Q: I have heard children and nursing mothers should limit the amount of tuna they consume due to high mercury levels found in the fish. Is this true?

A: Tuna is a favourite fish, present in over 90 per cent of households. In fact, approximately 20 per cent of U.S. fish consumption is from tuna. Children and pregnant women eat more than twice as much tuna as any other fish.

There are pros and cons when it comes to eating fish these days. The pros are that fish are a wonderful source of protein, low in saturated fat, and the cold water types offer a good source of omega 3 fatty acids. The cons of eating fish have to due with their toxicity level. In terms of tuna, one of the most highly eaten fish sources, the concern lies with the amount of mercury present in the fish. It is estimated that mercury levels in the environment have increased three to five times in the past century due to industrial operations such as pulp and paper processing, burning garbage and fossil fuels, mining operations and releases from dental offices. Mercury is an element that is toxic in all its forms. In fish, mercury appears in the form of methyl mercury which can be very damaging to the nervous system. Effects can range from learning disorders and developmental delays to headaches, migraines, muscle aches, depression, memory loss, skin rashes and seizures.

Mercury accumulation is of grave concern with pregnant or nursing mothers due to the dangerous neurological effects mercury can have on a fetus or infant. Large predator fish, such as swordfish, king mackerel, tilefish and shark, which feed on smaller fish, have a greater chance of accumulating methyl mercury because of their longer lifespan.

In March 2004, the U.S. Food and Drug Administration (FDA) and the U.S. Environmental Protection Agency (EPA) announced their revised consumer advisory on fish and mercury consumption. Their recommendations were the following:

1. Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.

2. Eat up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are lower in mercury.
• Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
• Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to six ounces (one average meal) of albacore tuna per week.

3. Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to six ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.

Due to the changing nature of fish recommendations and the continually rising levels of mercury, I find that I am more conservative in the amounts of fish I eat and recommend. According to a study conducted by a public interest group, the Mercury Policy Project, mercury levels were 30 per cent higher than the tuna industry had previously reported. Of the 48 tunas sampled, over three were found to contain mercury levels considerably higher than the Food and Drug Administration's recommendations. They concluded from the results that one of every 20 cans of white or albacore tuna should be recalled as being unsafe for human consumption. Because of the unknown amount of mercury you are truly consuming when eating tuna, I recommend pregnant or nursing mothers consume no more than six ounces of white tuna per month. Pregnant and nursing mothers can turn to other fish sources lower in mercury, such as wild Atlantic salmon and tilapia. For everyone else, six ounces of canned light (not white) tuna per week appears to be safe. For more information on mercury levels in seafood species, read this chart.