A large study conducted in Europe has shown that prolonged exposure to particulate air pollution contributes to lung cancer incidence, even at levels below the European Union thresholds.

Ambient air pollution had already been suspected of causing lung cancer when a team led by Dr. Ole Raaschou-Nielsen, of the Danish Cancer Society Research Center in Copenhagen, Denmark, undertook a prospective analysis to assess that relationship. Specifically, the researchers evaluated the association between lung cancer incidence in European populations across nine countries and long-term exposure to nitrogen oxides and particulate-matter (PM) air pollution from traffic, industry, and domestic heating.

Data from 312,944 participants in the European Study of Cohorts for Air Pollution Effects represented 4,013,131 person-years at risk. During a mean follow-up of 12.8 years, 2,095 persons received a diagnosis of lung cancer.

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As Raaschou-Nielsen and colleagues reported in The Lancet Oncology (2013;14[9]:813-822), they found no association between lung cancer risk and nitrogen oxides concentration. However, lung cancer risk rose by 18% for every increase of 5 micrograms per cubic meter of PM pollution with a diameter of less than 2.5 micrometers (referred to as PM2.5 pollution). For PM10 pollution (PM pollution with a diameter of less than 10 micrometers), every increase of 10 micrograms per cubic meter raised lung cancer risk by 22%. Stronger effects were indicated for adenocarcinomas.

An increase in road traffic of 4,000 vehicle-kilometers per day within 100 meters of a residence increased the risk for lung cancer, but traffic intensity on the nearest street (per 5,000 vehicles per day) did not.

The investigators wrote that they found no threshold of PM air pollution for which there was no risk for lung cancer. The threat was present even at PM air pollution concentrations below the existing European Union air quality limit values for PM2.5 (25 micrograms per cubic meter) and PM10 (40 micrograms per cubic meter).