The Daiichi nuclear power plant, struck by a huge quake and tsunami in March, released radiation into the atmosphere that was carried by winds and deposited widely by rain and snow in eastern Japan.
Setagaya, a major residential area in Tokyo about 235 km (150 km) southwest of the plant, said this week it found a radioactive hotspot on a sidewalk near schools.
The radiation there measured as much as 2.7 microsieverts per hour, higher than some areas in the evacuation zone near the plant.
Washing down the area with water did not help lower the radiation levels, Setagaya Mayor Nobuto Hosaka said but added that the district had been advised that it was safe for people to walk by.
The city of Funabashi in Chiba, near Tokyo, said on Thursday that a citizens’ group had measured a radiation level of 5.8 microsieverts per hour at a park and it was now making checks.
Government data this week showed radiation levels in the 20 km radius evacuation zone around the Daiichi plant ranged from 0.5 to 64.8 microsieverts per hour.
About 80,000 residents were forced to evacuate from this zone. The unit microsievert quantifies the amount of radiation absorbed by human tissue.
In Yokohama, radioactive strontium-90, which can cause bone cancer and leukemia, was detected in soil taken from an apartment rooftop, media reports said.
Strontium has been detected within an 80 km zone around the Daiichi plant, but this is the first time it has been found in an area so far away, the reports said.
There is no agreement among experts on the health impact of radiation exposure, but after Chernobyl, there was a substantial increase in cases of thyroid cancer in those exposed as children.
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.
Areas needing radiation cleanup in Japan could top 2,400 square km, and Japan may have to remove and dispose of enough radioactive soil to fill 23 baseball stadiums.
