Not all air pollution is the same when it comes to human mortality risk—some sources produce far more toxic particles than others, according to a study led by researchers from NYU Langone Medical Center and published online December 2 in the journal Environmental Health Perspectives.
Sources of fossil fuel emissions, including coal-fired power plants and diesel vehicles, were found to generate the most toxic particles of the sources examined in the first nationwide study of its kind, which included nearly 450,000 participants in 100 U.S. cities.
Specifically, the research team found that exposures to tiny particles (less than one ten-thousandth of an inch in diameter, or PM2.5) found in fossil fuel emissions were most closely associated with increased risk of death from ischemic heart disease, which includes heart attack.
The results are relevant to the United Nations Climate Change Conference, which is currently underway in Paris, according to the study authors. Conference delegates are discussing ways to reduce greenhouse gas emissions, and the new study results argue that reductions in coal burning may produce far more health benefits than controlling other sources, such as biomass burning.
PM2.5 particles, often composed of toxins like arsenic, selenium, or mercury, contribute to the development of potentially fatal heart and lung diseases because they are small enough to slip past the body's defenses and to be absorbed into the bloodstream and deep into the lungs. According to the World Health Organization, about 3 million people die each year from outdoor particulate matter present in air pollution exposure. The pollution sources that make the greatest contribution to these deaths, however, had not been previously discerned.
“Past studies of this kind have essentially assumed that all PM2.5 particles have the same toxicity, irrespective of their source,” says lead study investigator and health epidemiologist George D. Thurston, a professor of population health and environmental medicine at NYU Langone. “Our results indicate that, pound for pound, coal-burning particles contribute roughly five times as much to heart disease mortality risk as the average air pollution PM2.5 particle in the United States.” The study also found that PM2.5 from wind-blown soil and the burning of biomass, such as wood, were “non-significant contributors” to mortality risk related to PM2.5.
In their analysis, the NYU Langone-led research team used trace element “fingerprints” to estimate the contributions of different PM2.5 sources to mortality risk in a nationwide survey. Coal-burning particles, for example, contained traces of selenium and arsenic, traffic emissions contained elemental carbon, oil-combustion particles contained vanadium and nickel, soil particles contained calcium and silicon, and wood-burning particles contained potassium concentrations. The scientists concluded that the toxicities of PM2.5 particles depended on their chemical composition and the pollution source. That study data were collected between 1982 and 2004.
In addition to Dr. Thurston, study authors were C. Arden Pope of Brigham Young University; Michael Jerrett of the University of California, Berkeley; Daniel Krewski, Michelle Turner, and Yuanli Shi of the University of Ottawa; Susan M. Gapstur and W. Ryan Diver of the American Cancer Society; and Richard Burnett of Health Canada, Ottawa.