High levels of cesium isotopes are cropping up in dust at 42 incineration plants in seven prefectures, including Chiba and Iwate, an Environment Ministry survey of the Kanto and Tohoku regions shows.
According to the report, released late Saturday, the highest cesium levels in the dust ranged from 95,300 becquerels in Fukushima Prefecture and 70,800 becquerels in Chiba Prefecture to 30,000 becquerels in Iwate Prefecture.
But even the lower levels in the dust exceeded 8,000 becquerels per kilogram in Ibaraki, Tochigi, Gunma and Tokyo.
The 16-prefecture survey covered 469 incinerator operators in Tohoku and Kanto from late June, and was reported to a panel of experts at the ministry that is discussing how to safely bury incinerator ash and dust with cesium levels above 8,000 becquerels per kilogram.
Local governments have been instructed to temporarily store their ash and dust at disposal sites until the panel reaches a conclusion.
The ministry said it will ask the prefectures to continue monitoring radiation levels in the material.
Incinerator ash containing cesium was detected at seven facilities in Fukushima Prefecture, the report said.
The Environment Ministry asked prefectures to monitor cesium levels after dust with 9,740 becquerels per kilogram was found at an incineration plant in Tokyo's Edogawa Ward in June. Before that, the only prefectures that had collected and released such data were Gunma and Ibaraki.
The other prefectures that took part in the survey were Miyagi, Akita, Yamagata, Saitama, Kanagawa, Niigata, Yamanashi, Nagano and Shizuoka.