Avoiding Mercury in Fish

Topic Overview

What is mercury?

Mercury is a metal found naturally in the environment. Human activities, such as farming, burning coal, and using mercury in manufacturing, increase the mercury cycling through the air, water, and soil. In water, mercury changes its form and becomes methyl mercury. Fish absorb this mercury. When you eat fish containing mercury, you absorb the mercury, and at high levels it can be harmful. Mercury will leave the body over time in the urine, feces, and breast milk.

Do you need to avoid the mercury found in fish?

For most people, the level of mercury absorbed by eating fish and shellfish is not a health concern. Overall, fish and shellfish are healthy foods. They contain high-quality protein and other essential nutrients, are low in saturated fat, and contain omega-3 fatty acids, a type of essential fatty acid. A balanced diet that includes fish and shellfish can contribute to heart health and children's growth and development.

Nearly all fish and shellfish contain traces of mercury. However, some contain high levels. Eating large amounts of these fish and shellfish can result in high levels of mercury in the human body. In a fetus or young child, this can damage the brain and nerves (nervous system).

Because of the mercury found in fish, Health Canada advises the following people to limit eating fish high in mercury each month:¹

• Women who are or may become pregnant
• Nursing mothers
• Children age 11 and younger

Most people should not eat more than 150 g (5.3 oz) of fish that may be high in mercury each week.

If you are concerned about your or your child's mercury level, talk to your health professional or local health unit about testing.

How should you change your eating habits to reduce your exposure to mercury in fish?

Fish known to have higher mercury levels include escolar, marlin, orange roughy, shark, swordfish, and fresh or frozen tuna (not canned "light" tuna). Most people should not eat more than 150 g (5.3 oz) per week. But the following people should limit how much high-mercury fish they eat each month to:¹

• 150 g (5.3 oz) or less for nursing mothers or women who are or may become pregnant.
• 125 g (4.4 oz) or less for children 5 to 11 years of age.
• 75 g (2.7 oz) or less for children 1 to 4 years of age.

Limit how much canned albacore tuna you eat each week to:²

• 300 g (10.6 oz) or less for nursing mothers or women who are or may become pregnant.
• 150 g (5.3 oz) or less for children 5 to 11 years of age.
• 75 g (2.7 oz) for children 1 to 4 years of age.

Health Canada has no restrictions on eating fish and shellfish that are lower in mercury. These include salmon, cod, pollock, sole, shrimp, mussels, scallops, and canned "light" tuna.

The fish used in fish sticks and the fish sandwiches sold at fast-food restaurants are generally lower in mercury.

Should a woman who is not planning a pregnancy be concerned?

Mercury accumulates in your bloodstream over time and slowly leaves the body through urine, feces, and breast milk. If you eat a lot of fish high in mercury, it may take up to a year for your mercury levels to drop after you stop eating the fish. If you decide to become pregnant or have an unplanned pregnancy, you may have high levels of mercury. While elevated levels of mercury usually do not cause significant health problems, they may affect a developing fetus. If you are of child-bearing age, try to follow the guidelines above when eating fish.

Where can you get more information?

For specific information on:

• Your province's or territory's fish consumption advisories, see www.ec.gc.ca/MERCURY/EN/index.cfm.
• The fish or shellfish caught by family and friends in your local lakes, rivers, and coastal areas, check with your local fishing and public health authorities.

For general information on mercury in fish, see:

• Your local health unit or provincial public health agency.
• Health Canada's Web page on mercury at www.hc-sc.gc.ca/fn-an/securit/chem-chim/mercur/index_e.html.
• The Canadian Food Inspection Agency Web site at www.inspection.gc.ca/english/anima/fispoi/fispoie.shtml.

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Author:	Shannon Erstad, MBA/MPH Carrie Henley	Last Updated: May 29, 2007
Medical Review:	Renée M. Crichlow, MD - Family Medicine Anne C. Poinier, MD - Internal Medicine Kirtly Jones, MD - Obstetrics and Gynecology Deborah A. Penava, BA, MD, FRCSC, MPH - Obstetrics and Gynecology
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