Research Programs: Particulate Matter (PM) Health Effects
Research Approach

PM Health Effects

Clinical Studies

In a clinical study, the effects of exposure to PM can be monitored in a controlled setting.

Photograph of a clinical study Clinical studies are used to address research questions that are best studied in a highly controlled laboratory setting. In a clinical study, scientists can investigate the effects of individual pollutants by measuring a variety of health endpoints (e.g., lung function, heart rate variability, analysis of blood components) and can monitor the deposition and fate of pollutants in study participants. Clinical studies can also be used to identify and characterize biomarkers of exposure, dose, and effects. Additionally, using a clinical approach, scientists can use animals as surrogates for humans or can expose human cells to pollutants in vitro as a way to discover the molecular mechanisms by which pollutants exert their effects. Studies using animals or in vitro systems are especially important when human data is not available or cannot be obtained.

Epidemiological Studies

Through epidemiological studies scientists seek to uncover patterns in a population's response to pollutants such as PM.

Photograph of a community near a highway In contrast to clinical studies, epidemiological studies are conducted in less rigidly controlled, more natural settings through field studies or through the analysis of data collected about human populations. EPA scientists conduct two types of epidemiological studies to assess associations between exposure to PM and adverse health effects. In the first type, researchers follow relatively large groups of individuals and use questionnaires or a similar method to determine the incidence and distribution of relevant health effects. The second type, field studies, involves smaller numbers of individuals and employs repeated assessments of personal exposure to PM. The smaller numbers of subjects involved in field studies allow researchers to extend the information obtained in large scale epidemiological studies by including measurements of clinical health endpoints.

Initial studies by epidemiologists showed associations between PM concentrations and mortality and indicated that elderly people with cardiopulmonary disease (e.g., COPD, severe cardiovascular disease) were at the greatest risk for dying. Other epidemiological studies have linked PM levels with an increased use of medications, doctor visits, and hospital visits for individuals with pulmonary disease such as asthma.

Toxicological Studies

Toxicological studies provide the opportunity to investigate the chemistry and biology that explains how a toxin such as PM can cause adverse health effects.

Photograph of petri dishes Researchers who study the heath effects of PM from the perspective of toxicology conduct studies to identify and characterize the specific properties and constituents of PM that are responsible for causing adverse health effects. Toxicologists test the molecular, cellular, and systemic effects of PM in experimental settings using cell and tissue cultures, animals, and computer models. EPA toxicologists are interested in determining how PM constituents induce effects and in understanding the details of PM dosimetry and deposition.

Despite a strong consensus that exposure to PM induces adverse health effects and that these effects are worse in individuals with preexisting cardiopulmonary disease, relatively little is known about the specific physical or chemical characteristics of the particles that cause these effects or the mechanisms through which the adverse effects are induced. Numerous toxicological studies, as well as human panel studies, have been conducted to better characterize the effects of PM; and, while much has been learned, much remains to be discovered.

Future Efforts

While much progress has been made in recent years, many questions about the health effects of PM remain unanswered. EPA scientists, in collaboration with researchers in academia, other governmental organizations, and in private institutions, continue to explore the links between air pollution in the form of particulate matter and health effects. Studies are underway to discern the mechanisms through which PM causes adverse health effects, to determine which specific components of PM are responsible for these ill effects, and to uncover the traits that explain some individuals' sensitivity to PM exposure. The ultimate goal of scientific investigations into details about the health effects of PM is to provide a sound basis for defensible regulatory actions. In this way, the successes of EPA's PM health effects research program will further enable EPA to fulfill its mission of ensuring that the air in every American community is safe and healthy to breathe and that particularly susceptible individuals such as the elderly, children, and those with pre-existing health conditions are protected.