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LYON, FRANCE — Outdoor air pollution has been classified as a leading environmental cause of cancer by the World Health Organization (WHO), saying it has found "sufficient evidence" that exposure to pollutants in the air causes lung cancer and leads to an increased risk of bladder cancer.
Emissions from motor vehicles, industrial processes, power generation, the household combustion of solid fuel, and other sources pollute the ambient air across the globe. The precise chemical and physical features of ambient air pollution, which comprises a myriad of individual chemical constituents, vary around the world due to differences in the sources of pollution, climate, and meteorology.
Some of the world's leading experts in the field, including epidemiologists, toxicologists, atmospheric scientists, and cancer biologists, have now concluded that there is "sufficient evidence" that exposure to outdoor air pollution causes lung cancer. They also noted a positive association with an increased risk of bladder cancer.
The classification is based on both original research as well as an independent review of more than 1,000 scientific papers from epidemiologic studies that covered millions of people living across the world. The reviewed studies analyzed the carcinogenicity of various pollutants present in outdoor air pollution, especially particulate matter and transportation-related pollution.
The evaluation of the International Agency for Research on Cancer (IARC), which is part of the World Health Organization, showed an increasing risk of lung cancer with increasing levels of exposure to air pollution and particulate matter, which is a major component of outdoor air pollution and was evaluated separately.
"Air belongs to everybody, nobody has private air," said Dana Loomis, the deputy head of the IARC Monographs Section. "We can't do very much to change the air we breathe and we are all responsible for it, and so I think it's important to make the point that this really needs collective public health action to solve the problem."
Air pollution is already known to increase risks for a wide range of diseases, such as respiratory and heart diseases, but recent studies indicate that the disease burden may be far greater than previously thought. It also showed that exposure levels have increased significantly in some parts of the world, particularly in rapidly industrializing countries with large populations.
Exposure to ambient fine particles was recently estimated to have contributed 3.2 million premature deaths worldwide in 2010, due largely to cardiovascular disease, and 223,000 deaths from lung cancer. More than half of the lung cancer deaths attributable to ambient fine particles were projected to have been in China and other East Asian countries.
"The rule of the Monographs is to provide information to national and international organizations so that they can then carry it forward into policy action and guidelines in order to take action to solve the problem," Loomis said. "We provided this information now and next it's over to organizations like WHO and national governments to make decisions that are appropriate for their jurisdictions."
In the past, the IARC Monographs Program – dubbed the "encyclopedia of carcinogens" – has evaluated many individual chemicals and specific mixtures that occur in outdoor air pollution. These included diesel engine exhaust, solvents, metals, and dusts, but the latest research is the first time that experts have classified outdoor air pollution as a whole.
"Our task was to evaluate the air everyone breathes rather than focus on specific air pollutants. The results from the reviewed studies point in the same direction: the risk of developing lung cancer is significantly increased in people exposed to air pollution," Loomis explained. The program has evaluated more than 950 agents during its 40-year history, including more than 100 that were classified as carcinogenic to humans.