Ken Buesseler on his boat.
Six months after the accident at Fukushima Daiichi, the news flow from the stricken nuclear power plant has slowed, but scientific studies of radioactive material in the ocean are just beginning to bear fruit.
The word from the land is bad enough. As my colleague Hiroko Tabuchi reported on Saturday, Japanese officials have detected elevated radiation levels in rice near the crippled reactors. Worrying radiation levels had already been detected in beef, milk, spinach and tea leaves, leading to recalls and bans on shipments.
Off the coast, the early results indicate that very large amounts of radioactive materials were released, and may still be leaking, and that rather than being spread through the whole ocean, currents are keeping a lot of the material concentrated.
Most of that contamination came from attempts to cool the reactors and spent fuel pools, which flushed material from the plant into the ocean, and from direct leaks from the damaged facilities.
Japanese government and utility industry scientists estimated this month that 3,500 terabecquerels of cesium 137 was released directly into the sea from March 11, the date of the earthquake and tsunami, to late May. Another 10,000 terabecquerels of cesium 137 made it into the ocean after escaping from the plant as steam.
The leakage very likely isn’t over, either. The Tokyo Electric Power Company, the operator of the plant, said Sept. 20 that it believed that something on the order of 200 to 500 tons a day of groundwater might still be pouring into the damaged reactor and turbine buildings.
Ken Buesseler, a scientist at the Woods Hole Oceanographic Institution, who in 1986 studied the effects of the Chernobyl disaster on the Black Sea, said the Fukushima disaster appeared to be by far the largest accidental release of radioactive material into the sea.
Chernobyl-induced radiation in the Black Sea peaked in 1986 at about 1,000 becquerels per cubic meter, he said in an interview at his office in Woods Hole, Mass. By contrast, the radiation level off the coast near the Fukushima Daiichi plant peaked at more than 100,000 becquerels per cubic meter in early April.
Before Fukushima, in 2010, the Japanese coast measured about 1.5 becquerel per cubic meter, he said.
‘‘Chernobyl might have been five times bigger, over all, but the ocean impact was much smaller,’’ Mr. Buesseler said.
Working with a team of scientists from other institutions, including the University of Tokyo and Columbia University, Mr. Buesseler’s Woods Hole group in June spent 15 days in the waters off northeast Japan, studying the levels and dispersion of radioactive substances there and the effect on marine life.
The project, financed primarily by the Moore Foundation after governments declined to participate, continued to receive samples from Japanese cruises into July.
While Mr. Buesseler declined to provide details of the findings before analysis is complete and published, he said the broad results were sobering.
“When we saw the numbers — hundreds of millions of becquerels — we knew this was the largest delivery of radiation into the ocean ever seen,’’ he said. ‘‘We still don’t know how much was released.’’
Mr. Buesseler took samples of about five gallons, filtered out the naturally occurring materials and the materials from nuclear weapon explosions, and measured what was left.
The scientists had expected to find ocean radiation levels falling off sharply after a few months, as radioactive substances were dispersed by the currents, because, he said, “The ocean’s solution to pollution is dilution.’’
The good news is that researchers found the entire region 20 to 400 miles offshore had radiation levels too low to be an immediate threat to humans.
But there was also an unpleasant surprise. “Rather than leveling off toward zero, it remained elevated in late July,’’ he said, up to about 10,000 becquerel per cubic meter. ‘‘That suggests the release problem has not been solved yet.”
The working hypothesis is that contaminated sediments and groundwater near the coast are continuing to contaminate the seas, he said.
The international team also collected plankton samples and small fish for study. Mr. Buesseler said there were grounds for concern about bioaccumulation of radioactive isotopes in the food chain, particularly in seaweed and some shellfish close to the plants. A fuller understanding of the effect on fish that are commercially harvested will probably take several years of data following several feeding cycles, he said.
‘‘We also don’t know concentrations in sediments, so benthic biota may be getting higher doses and if consumed (shellfish), could be of concern,’’ he wrote later in an e-mail, referring to organisms that dwell on the sea floor.
The study also found that the highest cesium values were not necessarily from the samples collected closest to Fukushima, he said, because eddies in the ocean currents keep the material from being diluted in some spots farther offshore.
The overall results were consistent with those previously found by Japanese scientists, Mr. Buesseler said.
He said more research was urgently needed to answer several questions, including why the level of contamination offshore near the plant was so high.
“Japan is leading the studies, but more work is needed than any one country, or any one lab, can possibly carry out,” he said.
Author: DAVID JOLLY
Source: The New York Times