Ocean Currents, Natural Dilution Dissipate Japan’s Nuclear Risk

Ocean currents and natural dilution of sea water contaminated by Tokyo Electric Power Co.’s crippled nuclear plant are likely to spare marine life and the underwater ecosystem from devastation, scientists said.

Radioactive materials, including iodine-131, cesium-134 and cesium-137, were detected near the Southern discharge canal from the Fukushima Dai-Ichi nuclear power plant on March 21. Japanese regulators expect results tomorrow from their analysis of sea water from eight locations.

The ocean can absorb significant increases in cesium and iodine, the two most common radioactive isotopes coming from the plant, before it becomes unsafe for humans or marine animals, said Ken Buesseler, senior scientist at Woods Hole Oceanographic Institute in Massachusetts. Health authorities still are wise to monitor seafood, seaweed and other ocean products, he said.

“For cesium and iodine, they are soluble,” Buesseler said in a telephone interview. “This time of year off the coast of Japan, they would mix with water down 100 feet to 300 feet, and be diluted by a factor of about 100. The currents there would move it to the south, just north of Tokyo, and then out to sea.”

Tokyo Electric Power said it suspected the decay of radioactive fuel rods, composed of uranium and plutonium, five days after a March 11 earthquake and tsunami swamped the facility. Readings in seawater for iodine-131, which increases the risk of thyroid cancer, were 127 times higher than normal, while levels of cesium-134 were 25 times normal and those for cesium-137 were 17 times higher. Cobalt has also been detected.

Risk to Agriculture

Seafood isn’t a major risk compared to food from the land or radioactivity in the air, said Bill Camplin, group manager of radiological and chemical risk at the Centre for Environment, Fisheries and Aquaculture Science in Lowestoft, England. Elevated radiation levels have been found in milk and green leafy vegetables, including spinach and spring onions, grown near the plant 135 miles (220 kilometers) north of Tokyo.

“But my advice would be not to eat seafood caught from within the evacuation and sheltering zone,” or about 30 kilometers offshore, Camplin said in an e-mail. “Effects on wildlife in the sea are unlikely to be severe.”

The Food and Drug Administration yesterday banned produce, milk and milk products from four areas in Japan near the Fukushima plant from entering the U.S.

Seafood Consumption

Contaminated seafood is a particular concern in Japan, which is made up primarily of four islands and whose population eats more fish than any other nation except China. The country consumes about 9 million metric tons of seafood a year, according to the website of the Sea Around Us Project, a collaboration between the University of British Columbia and the Pew Environment Group. China ranked first with consumption of 13.6 million metric tons and the U.S. third at 4.7 million tons.

Iodine accumulates in seaweed and may already be present off Japan’s coast, Buesseler said. Because iodine starts to dissipate after a few days, the risk isn’t as long lasting as with cesium, which remains for decades, he said.

Elevated cesium levels may be a health risk, said Tom McKone, professor of environmental health sciences at the University of California, Berkeley. The human body treats it like potassium, an essential element, and it can penetrate soft tissue and muscle to give off whole-body radiation, he said.

Cesium has a half-life of 30 years, meaning it will remain for generations, compared with the much shorter 8-day half-life seen with radioactive iodine, said McKone, a senior staff scientist at Lawrence Berkeley National Laboratory.

Chernobyl and Black Sea

Experience with the Black Sea after the world’s worst nuclear disaster in Chernobyl, Ukraine, shows the risk in water may not be as great as that seen on land, said Buesseler, who has studied issue. Cesium levels in the Black Sea, located more than 400 miles from Chernobyl, were 10 times to 20 times higher than normal after the 1986 accident, he and colleagues found.

Cesium was already present in the Black Sea and the Pacific Ocean because of nuclear weapons testing done in the 1950s and 1960s, he said.

While the elevated levels sound dangerous, there is no direct damage done to sea life or humans from it, he said.

“You can safely bathe in the Black Sea, eat fish from the Black Sea and if you wanted to drink salt water, you could drink water from the Black Sea,” he said. “It is not at levels that are harmful for seafood consumption.”

Fukushima Plant

The 40-year-old Fukushima plant, built during Japan’s first wave of nuclear construction, withstood the country’s worst earthquake on record, only to have its power and back-up generators knocked out by the 7-meter tsunami that followed. Lacking electricity to pump water needed to cool the atomic core, engineers vented radioactive steam into the atmosphere to release pressure. A series of explosions ensued, blowing out concrete walls around some reactors.

Wind blew the radioactive plume offshore, into the Pacific Ocean, where the sheer volume of water is drastically diluting the radiation, said David Brenner, director of the Center for Radiological Research at Columbia University in New York, in a telephone interview.

“Dumb luck was the biggest factor in keeping the public health risk down,” Brenner said. Radiation levels in the ocean are probably too diluted to contaminate fish, though regulators still need to measure it, he said.

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