While the statement didn't comment on the source of the contamination, the announcement follows reports of radioactive material found in food after radiation leaks from the meltdown of three reactors at the Tokyo Electric Power Co. plant.
The tests covered 1,080 children aged up to 15 in three towns, Iwaki, Kawamata and Iitate, between 38 to 47 kilometers from the reactors. The tests between March 24 and 30 showed none of the children's thyroid glands exceeded the safety threshold of 0.2 microsievert per hour set by the Nuclear Safety Commission of Japan, according to the Aug. 17 statement.
At least one child had 0.1 microsievert per hour, the highest level observed, while more than half of those exposed absorbed 0.01 microsievert per hour, the statement said. Children are susceptible to poisoning from radioactive iodine, which can accumulate in the thyroid and cause cancer, according to the World Health Organization.
On June 6, Japan's Nuclear and Industrial Safety Agency said the reactor meltdowns at the plant released about 770,000 tera becquerels of radioactive material into the air between March 11 and March 16, doubling an earlier estimate.
That's about 14 percent of the radiation emitted in the Chernobyl disaster in modern-day Ukraine. About 2 million people in Ukraine are under permanent medical monitoring 25 years after the accident, according to the nation's embassy in Tokyo.
A becquerel represents one radioactive decay per second, which involves the release of atomic energy that can damage human cells and DNA, with prolonged exposure causing leukemia and other forms of cancer, according to the World Nuclear Association.
While 203 people were hospitalized and 31 died after the explosion at Chernobyl, about 400,000 children are considered to have received significant doses of radiation to their thyroid that merit monitoring, the embassy said.
Cases of thyroid cancer in Belarus, which neighbors Ukraine, increased for at least 10 years after 1986 in children younger than 14 and for almost 20 years among 20-24 year olds, according to research by Shunichi Yamashita of Nagasaki University, who was appointed as an adviser to Fukushima prefecture on radiation exposure.
Japan has no centralized system to check for radiation contamination of food, leaving local authorities and farmers conducting voluntary tests.
Products such as spinach, tea, milk, and fish have been found contaminated with cesium and iodine as far as 360 kilometers (224 miles) from the plant.
Adding to the concern, officials confirmed today rice from Hokota City, about 150 kilometers from Dai-Ichi, was found to contain low levels or cesium. It was the first confirmation of rice contamination since the March 11 accident.
To contact the reporters on this story: Chisaki Watanabe in Tokyo at email@example.com;