health Unit, School of Social and Political Science, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Claire
authors.initials: C
authors.lastname: Leppold
authors.affiliation: Research Institute of Innovative Medicine, Tokiwa Foundation, Iwaki, Fukushima, Japan.
authors.forename: Shigeaki
authors.initials: S
authors.lastname: Kato
authors.affiliation: Medical Governance Research Institute, Minato-ku, Tokyo, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kami
mesh_terms: D000293:Adolescent; D002588:Cesium Radioisotopes / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D003666:Decontamination; D004781:Environmental Exposure; D005260:Female; D062406:Fukushima Nuclear Accident; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007564:Japan; D008297:Male; D011829:Radiation Dosage; D011834:Radiation Monitoring; D014915:Whole-Body Counting
chemical_list: D002588:Cesium Radioisotopes