Traces of radioactive iodine have been detected in Tokyo and elsewhere in the Kanto area, the government said Sunday.
The traces were found after the science and technology ministry conducted a radiation study on precipitation and dust from the Fukushima No. 1 nuclear power plant.
While the direct impact on human health can’t be clearly determined from the measured figures alone, the ministry said separate studies on air and tap water in Tokyo and five other prefectures show there is no radiation threat in those areas.
Besides Tokyo, radioactive iodine was found in Saitama, Chiba, Yamanashi, Tochigi and Gunma prefectures, the Education, Culture, Sports, Science and Technology Ministry said.
In addition, traces of cesium were detected in Tochigi and Gunma after testing samples collected in a 24-hour period from 9 a.m. Friday. Tochigi, Gunma and Niigata border Fukushima Prefecture.
About 1,300 megabecquerels of iodine radioactivity were detected per sq. kilometer in Tochigi, 230 megabecquerels in Gunma, 51 megabecquerels in Tokyo, 64 megabecquerels in Saitama, 21 megabecquerels in Chiba and 175 megabecquerels in Yamanashi.
About 62 megabecquerels of cesium radioactivity were detected per sq. kilometer in Tochigi and 84 megabecquerels in Gunma.
A becquerel is the basic unit of radioactivity under the SI system. Health risk depends on one’s proximity to the radioactive material, the duration of exposure and other factors.