By Michael Conathan

In recent weeks, there has been a significant uptick in news from Fukushima, Japan. Officials from the Japanese government and the Tokyo Electric Power Company, or TEPCO, admitted that radioactive water is still leaking from the nuclear plant crippled by the 2011 earthquake and tsunami.

The new revelations about the amount of water leaking from the plant have caused a stir in the international community and led to additional scrutiny of Pacific Ocean seafood. Last week, South Korea announced it had banned all imports of Japanese seafood from a large area around Fukushima. And Al Jazeera reported that the cost to the region’s fishing industry over the past two years exceeds $3.5 billion.

Now, fears are mounting that the radiation could lead to dangerous contamination levels in seafood from more of the Pacific Basin. Numerous blog posts and articles expressed concern about the potential for higher concentrations of radioactive particles, particularly in highly migratory species such as tuna that may have encountered Fukushima’s isotopes—including highly dangerous and toxic materials such as cesium-137, strontium-90, and iodine-131—on their transoceanic travels.

Amid alarmist outcry and opposing assurances that the radiation levels in fish are no more harmful than what’s found in the average banana, I decided to dig a little deeper, and a few weeks ago, I posted a brief analysis on Climate Progress. After reading the comments on that piece, it became clear I needed to do a bit more homework.

I began by going straight to the source: Dr. Ken Buesseler, senior scientist in marine chemistry and geochemistry at the Woods Hole Oceanographic Institution. When I reached Dr. Buesseler by email, he was literally on his way out the door for a flight to Japan, where he is currently continuing his research on precisely this issue. But he took a moment to read my post and respond. His reaction:

Mike-
I like [your] line
Let’s be clear: leaked radiation is bad. This is a problem that needs urgent, international attention. But at least for now, I’m happy to reassure Joe Romm and all the parents of Facebook: your fish are not glowing with Fukushima radiation. Eat up!

Dr. Buesseler also pointed me to a Fukushima FAQ page on his department’s website that he set up to answer the influx of questions he has received on this particular issue.

In the context of seafood consumption, the most important thing to determine is the potential degree of harm that can come to someone who eats fish that may contain higher-than-normal quantities of potentially dangerous isotopes. This begs a few specific questions:

1. How much radiation is out there?
2. Where is it?
3. What concentrations are harmful to humans?

And of course:

4. Seriously? Radioactive bananas?

How much radioactive water are we talking about?
Last month, the Japanese government reported that the Fukushima plant was leaking approximately 300 tons, or 71,895 gallons, of contaminated water each day. That’s a lot of water—except when you compare it to the Pacific Ocean, which is estimated to contain 187,189,915,062,857,142,857 gallons. That’s 187 quintillion for those counting at home. So as a quick comparison, even if the site continues leaking 72,000 gallons per day for 10 years, the total amount spilled would be 262.8 million gallons. This is a tall drink of water to be sure, but it is still just .00000000014 percent of the volume of the Pacific Ocean. Of course, any amount of leaked radiation is bad, so we’ll get to the part about exactly how bad this stuff is in a minute.

It’s also likely that additional water could seep, or is already seeping, from various other containment devices—hence the news that Japan will construct ice dams or other containment structures to help hold back the radioactive flow. In short, this kind of engineering nightmare makes BP’s months-long struggle to plug the Macondo oil gusher in the Gulf of Mexico in 2010 look like a People magazine crossword puzzle (13 across: Skywalker pal Han ____).

Containing Fukushima radiation is not likely to be resolved anytime soon, so:

Where is the radiation going?
According to Dr. Buesseler’s FAQ:

The spread of cesium once it enters the ocean can be understood by the analogy of mixing cream into coffee. At first, they are separate and distinguishable, but just as we start to stir the cream forms long, narrow filaments or streaks in the water. The streaks became longer and narrower as they moved off shore, where diffusive processes began to homogenize and dilute the radionuclides.

Dr. Buesseler and others have suggested that radionuclides will reach U.S. shores “some time in late 2013 or 2014” but that “at the levels expected even short distances from Japan, the Pacific will be safe for boating, swimming, etc.”

Some studies predict that over the next 5 to 10 years, concentrations on the North American Pacific Coast could actually be higher than those off Japan, but the total amount of radioactivity will be well below the current levels near the crippled nuclear plant because of dilution throughout the Pacific Basin.

Should we be worried about the quantities found in our fish?
It goes without saying that we should monitor our seafood and water quality with extreme care. As for the specifics of what to look for, we turn again to Dr. Buesseler:

Seawater everywhere contains many naturally occurring radionuclides, the most common being polonium-210. As a result, fish caught in the Pacific and elsewhere already have measurable quantities of these substances. … cesium [forms] a salt taken up by the flesh that will begin to flush out of an exposed fish soon after they enter waters less affected by Fukushima. By the time tuna are caught in the eastern Pacific, cesium levels in their flesh are 10-20 times lower than when they were off Fukushima.

Cesium will still be more concentrated in larger, carnivorous fish higher up the food chain, such as bluefin tuna than in smaller fish with diets consisting more of plankton and algae, but because it will “flush out” of the fish’s flesh, concentrations will not necessarily mount over time.

An area of greater concern to Buesseler is the increasing quantity of strontium-90 detected in the waters near Fukushima. Unlike cesium, strontium accumulates in bone rather than muscle, and it is not rapidly flushed from the fish. The good news here is that aside from consumers of small fish such as sardines, which are eaten bone-in, most diners will not be eating strontium.

How is the federal government testing Pacific Ocean seafood?
The lead U.S. agency testing seafood for contamination is the Food and Drug Administration, or FDA. As of June 20, the FDA has tested 1,313 samples of food imported from Japan, including 199 seafood samples. Of those, just one—a sample of ginger powder—exceeded the level considered safe for consumption.

When contacted about its testing of domestically caught seafood, an FDA spokesman responded in an email, saying that “the FDA is not aware of any evidence suggesting that the domestic seafood catch contains harmful levels of radiation.” He further referenced a 2012 study from the Proceedings of the National Academy of Sciences, which found levels of cesium-137 and cesium-134 in bluefin tuna to be, according to an email from the FDA, “roughly 300 times lower than levels that would prompt FDA to investigate further to determine if there were a health concern.”

How does nuclear waste differ from the radiation from a banana?
Nuclear radiation exists in many places in our daily lives. Perhaps the most commonly cited example is the average, everyday banana.

Bananas have enough naturally occurring radiation that science communicators developed a metric called the Banana Equivalent Dose, or BED, as a means of explaining in user-friendly terms how much radiation a given thing emits. The BED represents the amount of radiation the body receives from eating one banana and roughly equates to 0.1 nanoseiverts. A seivert is the unit used to measure exposure. An arm x-ray is equivalent to 10 BED. A flight from New York to London: 400 BED. A chest CT scan: 70,000 BED. A fatal dose is roughly 80 million BED. Most of the radiation in bananas comes from potassium-40, which is processed naturally by the body, but some of it arrives in the form of polonium-210, the isotope used in a massive dose to kill former KGB agent Alexander Litvinenko in 2006.

Of course, the radiation in bananas is different from what’s in leaked nuclear wastewater. For starters, while bananas’ radioactivity occurs naturally, nuclear waste contains isotopes, including cesium-137, which are exclusively and deliberately generated by human activity—specifically, the process of nuclear fission.

Radiation released in the decay of radioactive isotopes is classified in three types—alpha, beta, and gamma—and each type has different strengths and properties. Banana radiation—potassium and polonium—is alpha radiation, while cesium and strontium fall in the strongest category, gamma rays. The radioactive particles also have different half-lives—a half-life is the amount of time it takes for 50 percent of a given compound to decay. The half-life of cesium-137 is 30 years; for polonium-210, it is 138.4 days.

So while eating a serving of Pacific bluefin tuna will expose someone to roughly one to five BED, according to a paper Buesseler and his colleagues published in the Proceedings of the National Academy of Sciences in late 2012, that does not mean the potential harm is the same as eating a handful of bananas. But so far, according to Dr. Buesseler and the FDA, we have no reason to fear the amount of radiation in domestically caught fish.

Recall that cesium-137 and other affiliated nasty particles have been part of our lives in varying quantities since the first nuclear tests occurred in the 1940s and ‘50s. While the Fukushima release represents a major influx of the material to the natural environment, when it comes to ocean contamination, it still represents little more than a drop in the proverbial bucket. At least for now, except for fish from the immediate area around the Fukushima plant, Pacific Ocean seafood remains safe to eat.

Michael Conathan is the Director of Ocean Policy at the Center for American Progress.