Radiation detected 400 miles off Japan coast
Tuesday, February 21, 2012 - 21:30 in Earth & Climate
Salt Lake City
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| Japan's Radioactive Ocean |
Radioactive contamination from the Fukushima power plant disaster has been detected as far as almost 400 miles off Japan in the Pacific Ocean, with water showing readings of up to 1,000 times more than prior levels, scientists reported Tuesday.
(Japan's ocean currents: 1. Kuroshio, 7. Oyashio. Credit:Tosaka, via Wikimedia Commons.)
But those results for the substance cesium-137 are far below the levels that are generally considered harmful, either to marine animals or people who eat seafood, said Ken Buesseler of the Woods Hole Oceanographic Institution in Massachusetts.
He spoke Tuesday in Salt Lake City at the annual Ocean Sciences Meeting, attended by more than 4,000 researchers this week.
The results are for water samples taken in June, about three months after the power plant disaster, Buesseler said. In addition to thousands of water samples, researchers also sampled fish and plankton and found cesium-137 levels well below the legal health limit.
"We're not over the hump" yet in terms of radioactive contamination of the ocean because of continued leakage from the plant, Buesseler said in an interview before Tuesday's talk. He was chief scientist for the cruise that collected the data.
The ship sampled water from about 20 miles to about 400 miles off the coast east of the Fukushima plant. Concentrations of cesium-137 throughout that range were 10 to 1,000 times normal, but they were about one-tenth the levels generally considered harmful, Buesseler said.
Cesium-137 wasn't the only radioactive substance released from the plant, but it's of particular concern because of its long persistence in the environment. Its half-life is 30 years.
The highest readings last June were not always from locations closest to the Fukushima plant, Buesseler said. That's because swirling ocean currents formed concentrations of the material, he said.
Most of the cesium-137 detected during the voyage probably entered the ocean from water discharges, rather than atmospheric fallout, he added.
Scientists assess radioactivity in the ocean from Japan nuclear power facility
Published: Friday, December 9, 2011 - 20:36 in Earth & Climate
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Ken Buesseler, WHOI
With current news of additional radioactive leaks from the Fukushima nuclear power plants, the impact on the ocean of releases of radioactivity from the plants remains unclear. But a new study by U.S. and Japanese researchers analyzes the levels of radioactivity discharged in the first four months after the accident.
It draws some basic conclusions about the history of contaminant releases to the ocean.
The study was conducted by Woods Hole Oceanographic Institution chemist Ken Buesseler and two colleagues based in Japan, Michio Aoyama of the Meteorological Research Institute and Masao Fukasawa of the Japan Agency for Marine-Earth Science and Technology.
They report that discharges from the Fukushima Dai-Ichi nuclear power plants peaked one month after the March 11 earthquake and tsunami that precipitated the nuclear accident, and continued through at least July.
Their study finds that the levels of radioactivity, while high, are not a direct threat to humans or marine life, but cautions that the effect of accumulated radionuclides in marine sediments is poorly known.
The release of radioactivity from Fukushima--both as atmospheric fallout and direct discharges to the ocean--represents the largest accidental release of radiation to the ocean in history.
Concentrations of cesium-137, a radioactive isotope with a 30-year half-life, at the plants' discharge points to the ocean peaked at more than 50 million times normal/previous levels.
Concentrations 18 miles offshore were higher than those measured in the ocean after the Chernobyl accident 25 years ago.
This is largely related to the fact, says Buesseler, that the Fukushima nuclear power plants are located along the coast, whereas Chernobyl was several hundred miles from the nearest salt water basins, the Baltic and Black Seas.
However, due to ocean mixing processes, the levels are rapidly diluted off the northwest coast of Japan.
The study used data on the concentrations of cesium-137, cesium-134 and iodine-131 as a basis to compare the levels of radionuclides released into the ocean with known levels in the sea surrounding Japan prior to the accident.
The resulting paper, Impacts of the Fukushima Nuclear Power Plants on Marine Radioactivity, is published in the current issue of the journal Environmental Science & Technology.
Salmon, caribou tested for radiation from Japanese reactor
Whether the salmon are affected by the radiation depends on what the salmon eat, Pitcher said, and also on the half-life of the particular radioactive isotope that entered the food chain from the reactor.
Pitcher said it is not likely the fish will reveal contamination, but it is important to test them and rule out the possibility. Other salmon species such as Koho and pink salmon do not migrate as far as sockeye and spend less time at sea, he said, so they are much less likely to be affected by the reactor failure.
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