In the last 15 years, salmon consumption has increased annually at a rate of 23 percent in the United States and 14 percent in much of Europe. To meet the burgeoning demand and to offset the decline of wild salmon, vast commercial fish farms have sprung up in coastal waters. Today, over half the salmon sold globally is farm-raised, and annual production has reached more than 1 million metric tons.

Thanks to the urgings of health officials to eat fish for a sound diet, salmon is now a dietary staple high in protein and omega-3 fatty acids. But this popular fish may turn out to be a poor choice for other reasons, so poor in fact, that swift federal intervention appears necessary.

A recent study of hundreds of samples of farm-raised salmon from around the world has found dangerously high levels of contaminants. Four of these chemicals have been thoroughly shown to raise the risk of cancer: PCBs, dioxins, dieldrin and toxaphene. Tissue from farmed salmon showed significantly higher levels of these and other environmental toxics than wild salmon.

The problem has likely existed since salmon farming began, but until now, the U.S. Food and Drug Administration, responsible for the safety of commercial fish, has failed to engage the issue.

In contrast, the U.S. Environmental Protection Agency has a long history of issuing advisories on fish consumption to protect public health. Popular sport fish, such as trout, bass and catfish, frequently live in waters contaminated with PCBs, mercury, dioxins and other industrial pollution. For this reason the EPA measures the level of contaminants and advises the public, primarily women of childbearing age and children, on the amounts of fish that can be safely eaten from a specific body of water.

The EPA's standards, however, are not applied to fish sold commercially. This is the responsibility of the FDA. Unfortunately, FDA's safety requirements reflect the agency's underlying concern with food production rather than public health. For example, it has no consumption standards for toxaphene in fish, and its guidelines for PCBs and dieldrin were loosely set to avoid regulatory interference with food production.

Yet based on the EPA's standards for allowable levels of harmful chemicals in an eight-once portion of fish, researchers found some farmed salmon so highly contaminated that only one portion could be safely eaten per month. By comparison, as many as eight meals of wild salmon per month were within EPA standards.

Based on the hundreds of samples from around the world, researchers also found that concentrations of toxics varied widely according to where salmon was raised. Farms in Washington state and Chile showed the lowest levels of chemicals, while those from the North Atlantic had the highest amounts.

The global trade in commercial fish means that a restaurant or market on the East Coast is as likely to sell salmon from Europe as from Chile. Consequently, consumers need to base their purchasing decisions on where salmon is raised rather than where they buy it.

Although the benefits of salmon have become a dietary given for millions of people, this species is exposed to a number of toxic environmental chemicals particularly when raised commercially, but the cause and effects were poorly documented until recently. Research now shows that salmon and other fish take in chemicals present in their food, which accumulate in fatty tissue over time. These same chemicals are passed to and accumulate in humans who eat contaminated fish. From this perspective, carnivorous fish such as salmon that feed high on the food chain can be especially harmful to health.

Penned fish are fed a diet of fish meal pellets and fish oil, but to add one pound of weight a salmon must eat almost three pounds of fishmeal. This high nutritional intensity equates with an equally high concentration of accumulated chemicals. These contaminants are not affected by cooking, and they are present, in varying degrees, whenever salmon is eaten.

The FDA set standards for PCBs and dieldrin 25 years ago, long before their link to cancer became clear. Meanwhile, salmon consumption has grown exponentially. Considering the repeated exposure to known carcinogens by eating farmed salmon, federal officials now have a responsibility to set consumption guidelines based on the criterion of public health.