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

PM Health Effects

EPA's research into the health effects of PM has produced a wealth of information. Highlights of the key accomplishments of the past six years include the following:

Validation of PM-associated health effects

Studies showing that exposure to ambient PM can adversely affect human health have been replicated and validated many times in a number of locations throughout the U.S. and the world. Research has shown that exposure to PM is associated with morbidity and mortality independent of the effects of other pollutants in the atmosphere. Recent studies have also underscored that the elderly with pre-existing cardiopulmonary disease are most at risk. In addition, other groups such as the very young, asthmatics, and diabetics may also be susceptible to the effects of PM. Even more striking are the findings that suggest that extended exposure to PM can lead to chronic disease and/or a shortened life span.

Credibility of exposure measures

Details about the relationship between PM measurements taken outdoors and the concentrations to which people were actually exposed was not known until quite recently. Results from exposure studies have verified that centrally located monitors can provide adequate measures of the amount of pollution to which people are exposed when they are used in community-based epidemiological studies. Exposure studies have also shown that gaseous co-pollutants such as ozone and nitrogen dioxide are not likely to interfere significantly with estimates of PM-associated health risks.

Advances in dosimetry

Clinical studies conducted in the past few years have shown that inhaled PM is distributed unevenly in the respiratory tract of people with lung disease. These studies also showed that as much as ten times more PM deposition can occur in local regions in the lungs of people with pulmonary disease. This may indicate that their increased susceptibility is due to what is, in effect, exposure to a higher dose of PM than is experienced by those whose lungs are not impaired.

Plausible biological mechanisms:

While only a few years ago scientists could not explain the trends in health effects observed through epidemiological studies from a biological basis, there are now multiple hypotheses to describe the mechanisms by which very small concentrations of inhaled PM can induce negative effects. Clinical studies and animal models that mimic human disease have produced several theories about how the physical and chemical properties of PM can produce the cardiovascular and pulmonary changes that contribute to increased illness and death. Somewhat surprisingly, there appears to be no single attribute that makes PM toxic, but size and certain chemical components (e.g., metals) appear to be involved.

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