STATS at George Mason University

July 18, 2006
Trevor Butterworth

The evidence in favor of eating fish rich in omega-3 fatty acids, such as salmon and trout, keeps on mounting. On July 10, the Archives of Opthalmology published a new study showing evidence that these acids reduced the risk of macular degeneration. The association isn't backed by clear evidence of a causal mechanism, but it builds on earlier research which found similar correlations. As the Seattle Post Intelligencer reported, "if you are still balancing the risks of and benefits of eating fish, stop. There is no contest."

And then the very next day, the PI sort of backtracked by warning that the risk of cancer from PCBs in salmon needed to be taken into account:

" there is another side to this story. As we've reported when we took on the matter of contaminants in salmon here, the calculus for any individual consumer needs to be, well, individual.

For example, cancer tends to get my people, so PCBs in salmon are something to be concerned about because PCBs promote cancer. My wife's forebears, on the other hand, tend to kick the bucket while clutching their hearts. So the dilemma for us is: how can she get the omega 3s -- "W-D 40 for the brain," according to this wide-ranging and worthwhile what-you-should-eat piece in yesterday's Vancouver Sun -- while I avoid the PCBs?

Click on "here" and you are taken right back to the study that launched a global health scare: Hites et al. And it's not just the Seattle Post Intelligencer. The New York Times Dining Section warned readersin March that "studies have shown that salmon farms can pollute the waters around them with their waste and the fish can contain dangerous levels of contaminants like PCB's and dioxin."

Consumer Reports' August issue also advises readers to buy wild Alaskan salmon because farmed salmon may contain higher levels of PCBs. Actually, a brace of studies have shown the opposite to be true - not that it matters either way, the levels being so low in both wild and farmed fish, and radically diminished after cooking and removing the skin.

In fact, even if you accept the worst-case scenario of the fish-scare mongers, the U.S. public is at much, much greater risk for injury and death from falling television sets. Really. Which, when added to what the media missed when they covered the publication of Hites et al. two years ago, is another reason to consider the sight-enhancing benefits of eating salmon.

Anatomy of a health scare: PCBs in Salmon
April, 2004
Trevor Butterworth

The Food and Drug Administration (FDA) is under increasing pressure to tighten its limits on contaminants in food after a recent study claimed that farm-raised salmon contained potentially dangerous levels of polychlorinated Biphenyls (PCBs), banned in the United States since 1979.

The warning generated enormous media coverage in the United States and around the world, even though FDA officials, industry experts and many independent scientists denied there was any health risk.

The authors of the study (Hites et al.), which appeared in the January 9 issue of Science magazine, relied on Environmental Protection Agency (EPA) guidelines for determining whether the PCB levels they found in farm-raised salmon were likely to increase the risk of cancer.

They claimed that the FDA limits were out of date and did not reflect recent research. Yet the EPA’s use of animal testing to determine whether a substance is a potential carcinogen in humans is highly controversial. Indeed, a previous STATS survey of America’s leading cancer experts found that a majority disagreed with the practice of assessing human cancer risks by giving animals a maximum tolerable dose of a suspected carcinogen.

In this case, the claim that PCBs levels in farmed salmon increase the risk of cancer is not supported by any scientific evidence showing that PCBs in fish or the environment have ever caused cancer in humans. In fact, research has not even shown that workers exposed, on a daily basis, to high levels of PCBs in industrial settings experience higher rates of cancer than the rest of the population.

Given the impact of health scares on the public and on industry, STATS analyzed breaking news coverage of the Science study to see whether the media accurately reported this controversy and provided the key scientific data the public needed to make sense of this study. The results are far from reassuring.


Assembling the ingredients for an international health scare.

A tale of two measures
The controversy over PCBs in farmed salmon is driven by two very different measures for evaluating the health risks from exposure to chemicals in food and in the environment; one is cautious, the other is extremely cautious.

Quantifying the risk
If we assume, for the moment, that the EPA limits represent a “true” assessment of the risk of cancer from PCBs, what, then, is that risk?

Do PCBs cause cancer in humans?
The problem with the EPA’s case against PCBs is that scientific research has yet to prove that prolonged exposure to high levels of PCBs in industrial settings causes cancer.

Dueling evidence - who’s right?
The scientific case for PCBs causing cancer in humans, based on chronic exposure in the workplace, remains unproven.

Do PCBs cause cancer in animals?
As far as the EPA is concerned, if a substance can be shown to cause cancer in animals, it must be treated as a probable carcinogen in humans.

Non-cancer health risks
Developmental problems and sample woes.

What you needed to know
What was the information you needed to make sense of the claim that farmed salmon posed a risk to your health?

Did the media provide you with this information?

Conclusion: Toxic fish or toxic reporting?
A new health risk study should be treated no differently than a rumor of political scandal: it needs to be checked out, thoroughly, before it appears in print.

Full tables

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