Focusing on Fine Particles

A new collection of scientific data on health effects linked to exposure to fine particulates is setting the stage for a major policy debate on air pollution. This government compendium of research findings from the past five years is an overture to possibly tougher regulations for air emissions.

In 1997, the Environmental Protection Agency broke new ground in clean air policy. That year, the agency for the first time set a standard for airborne fine particulate matter with a diameter of 2.5 µm or less (PM_2.5 ). Previously, EPA had addressed limits only for coarser particulates. PM_2.5 is believed to be more harmful to health than particulate matter composed of larger particles.

Industry, including chemical manufacturers, fought vigorously against the 1997 standard for PM_2.5 and a second air quality standard that tightened the limits for ground-level ozone issued in the same regulation. Opponents argued the regulation would cost too much to implement, but ultimately, the U.S. Supreme Court endorsed both the PM_2.5 and ozone standards.

Now, even before implementation of the 1997 standards is complete, EPA is reviewing them, beginning with the limit for PM_2.5. The agency is under court order to do so.

Under a consent decree reached with environmental groups last year, the agency is to make a preliminary decision by March 31, 2005, on whether to tighten, loosen, or maintain the current standard for PM_2.5. The consent decree requires EPA to make a final determination by Dec. 20, 2005, on whether to change the standard. However, the agency is expected to ask a federal court to extend those deadlines by several months. Meanwhile, the agency does not have to finish its review of the ozone standard until 2006.

EPA is preparing for its decisions on PM_2.5. It is in the final stages of assembling scientific data on particulate matter into a report known as a "criteria document." This would serve as the official scientific basis for any new regulatory standard, if EPA deems this is warranted. A federal court has set an Oct. 29 deadline for the agency to finish the PM_2.5 criteria document. The agency's Clean Air Scientific Advisory Committee is scheduled to complete its peer review of the final draft version of the criteria document in October.

AS A PRELUDE to completion of the criteria document and the agency's preliminary decision on the PM_2.5 standard, EPA earlier this month released a compendium of research findings from the past five years on particulate matter. J. Paul Gilman, EPA assistant administrator for research and development, emphasizes that the research report is not a regulatory decision.

However, the data in the report indicate to some observers that the agency plans to strengthen the PM_2.5 standard.

Perhaps the most notable scientific finding in the past five years is a quantitative link between exposure to fine particulates and both disease and death, according to the EPA research report. Health effects from inhaling these fine particulates were discovered to go beyond lung illnesses to include heart problems, it says.

Some research over the past five years has focused on whether chemical components of particles--which can include sulfates, nitrates, metals, or carbon--are associated with health effects. Data suggest that several metals and perhaps carbon or other substances may be linked to lung or cardiac problems, Gilman says.

He notes that the particulate matter varies in composition across the U.S. In much of the West, carbon makes up a substantial portion of particles. In the East, particulate matter has a higher content of sulfate, a compound that originates from coal-fired power plants.

"The things contributing to the health effects are going to be different from different particles," Gilman says. "It's not a simple picture."

Gilman adds that EPA officials hope further research will help tease out what components of particulates are linked to which health effects. This sort of data will help EPA make air standards and other regulations more effective, he says.

Among the other notable research findings in the past five years is that people with heart or lung disease are more likely to have continuous or more serious health problems after exposure to particulates. For instance, people with chronic obstructive pulmonary disease have smaller amounts of functioning lung tissue than do healthy people, Gilman explains. People with this disease end up with a greater concentration of particulates deposited in the working parts of their lungs--creating "hot spots" that may increase their susceptibility to health effects from exposure to particulate matter.

Opinions on what EPA's amassed research findings bode for policy on PM_2.5--and a possible tighter air quality standard--vary among lobbying groups.

Deborah Shprentz, a consultant to the American Lung Association on air quality standards, says the recently released research compendium and EPA's nearly finished criteria document "really make a strong case" for tightening the PM_2.5 standard. Both include medical evidence showing health effects occurring at PM_2.5 concentrations lower than the current limit, Shprentz tells C&EN. "That's indisputable," she adds. "The bottom line is clear," Shprentz says. "Particulate matter causes premature death and illnesses."

The current standard for PM_2.5 has two parts. One is a 24-hour exposure limit of 65 µg of particulates per cubic meter of air. The second is an annual average for PM_2.5 of 15 µg/m³. The American Lung Association is calling for EPA to tighten both prongs of the standard.

Shprentz notes that a preliminary document from EPA last year made a first stab at a possible new standard, suggesting a 24-hour exposure limit of 30 to 50 µg/m³ and an annual average of 12 to 15 µg/m³. Although this is not a formal proposal, "we think EPA is headed in the right direction," she says.

MEANWHILE, Kyle Isakower, manager of environmental affairs at the American Petroleum Institute, says nothing in the EPA research compendium suggests a standard for PM_2.5 that differs from the current limit for this pollutant. Plus, there is not ample evidence that supports tightening the 1997 standard, he says.

While research over the past half-decade has identified several plausible biological pathways through which PM_2.5 might allegedly cause health problems, investigators have made no conclusions on how these effects could occur, Isakower says. "There are a lot questions that still need to be answered," he says.

For instance, EPA has not yet identified a dose-response relationship between exposure to PM_2.5 and possible health effects, Isakower says. Without such information, "you really don't have much to go on in setting a [new] standard," he says.

The American Chemistry Council had no comments on the research compendium. However, ACC in coming months will focus greater attention on air quality standards, including the one for PM_2.5, says an ACC spokeswoman.

Within the next several weeks, EPA scientists are to complete the criteria document and pass it on to agency regulators. As policymakers determine by early next year whether and how to change the 1997 standard for PM_2.5, industry, environmental, and health groups are expected to become more vocal on the issue.

The research report and related documents are available electronically at http://www.epa.gov/pmresearch/pm_research_accomplishments.