A sewage plant in eastern Tokyo detected a highly radioactive substance in incinerator ash shortly after the nuclear crisis began at the Fukushima No. 1 nuclear power plant, metropolitan government sources revealed Friday.
The radioactive intensity of the substance was 170,000 becquerels per kilogram, the unnamed sources said.
The ash, which has been recycled into construction materials, including cement, was collected from a sludge plant in Koto Ward in March.
At almost at the same time that month, a radioactive substance with a radioactive intensity ranging from 100,000 to 140,000 becquerels per kg was also detected in ash at two other Tokyo sewage plants in Ota and Itabashi wards, the sources said.
After a month, the radiation levels had dropped to 15,000 to 24,000 becquerels per kg at the three sewage plants, they added.
The substance has yet to be identified and researchers are looking into whether it might be radioactive cesium, the sources said without elaborating.
Meanwhile, the municipal government of Maebashi, Gunma Prefecture, said Friday it has detected radioactive cesium of 41,000 becquerels per kg from incinerator ash collected Monday at a water sanitation facility.
It also said it found cesium with an intensity of 1,844 becquerels per kg in sludge and 17,090 becquerels per kg in molten slag that was processed at a high temperature.