Probably not what many people want to hear, who have been busy petitioning their local governments on the US west coast about the danger of "high levels" of Fukushima radiation.
According to the press release by Oregon State University, the researchers at Oregon State University and National Oceanic and Atmospheric Administration (NOAA) tested Pacific albacore tuna caught off the coast of Oregon between 2008 and 2012 and compared radioactive cesium levels, the first study to compare "before and after". The study is also the first to compare different parts of the fish.
The study seems to be the continuation of the study they published on October 2012.
The result was that the amount of radioactive cesium in post-Fukushima fish was triple that of pre-Fukushima fish, "at the most extreme level".
From the paper's abstract, here are the numbers, in MILLIBECQUEREL/Kg (millibecquerel=1/1000 of 1 becquerel) in WET WEIGHT:
Cesium-134: 18.2–356 mBq/kg of wet weight
Cesium-137: 234–824 mBq/kg of wet weight
Cesium-134: 0.0182 - 0.356 Bq/kg
Cesium-137: 0.234 - 0.824 Bq/kg
An unexpected side benefit of studying these fish was, according to the researchers, to better understand the albacore tuna migration, using radioactive cesium from Fukushima as a trace.
The press release by Oregon State University (4/28/2014; emphasis is mine):
Study finds only trace levels of radiation from Fukushima in albacore
CORVALLIS, Ore. – Albacore tuna caught off the Oregon shore after the Fukushima Daiichi power station in Japan was destroyed in a 2011 earthquake had slightly elevated levels of radioactivity but the increase has been minute, according to a newly published study.
In fact, you would have to consume more than 700,000 pounds of the fish with the highest radioactive level – just to match the amount of radiation the average person is annually exposed to in everyday life through cosmic rays, the air, the ground, X-rays and other sources, the authors say.
Results of the study are being published in the journal Environmental Science and Technology.
“You can’t say there is absolutely zero risk because any radiation is assumed to carry at least some small risk,” said Delvan Neville, a graduate research assistant in the Department of Nuclear Engineering and Radiation Health Physics at Oregon State University and lead author on the study. “But these trace levels are too small to be a realistic concern.
“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, or sleeping next to your spouse for 40 nights from the natural potassium-40 in their body,” he added. “It’s just not much at all.”
In their study, the researchers examined a total of 26 Pacific albacore caught off the coast between 2008 and 2012 to give them a comparison between pre-Fuskushima and post-Fukushima radiation levels. They discovered that levels of specific radioactive isotopes did increase, but at the most extreme level, they only tripled – a measurement that is only 0.1 percent of the radiocesium level set by the U.S. Food and Drug Administration for concern and intervention.
The researchers tested samples of the albacore from their loins, carcass and guts and found varying levels – all barely detectable. The findings are still important, however, since this is one of the first studies 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 co-author on the study.
The researchers next began looking at the radionuclide levels in different aged fish and found they were somewhat higher in 4-year-old albacore than in the younger fish. This suggests that the 3-year-old albacore may have only made one trans-Pacific migration, whereas the 4-year-old fish may have migrated through the Fukushima plume twice.
The majority of the 3-year-old fish had no traces of Fukushima at all.
Although it is possible that additional exposures to the plume could further increase radiation levels in the albacore, it would still be at a low level, the researchers pointed out. Additionally, as albacore mature at around age 5, they stop migrating long distances and move south to subtropical waters in the Central and West Pacific – and do not 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.
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.
“That’s kind of surprising, considering what a valuable food source they are,” Phillips said. “Fukushima provides the only known source for a specific isotope that shows up in the albacore, so it gives us an unexpected fingerprint that allows us to learn more about the migration.”
Other authors were Richard Brodeur of NOAA’s Northwest Fisheries Science Center, and Kathryn Higley, of the OSU Department of Nuclear Engineering and Radiation Health Physics. The study was supported by Oregon State University and the National Oceanic and Atmospheric Administration, with continued support from Oregon Sea Grant.
The abstract of the paper "Trace Levels of Fukushima Disaster Radionuclides in East Pacific Albacore" (emphasis is mine):
The Fukushima Daiichi power station released several radionuclides into the Pacific following the March 2011 earthquake and tsunami. A total of 26 Pacific albacore (Thunnus alalunga) caught off the Pacific Northwest U.S. coast between 2008 and 2012 were analyzed for 137Cs and Fukushima-attributed 134Cs. Both 2011 (2 of 2) and several 2012 (10 of 17) edible tissue samples exhibited increased activity concentrations of 137Cs (234–824 mBq/kg of wet weight) and 134Cs (18.2–356 mBq/kg of wet weight). The remaining 2012 samples and all pre-Fukushima (2008–2009) samples possessed lower 137Cs activity concentrations (103–272 mBq/kg of wet weight) with no detectable 134Cs activity. Age, as indicated by fork length, was a strong predictor for both the presence and concentration of 134Cs (p < 0.001). Notably, many migration-aged fish did not exhibit any 134Cs, suggesting that they had not recently migrated near Japan. None of the tested samples would represent a significant change in annual radiation dose if consumed by humans.
Researchers at Stanford University and Stony Brook University published the study on Pacific bluefin tuna in June 2013, which revealed radiation exposure from natural radioactive potassium and polonium (alpha nuclide) is significantly greater than exposure from Fukushima-derived radioactive cesium.