National / Science & Health

Extensive radiation study finds no internal cesium exposure in Fukushima children

by Mizuho Aoki

Staff Writer

An extensive study of internal radiation exposure in Fukushima Prefecture children detected no radioactive cesium among the examinees, according to the results of a study published Friday.

The study, the first of its kind, involved over 2,700 infants and small children mostly from Fukushima who could have been exposed to radiation during and after the Fukushima No. 1 power plant crisis in 2011. The children were examined by three local medical institutions: Hirata Central Hospital, Minamisoma Municipal General Hospital and Tokiwakai Hospital.

Published in the Proceedings of the Japan Academy magazine, the study examined 2,707 children up to 11 years of age from December 2013 to March 2015, using newly developed whole body counters designed especially for scanning small children.

The study found no cesium in the children, indicating that even if they did ingest food and water tainted with radiation, the levels of any radioactive isotopes present must have been negligibly low to avoid detection by such a high-precision machine.

The results were the same among children who ingested local produce and tap water and those who did not, the study showed.

Most were residents of Fukushima, but some were from neighboring prefectures, such as Ibaraki.

The new whole body counter, called a Babyscan, can detect as little as 50 becquerels of cesium in a young human body, which is about a fifth or a sixth of the amount measurable by other devices widely used to scan adults, the study said.

Even if cesium below Babyscan’s capabilities was present, the resulting exposure level would be less than 16 microsieverts a year, which is negligible, the study said.

The International Commission on Radiological Protection’s exposure limit under normal situations is 1 millisievert per year. It says a cumulative exposure of 100 millisieverts per year increases the chances of dying from cancer by 0.5 percent.

Masaharu Tsubokura, a University of Tokyo researcher who examined some of the children at Minamisoma Municipal General Hospital, which is less than 30 km from the crippled nuclear plant, said the result was quite surprising, given the Babyscan’s high sensitivity.

Roughly speaking, the study showed the children weren’t consuming even a becquerel of cesium per day, said Tsubokura, who co-wrote the report.

Although overall public interest in radiation exposure has declined in the past four years, anxiety lingers among many parents with small children, he said. Sadly, their understanding of radiation has not deepened much, he said.

Although several studies have shown that the internal radiation exposure of Fukushima residents is low, Tsubokura said there are plans to continue monitoring children.

“There are people who want us to continue the examinations and reserve a place where they can consult about them. And there are still many people who say they can’t eat produce grown in Fukushima. I believe our job is to continue checkups and to deal with each one of them sincerely,” he said.

Of the children examined, 638 were living in Minamisoma, 218 were former Minamisoma residents, and the rest were from outside the 30-km radius of the nuclear power plant.

The latter group includes 1,579 mostly from Koriyama and Miharu, west of the doomed plant, and from Daigo, Ibaraki Prefecture, as well as 272 mostly from Iwaki, to the south of the plant.