Such radioisotopes can pose serious health dangers if released into the environment in large enough amounts. But the concentrations being recorded in the United States and elsewhere are nowhere near levels to be of concern, said Rusty Lundberg, director of the Utah Department of Environmental Quality's Division of Radiation Control.
"We would see such a trend that we would be able to inform the public well before" the concentrations reached dangerous levels, Lundberg said.
There is no way to know how long it would take that much material to travel the 10,000 miles from Japan because of meteorological variables, he added.
Iodine 131 is among the most common radioisotopes associated with nuclear fission and one of the most dangerous, even though it has a radioactive half-life the time it takes for half its radioactive atoms to disintegrate of just eight days. That's because it can concentrate in the milk supply by settling on livestock forage. The human thyroid quickly absorbs iodine 131, raising the risk of cancer in that organ, particularly in children.
In Spokane, Wash., a March 25 milk sample yielded iodine 131, but in concentrations more than 5,000 times below the level of concern, the Food and Drug Administration said.
"Radiation is all around us in our daily lives, and these findings are a minuscule amount compared to what people experience every day. For example, a person would be exposed to low levels of radiation on a round-trip, cross-country flight, watching television and even from construction materials," said Patricia Hansen, a senior FDA scientist, in a news release about the general radiation risk arising from Japan's crisis.
The federal Environmental Protection Agency maintains a 125-station network as part of its RadNet program, created to monitor the effects of a terrorist-detonated nuclear device.
Some stations check air, precipitation, cow's milk and drinking water. Utah DEQ maintains a RadNet station in Salt Lake City, which checks only air and precipitation.
Lundberg has sent five air filters and a precipitation sample since the March 11 earthquake to the EPA's Alabama laboratory, but the results remain unavailable, he said Thursday.
The EPA has posted data from 12 geographically representative RadNet locations, including Boise, Idaho, and Las Vegas. Last week, those sites reported trace amounts of some radionuclides, principally iodine 131, but also cesium 137, tellurium 132 and iodine 133.
"These types of findings are to be expected in the coming days and are still far below levels of public-health concern," the agency said.
In response to Japan's nuclear crisis, the Desert Research Institute (DRI) in Nevada installed charcoal canisters at three sites in its 29-station network of radiation monitors. Those sites are generally equipped with small air filters that are removed every other week, but officials added charcoal cartridges because they are more sensitive.
The DRI's Community Environmental Monitoring Program (CEMP), which includes four stations in St. George, Cedar City, Milford and Delta, was set up 30 years ago downwind from the former Nevada Test Site, covering much of southern Nevada and southwestern Utah.
On Monday, Don Newman, a Cedar High School science teacher , pulled the 2-inch air filter from the CEMP station he oversees near the Southern Utah University campus and sent it to the institute's Las Vegas headquarters for gamma spectroscopy analysis, but results weren't available Thursday.
Samples taken last week from stations in Henderson, Nev., and Las Vegas revealed trace amounts of fission products consistent with materials released in a nuclear accident.
But the concentrations were so low that they were of no concern, and, in some instances, some of the isotopes weren't even detectable, said CEMP manager Ted Hartwell.
Various agencies are sharing data gathered from radiation monitoring stations. Radionuclides are produced in nuclear fission and are leaking from Japan's Fukushima-Dai-ichi power plant after a March 11 earthquake and tsunami crippled its cooling systems. Among fission products being detected in the United States are iodine 131, xenon 133 and cesium 137. But concentrations are far too low to threaten public health. For more information online:
Nevada's Desert Research Institute • http://cemp.dri.edu
Environmental Protection Agency • epa.gov/radiation
Utah Department of Environmental Quality's Division of Radiation Control • www.radiationcontrol.utah.gov