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Fact Sheet on Air Toxics

Toxic comes from the Greek word toxikon which referred to the poison smeared on an arrow. The meaning has changed but not the intent. Air toxics are poisonous airborne pollutants which exist in the atmosphere either as gases or attached to fine particles.

Some air toxics come from natural sources such as dust, forest fires, volcanic gases and soil erosion. But most are created by human activities including industrial processes, the manufacture and use of pesticides, and the burning of fossil fuels such as gas, oil or coal.

Air toxics find their way into the atmosphere in two ways. Some are emitted directly from cars, trucks and train engines or from factories which burn fossil fuels. Others are discharged into water or onto the land, and because they possess the characteristic known as volatility, they escape into the air as gases or attached to fine particles.

The atmosphere plays an important role in the environmental cycle of air toxics. Sometimes it can carry them thousands of kilometres from their source and wash them to earth as rain, snow, fog or mist. The atmosphere may also transform air toxics into even more dangerous chemicals.

Air toxics pose a serious threat to human health and to wildlife for three reasons.

First, they are poisonous, or may become poisonous after combining with other substances or bioaccumulating in the food chain. The toxics may cause death, disease, birth defects, genetic mutations and behavioural abnormalities as well as physiological or reproductive harm in organisms or their offspring.

Second, the toxics bioaccumulate in the fatty tissue of animals, and are difficult or impossible to metabolize or excrete. Even minute amounts may have a major effect on wildlife as the toxics build up to a dangerous level over the lifetime of the animal. Bioaccumulating in the food chain occurs when, for example, plankton which has absorbed toxic chemicals from the water is eaten by fish, which, after storing the toxics in fatty tissues, are then eaten by birds. Because the birds are at the top of this food chain, they may over time accumulate levels of toxics which are thousands of times higher than those in their prey, which themselves were thousands of times higher than those in the plankton.

Third, these toxics are persistent, meaning that they do not break down easily in the environment and may remain intact for decades or even centuries.

Environment Canada is involved in a range of research projects aimed at understanding how air toxics are emitted, transported, transformed and deposited by the atmosphere. Further, the department is heavily involved in the development and enforcement of regulations to prevent the emission of air toxics into the atmosphere.

The most common culprits:

The industrial world uses more than 65,000 commercial chemicals. In 1985, the International Joint Commission identified 11 pollutants which the Canadian-U.S. body considered critical.

1. Polychlorinated Biphenyls (PCBs) -- Although PCBs are no longer manufactured, they are still widely used in sealed electrical and hydraulic equipment.
2. Mirex -- All uses of this extremely persistent insecticide and flame retardant were banned in Canada in 1978.
3. Hexachlorobenzene (HCB) -- This was originally manufactured as a fungicide for crops and generated as a byproduct when pesticides were manufactured. The use of HCB has been restricted in Canada since 1971.
4. Dieldrin -- This chemical, which was used primarily as a pesticide, is no longer made in either Canada or the United States.
5. DDT -- DDT was introduced to North America as an insecticide in 1946. Although it was banned in Canada in 1989, DDT is still used elsewhere in the world and continues to be carried into Canada in the atmosphere.
6. 2,3,7,8-TCDD -- This is a dioxin. It is produced as a by-product by pulp and paper mills which use chlorine in their bleaching process. This dioxin is also created when chlorophenoxy herbicide is produced and chlorinated waste is incinerated.
7. 2,3,7,8-TCDF -- This is a furan which is structurally and chemically similar to 2,3,7,8-TCDD and is a by-product of the same industrial processes and waste incineration.
8. Benzo[a]pyrene -- This is a polycyclic aromatic compound which is formed by the incomplete combustion of fossil fuels, wood and tobacco and during the production of steel and coke. This compound is also formed when garbage is burned or when coal is liquified or turned into a gas.
9. Toxaphene -- This insecticide was widely used the United States until the late 1970s. Toxaphene is still used in the Third World.
10. Mercury -- In the past, mercury was widely used in the pulp and paper industry and in the manufacture of chlorine and caustic soda.
11. Alkylated lead -- This is produced mainly as a gasoline additive. Today, levels of this compound are decreasing as leaded gasoline is phased out.

Published by Authority of the Minister of the Environment
@ Minister of Supply and Services Canada 1992
Catalogue No. En56 97/1992E
ISBN 0-662-19934-0

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