Small amounts of radioactive cesium were found in the urine of 10 children in the city of Fukushima, confirming their internal exposure to radiation, citizens’ groups that carried out a survey said Thursday.
The groups, including Fukushima Network for Saving Children from Radiation, asked ACRO, a French independent radiation monitoring and sampling laboratory, to conduct tests on its members’ own children. ACRO conducted tests in Belarus after the Chernobyl accident.
The groups said they couldn’t judge whether the level of contamination was large or small, and urged the government to conduct thorough tests on all Fukushima children to find the precise levels of their internal exposure and take necessary measures to avoid any further contamination.
Cesium-134 and cesium-137 were detected in the urine samples of all 10 children aged between 6 and 16 who participated in the survey. The largest amount of cesium-134, which has a half-life of two years, was 1.13 becquerels per liter, found in the urine of an 8-year-old girl.
As for cesium-137, which has a half-life of 30 years, the largest amount was 1.30 becquerels per liter detected in a 7-year-old boy. No traces of iodine-131 were found in the test.
The government has set a safety limit of 200 becquerels of cesium per liter of water.
The samples were taken in late May in the city of Fukushima, more than 50 km from the Fukushima No. 1 plant.
“All (tested) kids are contaminated. . . . Currently the (government’s) policy is mainly on external exposure, but internal exposure should be taken into consideration,” ACRO Chairman David Boilley told a news conference in Tokyo.
Boilley said the exact levels of contamination can’t be judged by urine tests alone because there is no direct correlation between contamination found in urine and contamination in the entire body. It was difficult to judge the contamination level because the amounts of cesium detected were small, he added.
“If it’s mainly due to the plume (from the initial explosions at the Fukushima No. 1 reactors), considering samples were taken two months after the exposure, that means two months before, it was quite a large contamination,” Boilley said. “If it’s mainly due to the food, then it is minor contamination.”
To get a grasp on their contamination levels, continuing urine tests as well as more comprehensive internal tests for radiation known as whole-body counter exams are needed, he said.
Asked to convert the detected becquerel levels to sieverts, Boilley said: “We were not able to do (such a) calculation, because it depends on many parameters. And figures (we would get) may be wrong and we prefer not to give wrong figures,” he said.
Masahiro Fukushi, a professor of radiological science at Tokyo Metropolitan University, told The Japan Times it is very difficult to ascertain the dose of internal exposure when radioactivity found in the urine is very small.
“It’s very difficult to calculate when the detected amount is very small. Without knowing when and how the detected cesium got into their bodies, there is a huge possibility of making either an overestimation or an underestimation,” Fukushi said.
He said that the speed of absorption into and exiting from one’s body are different depending on whether the radioactive substances were ingested or inhaled.