WASHINGTON, Feb. 23 (UPI) -- The U.S. Geological Survey said it found low levels of radioactive particles from Japan's nuclear disaster in about 20 percent of its nationwide surveys.
Japan's Fukushima nuclear power plant was crippled by a magnitude-9 earthquake and ensuing tsunami in March. The disaster sparked fears that radioactivity would become a threat in the United States.
The U.S. Environmental Protection Agency had said it found trace amounts of radioactive iodine, cesium and tellurium from the Japanese nuclear accident at air monitors on the U.S. West Coast.
The USGS said it found radioactive particles in about 20 percent of the 167 sites it sampled in the United States. Most of that was found in samples along the West Coast.
The agency said that while it didn't assess human health risk, its monitoring confirmed that radiation levels were "far below" what's considered a threat to human health.
The EPA had said Americans receive radiation doses 100,000 times higher than levels coming from Japan during a typical round-trip international airplane flight.
The USGS said it estimated that it took about two weeks for radioactive particles from the failed nuclear plant to circle the globe.