STATS at George Mason University
 
   
 
Background

Last summer, another warning issued in a long peal of alarms about the food we eat. The Environmental Working Group (EWG), a small, non-profit “public interest watchdog” announced that it had found such high levels of polychlorinated biphenyls (PCBs) in farm-raised salmon in the United States that it would be unsafe for anyone to eat more than one eight-ounce fillet per month.

PCBs are a family of synthetic organic chemicals composed of 209 separate compounds that were widely used as coolants and lubricants in manufacturing for almost half a century. As experimental studies began to show evidence that some PCB compounds could be toxic, the United States banned their use in 1979. By this point, however, hundreds of thousands of tons of PCBs had been dumped into the nation’s rivers and lakes; and the chemical stability that had made PCBs so useful to industry meant that they would be slow to break down and disappear.

How much of an environmental threat these deposits present is still unclear. For example, the PCBs buried in the sediments of the Hudson River are not leaching into surface waters at a rate that appears likely to cause any health problems (which is why the Environmental Protection Agency’s decision to force General Electric to dredge the river may actually do more harm than good); on the other hand, the clean up of smaller hotspots that have leached at a much faster rate has cleaned up rivers and lakes that posed a genuine threat to publih health.

The issue is that being fat soluble, PCBs can be absorbed by and accumulate in the fatty tissue of marine and animal life, from where they can be passed on to humans. The question is at what point this process begins to threaten public health (if at all). The problem is that toxicology is bitterly divided over how to calculate these types of risk.

One side (which includes a majority of the world’s regulatory bodies) takes a cautious approach to the risk from contaminants; the other (which includes the Environmental Protection Agency and many environmentalists) takes an extremely cautious approach.

Unsurprisingly, the Environmental Working Group’s announcement that “cancer-causing chemicals” had made their way into farm-raised salmon proved irresistible to the media, even though the levels were well within Food and Drug Administration (FDA) and World Health Organization (WHO) limits. EWG discounted this objection by arguing that the FDA limits, established in 1984, were out of date, and did not reflect the latest scientific research on PCBs; this is why they based their risk assessment on the limits set by the Environmental Protection Agency (EPA), which were established in 1999.

While the FDA regulates commercial fish, setting PCB limits at 2000 parts per billion (ppb), the EPA is responsible for wild fish, which may be caught from heavily polluted lakes and rivers. As PCB levels in such fish can reach over 3000 parts per million (ppm), the EPA’s consumption guidelines are much stricter than the FDA’s limits. Thus, the EPA estimates that eating one eight-ounce piece of raw fish per month with PCB levels between 24 and 48 parts per billion will increase your risk of cancer by one in 100,000 over seventy years.

There were significant problems with the EWG study, in particular the tiny sample of fish upon which they based their warnings, which at 10 fillets was far too small to be scientifically credible. But then in January 2004, a much larger study — the largest to date on PCB levels in farmed salmon — appeared to confirm the group’s warnings. Scientists from Indiana University, the University of Michigan, the State University of New York at Albany and Cornell University (henceforth, Hites et al.) examined 246 samples of farmed salmon from around the world.

They found PCB levels that ranged from 51 parts per billion in farm-raised salmon in Scotland (the highest) to 18 ppb in Chile (the lowest). The average amounts for North America were 34ppb (Western Canada), 30ppb (Maine) and 18ppb (Washington). They also examined samples of wild salmon from Alaska and British Columbia, which revealed significantly lower levels of PCBs. Using the EPA’s limits as a reference point, Hites et al. recommended limiting farmed salmon consumption to one eight-ounce fillet per month.

The study appeared in the January 9 issue of Science magazine, and thus carried the imprimatur of peer-review by a prestigious journal. The authors were all reputable scientists at mainstream institutions (one of the authors, Jeffrey Foran, is also president of the environmental advocacy group, Citizens for a Better Environment). And in summing up what their findings meant for public health, they had simply spelled out the implications of the EPA’s limits on PCBs.

In short, all the ingredients were in place for an international health scare. Salmon, after all, is widely regarded as one of the most beneficial foods you could eat. Packed with omega-3 fatty acids, which research has shown to protect the heart from cardiovascular disease, the American Heart Association recommends that adults consume at least two (2-3oz) servings of fatty fish such as salmon per week - three times as much as the meager ration proposed by the Environmental Working Group and Hites et al. It seemed that consumers were faced with the choice between protecting against heart disease and risking cancer. Given the legacy of similar health scares in the past, the salmon industry faced the possibility of economic ruin.

But Hites et al.’s warnings did not go unchallenged. In the United States, FDA officials, toxicologists and industry representatives all vigorously disputed the threat from farmed salmon. In Europe, critics were came out swinging: the study was characterized on British television as an example of America trying to manipulate the market; salmon industry officials in Scotland and France talked of suing Hites et al.; and the Pew Charitable Trusts – the philanthropic organization who financed the study – was charged with environmental extremism.

As journalist Magnus Linklater wrote in the Times of London (15/01): “This is the true story of the salmon scare which threatened last weekend to bring British salmon farming to its knees. It is a sorry saga of flawed science, selective research and hidden commercial bias. That it was allowed into the pages of the apparently respectable journal Science is inexplicable. Its worldwide promotion by an organization with a vested interest in undermining farmed Atlantic salmon in favor of wild Alaskan salmon is a scandal.” all the ingredients were in place for an international health scare.

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