Technology & Science

Study confirms farmed salmon more toxic than wild fish

International study finds farm-raised salmon contained about 10 times more contaminants on average than wild salmon.

Farm-raised salmon contain higher levels of PCB and other toxins than salmon caught in the wild, according to a new, international study.

Researchers tested for contaminants such as PCBs, dioxins and pesticides in 700 salmon bought from around the world. They found the trace amounts of toxins were 10 times higher on average in the farmed fish.

"We are certainly not telling people not to eat fish," said study co-author David Carpenter of the University at Albany, N.Y. "We're telling them to eat less farmed salmon."

Consumption of farmed salmon has grown since the mid-1980s by 15 per cent a year in Canada.

Salmon raised in northern Europe was the most contaminated, followed by North America and Chile. Given the global nature of the industry, the scientists' warning is universal.

For years, consumers have been told to eat fish at least twice a week to prevent heart disease. Salmon in particular is high in heart-healthy omega-3 fatty acids, and low in mercury contamination.

But as fish-eaters, salmon are fairly high in the food chain, which means they tend to accumulate more toxins in their bodies than herbivores.

Many of the toxins studied are thought to trigger cancers and threaten the immune or reproductive system.

Farmed salmon eat fish oil and meal from a few species of ocean fish, which can concentrate the contaminants. Some fish farmers are now switching to plant-based protein feeds. Wild salmon have a more varied diet.

"Our number one concern is the consumer and we don't like the fact that the contaminants are in our food supply," said David Ridout of the Canadian Aquaculture Industry Alliance. "We're doing everything we can to reduce that."

The researchers bought farm-raised Atlantic salmon from five European cities, nine American cities and Toronto and Vancouver. They also bought wild salmon from the west coast of North America.

Using the U.S. Environmental Protection Agency's cancer risk estimates, the researchers suggested people eat no more than 55 grams of the most contaminated salmon a month, or a quarter of a normal portion.

* Coverage from CBC New Brunswick * Coverage from CBC British Columbia

For Canadian farmed salmon, the limit would be half a portion a month.

Salmon farmers, Health Canada and the Canadian Food Inspection Agency, however, say the study shows farmed salmon is safe since the contaminant levels did not exceed U.S. Food and Drug Administration safety limits.

The FDA notes the study tested raw salmon with the skin on; removing the skin and grilling would remove a significant amount of the toxins from the fat.

The study appears in Friday's issue of the journal Science. It was funded by the Pew Charitable Trusts.