A radiation hotspot has been detected in Tokyo seven months into Japan's nuclear crisis, but local officials said on Thursday that the high readings appeared to be coming from mystery bottles stored under a house, not the tsunami-crippled Fukushima atomic plant.
The Fukushima Daiichi nuclear power plant, struck by a devastating quake and tsunami in March, has released radiation into the atmosphere that has been carried by winds, rain and snow across eastern Japan.
Officials in Setagaya, a major residential area in Tokyo about 235 km (150 miles) southwest of the plant, said this week it found a radioactive hotspot on a sidewalk near schools, prompting concerns in the country's most populated area far from the damaged nuclear plant.
The radiation measured as much as 3.35 microsieverts per hour on Thursday, higher than some areas in the evacuation zone near the Fukushima plant, the centre of the world's worst nuclear disaster since Chernobyl 25 years ago.
But the local government found several bottles under the floor of a nearby house emitting high levels of radiation.
"A measuring device, when pointed at them, showed very high readings. Radiation levels were even exceding the upper limit for the device," Setagaya Mayor Nobuto Hosaka told a news conference.
Officials from the Education Ministry are now looking into the matter, including the contents of the bottles. Public broadcaster NHK said no one had been living in the house in question.
The city of Funabashi, near Tokyo, said that a citizens' group had measured a radiation level of 5.8 microsieverts per hour at a park, but that the city's own survey showed the highest reading at the park was a quarter of that level.
Radiation levels in the 20 km radius evacuation zone around the Fukushima Daiichi plant ranged from 0.5 to 64.8 microsieverts per hour, government data showed this week.
About 80,000 residents have evacuated this zone. A microsievert quantifies the amount of radiation absorbed by human tissue.
In Yokohama, also near Tokyo, radioactive strontium-90, which can cause bone cancer and leukaemia, was detected in soil taken from an
apartment rooftop, media reported.
Strontium has been detected within an 80 km zone around the Fukushima Daiichi plant, but this is the first time it has been found in an area so far away, local media added.
Radiation exposure from natural sources in a year is about 2,400 microsieverts on average, the UN atomic watchdog says.
Japan's education ministry has set a standard allowing up to 1 microsievert per hour of radiation in schools while aiming to bring it down to about 0.11 microsievert per hour.