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Across the vast Pacific, the mighty bluefin tuna carriedradioactive contamination that leaked from Japan's cripplednuclear plant to the shores of the United States 6,000 miles away the first time a huge migrating fish has been shown to carryradioactivity such a distance. "We were frankly kind of startled," said NicholasFisher, one of the researchers reporting the findings online Mondayin the Proceedings of the National Academy of Sciences . The levels of radioactive cesium were 10 times higher than theamount measured in tuna off the California coast in previous years.But even so, that's still far below safe-to-eat limits set bythe U.S. and Japanese governments. Previously, smaller fish and plankton were found with elevatedlevels of radiation in Japanese waters after a magnitude-9earthquake in March 2011 triggered a tsunami that badly damaged theFukushima Dai-ichi reactors. ( MORE : Japan s Next Nightmare: Health Problems from Radiation Exposure ) But scientists did not expect the nuclear fallout to linger in hugefish that sail the world because such fish can metabolize and shedradioactive substances. One of the largest and speediest fish, Pacific bluefin tuna cangrow to 10 feet and weigh more than 1,000 pounds. They spawn offthe Japan coast and swim east at breakneck speed to school inwaters off California and the tip of Baja California, Mexico. Five months after the Fukushima disaster, Fisher of Stony BrookUniversity in New York and a team decided to test Pacific bluefinthat were caught off the coast of San Diego. To their surprise,tissue samples from all 15 tuna captured contained levels of tworadioactive substances cesium-134 and cesium-137 that werehigher than in previous catches. ( MORE : Memorial Day Food Safety: Tips for Handling Fruits and Veggies ) To rule out the possibility that the radiation was carried by oceancurrents or deposited in the sea through the atmosphere, the teamalso analyzed yellowfin tuna, found in the eastern Pacific, andbluefin that migrated to Southern California before the nuclearcrisis. They found no trace of cesium-134 and only backgroundlevels of cesium-137 left over from nuclear weapons testing in the1960s. The results "are unequivocal. Fukushima was thesource," said Ken Buesseler of the Woods Hole OceanographicInstitution, who had no role in the research. Bluefin tuna absorbed radioactive cesium from swimming incontaminated waters and feeding on contaminated prey such as krilland squid, the scientists said. As the predators made the journeyeast, they shed some of the radiation through metabolism and asthey grew larger. Even so, they weren't able to completelyflush out all the contamination from their system. "That's a big ocean. To swim across it and still retainthese radionuclides is pretty amazing," Fisher said. ( MORE : Salmonella in Dog Food Sickens 14 People Across U.S. ) Pacific bluefin tuna are prized in Japan where a thin slice of thetender red meat prepared as sushi can fetch $24 per piece at topTokyo restaurants. Japanese consume 80 percent of the world'sPacific and Atlantic bluefin tuna. The real test of how radioactivity affects tuna populations comesthis summer when researchers planned to repeat the study with alarger number of samples. Bluefin tuna that journeyed last yearwere exposed to radiation for about a month. The upcoming travelershave been swimming in radioactive waters for a longer period. Howthis will affect concentrations of contamination remains to beseen. Now that scientists know that bluefin tuna can transport radiation,they also want to track the movements of other migratory speciesincluding sea turtles, sharks and seabirds. MORE : Strip Search: How Safe Are Airports New X-Ray Scanners?. I am an expert from cartonmakingmachines.com, while we provides the quality product, such as China Paper Slitting Machine , Folder Gluer Machine, Cardboard Box Making Machine,and more.
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