A CRITICAL-REVIEW OF THE EVIDENCE ON PARTICULATE AIR-POLLUTION AND MORTALITY

We review epidemiologic studies of particulate air pollution and morta lity in U.S. cities with respect to important methodologic issues. Man y of these studies suffer from serious deficiencies in their control o f the confounding effects of other pollutants. As a consequence, the s mall risks reported to be associated with the particulate component of air pollution could easily be attributed to residual confounding by c opollutants. Most studies, moreover, have not considered modification of air pollution effects by seasonal factors, making the interpretatio n of the estimated risks difficult. We use a new analysis of mortality in Philadelphia that considers four pollutants simultaneously as well as seasonal effects to illustrate the methodologic issues raised in t his paper. Air pollution, which is a complex mixture, appears to be as sociated with mortality even at the generally low levels of pollution in U.S. cities, but currently neither the statistical tools nor the bi ological understanding of mechanisms exists to tease out the contribut ion made by each component of this mixture. We conclude that it is not possible with the present evidence to show a convincing correlation b etween particulate air pollution and mortality.