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California bluefin tuna show traces of Fukushima radiation


A sushi chef displays a block of fat meat tuna from a 269 kg bluefin tuna to serve at the sushi restaurant Sushi-Zanmai near Tokyo's Tsukiji fish market on Jan. 5, 2012.


Yoshikazu Tsuno

Scientists have found traces of radiation in bluefin tuna caught off the coast of California, months after the Fukushima nuclear disaster in Japan.

The levels of radioactivity are still well below US and Japanese safety limits, the Guardian said.

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According to a study published yesterday in the Proceedings of the National Academy of Sciences journal, small amounts of radioactive cesium isotopes were detected in 15 Pacific bluefin caught near San Diego in August last year.

The fish showed levels of cesium-137 and cesium-134 that were 10 times higher than in tuna caught previously in the same area.

According to the BBC, while isotope 137 can remain in seawater for years, cesium-134 decays much more quickly and therefore gives a clear indication that it originated from the Fukushima accident, less than five months before the fish were caught.

The leak at the Fukushima Daiichi nuclear plant released radioactive material into the Pacific Ocean, the New Scientist explained, material which fish can pick up from the water they swim in and the food they eat.

In turn, predators that eat contaminated fish will accumulate a higher concentration of cesium due to an effect known as biomagnification, Bloomberg reported.

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The study's authors are not warning of a public health risk, however.

"I wouldn't tell anyone what's safe to eat or what's not safe to eat," lead author Daniel Madigan, a marine biologist at Stanford University, told Reuters. "It's become clear that some people feel that any amount of radioactivity, in their minds, is bad and they'd like to avoid it. But compared to what's there naturally... and what's established as safety limits, it's not a large amount at all."

In fact, according to New Scientist, the radiation may even allow biologists to learn more about the migration patterns of other sea animals such as turtles and sharks, by using the levels of isotopes in their systems to calculate when they passed through Japanese waters.

The research team expects the radiation to decline gradually, co-author Nicholas Fisher of Stony Brook University told Bloomberg. They plan to conduct a follow-up study later this year. 

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