The United Nations agency in charge of researching cancer makes no bones about it: Air pollution is killing us. The International Agency for Research on Cancer (IARC), part of the UN's World Health Organization, this week classified outdoor air pollution as carcinogenic to humans. Specifically, the IARC links air pollution to lung cancer as well as an increased risk of bladder cancer.

The IARC came to the conclusions after reviewing the latest scientific research about air pollution and cancer rates. According to their data, an astonishing 223,000 lung cancer deaths in 2010 (the most recent data available) could be attributed to air pollution. More than half of those lung cancer deaths occurred in China and other East Asian countries and were linked to ambient fine particles in air pollution. Particulate matter and gases from air pollution were both linked to overall health risks.

"The air we breathe has become polluted with a mixture of cancer-causing substances," Dr. Kurt Straif, Head of the IARC Monographs Section, said in a press release (pdf). "We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths." Other health risks attributed to air pollution include respiratory and heart diseases.

The IARC Monographs Section normally focuses on individual chemicals or other substances — such as asbestos, tobacco smoke, ultraviolet radiation and plutonium — that can be linked to cancer risk. For their new report they took a broader scope and looked at outdoor air as a whole. According to the report, the biggest sources of outdoor air pollution are transportation (including cars, trucks and airplanes), power plants, residential heating and cooking, and industry and agriculture.

Although the levels and effects of outdoor air pollution vary around the world and are at their worst in industrialized nations, the IARC emphasized that this should be considered a worldwide problem.

The IARC hopes this new report will be taken as a call to action. "Classifying outdoor air pollution as carcinogenic to humans is an important step," said IARC director Dr. Christopher Wild. "There are effective ways to reduce air pollution and, given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay."

The IARD has published a free, 13-chapter e-book detailing the risks of air pollution in great detail. The book, available in ePUB format, covers the geographical distribution of air pollutants, its sources, how its effects combine with other pollutants and agents, genetic risk factors, and how all of these pollutants link to cancer in humans.

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