Two forms of radioactive cesium from Japan's Fukushima nuclear disaster have reached the continental shelf off British Columbia, but in concentrations far too low to represent a radiological hazard.
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Small concentrations of cesium also have also been found in water samples along the U.S. West Coast. But only one of the two forms of cesium have appeared, and its concentration is no higher than it was prior to the 2011 earthquake and tsunami that led to the partial meltdowns of three of the Fukushima plant's four reactors and compromised storage pools for spent fuel.
"I'm the first person to say radioactivity can be quite dangerous, we should be concerned. But maybe not at the levels we're going to expect coming across from Japan," said Ken Buesseler, a marine scientist at the Woods Hole Oceanographic Institution, at a briefing uring the ocean-sciences meeting, which was organized by three marine-science organizations.
At issue are two forms of radioactive cesium: cesium-134 and cesium-137. Both are byproducts of nuclear fission from nuclear power plants as well as nuclear weapons tests. Cesium-137 is of greater concern because it has a half-life of 30 years, compared with two years for cesium-134.
The oceans have low concentrations of cesium-137, a byproduct of atmospheric nuclear weapons tests in the 1950s and 60s. The cesium-134 from those events decayed long ago. So when cesium-137 and cesium-134 appear together, the presence of the shorter-lived cesium isotope signals that the two came from Fukushima, explained John Smith, a chemical oceanographer at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia.
The far end in a line of measuring stations extending nearly 1,000 miles west from the mouth of British Columbia's Juan de Fuca Strait detected the arrival of cesium from Fukushima in 2012. But in 2013 it was detected all along the line up to the continental shelf.
For the U.S. West Coast and Hawaii, no cesium-134 has been detected yet, and cesium-137 remains at background levels. But based on modeling results, the U.S. West Coast could see the leading edge of a plume of cesium from Fukushima arrive at the continental shelf this year. ■
A strong storm that originated over the Pacific has tracked through the Great Basin and is currently transitioning across the Rockies to redevelop across the central High Plains later today into early Saturday morning.