In a groundbreaking Oct. 17 announcement, the International Agency for Research on Cancer (IARC), an agency of the World Health Organization, classified outdoor air pollution as a known cause of lung cancer. The agency also found that particulate matter (PM), a major component of air pollution better known as “soot,” is a known cause of lung cancer.  After an extensive review of more than 1,000 scientific studies from five continents, a committee of some of the world’s leading experts on air pollution and health convened by the IARC Monographs Programme concluded that there is sufficient evidence that exposure to outdoor air pollution causes lung cancer. Though IARC has previously evaluated the health impacts of various components of outdoor air pollution, such as diesel engine exhaust, metals, and solvents, this is the first time that outdoor air pollution in general has been classified as a cause of cancer.

The IARC evaluation found strong scientific evidence of an increased risk of lung cancer with increasing exposure to air pollution in general and issued a similar finding for particulate matter. Although the composition of air pollution and levels of exposure can vary dramatically between locations worldwide, the IARC conclusions apply to all regions of the world. The IARC assessment of the link between PM and lung cancer contrasts with findings from the U.S. Environmental Protection Agency’s (EPA) 2009 assessment of the PM health science,  which classified the PM-lung cancer scientific evidence as only “suggestive of a causal relationship.” 

The IARC findings have significant implications for U.S. air pollution control efforts. The EPA sets air quality standards to protect public health based on assessments of the health effects of individual pollutants rather than outdoor air pollution in general.  Air pollution control rules are then developed for specific sources of these individual pollutants in order to achieve the health-based standards.

However, in the real world, we are exposed to a toxic soup of various different air pollutants and chemical mixtures, which interact and combined can have a greater health impact than each of the individual components. This concept was recognized more than 40 years ago and incorporated by Congress into the Clean Air Act of 1970, which provides the foundation of today’s air pollution control efforts. In providing instruction to EPA for developing air pollutant health assessments, Congress expressly required EPA to consider “the types of air pollutants which, when present in the atmosphere, may interact with such pollutant to produce an adverse effect on public health or welfare” (emphasis added).

Given the generally accepted scientific consensus that even very low levels of exposure to environmental pollution increases the risk of cancer, the IARC findings suggest that reductions in U.S. air pollution beyond levels set as “safe” for individual pollutants, especially for particulate matter and transportation-related pollutants that were the focus of many of the reviewed studies, would provide additional public health benefits in avoided lung cancers.