WHO Thyroid Dose Estimation f ollowing the Fukushima Daiichi NPP accident

1. WHO Thyroid Dose Estimation following the Fukushima Daiichi NPP accident International Workshop on Radiation and Thyroid Cancer 22 February, Tokyo, JAPAN

2. Outline • WHO's mandate • First-year dose estimation (preliminary dose estimation report) • Lifetime dose estimation (health risk assessment report) • Discussion

3. World Health Organization • Function: act as the UN directing and coordinating authority on international health work • Objective: "the attainment by all peoples of the highest possible level of health" • Definition: "HEALTH is a state of COMPLETE physical, mental and social well-being and not merely the ABSENCE of disease or infirmity" (Constitution, 1948)

4. Joint Radiation Emergency Management Plan (2010)

5. Health Risk Assessment Purpose • Fulfil WHO's role and responsibilities under the Joint Radiation Emergency Management Plan • Provide information for policy makers and health professionals in WHO Member States, as well as international organizations • Give an indication of the health implications of the accident

6. Health Risk AssessmentThe classical steps Hazard Identification Dose-response Relationship Exposure Assessment Exposure Assessment Risk Characterization Published 23 May 2012

7. Independent experts Lynn Anspaugh Mikhail Balonov Carl Blackburn Florian Gering Stephanie Haywood Jean-René Jourdain Gerhard Proehl Shin Saigusa Jane Simmonds Ichiro Yamaguchi and other contributors listed in the report Observers:

8. Health Risk Assessment Hazard Identification Hazard Identification Dose-response Relationship Dose-response Relationship Exposure Assessment Exposure Assessment Published 28 February 2013 Risk Characterization Risk Characterization

9. Independent experts Makoto Akashi Billy Amzal Lynn Anspaugh Anssi Auvinen Nick Gent Peter Jacob Dominique Laurier Charles Miller Otsura Niwa Roy Shore Richard Wakeford Linda Walsh Wei Zhang and other contributors listed in the report Observers:

10. ScopePreliminary dose estimation • Radiation doses to the public for the first year following the accident • Doses characteristic of the average doses, assessed for different age groups in locations around the world • Excludes • Doses within 20 km of the NPP • Doses to workers • Health risks and public health actions

11. Geographical coverage • Locations in Fukushima Prefecture where dose might be higher • The rest of Fukushima prefecture (less affected) • Other prefectures in Japan • Countries neighbouring Japan • Other regions of the world 

12. Effective dosesand equivalent doses to the thyroid for the first year after the accident in: 1 year old infants, 10 year old children and adults Exposure through drinking tap water used in the preparation of infant formula was considered for 6 month old infants Foetus and breast-fed infants not separately calculated but considered in the text Dosimetric endpoints These age groups provide a sufficient level of detail to characterize radiological impact with consideration of younger, more sensitive population

13. Assessed exposure pathways IAEA report on Environmental consequences of the Chernobyl accident and their remediation: twenty years of experience (2006)

14. General approach • As far as possible, doses were based on environmental measurements (ground, soil, food….) • Primary source of measurement data for Japan was provided by the Government of Japan • Where data were insufficient, modelling was used based on an estimated source term in combination with environmental measurements • The dose estimation was based on data available up-to mid September 2011, and extrapolations were used to calculate the first-year dose

15. Technical annexes

16. Dose assessment inside JapanExternal and Inhalation Input data based on measurements published by MEXT (Ministry of Education, Culture, Sports, Science and Technology in Japan) (http://radioactivity.mext.go.jp/en/) Doses estimated by the Russian Institute of Radiation Hygiene (IRH) and by the German Federal Office of Radiation Protection (BfS) Similarities/differences in the methodologies discussed in the report

17. Dose assessment inside JapanIngestion Doses estimated by WHO on the basis of measurements of radioactivity concentration Monitoring of food originating in Japan (both as marketed in Japan and in foods exported from Japan) received/compiled by WHO through its INFOSAN network Food consumption survey (2009) provided by the Japanese National Institute for Health and Nutrition (NIHN)

18. AssumptionsIngestion doses inside Japan • All people in Fukushima prefecture consumed only food produced in Fukushima prefecture (possible dose overestimation) • Losses due to radioactive decay between the point of food ‘marketing’ and the time of consumption not included, neither are losses due to food preparation and losses during cooking Food sourcing and normal food distribution practices likely to have been significantly altered by the impact of the tsunami, the earthquake, and public protection measures

19. AssumptionsConsideration of protective actions Movement of people < 20km radius: not considered (people evacuated) 20-30 km: not specific considerations for sheltering "Deliberate evacuation zone": the assessment assumed relocation at 4 months Stable iodine: it was assumed that KI tablets were not taken in Japan nor elsewhere Food and water restrictions: the assessment does not explicitly model the effect of the imposition of food and water restrictions, it is implicit since the assessment is based on monitoring results reported by the GoJ

20. ResultsThyroid doses

21. For the populations that were relocated, it was assumed that people stayed there up to 4 months and then moved to the least contaminated zones of Fukushima prefecture

22. Sources of uncertainties • Considerable variation in environmental monitoring • Variability of human behaviour patterns and locations • Air concentrations based on deposition measurements • Inhalation dose estimates cautiously assume the iodine was in elemental vapour form • Degree of shielding provided by housing • Use of ICRP dose coefficients for Japanese population • Source term • …..

23. Validation of resultsHuman measurements Comparisons with in vivo human measurements Thyroid monitoring of >1,000 children in Fukushima between 24 and 30 March 2011 Whole body monitoring on 3,373 Fukushima residents Monitoring of citizens coming back from Tokyo (France and Germany); monitoring of citizens living in Tokyo (Russia) In vivo measurements may be regarded as broadly in accordance with the dose assessment, considering "snapshots" at a particular time: do not include intakes that may have place later over the 1st year and/or short-lived RN only consider internal exposure (not external)

24. Health risk assessment • The Lifetime Attributable Risk (LAR) for different cancer types requires the dose to the affected organ over the lifetime • The ratio of lifetime dose to first-year dose was assumed to be 2, based on Chernobyl experience and taking into account differences with the Fukushima accident

25. Example of annual dose distribution

26. Thyroid doseGeneral Population • The approach used to calculate lifetime doses for the other organs (i.e. ratio lifetime dose/first-year dose equal to 2) was only applied to the component of the thyroid dose due to external exposure from the ground

29. Exposure of emergency workers • Data were provided by TEPCO for 23,172 workers up to March 2012: • TEPCO workers (24%) and contractors (76%)

30. Thyroid doseEmergency workers Four exposure scenarios assumed • ~ 66% of workers; total effective dose of 5 mSv • ~ 33% of workers; total effective dose 30 mSv • < 1% of workers; total effective dose of 200 mSv • 2 workers with total effective dose of 700 mSv and high thyroid doses due to 131I intake

31. Organ doses Scenarios for emergency workers

32. Conclusions • Effective doses were very low outside Japan and in much of Japan • Effective doses are estimated to be less than 50 mSv in Fukushima prefecture • Thyroid doses were mainly received during the first year and were highest in the most affected areas • Unlike other organs, the thyroid doses for infants were estimated to be nearly twice compared to adults • The doses estimated in the example locations of Fukushima prefecture may be somewhat overestimated: • Relocation of residents assumed at 4 months (some were relocated earlier); • Other protective measures only partially taken into account, due to lack of more detailed information • Dominant exposure pathways were inhalation and external exposure early after the incident • Comparison with human measurements gives confidence that the estimated results were not under-estimating the doses in Japan