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Exposure and Health Effects of Mixtures of Air Pollutants

The air we breathe is a mix of pollutants that come from different sources or are created from different chemical reactions in the atmosphere. The type of air pollutants in the air can vary by the area of the country, proximity to sources of pollutants such as traffic or industry and the time of year, such as summer when ozone is more common.

EPA is actively considering approaches to manage air quality in a more integrated manner to take into account emissions and exposures of multiple pollutants in the atmosphere, called multipollutant mixtures, rather than single pollutants. To support this effort, critical science is being conducted to advance understanding of the exposures and health effects of air pollution mixtures.

  • What are the health effects of air pollution mixtures?

    Researchers are studying whether exposure to multiple pollutants may increase the severity of health effects, compared to exposure to pollutants individually.

    Research is under way with a large longitudinal study called CATHGEN to understand the acute and chronic health effects of pollutant mixtures as well as individual effects on the cardiovascular system. Genetic and epigenetic factors are being evaluated to determine if they make individuals more at risk to air pollutants.  

    A multi-city/multipollutant study (MCMP) is being conducted to assess the impact of independent and multiple pollutants on the frequency and timing of adverse health events such as hospitalizations and death.  This population-based study will examine specific health conditions across multiple US cities for the general population and for populations of individuals who are at risk due to underlying health status, chronically higher exposures to air pollutants and other social factors.

    Timing of exposure may also play a factor in health effects. Studies are being conducted to determine whether sequential exposure (one after the other) or simultaneous exposure to air pollutants has a greater effect than exposure to single air pollutants.

  • Who is at risk to multipollutant exposures?

    Considerable progress has been made in identifying and characterizing populations at risk for exposure to single pollutants that are regulated under the Clean Air Act.  Research has shown that people with asthma, heart disease or other lung and heart problems are more sensitive to the effects of outdoor air pollution.

    Research is being conducted to understand why certain people may be disproportionately at risk of multipollutant exposures and effects.

    For example, although exposure to ozone may primarily target the respiratory system, "real-world" combined exposures to particulate matter, ozone and hazardous air pollutants may affect multiple target organs. Multipollutant exposures may elicit acute, adaptive responses across the respiratory, cardiac, vascular, immunologic, neurological and other organ systems.

    As part of this effort, researchers are also identifying and evaluating intervention strategies that can reduce the adverse health effects of air pollutants in at risk populations.

  • How are people exposed to multipollutants?

    To understand the health effects of multipollutants, researchers need more information on how and to what degree people are exposed to the pollutants. The current monitoring network may not provide enough information to adequately assess multipollutant exposures.

    Research is being conducted to develop exposure models and methods and new scientific approaches to improve multipollutant exposure estimates. They are developing multipollutant indicators to characterize exposure to and effects of complex mixtures of pollutants. Recent multipollutant exposure and epidemiological field data will be examined to study the spatial and temporal variability of the multipollutant environment.

  • What are the impacts of individual and multiple exposures to nearby sources of pollutants? What are the options to reduce emissions?

    More than a third of the U.S. population lives, works, commutes or goes to schools in close proximity to air-pollution sources (e.g. roads, airports, power plants, factories, agriculture, ports, biomass burning, small point sources such as dry cleaners, etc.). As a result, they may be exposed to direct emissions from these sources.

    In addition, these near-source populations have been shown to be at increased risk for adverse health effects compared with the general population. Understanding near-source air quality, exposures and health effects is essential to evaluate the impacts of specific sources and properly select strategies to eliminate or reduce emissions and exposures.

    Research is being conducted to improve understanding of emissions and exposures to different pollutant mixtures within different micro-environments such as areas near ports or roadways.

  • What new methods and approaches are needed to understand exposures and health effects to pollutant mixtures?

    New approaches are needed to provide insights into the complex interactions and human health effects of multipollutant exposures. Research on the mode of action (MOA) of multipollutant mixtures in biological systems is illustrating how air pollutants can be grouped together based on their common MOA. New statistical techniques are being developed to better understand how combinations of air pollutants influence human health effects. New approaches are also being developed to rapidly screen complex mixtures containing dozens of pollutants to determine which ones are the most toxic or require further study. The data and findings from these studies are being used to refine computational models that can be used to estimate effects of complex multipollutant mixtures.

Related Resources

  • CATHGEN Research Project Exit- Research is under way with a large longitudinal study called CATHGEN to understand the acute and chronic health effects of pollutant mixtures as well as individual effects on the cardiovascular system. Genetic and epigenetic factors are being evaluated to determine if they make individuals more at risk to air pollutants. The study is being done in collaboration with Duke University’s School of Medicine. The study is supported by health records derived from nearly 10,000 people living in North Carolina from 2001 to 2011 and who had a cardiac catheterization done at Duke.
  • Exposure Publications for Air Research

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