A consumer's dilemma hit millions of salmon lovers smack in the face earlier this month when scientists reported high levels of pollutants in farm-raised salmon. That's the affordable salmon, which now ranks as America's favorite fish, aside from canned tuna and shrimp.

Should they still snare a slab of farmed salmon for $4-$5 a pound at the supermarket, and order the restaurant's grilled salmon special? Or is it safer to pay sticker-shock prices for grown-up-in-the-wild fish?

Should they still eat salmon at least twice a week for its heart healthy omega-3 fats, as the American Heart Association long has recommended? Or should they heed the new study's advice and limit consumption?

The study, headed by Dr. Ronald A. Hites of Indiana University and published in the journal Science, compared pollutant levels in more than two tons of farmed and wild salmon from different areas of the world.

Farmed salmon contained levels of 13 pollutants that averaged 11 times higher than those in wild salmon. The researchers concluded that people could safely eat the most heavily contaminated salmon only six times a year.

The pollutants, termed dioxin-like compounds, or DLCs, are found everywhere in the environment. Fish and other animals absorb them in food, and the chemicals build up in their fat. Humans pick them up mainly from eating fish, meat and dairy products. Farmed salmon get DLCs from the fish chow used to fatten them in pens.

Scientists suspect that high levels of DLCs can increase the risk of certain cancers, harm the developing brains of fetuses and infants, and produce other unhealthy effects.

Farmed salmon is raised in net-enclosed pens in coastal areas of northern Europe, North America and Chile. Fish farming changed salmon from a pricey seasonal delicacy into a deliciously affordable year-round staple. But it also stirred fierce controversy because the farms put fishermen out of work and damaged local environments.

In deciding whether to eat salmon, consumers should know that the latest study found only a small increase in risk, according to Dr. Charles Santerre, an authority on chemical contaminants in food at Purdue University who was not involved in the research.

"The risks were extremely low -- on the order of 1 in 100,000," Santerre said in an interview. "That means if 100,000 people ate eight ounces of farm-raised salmon twice a week for 70 years, contaminants in the fish would cause one additional case of cancer. The cancer risk from salmon is small compared to the benefits on the heart."

The study will have no immediate effect on the heart association's recommendation, first issued in 1996, that people eat salmon and other fatty fish at least twice a week.

Dr. Alice Lichtenstein of Tufts University, a member of the heart association nutrition panel that drafts such recommendations, said the new study probably will be discussed at the group's next meeting in April.

"Right now, cardiovascular disease is still the leading cause of death in the United States," she said in an interview. "For most of the population, the risk of cardiovascular disease far outweighs the risk of these contaminants."

The heart association "scientific statement" on fish consumption, updated in 2002, points out that omega-3 fatty acids, like those in salmon, seem to reduce the risk of heart attacks and of sudden death from heart attacks.

About 1.1 million people suffer a heart attack each year in the United States, and 500,000 die. Half are sudden deaths, occurring within an hour of the first symptoms and before the person reaches a hospital.

The recommendations state that people should eat not just salmon but a wide variety of fish to minimize exposure to mercury and other contaminants. Good sources of omega-3 fats include tuna, mackerel and other oily fish; cod liver oil; and walnuts and flaxseeds. Pills containing fish oil and other omega-3 supplements also are available.

Liechtenstein noted that the guidelines advise consumers to be aware of both the risks and benefits of fish consumption in their particular stage of life. For children and pregnant women, for instance, who have a low heart attack rate, the risks from contaminants in fish may outweigh the benefits of omega-3s. For older men and women, who have a higher risk of heart attack, the benefits "far" outweigh the risk, the guidelines state.

Dr. Robert Lawrence of Johns Hopkins University noted another way in which the salmon study can help consumers fine-tune their decisions. He chaired a National Academy of Sciences panel that in 2003 considered ways to reduce DLCs in the food supply.

"The salmon study has now provided some of the much-needed data to guide consumers on their choice of salmon, based on geographic origin and whether farmed or wild," he said in an interview.

Consider geography. The highest DLC levels were in salmon farmed in Northern Europe, followed by North America and Chile (where levels in farmed salmon were only slightly higher than in wild salmon).

About 56 per cent of the farmed salmon sold in the United States comes from Chile, 36 per cent from Canada, and only 7 per cent from Europe, according to Santerre. His advice to those concerned about the DLC risk: Check the country of origin when buying or ordering salmon.

The national academy study concluded that limiting fish consumption was not the right solution to DLC contamination because of the health benefits of omega-3 fats. It called for measures to reduce DLCs in farmed and wild fish.

That can be done, Lawrence said, by changing ingredients in the fish chow used on commercial salmon farms. Salmon feed now is made from meal and oil obtained from small marine fish that contain DLCs. Processing further concentrates the DLCs. Some fish chow contains rendered fat from cows and other animals, which also contains DLCs.

"The real story here is that current practices of farmed salmon are not sustainable and have important human health and ecosystem impacts," Lawrence said. "The industry has to change the way it harvests and makes fish food to break the cycle of DLCs entering the human food supply."

Commercial salmon farmers say they are changing their practices.

SalmonChile, the industry group for Chilean companies, which produce one-third of the world's salmon, said DLC levels dropped by 28 percent between 1998 and 2001.

The study results may not accurately reflect contamination levels today because the samples were bought in 2001, the group said, noting that further reductions have occurred over the past two years.