This world map shows radiation level in the oceans in 1990, mostly from nuclear weapons testing, measured in Becquerels. Credit: Woods Hole Oceanographic Institution |
Among
the casualties of the March 11, 2011, earthquake and resulting tsunami
in Japan was the country’s Fukushima Daiichi nuclear power plant.
A
result of the loss of electricity, overheating at the power plant led
to significant releases of iodine, cesium and other radioisotopes to the
environment.
Japanese
officials recently raised the severity of the nuclear power plant
incident to level 7, the highest level on the international scale and
comparable only to the Chernobyl incident 25 years ago, says Ken
Buesseler, a chemical oceanographer at the Woods Hole Oceanographic
Institution.
“When it comes to the oceans, however,” says Buesseler, “the impact of Fukushima exceeds Chernobyl.”
Radionuclides
in seawater have been reported from the Fukushima plant’s discharge
canals, from coastal waters five to ten kilometers south of the plant,
and from 30 kilometers offshore.
“Levels
of some radionuclides are at least an order of magnitude higher than
the highest levels in 1986 in the Baltic and Black Seas, the two ocean
water bodies closest to Chernobyl,” says Buesseler.
This is a satellite image from 160 kilometers (100 miles) north of the Fukushima nuclear power plant in Japan. Japan’s two large ocean currents — the Kuroshio and the Oyashio — converge here. Credit: NASA |
He
has been awarded a rapid-response grant from the National Science
Foundation’s (NSF) Division of Ocean Sciences to establish baseline
concentrations of several radionuclides in the Atlantic and Pacific
Oceans.
“Finding
this information early on is key to understanding the severity of the
releases and related public health issues,” says Buesseler.
He
and colleagues will establish a baseline radionuclide data set for the
Atlantic and Pacific Oceans, using an east-to-west network of sampling
stations where the ability to retrieve ocean water samples already
exists.
Researchers
learned much from Chernobyl about the fate of radioactive fallout
delivered to the oceans, and about using that fallout as a “tracer” for
how fast ocean waters mix and sediments accumulate.
“After
Chernobyl, fallout was measured not only in samples close to the site,
such as those in the Black Sea, but as far afield as the north Pacific
Ocean,” Buesseler says.
Because
the atmosphere and oceans are linked, scientists would expect
radionuclides present in the atmosphere also to appear in the ocean,
albeit at very low levels, says chemical oceanographer Henrieta Dulaiova
of the University of Hawaii.
Dulaiova has also been awarded a rapid-response grant from NSF’s Division of Ocean Sciences to study the fallout.
She
is monitoring ocean waters to establish baseline concentrations of
radionuclides, and to determine the spreading of released radionuclides.
“Like
the people of Japan–though certainly to a lesser degree–we are
dealing with a radiochemical situation that will be with us for a long
time,” says Don Rice, director of NSF’s chemical oceanography program.
Hundreds of liters of seawater are sampled for radioactivity from the central Pacific Ocean. Credit: Henrieta Dulaiova, University of Hawaii |
“To
understand how the ocean and atmosphere have handled this contamination
in the years ahead, we must first get a snap-shot of the situation
today,” says Rice. “Buesseler and Dulaiova are doing just that.”
Dulaiova’s
study is focused on the central Pacific Ocean, and includes coastal and
offshore waters off Hawaii, Guam and the Midway Islands.
“Hawaii’s
proximity to Japan makes it an important monitoring point,” says
Dulaiova. “We’re conducting weekly coastal and monthly offshore water
sample collections.”
Bi-weekly samples from Guam are also collected, and samples are obtained from ships cruising the western Pacific.
The
samples are then analyzed for cesium isotopes, whose signature allows
scientists to identify radionuclides released from Fukushima.
Dulaiova is also planning to look at other radionuclides such as iodine, strontium and some actinides that were released.
“The
information is needed,” she says, “so that any subsequent efforts to
understand the severity of the releases, the bioaccumulation of
radionuclides in the ocean food web, and ocean processes and spreading
patterns of the released radioisotopes, all have good baseline data.”
The researchers hope to develop an understanding of marine radionuclides on a global scale.
SOURCE: National Science Foundation
