As the nationwide debate continues over whether to tighten air quality standards, a body of scientific research has emerged that calls into question many of the assumptions underlying EPA’s proposal on particulate matter (PM) and ground-level ozone.
In defending its proposal, EPA has repeatedly said its initiative will reduce by 20,000 annually the number of premature deaths resulting from exposure to PM. But in a study published in the journal Epidemiology a few months before EPA announced its initiative, Suresh H. Moolgavkar and Georg Luebeck noted that many studies of the association between air pollution and mortality suffer from serious deficiencies in their control of the confounding effects of other pollutants.
“Air pollution, which is a complex mixture, appears to be associated with mortality even at the generally low levels of pollution in U.S. cities, but currently neither the statistical tools nor the biological understanding of mechanisms exist to tease out the contribution made by each component of the mixture,” they write. “We conclude that it is not possible with the present evidence to show a convincing correlation between particulate air pollution and mortality.”
Similar doubts about the quality of the underlying data supporting EPA’s PM proposal have been expressed by environmental analysts Frederick W. Lipfert and Ronald E. Wyzga. The two question EPA’s call for strengthening the PM standard to 2.5 microns or less in diameter. Citing a study (“Is Daily Mortality Associated with Fine Particles?” by FIRST Schwartz, FIRST Dockery, and FIRST Neas), EPA has made the case that tightening the PM standard to ever-smaller particles will result in significant health benefits, including lower mortality.
But Lipfert and Wyzga argue that after allowing for measurement errors, the treatment of missing data, and other factors, Schwartz, Dockery, and Neas should have concluded that “there is no apparent significant difference in mortality associations by particle size.” Indeed, Lipfert and Wyzga go so far as to say that “it is not clear whether the observed mortality responses can be attributed with confidence to any component of PM.” (emphasis in the original) Addressing the air quality issue from another perspective, J.W. Anderson of Resources for the Future, a Washington-based think tank, points out that the language and the science of the Clean Air Act (CAA) are obsolete. When the original CAA was enacted in 1970, he writes, Congress assumed every pollutant had a threshold–a concentration below which it is too thinly dispersed to have any effects. Congress told EPA to find the threshold and set the standard below it at a level that would protect public health “with an adequate margin of safety.”
Anderson observes, however, that as methods of measurement become more sensitive, “the impossibility of finding zero risk becomes clearer.” Some pollutants have no threshold and, as EPA has acknowledged, ozone and PM may be among them. This means EPA cannot carry out the letter of the law because science shows there are no clear thresholds for harm. “The result,” Anderson says, “is that EPA is required to make policy judgements about how far to go in tightening standards, but these judgements are open to attacks in the courts.”
EPA Acknowledges Error
The doubts raised about the quality of the underlying data behind EPA’s proposal have recently been acknowledged by the agency itself. On April 2, EPA confirmed that it had overestimated the public health benefits of its air quality proposal. Citing a “technical error in the characterization of data” uncovered by an independent scientist in the process of reviewing EPA’s files, the agency has been forced to lower its estimate of the number of premature deaths avoided by implementation of its proposal by one-fourth, from 20,000 to 15,000. The embarrassing admission is expected to focus increased public and Congressional attention on the process by which EPA reaches its regulatory decisions.
PF: For the full text of the Moolgavkar-Luebeck article, see Epidemiology 1996:7:420-428. J.W. Anderson’s article is available from Resources for the Future at 202/328-5018. The Lipfert-Wyzga study is available from PolicyFax at 847/202-4888. Request document #????????
