Evacuating outside Fukushima reduced internal radiation only slightly: study

3 October 2015

Internal radiation exposure as a result of the nuclear disaster at Tokyo Electric Power Co.’s Fukushima Daiichi plant was slightly lower among those who evacuated out of Fukushima Prefecture when compared with those who did not, but the difference was not clinically significant, according to an analysis by physician Masaharu Tsubokura and other researchers at the Minamisoma Municipal General Hospital.

While internal exposure resulting from contaminated air inhaled during the initial stage of the crisis existed, the dosage was minimal, according to the study published recently by the group in an international medical journal.

The researchers analyzed the results of internal radiation exposure tests conducted on 521 people at the hospital four months after the March 2011 nuclear accident. Among them, 232 people, or 44.5%, evacuated within Fukushima Prefecture, while 209 people, or 40.1%, found shelter in other prefectures. Almost all of those who evacuated did so within a week of the disaster. Cesium-134 was detected in 279 people, or 53.4% of all who were tested.

By comparing figures adjusted to reflect conditions such as gender and lifestyles to analyze the relationship between evacuation and internal radiation exposure dosages, the group found that the relative risk correlation when compared with those who did not evacuate at all was 0.88 for those who evacuated indoors within the prefecture, and 0.86 for those who fled to other prefectures. This difference was not of significance to cause concern from a medical viewpoint.

The researchers believe the limited difference in internal exposure between those who evacuated outside the prefecture and those who did not was partly due to the effectiveness of food regulations imposed after the disaster.

(Translated by Kyodo News)