Toxic air pollution linked to cancer
Melissa Galea Holmes, MSc, MA
Air pollution isn't just bad for the environment--it's also full of toxins that can lead to lung diseases and cancer.
Air pollution is a well-known cause of chronic health problems including asthma, bronchitis, and cardiovascular disease. The latest evidence now reveals that airborne toxins are also a leading cause of cancer.
Air pollution kills
A landmark report by the World Health Organization (WHO) found 223,000 deaths from lung cancer worldwide were a result of air pollution. After reviewing over 1,000 studies, the WHO International Agency on Research for Cancer classified air pollution as “carcinogenic to humans”—the same category as cigarette smoke.
Air quality is affected by a multitude of chemical, physical, and biological agents that are released into the atmosphere.
Pollutants known to increase health risk and environmental damage are called criteria air contaminants (CACs). This group of chemicals is closely monitored and regulated by federal and international standards. CACs include sulphur and nitrogen oxides, primary particulate matter, volatile organic compounds, ammonia, and carbon monoxide.
Health impact of CACs
The greatest danger of CACs is their potential to react with one another to create ozone and secondary particulate matter—key markers of poor air quality.
Long-term exposure has been linked to respiratory ailments including asthma and chronic obstructive pulmonary disease, diabetes, and cardiovascular disease. Even daily fluctuations in ozone and particulate matter often lead to increased hospitalizations and death.
We now know that inhaled toxins also cause cancer. Air pollution triggers a number of pathways leading to the development of cancer, including oxidative stress, DNA damage, and modified gene expression.
Ozone: A ground-level problem
Ozone belongs in the stratosphere, where it protects us from harmful ultraviolet radiation. At ground level, it is the intoxicating precursor to smog and a known respiratory irritant. Although we link it to hot and hazy summer days, ozone pollution is a problem year-round due to increased vehicle use and residential wood heating in the winter.
Day to day, ozone levels are lowest at sunrise and dawn. To minimize exposure, try to schedule outdoor activities and exercise outside of peak hours and check your local weather report for ambient levels before heading out at midday or during rush hour.
Particulate matter is a global term for a range of airborne particles that are small enough in size to breathe in. Fine particulate matter poses the greatest health risk because it can travel to the deepest lung tissue. Long-term exposure to these tiny toxins causes low-grade inflammation and leads to higher risk of many diseases, including lung cancer.
Alongside ozone and particulate matter, polycyclic aromatic hydrocarbons (PAHs) are another primary concern. Long-term exposure is directly linked to lung cancer.
PAHs result from incomplete combustion of organic, carbon-based materials including fossil fuels. In the past, the primary sources of PAHs were natural events such as forest fires and volcanic eruptions. Today, human activity, especially vehicle use, is responsible for most PAHs in the atmosphere.
Sources of air pollution
Just how do these chemicals end up in our breathing space? Primary pollutants travel directly from a source—a chimney or exhaust pipe, for example—while others, called secondary pollutants, form within the atmosphere through chemical reactions with other particles or with sunlight.
Different sources of pollution, combined with the local climate, geography, and weather, mean the ambient air quality in any given province, city, neighbourhood—or even a particular street corner, depending on the wind—can be unique.
It is no surprise that densely populated, highly industrialized, and urban spaces have high levels of primary pollutants—vehicle emissions trapped by tall buildings and energy emissions from homes and workspaces are constantly clogging the air.
In 2010 alone, exposure to fine particulate matter was estimated to have contributed to 3.2 million premature deaths around the world, mainly due to heart disease and lung cancer. But air has no boundaries, and rural areas are also affected. A large amount of fine particulate matter is generated outside the local area and has probably clocked more mileage than the average car.
Transport of pollutants between Canada and the US is a widely documented problem. In 1991, the Canada-United States Air Quality Agreement was established with the aim of reducing pollution cooperatively, and it continues to drive joint initiatives to monitor and improve the environment.
Higher concentrations of particulate matter and CACs, especially sulphur dioxide and nitrogen oxide, are found in both countries as a result of transboundary movement. The corridor that lies within 500 km of the border is immediately affected and has been the focus of joint monitoring.
But pollutants can be carried outside of this boundary and concentrated in key areas, expanding the potential for health risk. For example, regions where predominant winds are southerly—such as the eastern provinces—have poorer air quality as a result of pollutants travelling from the US.
A global issue
While Canada and the US have long been working together, the problem of transboundary air pollution has a much wider bandwidth. Arctic Canada has higher levels of heavy metals as a result of air travelling from Europe and Asia. Reducing pollution requires cooperation not just across North American borders—but globally.
Driving the problem
Transportation is one of the largest sources of air pollution in Canada. Automobiles, as well as off-road vehicles and lawn and garden equipment, contribute 25 to 40 percent of most pollutants—and up to 75 percent of carbon monoxide. Air quality is poorest within 500 m of a major roadway, and people living and working in these areas have a greater health risk.
Alternative fuels have long been under development, but aren’t immune to controversy either, and some argue that they need to be more rigorously studied and tested. While diesel is generally more polluting, some research suggests that older, poorly maintained gas-powered vehicles can be worse. Pollutants are emitted not only from the tailpipe, but also from worn-down tires and metallic components. Keeping your car well maintained can reduce your impact on the environment.
By 2017, all new automobiles in Canada and the US will be required to meet tougher standards, with stricter limits on emissions and reduced sulphur in gasoline. Nevertheless, we need to reduce our use of cars—try carpooling to work, use public transport, or commute by bike or foot.
Indoor air pollution
You might be thinking the best option is to lock yourself indoors. But air quality at home, and in workplaces and schools, can also negatively affect health. Pollutants can be transported from the outdoors or can originate from an indoor source, such as a wood-burning stove, tobacco smoke, and chemicals released from upholstery and furniture. To minimize exposure, keep your home well-ventilated, maintain your furnace, and use the exhaust fan during stovetop cooking.
Policy on pollution
Monitoring and regulation of air pollutants falls under the Canadian Environmental Protection Act, 1999, which aims to prevent pollution and protect both the environment and human health.
Emissions of air pollutants have declined across the country since 2000, but Canada is still one of the top polluters among G8 nations. A large part of the problem is economic—international demand for Canada’s resources, and their industrial extraction and use, leads to increased pollution.
Despite reduced emissions, current levels of air pollution are still affecting health. The Canadian Ambient Air Quality Standards, announced in 2013, set stringent standards and annual targets for fine particulate matter and ozone levels. But the objectives are voluntary, meaning provinces and territories may be less likely to take action. In addition, Canadians are still susceptible to the volumes of pollutants emitted across the border.
What can we do now?
We have long known that air pollution is linked to respiratory and cardiovascular illness—and we now know it is a cause of cancer. Reversing the damaging effects of air pollution to our environment and health will take time. For now, there are measures each of us can adopt to minimize exposure, reduce our impact on air quality, spur government action, and protect our health.
Take action against air pollution
Detox from daily air pollution exposure
Some nutrients found in foods or supplements may play a role in cancer prevention. As always, speak to your health care practitioner before taking a new supplement to make sure it’s right for you.