Environmental risks

Some substances in the air, water or soil may increase a person’s risk of cancer. These natural or manufactured substances are sometimes called environmental contaminants. Environmental contaminants may be present in the home, at work or outside.

Research studies

Researchers use 3 main ways to study environmental contaminants:

• Toxicology studies look at what is toxic or harmful in substances.
• Animal studies test the effects of toxic substances in laboratory animals.
• Epidemiology studies look at links between risk factors and disease in people.

Other types of studies gather data that helps governments and policy-makers understand the effects of exposure to potentially harmful chemicals. Human biomonitoring studies identify and measure chemicals that we are exposed to and have built up in our bodies over time. For more information on human biomonitoring of environmental chemicals, visit the Health Canada website.

All of these studies improve our understanding of the link between harmful substances in our environment and cancer. However, these studies have certain limitations that make it difficult to fully understand the relationship between many environmental contaminants and cancer.

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Level of risk

Certain environmental contaminants might play a role in the development of some cancers, but current scientific evidence has not confirmed or ruled them out as possible risk factors. Scientists continue to study and debate the role of environmental contaminants in the development of cancer.

There is currently a lot of debate about how many cancers are related to exposure to environmental contaminants. While the exact percentage of cancers associated with this type of exposure is not known, research suggests that people who are continually exposed to cancer-causing substances in the environment generally have a higher risk of developing certain cancers.

Most of the environmental contaminants known to cause cancer in humans were identified through studies that looked at groups of people who shared occupational exposure to carcinogens. These people had a greater exposure to these potential cancer-causing substances than in people the community or at home.

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Exposure

Sometimes people can’t avoid being exposed to environmental contaminants or they may not know they are being exposed to them. People are exposed to different environmental contaminants for varying lengths of time and at different levels. This makes it hard to figure out how much exposure a person has had to any one substance or chemical. Also, exposure to a combination of environmental contaminants may increase a person’s risk more than each substance or chemical alone.

Exposure in children

Much of the research on the links between the environment and cancer has focused on exposure in adults. We know less about how exposure to environmental contaminants early in a child’s life affects the risk for cancer. This is because cancer in children is uncommon and it is hard to identify past exposure levels in children.

Children may be exposed to environmental contaminants in 2 ways:

• Prenatal exposure happens before a baby is born. It may come from the father when the baby is conceived or from the mother during pregnancy. For example, environmental contaminants could be absorbed by the mother and passed through the placenta to an unborn child. They may also damage the father’s sperm.
• Children may be exposed to environmental contaminants in the home or outside after they are born.

Researchers are studying childhood exposure to harmful environmental substances. They believe that children may be more vulnerable to environmental contaminants that can increase the risk of cancer and other health problems.

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Identifying cancer-causing substances

To determine whether a substance may increase the risk of cancer, researchers carefully review the scientific evidence from studies done in people and in the laboratory. Based on the weight or strength of the evidence, major scientific agencies that study the effect of exposures draw a conclusion about the risk of cancer associated with exposure to a particular substance. These agencies then classify substances according to their cancer-causing potential in humans. A few of them are listed in the table below.

Some cause-and-effect relationships between environmental contaminants and cancer are not fully understood. Finding and studying higher than expected numbers of cancer cases among a group of people who share something in common, such as where they live or work, can provide important clues to possible environmental exposures.

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Reducing your risk

Both individual action (taking steps to reduce your exposure) and public policies can help prevent or reduce exposure to cancer-causing substances in the environment. Whenever possible, exposure to cancer-causing substances should be identified and stopped by using safer alternatives. When it is not possible to stop exposure completely, exposure should be reduced to the lowest possible levels.

Some general actions you can take to reduce or prevent exposure to cancer-causing substances in the environment include:

• Avoid cancer-causing substances.
• Eliminate or limit exposure to potentially harmful and cancer-causing substances by using non-toxic materials (for example, non-toxic glue and paint) whenever possible.
• Follow safety instructions at home and at work when using, storing and disposing of harmful materials or chemicals. Read and carefully follow the manufacturers’ directions for safely using and storing hazardous chemicals. Health Canada and Environment Canada often have guidelines for handling harmful substances.

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