Following a CBC investigation that found mercury levels above the allowed limit, Health Canada issued new consumption guidelines on Monday for canned albacore tuna for women and children.

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An Ottawa lab measured the mercury content of 60 cans of tuna with their labels removed to ensure blind testing. ((CBC))

The tuna may routinely exceed Canada's mercury guidelines, the investigation has learned, but until Monday, Health Canada failed to warn consumers about the potential danger.

The health benefits of eating tuna have been widely established; it is a relatively inexpensive source of high-quality protein, low in saturated fat and contains omega-3 fatty acids, touted for their heart-protective benefits.

But tuna also contains mercury, a dangerous contaminant that can affect the heart, brain and immune system.

However, prior to CBC's investigation, if you read Health Canada's advice on the matter, you would have thought you had nothing to worry about.

Health Canada has established a guideline level of 0.5 parts per million (ppm) for mercury in commercial fish.

The Canadian Food Inspection Agency tests canned tuna before it gets to store shelves to ensure it meets the 0.5 ppm guideline.On average, six per cent of the albacore tuna it tests fails and is pulled before it gets to grocery stores.

"I have confidence in the program that we operate, that it continues to serve the public well in providing assurance that the products in the marketplace predominantly meet the guideline level," says CFIA spokesman Paul Mayers.

CBC put that claim to the test, conducting the first public survey of its kind to examine the mercury content in the canned tuna that makes it to store shelves.

13% exceeded guidelines

Sixty cans of albacore, or "white" tuna, were purchased at nine grocery stores in Vancouver, Winnipeg and Toronto. Studies have shown "white" tuna is typically higher in mercury content than "light" tuna, because it's generally a larger, older fish that has accumulated more mercury.

MERCURY IN FISH

Mercury is a naturally occurring element that's found in soil and rocks as well as bodies of water. We absorb trace amounts of it from dental fillings, air and water pollution and from the food we eat. Fish tend to be our largest source of mercury.

High levels of mercury can damage our nervous systems and can inhibit brain development in young children. It's not clear what the long-term effects of extremely low levels of mercury are.

Mercury binds tightly to the proteins in fish tissue. Most fish will contain trace amounts of mercury, depending on the level of mercury in their environment and their place in the food chain.

The bigger the fish and the higher up the food chain it is, the more mercury it will tend to contain. Large predatory fish species tend to have higher levels than non-predatory fish or species farther down the food chain.

The tuna was tested at the University of Ottawa's Centre for Advanced Research in Environmental Genomics, which is internationally recognized for its work with mercury.

"I was surprised. They were a good deal higher than I'd thought," said Dr. David Lean, who supervised the testing. "Clearly these tuna should not be eaten on a regular basis," he added.

Thirteen per cent of the tuna tested exceeded Health Canada guidelines.

"This is not to say if you eat fish above 0.5 you're going to drop dead tomorrow, or if you eat fish a little bit lower you're going to be fine. It has to do a lot with how much of it you eat," Lean said.

"But we were seeing numbers as high as 0.9, which is almost double the guideline. So why are they on the shelf? Why are we not protected?"

Results no surprise to CFIA

Paul Mayers, a spokesman for the Canadian Food Inspection Agency, said the organization does the best it can.

"Our view was that the results don't represent a surprise," he told CBC.

The CFIA actually allows mercury levels up to 0.54, due to its system of rounding to one decimal point, so only eight per cent of the tuna tested should not have been for sale, officials said.

As for why so many cans that exceeded even the 0.54 guideline are on grocery-store shelves, Mayer said it's inevitable.

"I'm not saying that compliance can never improve. What I'm saying is we will not get 100 per cent when we're dealing with a ubiquitous environmental contaminant."

Other countries, such as the United States, have issued advisories to consumers about the potential dangers of canned tuna — including special advice to pregnant and nursing women, because too much mercury can cause neurological damage, especially in children and fetuses.

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Dr. David Lean supervised the testing of the tuna in Ottawa's Centre for Advanced Research in Environmental Genomics. ((CBC))

Safe consumption advice ranges from no more than one can of albacore tuna a week in some jurisdictions to none at all in others.

While Health Canada does warn about consumption of fresh and frozen tuna,its website, until Monday, said limiting canned tuna consumption was not necessary.

"We are making available this information right now because of the interest in canned albacore tuna in particular," Health Canada's Samuel Godefroy told CBC on Monday afternoon.

The new guidelines indicate that "Canadians can rest assured that there is no reason to stop eating canned tuna."

However, it suggests that "as a precaution":

  • Pregnant or breastfeeding women can eat up to four servings of canned albacore tuna per week.
  • Children between the ages of one and four years can eat up to one serving per week.
  • Children between the ages of five and 11 years can eat up to two servings per week.

One serving of tuna is 75 gm, 2½ oz, 125 mL, or ½ cup.

Tuna consumer finds own mercury levels high

Ottawa's Kevin Walker found out about the risks of eating too much canned tuna the hard way. Walker, a health-conscious consumer, used to eat two to three cans of tuna per day for its health benefits.

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Toxicologist Dr. David Lean examines mercury test results with Kevin Walker. ((CBC))

Lean tested Walker's body for mercury content and found it was four times higher than levels recommended by the U.S. Environmental Protection Agency.

"If I hadn't met David, my levels would probably be at a dangerous level," said Walker. "I think it's irresponsible on Canada's part, Health Canada, for not educating the public about the concern of consuming too much tuna."

It took one year for Walker's mercury levels to drop to normal after he stopped eating canned tuna.

Now he's eating it again, but says he's following American guidelines to get the maximum health benefits with a minimum of mercury.

The Canadian Food Inspection Agency has begun an investigation based on the CBC's test results. The agency says it will recall product, if it finds such a move is justified.