Traces of radioactive cesium have been discovered in schoolchildren in Fukushima Prefecture, according to the Minami-Soma municipal general hospital.
Half of the elementary and junior high school students in Minami-Soma who underwent radiation checks since late September were found with low levels of radioactive cesium-137, the hospital reported.
"We will offer periodic checks to students to keep records of their health conditions," said a hospital worker in charge.
The hospital is uncertain whether the students inhaled airborne radiation or ingested it through radiation-contaminated foodstuffs after the March 11 Fukushima No. 1 nuclear power plant accident.
Radioactive cesium-137 was detected at below 10 becquerels per kilogram of a student's weight in 199 students. The substance was also found at from 10 to less than 20 becquerels in 65 students; 20 to less than 30 becquerels in three students; and 30 to below 35 becquerels in one student, the hospital said.
Despite the substance's half-life of about 30 years, it will be discharged from the body through bowel movements and other bodily functions. The discharge process takes 100 days for adults, but only 30 days for first- to third-grade elementary school students, who have faster metabolism rates.
Much remains unknown as to the effects of low levels of internal radiation exposure on human health. Detailed data on such effects were not available from the 1945 atomic bomb blasts in Hiroshima and Nagasaki or from the 1986 Chernobyl nuclear accident.
Given that precise values of internal exposure--albeit trace amounts--were identified this time, continued checks are expected to provide more accurate measurements of radiation amounts entering the body through inhaling at the time of the onset of the Fukushima crisis, as well as through ingestion following the accident. Such measurements will enable a closer probe into the relationship between internal exposure and health damage, allowing for monitoring of increases in internal radiation through foods, sources said.
"If radiation checks are conducted again on the students in a few months to determine if any change between the two checks has arisen, we can roughly estimate (the radiation amounts entering the body through inhaling and through ingesting)," said Masaharu Tsubokura, a doctor at the University of Tokyo's Institute of Medical Science.
Tsubokura added that nationwide government-led efforts are needed (for such measurements).
The Institute of Radiation Safety Belrad, a radiation research organization in Belarus, handled radiation exposure measures after the Chernobyl accident. The institute set hazardous levels for children at 70 becquerels of radioactive cesium per kilogram of their weight and caution levels at 20 becquerels.
Tetsuji Imanaka, an assistant professor of nuclear power engineering at the Kyoto University Research Reactor Institute, said, "The human body naturally contains radioactive potassium-40 of between 50 to 60 becquerels per kilogram. If the level reaches 30 becquerels, you may want to take action to lower radiation levels within the body."
In August, the thyroid glands of 45 percent of children aged 15 and under in Iwaki, Kawamata, Iitate, all in Fukushima Prefecture, were found to have exposure to radiation, according to the government's headquarters handling the Fukushima crisis. Children are said to be particularly vulnerable to thyroid gland cancer due to radiation exposure.
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