Trace amounts of radioactive iodine from Japan's crippled nuclear reactors have been found in drinking water in Washington State and Idaho, the Environmental Protection Agency announced late Monday.
The levels of iodine-131 found -- about 0.2 picocuries per liter -- in drinking water samples from Boise, Idaho, and Richland, Wash., are so small that EPA officials estimate that an infant would have to drink nearly 7,000 liters to receive a dose of radiation equivalent to a day's worth of normal background radiation.
"Earlier precipitation samples collected by EPA have shown trace amounts of radioactivity, so EPA has expected to find results such as these in some drinking water samples," the statement read. "Similar findings are to be expected in the coming weeks."
The EPA's standard for the maximum level of iodine-131 in drinking water is 3 picocuries per liter. Iodine-131 can be harmful in higher amounts, particularly to infants and young children, because it concentrates in the thyroid gland and can lead to cancer.
Drinking water tested free of detectable levels of radioactive contaminants in several other U.S. cities, including Seattle; Portland; Idaho Falls, Idaho; New Orleans; Bismarck, N.D.; Austin, Texas; and Lynchburg, Va.
Also on Monday, the EPA reported elevated levels of radionuclides in rainwater from Olympia, Portland and cities in Alabama, California, Connecticut, Idaho, Minnesota, New York, Ohio and Tennessee. Levels of iodine-131 ranged as high as 242 picocuries per liter in Boise. Levels in Olympia, Wash., and Portland, Ore., were 125 picocuries per liter and 87 picocuries per liter, respectively.
Although those levels are several times higher than the EPA's drinking-water standard for iodine-131, the agency says that the standard is designed to protect a person who drinks contaminated water daily for 70 years. However, because the isotope has a half-life of eight days, levels of iodine-131 are expected to drop quickly.
A sample of milk from Spokane, Wash., tested positive last week for what the EPA says is harmless traces of iodine-131.