High levels of soil contamination caused by radioactive cesium have been detected in Tokyo and neighboring Kanagawa Prefecture, but only sporadically, according to the science ministry.
High levels of soil contamination caused by radioactive cesium have been detected in Tokyo and neighboring Kanagawa Prefecture, but only sporadically, according to the science ministry.
On Oct. 6, it released its latest version of a map showing soil contamination by cesium 134 and 137 due to the accident at the Fukushima No. 1 nuclear power plant, adding Tokyo and Kanagawa Prefecture to the previous version.
Contamination in the Tokyo metropolitan area is limited. Relatively high levels of cesium accumulation were detected only in some areas, such as Tokyo's Katsushika Ward, Okutama, western Tokyo, and the town of Yamakita, Kanagawa Prefecture.
The ministry, through aerial surveys, measured amounts of cesium 134 and 137 accumulated in soil between Sept. 14 and 18. It also measured actual concentrations in soil at some locations.
Accumulations of cesium 137 in parts of Katsushika Ward and the town of Okutama were between 30,000 and 60,000 becquerels per square meter. No place in Kanagawa Prefecture recorded those levels.
Cesium 137 will have a long-term impact on the environment because its half-life period is 30 years, compared with two years for cesium 134.
Accumulations were 10,000 becquerels per square meter or higher in parts of Edogawa and Adachi wards, near Katsushika Ward, and the village of Hinohara, near Okutama.
Measurements were mostly less than 10,000 becquerels elsewhere in Tokyo.
In Kanagawa Prefecture, accumulations were 10,000 becquerels per square meter or higher in parts of Yamakita, Sagamihara's Midori Ward and the village of Kiyokawa.
Other places in the prefecture recorded less than 10,000 becquerels.
After the 1986 Chernobyl nuclear power plant accident in the former Soviet Union, areas with 37,000 becquerels of cesium 137 per square meter or more were designated as the contaminated zone.
Radiation levels were higher than 0.2 microsievert per hour in parts of Katsushika Ward and Okutama. Annualized figures exceed 1 millisievert in additional radiation.
The government has said it will provide financial support in removing radioactive materials if annual additional radiation levels are 1 millisievert or more.