The Tokyo metropolitan government on Wednesday warned residents against using tap water to feed infants after high levels of radioactive iodine were confirmed at a water purification facility in Katsushika Ward.
The advisory was directed at residents in Tokyo's 23 wards and five cities to the west--Musashino, Mitaka, Machida, Tama and Inagi--to which the purification center provides water.
Chiba Prefecture was to issue similar warnings to its citizens because a large portion of that prefecture draws water from the same source, the Tonegawa river.
Officials said iodine levels of 210 becquerels per liter were confirmed from samples at the Kanamachi water purification center.
The health ministry has recommended against using water with iodine concentration of more than 100 becquerels per liter when preparing baby formula for infants.
Still, the amount detected was lower than the safety limit of 300 becquerels that the Nuclear Safety Commission of Japan set for consumption by adults.
Officials also warned people against panicking by explaining that the government limits were set "on the assumption that water is consumed over an extended period of time."
"There is no health risk from drinking the water if alternative water sources cannot be secured, as long as consumption does not continue for a long period of time," a metropolitan government official said.
Officials at the Ministry of Health, Labor and Welfare said that even if the water is consumed by expecting mothers or women breastfeeding their children, the iodine will not affect fetuses or babies.
They added that there is no problem in using the water for baths or other daily purposes, such as washing laundry.
Tokyo metropolitan government officials collected samples from the water purification facility on Tuesday to check the effects of possible fallout in rain following the Fukushima No. 1 nuclear power plant accident caused by the March 11 Great East Japan Earthquake.
The metropolitan government received a notice at 11 a.m. Wednesday that levels exceeding the standard had been confirmed.
A sample taken at 9 a.m. Wednesday had a reading of 190 becquerels.
Officials said they believe the radioactive fallout had mixed into rain that fell Monday, resulting in a higher concentration.
Asked why an announcement was made more than a day after the samples had been gathered, an official said: "We worked as fast as possible. We don't think that the announcement was delayed."
Radioactive iodine is believed to cause thyroid cancer and other ailments after it enters the body. Stricter limits have been set for children because they are more vulnerable to iodine accumulation in thyroid glands.
The metropolitan government had been monitoring iodine levels in tap water at a facility in Shinjuku Ward since March 18. However, only minute traces were observed, officials said.
The Ministry of Agriculture, Forestry and Fisheries was expected to notify trade groups for manufacturing, distribution and marketplaces that there was no problem in using Tokyo tap water for such purposes as processing food.
"The health ministry standards are quite strict because they were set with extended consumption running for about a year in mind," said Michiaki Kai, a professor specializing in radiation safety and health at the Oita University of Nursing and Health Sciences.
But he added that infants should avoid drinking tap water as much as possible.
Kai said radiation in the water purification facility pools will drop considerably after about a month because the half-life period, the time needed for radiation levels to be reduced in half, is about eight days for iodine.
He added that it was necessary to continue monitoring the iodine levels.
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