13 August 2012
In response to the Great East Japan Earthquake and the Fukushima Daiichi nuclear disaster, the Fukushima Health Management Survey is being conducted in Fukushima Prefecture to monitor, ensure and promote the long-term health of the residents. The Fukushima Health Management Survey consists of the Basic Survey and detailed surveys. The Basic Survey targets the entire population of Fukushima Prefecture. Estimates of external radiation doses are based on the records of movement of each resident after the nuclear accident on 11 March 2011.
1. Response rates as of 31 July 2012
The questionnaire was distributed to 2,047,156 respondents out of a target population of 2,056,994. In total, 469,041 residents responded for an effective response rate of 22.8% (Table 1). The response rate was higher (55.8%, 16,209/29,044) in a preceding survey that targeted high-priority areas (Yamakiya/Kawamata, Namie and Iitate).
2. Estimated external radiation doses
The cumulative effective doses of radiation to respondents for the four months after the nuclear accident were calculated using the dose calculation system developed by the National Institute of Radiological Sciences. Doses were based on the records of movement of the residents between 11 March 2011 and 11 July 2011.
The estimated radiation doses for an additional 11,094 residents (including 545 radiation workers) were calculated between 12 June and 31 July 2012 (219 from high-priority target areas and 10,875 from other areas). Radiation doses for a total of 36,761 residents (including 1903 radiation workers) have been estimated to date.
3. Evaluation of results
Doses for the 11,094 previously mentioned residents (219 from high-priority target areas and 10,875 from other parts of Fukushima) were newly calculated between 12 June and 31 July 2012. Thus, effective external radiation doses for 36,761 residents in total have been estimated so far (15,743 from high-priority target areas and 21,018 from other parts of Fukushima).
Estimated radiation doses were all <5 mSv for respondents that were not radiation workers living outside high-priority target areas. Doses for nearly all residents of Aizu and Minami-aizu were <1 mSv. The doses for 86.7% of respondents from the Soso area were also <1 mSv. When radiation doses for the 219 residents from high-priority target areas were calculated, the coverage rate increased to 97.1%.
The highest effective dose among the most recent respondents (excluding radiation workers) was estimated to be <15 mSv, not exceeding the highest level of 25.1 mSv observed in the previous estimation. Since previous epidemiological studies indicated no significant health effects at doses <100 mSv, we concluded that radiation doses estimated to date are unlikely to cause adverse effects on health in the residents included in the survey, although the estimation was limited to the cumulative effective dose for the first four months after the nuclear accident occurred.
The responses to the basic survey (estimated radiation doses and records of movement) shall continue to be collected and stored safely. These data will be used fairly to promote the health of Fukushima residents in the long term.