Air pollution major cause of cancer, WHO says

The air we breathe is laced with cancer-causing substances and is being officially classified as carcinogenic to humans, the World Health Organization’s cancer agency said yesterday.

The International Agency for Research on Cancer cited data indicating that in 2010, 223,000 deaths from lung cancer worldwide resulted from air pollution, and said there also was convincing evidence that it increases the risk of bladder cancer.

Depending on the level of exposure in different parts of the world, the risk was found to be similar to that of breathing in second-hand tobacco smoke, said Kurt Straif, head of the agency’s section that ranks carcinogens.

“Our task was to evaluate the air everyone breathes rather than focus on specific air pollutants,” deputy head Dana Loomis said in a statement. “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.”

Air pollution, mostly caused by transportation, power generation, industrial or agricultural emissions, and residential heating and cooking, already is known to raise risks for a wide range of illnesses, including respiratory and heart diseases.

Research suggests that exposure levels have risen significantly in some parts of the world, particularly countries with large populations going through rapid industrialization, such as China.

The IARC reviewed thousands of studies on air pollution tracking populations over decades and other research, such as those in which mice exposed to polluted air experienced increased numbers of lung tumors.

In a statement released after reviewing the literature, the agency based in Lyon, France, said both air pollution and “particulate matter” — a major component of it — now would be classified among its Group 1 human carcinogens.

That ranks them alongside more than 100 other known cancer-causing substances, including asbestos, plutonium, silica dust, ultraviolet radiation and tobacco smoke.

Air pollution is highly variable over space and time.

But although both the composition and levels of air pollution can vary dramatically from one location to the next, IARC said its conclusions applied to all regions of the world.

“Our conclusion is that this is a leading environmental cause of cancer deaths,” Dr. Christopher Wild, director of IARC, said at a news conference in Geneva.

Wild said he hoped the comprehensive evidence would help the WHO, which is revising its global 2005 guidelines on air quality. The U.N. agency makes recommendations on public-health issues to its 193 member states.

Asked why it had taken so long to reach the conclusion, Wild said that one problem was the time lag between exposure to polluted air and the onset of cancer.

“Often, we’re looking at two, three or four decades once an exposure is introduced before there is sufficient impact on the burden of cancer in the population to be able to study this type of question,” he said.

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