Though cesium levels have tripled, the tuna is still safe to eat, researchers say.
Still, those levels were a thousand times lower than the maximum safe level set by the U.S. Department of Agriculture.
"You can't say there is absolutely zero risk because any radiation is assumed to carry at least some small risk," said the study's lead author, Delvan Neville, a graduate research assistant in OSU's Department of Nuclear Engineering and Radiation Health Physics. "But these trace levels are too small to be a realistic concern."
Researchers tested 26 Pacific albacore. Some had been caught between 2008 and the March 2011 tsunami and nuclear accident. Others were caught between the accident and 2012.
They discovered that levels of specific radioactive isotopes did increase after the accident, although by a minute amount.
"A year of eating albacore with these cesium traces is about the same dose of radiation as you get from spending 23 seconds in a stuffy basement from radon gas," Neville said.
The researchers tested samples of the albacore from their loins, carcasses and guts and found varying levels of radiation – all barely detectable. The study is the first to look at different parts of the fish.
"The loins, or muscle, is what people eat and the bioaccumulation was about the same there as in the carcass," said Jason Phillips, a research associate in OSU's College of Earth, Ocean and Atmospheric Sciences and a co-author on the study.
The researchers also found that radionuclides were somewhat higher in 4-year old fish than 3-year old fish, suggesting that the younger albacore may have made only one trans-Pacific migration, while the older fish may have migrated through the Fukushima plume twice.
The majority of the 3-year-old fish had no traces of Fukushima radiation at all.
Although it is possible that additional exposure to the plume could further increase radiation levels in the albacore, it would still be at a low level, the researchers said.
The plume is expected to reach the West Coast this month. Federal agencies aren't testing for it, but the Oregon Health Authority tests quarterly samples of seawater. Its next test is scheduled for May 13.
No Oregon agency does radiation testing on seafood for human consumption, either caught locally or imported from other countries, said Bruce Pokarney, spokesman for the Oregon Department of Agriculture.
Little is known about the migration patterns of young albacore before they enter the U.S. fishery at about three years of age, Phillips said.
Albacore mature at around age five, stop migrating long distances and move south to subtropical waters in the Central and West Pacific. They don't return to the West Coast of the United States.
"The presence of these radioactive isotopes is actually helping us in an odd way – giving us information that will allow us to estimate how albacore tuna migrate between our West Coast and Japan," Neville said.
The study has been published in the journal Environmental Science and Technology.
"This basically worked out as a pilot study," Neville said. "Because we did find these results, we were able to get a grant to look at albacore in much higher numbers all along the West Coast," Neville said.
Read the study here: http://bit.ly/1k75sbg
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