Radioactive bluefin tuna crossed the Pacific to US
Across the vast Pacific, the mighty bluefin tuna carried radioactive contamination that leaked from Japan's crippled nuclear plant to the shores of the United States 6,000 miles away — the first time a huge migrating fish has been shown to carry radioactivity such a distance.I'm not surprised that some cesium (Cs) survived the trip across the ocean in tuna. The biological half-life of Cs is estimated to be on the the order of weeks to months, and it take approximately 10 half-lives for a substance to vanish below detection due to such a depuration process. Moreover, it's likely that the loss kinetics are multiphasic, with the loss half time being estimated on the the fastest phase. Some Cs incorporated in more slowly exchanging pools will likely remain.
"We were frankly kind of startled," said Nicholas Fisher, one of the researchers reporting the findings online Monday in the Proceedings of the National Academy of Sciences.
The levels of radioactive cesium were 10 times higher than the amount measured in tuna off the California coast in previous years. But even so, that's still far below safe-to-eat limits set by the U.S. and Japanese governments.
Previously, smaller fish and plankton were found with elevated levels of radiation in Japanese waters after a magnitude-9 earthquake in March 2011 triggered a tsunami that badly damaged the Fukushima Dai-ichi reactors.
But scientists did not expect the nuclear fallout to linger in huge fish that sail the world because such fish can metabolize and shed radioactive substances.
Actually, I remain unconcerned about the radioactive Cs in Pacific tuna. Besides the fact that Georgia would never buy expensive, large Blue Fin Tuna, I have had enough experience with radioactivity analysis to know that it's incredibly sensitive, and it required heavy shielding and careful background correction to find the signal in the fish.