Rainfall that fell on the city of Boise two weeks ago registered the highest levels of radioactive contamination in the United States from the ongoing nuclear-power-plant crisis in Japan.
But public health officials say there is no reason for alarm.
"These results are far below any levels of public health concern," said Hanady Kader, a spokeswoman for the U.S. Environmental Protection Agency.
"While short-term events such as these do not raise public health concerns, EPA has taken steps to increase the level of monitoring of precipitation, drinking water and other potential exposure routes," Kader said.
The EPA monitors radiation at 100 sites across the U.S. with its Radnet monitoring system, receiving data from real-time satellite, air filters, drinking water, precipitation and milk testing.
Rainfall in Boise on March 22 contained 242 picocuries per liter of iodine-131, a radioactive isotope of iodine resulting from nuclear fission. The concentration was 80 times the EPA's maximum allowable limit of 3 picocuries per liter, but health officials say the quickly decaying isotope will be rendered harmless in about 80 days due to its relatively short half-life.
"Every eight days the strength of iodine-131 is cut by half," said Mark Dietrich, technical services administrator with the Idaho Department of Environmental Quality.
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"The fact that we are detecting it even in miniscule samples indicates it's from Japan. Usually, you would see none," Dietrich said.
Dietrich said DEQ has also been picking up iodine-131 on air filters for two weeks at the Idaho National Laboratory near Arco, and that the isotope has shown up in at least one public drinking water system in Boise.
Kader said the maximum allowable contamination level of 3 picocuries per liter was based on "chronic exposures" over the course of a lifetime of 70 years.
"The levels seen in rainwater are expected to be relatively short in duration," she said.
On March 11, a massive earthquake and tsunami damaged the Fukushima Daiichi power plant, causing the worst nuclear disaster since an explosion at a nuclear plant in Chernobyl, Ukraine, in 1986.
Tom Shanahan, public information manager for the Idaho Department of Health and Welfare, said the U.S. Food and Drug Administration has banned food imports from regions contaminated by the nuclear disaster in Japan.
"A lot of the shipping ports were damaged by the tsunami, so you haven't seen much coming in since the incident," he said.
ABC News reported Thursday that tuna will begin migrating from areas off the coast of Japan toward the West Coast of the U.S. in coming weeks.
"Some of them may have spent time in the most radioactive waters on Earth," ABC reported.
For the latest EPA radiation monitoring results and answers to frequently asked questions, go to www.epa.gov/japan2011.
"The best action for citizens right now is to stay informed, and our website offers a wealth of up-to-date resources," Kader said.
Tony Evans: tevans@mtexpress.com
