Radiation found in Tokyo tap water

Radioactive iodine exceeding the safety standard for infants but not children or adults was found Wednesday in water at a Tokyo purification plant, the Japanese prime minister's office said.

The level was about twice the safety standard for infants up to 1 year and two-thirds that for adults, the prime minister's office said. Parents were advised to give only bottled water to infants.

"These aren't huge doses we're talking about here," said Donald Milton, director of the Maryland Institute for Applied Environmental Health. "The safe doses are set down at quite low levels in order to give safety margins."

Still, the news, in the wake of radiation from Japan's damaged nuclear power plant after the March 11 earthquake and tsunami, led anxious Japanese residents to clear store shelves of bottled water. Radiation from the Fukushima Dai-ichi Nuclear Power Station has not only seeped into water, but also into raw milk, seawater and 11 kinds of vegetables.

The thyroid gland uses iodine to make thyroid hormone, and it can't tell the difference between radioactive or stable isotopes. It's "very efficient at gobbling up and scavenging almost every molecule of iodine it comes across," said Alan Lockwood, professor of neurology and nuclear medicine at the University of Buffalo.

And, Milton said, "infants with a growing thyroid and a tremendous need for thyroid hormone are more susceptible to taking up a lot of the iodine from their diet," helping to explain why the infant safety standard is so low.

Scott Davis, a University of Washington epidemiologist who studies the effects of radiation exposure at the Fred Hutchinson Cancer Research Center, called the relationship between age and thyroid cancer risk due to radioactive iodine "striking." "The effect on young people and infants is much different than on people exposed as adults," he said.

Besides infants, Milton said, it would be "reasonable" for pregnant or nursing women to avoid drinking tap water contaminated with radioactive iodine so their fetuses or infants aren't exposed.

The only excess malignancies linked to the 1986 Chernobyl nuclear disaster have been thyroid cancers in people who were young children or teens at the time. Lockwood noted that the risk of exposure to radioactive iodine doesn't suddenly drop on a baby's first birthday but gradually decreases as children age.

Meanwhile, smoke from one of the reactor buildings Wednesday led to an evacuation of Japan's crippled Fukushima plant, further delaying repair efforts.

The toll climbed again, and now exceeds 9,500 dead and 16,000 missing. More than a dozen small aftershocks rumbled offshore, a pattern likely to continue for months, according to the U.S. Geological Survey.

The evacuation at the Fukushima plant halted the planned restart of automatic cooling pumps at a reactor building that may have a leaky reactor and an overheating spent nuclear fuel rod pool.

Black smoke from that pool area sparked the evacuation, according to Tokyo Electric Power Co. Radiation readings did not rise at the plant, and seawater cooling efforts continued. Workers will not be allowed to return to the plant until this morning.

"Some progress is being made," said nuclear engineer David Lochbaum of the Union of Concerned Scientists, a nuclear industry watchdog. Lochbaum added that continued evacuations and damaged equipment have slowed efforts to move the plant past the crisis.

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