ABSTRACT
In the past decade, an abundance of epidemiological studies have reported adverse health effects associated with environmental exposure to airborne particulate matter at the relatively low concentrations found currently in the United States and other developed countries. Toxicological and clinical studies have not reported adverse health effects from controlled exposures to models of particulate matter except at extremely high concentrations (see Chap. 18). The estimated risks associated with particulate matter at concentrations observed in most developed countries are small; that is, excess relative risks of 20% or less. The ability of epidemiology to detect relative risks of this magnitude has been questioned (1). Moreover, the lack of supporting toxicological and clinical evidence has raised questions about the validity and generalizability of these epidemiological findings (2). Nevertheless, these findings have been robust and consistent across many settings, and have stimulated a revision of the ambient air quality standards for particulate matter in the United States (3).
