Around 45 percent of children in Fukushima Prefecture checked by the prefectural and central governments in late March experienced thyroid exposure to radiation, although in all cases in trace amounts that didn’t warrant further examination, officials of the Nuclear Safety Commission said Tuesday.
The survey was conducted on 1,080 children from newborns to age 15 in Iwaki, Kawamata and Iitate from March 26 to 30 in light of radiation leaking from the Fukushima No. 1 nuclear plant.
Among children who tested positive for thyroid exposure, the amounts measured 0.04 microsievert per hour or less in most cases. The largest exposure was 0.1 microsievert per hour, equivalent to a yearly dose of 50 millisieverts for a 1-year-old.
None of those surveyed was exposed to more than 0.2 microsievert per hour, the government’s benchmark for conducting more detailed examinations, according to the officials.
Scientific surveys of hibakusha from Hiroshima and Nagasaki have indicated that exposure of 100 milisieverts in total could increase cancer morality risk by 0.5 percent.
Meanwhile, a survey of soil at four locations in the city of Fukushima on June 26 found that all samples were contaminated with radioactive cesium, measuring 16,000 to 46,000 becquerels per kilogram and exceeding the legal limit of 10,000 becquerels per kg, citizens’ groups said Tuesday.
The city, about 60 km northwest of the crippled plant, doesn’t fall within the 20-km no-entry zone or nearby evacuation areas.
The citizens’ groups, led by the Fukushima Network to Protect Children from Radiation, had asked Kobe University professor Tomoya Yamauchi, an expert in radiology, to lead the survey.
Another sample taken from a street ditch — where nuclear fallout often accumulates — registered as much as 931,000 becquerels per sq. meter, surpassing the 555,000 becquerels per sq. meter limit for compulsory resettlement in the 1986 Chernobyl nuclear accident. Samples from the other three locations measured between 326,000 and 384,000 becquerels per sq. meter.
An earlier survey on soil in the city of Fukushima by the science ministry has found 37,000 becquerels of radioactive substances per 1 kg — equivalent to 740,000 becquerels per sq. meter.