EPA Tightens Some Air Regulations

By Erik Stokstad and Carolyn Gramling
ScienceNOW Daily News
21 December 2005
The Environmental Protection Agency yesterday proposed new rules that would cut almost in half the maximum amount of fine particulates that people should breathe over 24 hours. However, the agency did not reduce the average annual amount allowed, rejecting the advice of its own scientists and its scientific advisory panel. In another development, the experimental evidence for harm from long-term exposure to particulates was strengthened this week by a new study of laboratory mice.

Many studies have shown that the inhalation of small particles--widespread byproducts of combustion--can harm health and even lead to the premature death of people suffering from lung and heart disease. The evidence is particularly strong for short-term exposure during bouts of poor air quality, although questions remain as to the mechanism (Science, 25 March, p. 1858). EPA first began to regulate air particulates based on their size--10 microns and smaller--in 1987. A decade later, it added rules for fine particles 2.5 microns (PM 2.5) or less. Under a court-ordered deadline, these rules had to be updated by the end of this month.

The agency proposes lowering the standard for 24-hour exposure for PM 2.5 from 65 micrograms per cubic meter (g/m) to 35 g/m. That matches the upper end of what EPA scientists and the Clean Air Scientific Advisory Committee (CASAC) recommended. The 24-hour standard for coarser (PM 10) particles would be reduced from 150 g/m to 70 g/m and will focus on urban rather than rural dust, which is less likely to be harmful.

But EPA veered from its advisory committee when it chose to keep the existing long-term standard of 15 g/m, not lower it to 13 to 14 g/m as CASAC called for. "If they don't lower the long term standard, they're not addressing the greatest risks," says epidemiologist George Thurston of New York University. CASAC chair Rogene Henderson of the Lovelace Respiratory Research Institute in Albuquerque, New Mexico, says the committee made its recommendation because some studies indicate that the current level has not eliminated adverse health effects from PM 2.5. EPA did not explain its decision, noting only that it was "based on its assessment of several expanded, re-analyzed, and new studies."

One study too new to be included provides strong evidence that exposure to tiny particles of soot and dust could make already at-risk patients even more susceptible to heart disease. Lung Chi Chen of the New York University School of Medicine in New York City and his colleagues exposed heart disease-prone mice to polluted air. After 6 months of exposure to air with PM 2.5 levels matching the current EPA standard, pollution-breathing mice had arteries that were 19% clogged with plaque, compared with 13% for mice breathing filtered air. For mice on a high-fat diet, the pollution effect was even more dramatic: 42% compared to 26%, the researchers report today in the Journal of the American Medical Association.

EPA will accept public comments on its proposal for 90 days and hold three public hearings. It will finalize its revisions by 27 September 2006, but states will have until 2015 to meet the final standards.