More than 40 percent of children from Fukushima Prefecture tested for thyroid abnormalities, such as small cysts or lumps, but that rate is not troubling because it roughly matches data elsewhere in Japan, the Environment Ministry said March 8.
"The results in Fukushima Prefecture were approximately the same as in the other prefectures," said Yasuo Kiryu, a senior ministry official in charge of radiological health control.
The government of Fukushima Prefecture has been conducting ultrasound thyroid gland tests on about 360,000 children and young adults who were aged 18 or under when the disaster at the Fukushima No. 1 nuclear plant began to unfurl in March 2011. Babies born after the accident were not included.
By January, tests were complete on about 133,000 individuals, and 41.2 percent of them were diagnosed with cysts of up to 2 centimeters in size and lumps measuring up to 5 millimeters on their thyroid glands.
Experts believe cysts and lumps of that size pose no particular concern.
But there was no telling if that incidence rate was particularly high or reflected contamination from radioactive iodine released from the nuclear plant because it was the first time high-performance ultrasound devices had been used to test children's thyroid glands in such a comprehensive study.
To obtain control data for comparison, the Environment Ministry tested 4,365 children aged between 3 and 18 in three other cities far from Fukushima, using ultrasound devices of the same performance and diagnostic standards.
The samples were taken in Nagasaki, the capital of Nagasaki Prefecture, Kofu, the capital of Yamanashi Prefecture, and Hirosaki, Aomori Prefecture.
The surveys found cysts measuring up to 2 cm and lumps measuring up to 5 mm in 56.6 percent of the children tested. Larger cysts and lumps were found in 1.0 percent of them, compared with 0.6 percent in the Fukushima children.
"The survey found that the situation in Fukushima is not abnormal," said Shigenobu Nagataki, a professor emeritus of radiology at Nagasaki University.
But he added: "Tests in Fukushima should continue over the subjects' lifetimes. And to account for regional differences, it is necessary to compare the test results against those on children born after the nuclear disaster in Fukushima Prefecture."
The prefectural government has said it plans to continue conducting tests on the children involved throughout their lifetimes.
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