CORVALLIS, Oregon -- Samples of albacore tuna caught off the West Coast of the United States show minute traces of radiation that can be traced to the Fukushima reactor disaster, according to an interdisciplinary team of scientists from Oregon State University and the National Oceanic and Atmospheric Administration.
The radiation levels in fish analyzed to date are far below anything that would pose a risk to humans who consume the fish, the research team emphasized. The findings are preliminary; additional fish remain to be tested.
But the findings could reveal new information about where Pacific albacore travel during their migratory lives and how what happens in one part of the ocean can affect the food web thousands of miles away.
The team has collected and tested fish caught off the U.S. West Coast both before and after the devastating March 2011 Japanese tsunami and subsequent release of radioactive material into the ocean by the Fukushima Daiichi nuclear reactor.
"We're still processing new fish, but so far the radiation we're detecting is far below the level of concern for human safety," said Delvan Neville, a graduate researcher with OSU's Radiation Health Physics program and a co-investigator on the project.
People are constantly exposed to radiation from the natural environment, Neville pointed out. "To increase their normal annual dosage of radiation by just 1 percent, a person would have to eat more than 4,000 pounds of the highest (radiation) level albacore we've seen."
Neville will present the team's preliminary findings on Oct. 27 at the Heceta Head Coastal Conference in Florence. Richard Brodeur, the NOAA Northwest Fisheries Science Center biologist who serves as lead investigator on the project, reported the same findings to the recent annual meeting of PICES, the North Pacific Marine Science Organization, in Japan. The researchers also plan scientific journal articles.
The OSU team's findings are consistent with those of California researchers who announced in May that they had found traces of Fukushima-linked radionuclides in bluefin tuna caught off the California coast. The bluefin news came as a surprise to the scientific and regulatory community. Shortly after the March 2011 Japanese tsunami and reactor disaster, the U.S. Environmental Protection Agency, Food and Drug Administration and NOAA jointly expressed "high confidence" in the safety of U.S. seafood products, suggesting it was unlikely that migratory fish such as tuna would be contaminated to "significantly elevated radiation levels."
Relying on agency statements, fisheries organizations such as the Oregon Albacore Commission predicted that 2-to-5-year-old albacore, a mainstay of the U.S. troll and pole fishery, would be unaffected because their migration patterns do not take them through the waters where the radiation leak occurred.
But scientists differ on the details of albacore migration and behavior. Some suggest that not all albacore follow the same migration routes between western Pacific waters and feeding grounds off the U.S. West Coast. Some believe North Pacific albacore may even comprise two separate sub-stocks with different migratory paths.
That's one of the questions Jason Phillips, then a graduate fisheries researcher in OSU's College of Earth, Ocean, and Atmospheric Sciences, was investigating with support from Oregon Sea Grant, when the 2011 disaster struck Japan. He wondered whether the radiation released by the Fukushima nuclear plant could be used as a "natural tag" to help unravel some of the questions about fish migration. He put together a pilot study, but soon found he needed more fish samples and access to additional equipment for detecting and measuring extremely low levels of radiation.
Brodeur, the NOAA biologist overseeing Phillips' research, introduced him to Neville, a graduate student in OSU's Radiation Health Physics program who was looking for Ph.D. research topics and who had access to the specialized instruments needed to analyze the albacore samples for the type of radionuclides released by the Japanese reactor. He also obtained a modest NOAA grant to support the research.
The researchers first identified two Fukushima-linked isotopes Cesium-137 (Cs-137) and Cesium-134 (Cs-134) this July, in samples of fish caught and frozen in 2011.
This particular combination of radioactive isotopes is produced by fission in nuclear reactors, and less commonly, nuclear weapons. Cs-134, in particular, is considered key to the Fukushima nuclear "fingerprint" because it decays very rapidly, with a half-life of just more than two years. While Cs-137, which persists for decades in the environment, could come from other possible sources, scientists say, the Cs-134 could only have come from the Fukushima reactors.
But the team needed more evidence to support the radioactivity findings. Phillips spent this summer collecting more fish at sea, off Oregon and Washington, as well as from scientists, fishermen and other sources along the West Coast. Neville ran more tests, validating his methods against freeze-dried fish standards tested by dozens of labs and got the same results. They also shared fish samples with the Washington state Office of Radiation Protection, where radiation health physicist Lynn Albin is analyzing them as an additional check.
As more fish were tested, the results were consistent with the initial findings: No Cs-134 in fish caught before the disaster, but traces of the isotope in a significant number of fish caught since.
"This is what we've seen after testing about 70 pounds of tuna," Neville said. "When you've run one or two samples, you can't really say much about the population you're testing yet. When you've run five or six, you could make some guesses. When you're up to, at this time, 18 samples and everything has fallen fairly neatly into two groups of results, you can start to make some predictions about that population.
"What we can say is that we have detected Cs-134 in fish thousands of miles from where that Cs-134 came from, and over a year since it was released," Neville added. "It's very interesting scientifically, and it can tell us more about tuna migration and what happens to radioactive releases, but it's nowhere near enough to be concerned about food safety."
Jason Phillips, whose fisheries research launched the investigation, says it will take more work to unravel the mysteries of albacore migration.
"We are finding evidence that the albacore caught in Oregon and Washington in the summer have spent the winter in different locations in the North Pacific," he said. "But other researchers have been trying to figure out how albacore migrate for decades. We need to increase the number of fish and locations we test before we can start getting at the bigger questions."
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