International Agency for Research on Cancer
150, cours Albert Thomas
On behalf of the International Agency for Research on Cancer Monograph Working Group IARC, Lyon, France.
A multidisciplinary Working Group of experts organised by the International Agency for Research on Cancer (IARC) has classified outdoor air pollution and particulate matter in outdoor air pollution as carcinogenic to humans (IARC Group 1). The Working Group's unanimous evaluation was based on a comprehensive review of the scientific literature and found sufficient evidence of carcinogenicity in humans and experimental animals, strongly supported by mechanistic evidence. Outdoor air pollution is a complex mixture originating from numerous sources, including transport, power generation, industry, agriculture, domestic heating, and natural processes. The levels vary over space and time, and have generally declined in Europe and North America, while they have risen in some rapidly industrialising countries, notably in Asia. Epidemiologic studies of millions of people in Europe, North America and Asia consistently show that exposure to outdoor air pollution measured by several indicators, including the concentrations of pollutants in the air and measures of exposure to traffic, is associated with increased risk of lung cancer. Among the specific pollutants considered, airborne particulate matter is associated most consistently with increased risk of lung cancer and shows a positive exposure-response relationship with the level of exposure. There is also limited evidence that exposure to outdoor air pollution is associated with bladder cancer. Laboratory animals exposed to polluted air by inhalation or treated with extracts from particulate matter also showed increased incidence of tumours. Supporting data come from many studies in humans, animals, plants and experimental systems that show increases in genetic damage, including cytogenetic abnormalities, mutations in both somatic and germ cells, and altered gene expression, which have been linked to increased cancer risk in humans. It has been estimated that about 15% of all lung cancer worldwide is attributable to particulate air pollution. While there is clear evidence that outdoor air pollution is carcinogenic, virtually all of the existing health studies were conducted in countries where pollution levels are relatively low on the global scale, with effects observed even at levels below current air quality standards and guidelines. There is thus a need for more research in highly polluted areas, as well as for public health action.