The case of the radioactive tuna

Earlier this week, a friend of mine posted a link on Facebook to a blog post entitled “Radioactive bluefin tuna caught off California coast.” As a keen consumer of sushi, she was alarmed. As a skeptical scientist, I decided to investigate.

The blog post appeared on 24 August on the website Liberals Unite, which bills itself as “the 24-hour news magazine for discerning liberals.” As far as I could tell, the post was inspired by a news story in the Wall Street Journal dated 29 May 2012. The WSJ story, in turn, originated in a paper that appeared the same day in the Proceedings of the National Academy of Sciences.

The PNAS paper reported—to quote the abstract—"unequivocal evidence that Pacific bluefin tuna, Thunnus orientalis, transported Fukushima-derived radionuclides across the entire North Pacific Ocean.” Levels of the two radionuclides, the gamma-emitters cesium-134 and cesium-137, were 3% higher than in fish tested before the disaster.

Together, the blog post, the news story, and the research paper show how scientific results can be distorted to serve a political end—in this case, opposition to nuclear power.

The author of the blog post, Ann Werner, is a retired TV actor who writes horror stories. Her first novel, CRAZY (ARK Stories, 2013), “takes you into the mind of a fiendish serial killer who, fueled by Satanic fantasies and a mysterious Guardian, wreaks havoc in Hollywood.” Her blog post about the radioactive tuna was also alarming. She begins:

She goes on to cite the WSJ story and then starts speculating. Given that the dumping of radioactive contaminants into the waters around the stricken power station has continued, she writes, tuna could be more contaminated now than they were when the authors of the PNAS paper performed their tests.

Unaware of more recent measurements and unwilling or unable to make an estimate, Werner instead quotes some information about cesium’s health effects, which, at high doses, culminate in “coma or even death.” As if to heighten the alarm, she also includes the far-from-fleeting halflives of the two radionuclides found in the fish: 2 years for ¹³⁴Cs; 30 years for ¹³⁷Cs.

After acknowledging that the US Food and Drug Administration says the contaminated tuna are safe to eat, she asks rhetorically whether the FDA’s assurances amount to just “another attempt to quell a public backlash in the face of an unprecedented event that, as yet, has no solution and no end in sight?”

Nothing in Werner’s blog post is scientifically wrong (except, perhaps, the impression she gives that cesium exists in seawater as “particles,” when, in fact, it exists as dissolved salts such as cesium chloride). She is right to challenge official assurances and right to decry the environmental impact of the Fukushima disaster.

Nevertheless, the leap she makes from a contamination level that’s just 3% above normal to one that leads to “coma or even death” is unjustifiably wide. In absolute terms, the radioactivity found in the tuna was 4.0 ± 1.4 becquerels per kilogram for ¹³⁴Cs and 6.0 ± 1.5 Bq/kg for ¹³⁷Cs. Thanks to its high potassium content, a typical banana radiates at 15 Bq.

An unexpected tool

The author of the WSJ story was veteran science reporter Robert Lee Hotz. Hotz told his readers up front that the radiation in the contaminated tuna was one tenth of what US and Japanese authorities consider unsafe.

Like the authors of the PNAS paper—Daniel Madigan, Zofia Baumann, and Nicholas Fisher—Hotz focused more on the discovery that migrating fish can transport radiation across vast distances than on any health risks. Indeed, for Madigan, Baumann, and Fisher, the accidental contamination could turn out to be “an unexpected tool for examining migratory origins of apex predators in the Pacific Ocean.”

What’s more, as Hotz noted, the radioactivity in the waters off eastern Japan was 10 000 times higher than normal for weeks after the disaster. But in the tuna, the radioactivity was just 1.03 times higher. Tuna, it seems, are not efficient vectors of transcontinental contamination.

Given that Werner’s post appeared on an avowedly liberal website, I wondered whether the site’s readers were persuaded by her giant leap of suggestion. Could liberals be as irrational about radiation as some conservatives are about climate change?

The numerous comments left on the blog paint a mixed picture. Some were flippant (“Great we will soon all glow in dark”). Some shared Werner’s skepticism (“Any assurances by the FDA are invalid based on previous performance”). But a significant number charged Werner with being needlessly alarmist (“You guys are complete, total, and utter morons! Ever take a physics class! Everything on this planet is radioactive!”).

Surprisingly, given that it would have served her antinuclear agenda, Werner missed a fact that Hotz included in his story. The background level of ¹³⁷Cs in tuna is not what you’d expect for fish swimming in a pristine ocean. Rather, it’s five times higher as a result of atmospheric nuclear tests that took place decades ago.