Fukushima radiation has reached U.S. shores
©
Christopher Furlong / Getty Images Tanks holding radiation contaminated water
at the Tokyo Electric Power Co.'s embattled Fukushima Daiichi nuclear power
plant on February 25, 2016 in Okuma, Japan.
Cesium-134, the so-called
fingerprint of Fukushima, was measured in seawater samples taken from Tillamook
Bay and Gold Beach in Oregon, according to researchers from the Woods Hole
Oceanographic Institution. Because of its short half-life,
cesium-134 can only have come from Fukushima. For the first time, cesium-134 has
also been detected in a Canadian salmon, according to the Fukushima InFORM
project, led by University of Victoria chemical oceanographer Jay Cullen.
In both cases, levels are extremely
low, the researchers said, and don’t pose a danger to humans or the
environment.
Massive amounts of contaminated
water were released from the crippled nuclear plant following a 9.0 magnitude
earthquake and tsunami in March 2011. More radiation was released to the air,
then fell to the sea. Woods Hole chemical oceanographer
Ken Buesseler runs a crowd-funded, citizen
science seawater sampling project that
has tracked the radiation plume as it slowly makes its way across the Pacific
Ocean. The Oregon samples, marking the
first time cesium-134 has been detected on U.S. shores, were taken in January
and February of 2016 and later analyzed. They each measured 0.3 becquerels per
cubic meter of cesium-134.
Buesseler’s team previously had
found the isotope in a sample of seawater taken from a dock on Vancouver Island,
B.C., marking its landfall in North America. In Canada, Cullen leads the InFORM
project to assess radiological risks to that country’s oceans
following the nuclear disaster. It is a partnership of a dozen academic,
government and non-profit organizations. Last month, the group reported that
a single sockeye salmon, sampled from Okanagan Lake in the summer of 2015, had
tested positive for cesium-134.
The level was more than 1,000 times
lower than the action level set by Health Canada, and is no significant risk to
consumers, Cullen said. Buesseler’s most recent samples off
the West Coast also are showing higher-than background levels of cesium-137,
another Fukushima isotope that already is present in the world's oceans because
of nuclear testing in the 1950s and 1960s. Those results will become more
important in tracking the radiation plume, Buesseler said, because the short
half-life of cesium-134 makes it harder to detect as time goes on.
Cesium-134 has a half-life of two
years, meaning it’s down to a fraction of what it was five years ago, he said.
Cesium-137 has a 30-year half-life. A recent InFORM analysis of
Buesseler’s data concluded that concentrations of cesium-137 have increased
considerably in the central northeast Pacific, although they still are at
levels that pose no concern.
“It appears that the plume has
spread throughout this vast area from Alaska to California,” the scientists
wrote.
They estimated that the plume is
moving toward the coast at roughly twice the speed of a garden snail. Radiation
levels have not yet peaked. “As the contamination plume
progresses towards our coast we expect levels closer to shore to increase over
the coming year,” Cullen said.
Even that peak won’t be a health
concern, Buesseler said. But the models will help scientists model ocean
currents in the future. That could prove important if there
is another disaster or accident at the Fukushima plant, which houses more than
a thousand huge steel tanks of contaminated water and where hundreds of tons of
molten fuel remain inside the reactors. In a worst-case scenario, the fuel
would melt through steel-reinforced concrete containment vessels into the
ground, uncontrollably spreading radiation into the surrounding soil and
groundwater and eventually into the sea.
“That’s the type of thing where
people are still concerned, as am I, about what could happen,” Buesseler said.
Scientists now know it would take
four to five years for any further contamination from the plant to reach the
West Coast.
Tracking the plume
Scientists are beginning to use an
increase in cesium-137 instead of the presence of cesium-134 to track the plume
of radioactive contamination from Japan’s Fukushima nuclear disaster. These
figures show the increase in cesium-137 near the West Coast between 2014 and
2015. Graphic courtesy Dr. Jonathan
Kellogg of InFORM, with data from Dr. John Smith, Department of Fisheries and
Oceans Canada, and Dr. Ken Buesseler, Woods Hole Oceanographic Institute.
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