Air Pollution to Blame for 223,000 Lung Cancer Deaths Annually

Issue 23, Summer/Fall 2014

Dirty Air Joins World Health Organization's List Of Official Carcinogens

People inhale about 10,000 liters, or about 2,500 gallons, of air each day. As a result, damaging doses of contaminants in the air reach the lung, even for pollutants present in low concentrations. These contaminants include cancer-causing agents that reflect man’s activities and also some naturally occurring carcinogens, such as radon.

For more than 100 years, dating to the identification of radon as a cause of lung cancer in Eastern European underground miners, we have known that breathing contaminated air can cause lung cancer. Now, the list of such contaminants is large and includes tobacco smoke, whether inhaled by active smokers or involuntarily by nonsmokers, radon, asbestos, diesel exhaust, and other agents.

World map

In October 2013, the International Agency for Research on Cancer (IARC), the World Health Organization agency concerned with cancer causes and control, classified “outdoor air pollution” as a cause of cancer. The Working Group convened by IARC, a multidisciplinary group of scientists, found the evidence to be sufficiently strong to classify outdoor air pollution as a Group 1 carcinogen, indicating that the evidence is definitive.

In making this classification, the Working Group considered the full scope of evidence available: the sources of air pollution and the various pollutants in the outdoor air pollution mixture; studies on the mechanisms by which outdoor air pollution could cause lung cancer; animal studies; and epidemiological studies that have tracked cancer risks in relation to air pollution exposure. The total package of evidence made a convincing case for the causation of cancer by outdoor air pollution.

Around the world, known carcinogens, primarily arising from combustion, are present in outdoor air in cities and samples of particles collected from the air in cities around the world have mutagenic activity, meaning that they can alter a person’s DNA.

The figure shows estimated levels of small particles (known as PM2.5) around the world. The map shows that much of the world’s population lives in places with high levels of particles – a good general indicator of carcinogens in the air.

The epidemiological studies, primarily carried out in Canada, the United States, and Europe, show that lung cancer risk rises as exposure to air pollution increases. This body of evidence met the agency’s widely accepted criteria for determining that outdoor air pollution causes cancer; the Working Group specifically linked lung cancer to air pollution.

Given this classification and the ubiquity of outdoor air pollution, the magnitude of the burden of cancer attributable to air pollution is an immediate concern. In announcing the classification, IARC’s press release led with “Outdoor air pollution a leading environmental cause of cancer deaths.” That characterization reflected the estimates for 2010 made by the Global Burden of Disease project, which systematically analyzes the extent to which many different factors contribute to causing ill health and disability and death.

Air pollution

For lung cancer, the Global Burden team estimated the levels of airborne particles, a useful indicator of air pollution generally, by using actual measurement data, satellite information and other data in a prediction equation. The lung cancer risk at particular levels of particles was obtained from epidemiological studies.

The IARC team reviewed data from the studies to calculate the number of lung cancer deaths caused by air pollution, yielding a figure of 223,000 per year.

This means that air pollution accounted for about 15% of the total of the approximately 1.5 million lung cancer deaths worldwide in 2010. For comparison, smoking caused over 965,000 lung cancer deaths worldwide in 2010.

For the United States, the estimate for lung cancer deaths attributable to air pollution is around 10,000 in 2010, but the figures are far higher for China at 140,000 deaths and India at 13,000, based on data from the Global Burden of Disease project.

These estimates do not account for the full burden of cancer caused by air pollution, as indoor air pollution from cooking, heating, and other sources is not included.

What are the consequences of the IARC classification? In the United States, air pollution concentrations and major sources, such as vehicles and power plants, are closely regulated and air quality has improved greatly over the four-decade span since the passage of the Clean Air Act. The IARC classification will not have immediate implications in the United States, but will be acknowledged in the evidence-based process by which air pollution standards are periodically revised.

Air Pollution

The IARC classifications have global reach, however, and the designation of outdoor air pollution as a cause of cancer has immediate implications for countries with growing and increasingly polluted megacities. In cities and even broad regions of China and India, outdoor air pollution concentrations are rising and reaching levels that threaten public health on a day-to-day basis.

The IARC classification adds to the urgency of taking action to effectively manage air quality. For the long-term, millions of people are involuntarily breathing cancer-causing air and their governments need to take action urgently.

Jonathan M. Samet, MD, MS

Jonathan M. Samet, MD, MS
Distinguished Professor and Flora L. Thornton Chair
Department of Preventive Medicine
Keck School of Medicine of USC
Director, USC Institute for Global Health
University of Southern California
Los Angeles, CA