Science 6 January 2006:Vol. 311. no. 5757, p. 27
News of the Week
ENVIRONMENTAL REGULATION:New Particulate Rules Are Anything but Fine, Say Scientists
Cutting in half the maximum amount of fine particles that people should breathe over 24 hours sounds impressive. But critics of this revision to air pollution standards, proposed last month by the U.S. Environmental Protection Agency (EPA), say the new daily threshold will only marginally improve public health. They say a truly dramatic reduction in mortality rates requires lower annual exposure levels, too.
In fact, an outside panel that made such a recommendation is not happy with EPA's decision. "What is the point of having a scientific advisory committee if you don't use their judgment?" wonders Jane Koenig of the University of Washington, Seattle.
EPA Administrator Stephen Johnson didn't answer that question during a 20 December teleconference announcing the standards but said he had thought long and hard about the data. "I made my decision based upon the best available science," he explained. "And this choice requires judgment based upon an interpretation of the evidence."
Studies have shown that inhaling the small particles that make up soot--a widespread byproduct of combustion--harms health, although the mechanisms are not all clear (Science, 25 March 2005, p. 1858). Bad air days can trigger asthma attacks, for example, and even kill people suffering from lung or heart disease. Even chronic exposure to lower levels of soot leads to health problems and premature death.
In 1997, EPA first regulated fine particles measuring 2.5 micrometers (PM 2.5) or less. As part of a settlement in a suit brought by the American Lung Association, EPA was required to propose revised PM 2.5 rules by the end of 2005. The new standards would lower the maximum allowable 24-hour exposure for PM 2.5 from 65 micrograms per cubic meter (g/m3) to 35 g/m3. That's within the range recommended by the agency's Clean Air Scientific Advisory Committee (CASAC) but still on the high side. EPA ignored other suggestions, most notably declining to reduce the average annual PM 2.5 standard of 15 g/m3 to 13 or 14. Such a reduction could make a big difference in public health, scientists have found.
EPA models for nine major U.S. cities predict that the tightest daily and annual standards recommended by CASAC would cut the roughly 4700 deaths due each year to PM 2.5 in those cities by 48%. In contrast, death rates would drop by 22% under the agency's proposal to tighten only the daily standard. EPA didn't make a nationwide tally of lives saved under any of the proposals, but epidemiologist Joel Schwartz of Harvard School of Public Health in Boston, using an annual standard of 14 g/m3, came up with 9000 or more. Having a looser standard is "completely unjustified by the science," he says.
EPA plans three public hearings on its proposal and will accept public comments until early April. "This isn't over," vows CASAC chair Rogene Henderson of the Lovelace Respiratory Research Institute in Albuquerque, New Mexico, who says the committee will reiterate its case. The final revisions are due out in September.