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Fresh air polluted by exhaust fumes and industrial emissions causes lung cancer, a team of World Health Organisation experts has officially declared.

Outdoor air pollution was officially classified as carcinogenic to humans by the cancer arm of the WHO after a review of the latest scientific evidence from around the world.

The International Agency for Research on Cancer (IARC) also highlighted an apparent link between air pollution and an increased risk of bladder cancer, although the findings were less conclusive.

Levels of pollution vary widely between urban and rural areas, but the working group said their findings applied to all regions of the world, and sent a “strong signal” to governments to tackle the problem immediately.

Dr Kurt Straif, head of the IARC Monographs Section which identifies environmental causes of cancer, said: “The air we breathe has become polluted with a mixture of cancer-causing substances.

“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.”

The latest available data suggest that in 2010, air pollution was responsible for the deaths of 223,000 lung cancer patients around the world.

Scientists from the IARC studied more than 1,000 academic papers on polluted air and, separately, small particles found in polluted air.

They found that the risk of developing lung cancer rises in tandem with increasing levels of either, concluding for the first time that outdoor air pollution is a cause of cancer.

Prof David Phillips of King’s College London, a member of the working group, said there was no particular threshold at which pollution becomes dangerous. “The higher the pollution, the greater the cancer risk,” he explained. “It does not suddenly kick in at a particular level.”

The programme had previously classed a variety of individual chemicals and mixtures found in polluted air as carcinogens, such as diesel engine exhaust, solvents, metals, and dusts.

Dr Dana Loomis, deputy head of the IARC monographs section, explained: “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.”

Although the findings do not come as a surprise, they are likely to significantly increase the pressure on governments around the world to tackle pollution, which has risen rapidly around the world during industrialisation and was already known to raise the risk of conditions like heart and respiratory diseases.

Traffic, power stations, industrial and agricultural emissions, and cooking and heating in the home are the main causes of air pollution.

Dr Christopher Wild, director of the IARC, said: “Classifying outdoor air pollution as carcinogenic to humans is an important step. 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.”