By Laura Zuckerman
SALMON, Idaho (Reuters) - Smoke from a wildfire in Idaho that burned mining sites with traces of uranium and thorium contained elevated levels of radiation, but none that posed a risk to human health, state officials said on Friday.
The state Department of Environmental Quality last month took air samples in North Fork, a town in the burn zone in east-central Idaho, after the so-called Mustang Complex fire swept through a former uranium mine and two abandoned gold mines.
Health officials said then they believed risks to people's health was low, and the latest findings back up that assessment. Residents in the area had expressed worries about the smoke.
Paul Ritter, health physicist with the state environmental agency, said in the area of the mining sites, smoke from the fire showed amounts of radiation roughly equivalent to emissions from a fire in 2000 that charred parts of Los Alamos National Laboratory, the nuclear weapons design facility in New Mexico.
"The readings are definitely elevated but not out of line with what has been measured in fires before. It is not a risk," he said.
Americans are exposed to an estimated 310 millirems of radiation a year from natural sources, including some rocks and soils, according to the U.S. Nuclear Regulatory Commission.
An analysis of air samples in North Fork showed residents would have been exposed to 0.5 millirems of radiation in a 30-day period. That compares to a dose of 5 millirems delivered by a round-trip transcontinental flight, Ritter said.
"Residents certainly weren't in a bad state in terms of airborne radioactivity," he said.
The Mustang Complex fire has consumed nearly 340,000 acres of canyon lands and pine forests since it was ignited by lightning in late July in the Salmon-Challis National Forest.
Even without a danger from radioactivity, smoke from the blaze has posed a danger to residents, especially the young and the elderly, because it carries fine soot particles that can worsen existing respiratory or cardiovascular ailments.
The smoke triggered unhealthy air readings for more than a month in North Fork and Salmon in a pollution event that Idaho health officials said was unprecedented for its duration and predicted impacts on human health.
The findings of no significant risk from radiation did not ease concerns about exposure for Cindy Hallen, who lives 10 miles from the former uranium operation.
"There are too many unknowns," she said.
Estimates indicate that Idaho wildfires this year already have been responsible for more air pollutants being released into the atmosphere than all automobiles and industrial sources in the state, Governor C.L. "Butch" Otter said in a statement.
(Editing by Alex Dobuzinskis and Eric Walsh)