The Department of Energy and Environmental Protection Agency, in a joint statement, said the minuscule radiation detected by one of its monitoring stations in Sacramento (California) was of similar level of the radioactive isotope Xenon-133 -- noble gas produced during nuclear fission that poses no concern at the detected level.
"It was consistent with a release from the Fukushima reactors in Northern Japan," the statement said. The levels detected were approximately 0.1 disintegrations per second per cubic meter of air (0.1 Bq/m3), which results in approximately one-millionth of the dose rate that a person normally receives from rocks, bricks, the sun and other natural background sources, it stated.
"These types of readings remain consistent with our expectations since the onset of this tragedy, and are to be expected in the coming days," agencies said.
Following the explosion of the Chernobyl plant in Ukraine in 1986 – the worst nuclear accident in world history – air monitoring in the United States also picked up trace amounts of radioactive particles, less than 1,000th of the estimated annual dose from natural sources for a typical person, it added.