Mercury: Effects on Human Health : Part 2

by Health Canada

(Page 2 of 2)

Organic Mercury Compounds (Methyl mercury)

Mercury can change from one form to another in the environment. Methyl mercury tends to accumulate to some degree in all fish, but especially in the predatory fish noted above. Methyl mercury is absorbed through the intestines and distributed throughout the body. It readily enters the brain, where it may remain for a long period of time. In a pregnant woman, it can also cross the placenta into the fetus, building up in the fetal brain and other tissues. Methyl mercury can also be passed to the infant through breast milk.

A child's developing nervous system is particularly sensitive to methyl mercury. Depending on the level of exposure, the effects can include a decrease in I.Q., delays in walking and talking, lack of coordination, blindness and seizures. In adults, extreme exposure can lead to health effects such as personality changes, tremors, changes in vision, deafness, loss of muscle coordination and sensation, memory loss, intellectual impairment, and even death.

The Risks of Mercury Poisoning

In general, Canadians are not at risk from mercury poisoning. However, people exposed to elevated levels of mercury may experience health problems ranging from rashes to birth defects, even death in cases of extreme poisoning.

People who consume large amounts of fish, marine mammals and wild game as part of their daily diet increase their risk. The developing fetus and children of women who have consumed large amounts of fish and marine mammals during pregnancy are the most susceptible to health problems. Children, who tend to put things in their mouths, may increase their intake of mercury through soil and contaminated objects.

In regions such as the Arctic, the traditional diet may include large quantities of fish and/or marine mammals at certain times of the year. However, this traditional diet has many nutritional and socio-cultural benefits, which must be weighed against the potential risks.

If you are concerned about mercury exposure, samples of hair, blood and urine can be taken in a doctor's office or health clinic and tested.

Minimizing Your Risk

Elemental mercury from dental fillings doesn't generally pose a health risk. There is, however, a fairly small number of people who are hypersensitive to mercury. While Health Canada does not recommend that you replace existing mercury dental fillings, it does suggest that when the fillings need to be repaired, you may want to consider using a product that does not contain mercury.

Pregnant women, people allergic to mercury and those with impaired kidney function should avoid mercury fillings. Do not have mercury fillings removed when you are pregnant because the removal may expose you to mercury vapour. When appropriate, the primary teeth of children should be filled with non-mercury materials.

Predatory fish such as shark, swordfish, fresh and frozen tuna (not canned), have higher levels of mercury and should be consumed only occasionally. The health benefits of eating fish outweigh the risk of exposure to mercury if Health Canada consumption guidelines are followed. If you are an adult, limit your intake of these fish to no more than one meal per week. Pregnant women, women of child-bearing age and young children should be especially careful and limit their intake of these fish to no more than one meal a month.

For information on sport fish caught in local waters, check with your provincial or territorial authority on any advisory that may have been issued for that area.

The Government of Canada's Role

The Government of Canada issues retail fish consumption advisories, while the provincial and territorial agencies issue advisories on sport fish. The Canadian Food Inspection Agency enforces a guideline for mercury in fish. It applies to all fish except shark, swordfish, and fresh and frozen tuna, for which meal limits are recommended.

The Government of Canada is working in a number of areas to reduce the use and release of mercury into the environment. In 2000, the Canadian Council of Ministers of the Environment developed several Canada-wide standards to reduce mercury release to the environment. Standards have been, or are being, developed for certain mercury-containing products and for mercury emissions from selected industries. The Government has also helped set up the Northern Contaminants Program and the National First Nations Environmental Contaminants Program. Canada also has Cosmetic Regulations. These regulations contain restrictions for mercury; it is only permitted as a preservative ingredient in cosmetics intended for use in the area of the eye.

Although Canada will continue to reduce mercury releases, efforts must also be made elsewhere. Much of the mercury deposited on our lakes and soil comes from other countries. Canada is taking an active role in regional and international efforts to reduce mercury in the environment globally. The Government is working with the USA and Mexico through the North American Commission for Environmental Co-operation to address mercury issues under the North American Regional Action Plan on Mercury.

About the Author

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Health Canada is the Federal department responsible for helping Canadians maintain and improve their health, while respecting individual choices and circumstances.