Nuclear Tuna Is Hot News, But Not Because It's Going To Make You Sick

May 30, 2012
Originally published on May 30, 2012 5:17 am

What snarky headline writer could resist a story about "hot tuna?" Or how about "tuna meltdown?"

Really, it seems just plain daffy to ignore a new study that says some Pacific bluefin tuna picked up traces of radioactive material from the Fukushima nuclear disaster last year and brought it across the Pacific Ocean.

And while, as a rule, we avoid making light of nuclear disasters, the tuna story is actually just plain curious, rather than threatening, once you understand the context.

You see, Pacific bluefin tuna spawn off the coast of Japan. They are superb swimmers, so in a few months time, they make it across the Pacific to the coast of Mexico and Southern California to feed — and then get caught. They are also delicious, pricey and on the verge of population collapse, according to Monterey Bay Aquarium Seafood Watch.

Last summer, scientists bought 15 of these beautiful fish from the docks in San Diego to check them for contaminants.

Fish do carry contaminants. Most significant from the standpoint of public health is methyl mercury, which is a neurotoxin. It's especially a risk for developing fetuses, which is why the U.S. government urges women of child-bearing age to limit their tuna consumption.

The researchers are still waiting for their mercury results on this particular batch of fish. But Monday they published other findings in the journal Proceedings of the National Academy of Sciences.

Sure enough, the tuna from Japan had picked up traces of radioactive cesium, according to Nicholas Fisher and Zofia Baumann at Stony Brook University, and Daniel Madigan at Stanford University, who co-wrote the article.

The cesium was a blend of two different varieties – cesium-134 and cesium-137. The exact mix of these isotopes creates a signature showing that the radiation came from the multiple meltdowns last March in Fukushima.

Fisher says they weren't actually worried about radioactive cesium as a health risk. They tested the flesh, "mostly just to see if it we could detect it, and we were quite surprised, I must say. We did not expect to see this radioactivity retained by the fish during their trans-Pacific voyage, which we estimates takes from three to four months."

Yes, radiation in seafood seems scary. But here's the catch (if you pardon the expression). Tuna, like every other food on the planet, already contains naturally occurring radiation. It has potassium-40 and polonium-210. It always has and it always will. In addition, seafood in general contains a trace of cesium-137 left over from nuclear weapons testing in the 1950s and 1960s.

So the question is, how much more radiation did these particular tuna fish contain? The answer is: A trivial amount. In fact, radiation from the cesium is 30 times less than the radiation that's already in the fish naturally in the form of potassium-40, according to the research paper. And the natural polonium-210 packs a radiation dose 200 times larger than the dose from the cesium.

Really, the result is a testament to how well scientists can now measure tiny amounts of radiation. And of course it's a remarkable lesson in how wildlife can be traced using accidental "tags" instead of using the labor-intensive plastic ones.

If you are still worried about the cesium from Fukushima, Robert Emery at the University of Texas Health Science Center at Houston says you'd need to eat 2.5 to 4 tons of tuna in a year to get a dose of cesium-137 that exceeds health limits. That's a lot of sushi.

Yes, bluefin is used primarily for sushi. And, much of the Pacific bluefin tuna that's caught off the coast of Mexico and Southern California is shipped right back across the ocean, to be sold at the lucrative seafood markets — in Japan.

For more on this story, tune in to my piece on Morning Edition tomorrow.

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In the next few minutes, we're going to hear about some of the world's more elegant seafood. That would be: caviar, coming from and unexpected place, and bluefin tuna from and unfortunate place.


And that would be Japan. Last years' nuclear meltdown at the Fukushima power station contaminated marine life. And it turns out some of those fish have made their way across the Pacific Ocean into American waters.

MONTAGNE: Still, experts say the amount of radioactivity found in the fish is far too small to pose a health risk. NPR's Richard Harris has more.

RICHARD HARRIS, BYLINE: Pacific bluefin tuna are magnificent creatures. When they are not being overfished for sushi - as they are around the world - they are making incredible ocean voyages.

NICHOLAS FISHER: Bluefin tuna spawn in waters in the western Pacific, including waters around Japan. And they actually swim across the entire Pacific Ocean and make it to waters off California and Mexico.

HARRIS: Nicholas Fisher at Stony Brook University studies the contaminants that end up in Pacific bluefin tuna. Methyl mercury is the main concern. It can damage brain tissue. That's why pregnant women in particular are urged to limit their consumption of tuna.

Last summer, Fisher and his colleagues collected 15 bluefin tuna from fishermen in San Diego to look for contaminants. Since the Fukushima meltdowns happened at about the time those fish were swimming off Japan, the researchers decided to see if they could find any radioactive material in the flesh.

FISHER: It was mostly just to see if we could detect it. And we were quite surprised.

HARRIS: They did find traces of radioactive cesium, as they report in the Proceedings of the National Academy of Sciences. And they could tell by the mix of two types of cesium that the material came from Fukushima. The amounts were tiny. Fish already contain traces of naturally occurring radioactive elements such as potassium-40. And that natural radiation in the fish flesh was far greater than the added radiation from Fukushima by a factor of 30.

Bob Emery, at the University of Texas Health Science Center at Houston, says radiation may be spooky, but in this case there's no health risk.

BOB EMERY: In order for a member of the general public to reach the annual public dose limit, they'd have to eat between 5,000 and 8,000 pounds of tuna.


HARRIS: In a year. And by the way, much of the bluefin tuna caught of the West Coast is actually shipped back to Japan to be sold in its lucrative sushi market. But the idea of radioactive tuna sparked the imagination of editors around the world, and sent marine biologist Nick Fisher scrambling.

FISHER: Literally every 30 seconds, there's another request for an interview from as far a field as Korea, Al Jazeera television. I mean, I don't commonly get, you know, inquiries from Al Jazeera.

HARRIS: The cool part of his research is that this otherwise miserable tsunami and nuclear meltdown has created a natural tracer for biologists. By tracking the cesium, Fisher says they can study the movements of migratory sea life.

FISHER: And this would include other fish. It could include birds, mammals, turtles. So we think this could be actually a very useful tool.

HARRIS: That is, once the hot tuna story dies down a bit.

Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.