After Fukushima, small quantities of radiation have been found in bluefin tuna. How worried should we really be?
If you’re like me, you prefer your sushi slathered with just enough spicy wasabi to inflict a painfully pleasurable jolt of heat. But even if you’re not a fan of the bright green, searingly hot sushi-bar condiment, I’m guessing you’d still probably opt for it over a far less appetizing source of heat: radiation. Specifically, radioactive metals that were deposited into the sea near the coastal city of Fukushima, Japan, after the nuclear accident that took place there two years ago this week.
In two separate instances in 2011 and 2012, quantities of ionizing radiation were found in samples of bluefin tuna that had migrated from waters near the site of the Fukushima disaster, where the large fish spawn, to the southern California coastline, where they were eventually caught. In the first of these instances, Daniel Madigan, a marine biology graduate student at Stanford, bought 15 tuna steaks from dockside fishermen in San Diego and sent them off to a lab for testing. Madigan knew the migration patterns of the bluefin; at the time, which was less than six months after the accident, he was acting on little more than a hunch.
When the lab results came back, however, he was shocked to learn that every one of the 15 steaks had tested positive for the presence of two radioactive metals that had leached into the ocean after the meltdown: cesium-134 and its far more dangerous cousin, cesium-137. As a more methodologically formal follow-up, last year Madigan tested 50 more slabs of SoCal-caught tuna to see if he could still pick up any cesium signals. He did. (A report based on the study was published last month in the peer-reviewed journal Environmental Science and Technology, which is published by the American Chemical Society.)
Stories you’ll read about Madigan and his unsettling findings all have one thing in common: Buried somewhere, usually about halfway down the page, is a paragaph telling you not to get too freaked out about the idea of hot tuna, given several facts. According to Madigan’s own report, the cesium levels he found in the tuna gave off less radioactivity than other, naturally occurring isotopes that could be found in the fish. The broader implication is that we’re all being exposed to varying levels of naturally occurring radiation (often referred to as “background radiation”) as we go about our daily lives. This “Don’t panic!” narrative is then typically reinforced with a comforting-sounding comparison between the amount of radiation you’re likely to ingest by eating Fukushima-irradiated tuna and the amount you’re likely to ingest by, say, eating a banana (which is rich in potassium, a radioactive isotope).
But maybe it’s actually worth unpacking that comparison just a bit.
For starters, the potassium in bananas — levels of which our bodies, via homeostasis, calibrate and keep at a relative constant — can’t be compared in good faith to a truly nasty radionuclide like cesium-137, which is commonly found in the immediate aftermath of nuclear-reactor accidents and nuclear-weapons tests. (To get severe radiation poisoning from bananas, you’d have to eat about 20 million of them. In 1987, a small cake of cesium-137 that had been pried out of a discarded piece of medical equipment ended up killing four people who came in contact with it, and sickened hundreds more.)
But even more significantly, these comparisons rarely, if ever, cite in any depth the theory that has become a cornerstone of the modern science surrounding low-dose radiation exposure and its role in the eventual development of cancer. In a nutshell, this theory, which was developed in the late 1950s and is known today as the linear no-threshold model (LNT), holds that there is no agreed-upon “safety threshold” for ionizing radiation, and that in terms of cancer risk, there’s no real difference between one big dose of radiation and a bunch of little doses. As the National Academy of Sciences concluded in its 2006 review committee report: “A comprehensive review of the biology data led the committee to conclude that the risk [from radiation exposure] would continue in a linear fashion at lower doses without a threshold and that the smallest dose has the potential to cause a small increase in risk to humans.”
The LNT model isn’t without its doubters and skeptics. But as of right now, those skeptics don’t include organizations such as the U.S. Environmental Protection Agency, the U.S. Nuclear Regulatory Commission, and others considered to be among the more trusted sources of scientific opinion. Taken together, these official affirmations of the LNT should be thought of as representing the scientific consensus — at least until such time as the voices of dissent begin to outnumber the voices of agreement. But that day seems unlikely.
So if the LNT is good enough to be accepted by the likes of the EPA, and low-dose radiation is showing up in bluefin tuna that’s presumably making it to market, then why aren’t federal agencies like the Food and Drug Administration and the National Oceanic and Atmospheric Administration suddenly making lots of announcements about suspect sashimi? Two months after the Fukushima disaster — which, it’s worth remembering, represented the largest accidental release of radioactivity into the ocean in human history — these two agencies, in a joint announcement, declared that the presence of “longer-lived radionuclides such as Cs-137” had not been detected by the FDA “in any fish imported from Japan,” and also that “longer-lived radionuclides found by Japanese tests have been at levels below the FDA threshold” considered to be unsafe — and, even then, not found in any tuna. Madigan’s research would seem to belie that assertion.
The answer may be, quite simply, that when it comes to things nuclear, an official policy of non-alarmism tends to trump one that would give consumers as much information as they’d like — and deserve — to have. In a special 2012 issue of the Bulletin of Atomic Scientists dedicated to the single topic of low-dose radiation, Gordon Thompson, executive director of the Institute for Resource and Security Studies, wrote about this phenomenon:
Within the policy realm, experts should not support the LNT hypothesis and then distance themselves from its logical implications. They should, therefore, recognize the existence of real, but masked, health effects at low radiation doses, albeit with some quantitative uncertainty. […] Public fear does not provide a reason to hide the logical implications of the LNT hypothesis. An attempt by experts to hide these implications is likely to be counterproductive. The truth would probably be revealed eventually, leading to diminished public faith in the relevant experts and in science in general. Ultimately, public fear could be exacerbated. Also, when experts consider public fear, they should account for contemporary views on individual agency. In past years, well-meaning doctors would often withhold a diagnosis of cancer to avoid alarming a patient. Now, such behavior is generally regarded as patronizing and obsolete.
In a 2012 ABC News report that ran in the wake of Madigan’s first bluefin study, Dr. Michael Harbut, director of the Environmental Cancer Program at Wayne State University’s Karmanos Cancer Institute, expressed his concern over the same unwillingness of authorities to be open with the public. “We don’t see people dying left and right all over the West Coast from radiation poisoning,” Harbut acknowledged. “But to say this is nothing to worry about is equally irresponsible, because you have radioactive material ingested by fish, which is in turn being eaten by people.”
He then added, “I think that the appropriate government agencies have to appoint appropriately trained people to give the public an honest assessment. Not something tailor-made for ignorance, like ‘This will definitely kill you,’ or ‘This poses absolutely no risk to human health.’ We’ve gone too far in poisoning the world to settle for simple ‘yesses’ and ‘nos’ like that.”
Understandably, government authorities and scientists don’t want to unduly alarm citizens and consumers. But their nonchalance regarding the impacts of low-dose radiation runs counter to the official scientific consensus. At best it engenders ignorance; at worst it instills a false sense of security. Both outcomes preclude people from fully participating in their own health decisions. By glossing over the accepted science in favor of doling out more smiling assurances, the reaction these authorities are presumably trying to avoid — alarm — is the one they’ll end up achieving.
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