Mobile-Source Air Toxics: A Critical Review of the Literature on Exposure and Health Effects

Special Report 16, November 2007

A Special Report of the Institute's Air Toxics Review Panel.

Special Report 16 summarizes the health effects of exposure to the 21 mobile-source air toxics (MSATs) defined by the 2001 EPA mobile-source rulemaking and critically analyzes the literature for a subset of seven MSATs (acetaldehyde, acrolein, benzene, 1,3-butadiene, formaldehyde, naphthalene, and polycyclic organic matter*). The report also assesses and summarizes research gaps and unresolved questions, as understood in the context of the current regulatory agenda. The report focuses on MSATs for which mobile sources are a sizable source of human exposure and for which existing data suggest that health effects might be observed at concentrations approaching those found in ambient air. For each MSAT, the following questions are addressed: (1) To what extent are mobile sources a significant source of exposure to this MSAT? (2) Does this MSAT affect human health? (3) Does this MSAT affect human health at environmental conditions?

Special Report 16 describes a review performed by a Special Panel with expertise in exposure assessment, toxicology, clinical medicine, and epidemiology. The Panel reviewed the peer-reviewed literature on MSATs, reached key conclusions, and made recommendations for future research. The completed report was reviewed by experts in a variety of fields and amended to reflect their useful comments and critiques.

*The Panel elected not to focus on a critical review of diesel exhaust, a substantial contributor to human exposure and to health risks in the overall context of MSATs, because HEI and many others (e.g., the U.S. Environmental Protection Agency and the California Air Resources Board) have recently reviewed these issues. Instead, the Panel has provided an expanded summary of diesel exhaust reviews.

The files posted below include the complete Special Report 16 (including Appendix A) as printed, an Executive Summary, and Appendices B-E. Appendices B-E contain links to many sources of information used by the HEI Air Toxics Review Panel when conducting its critical literature review; because these tables are lengthy and interactive, they are available only in electronic files (on a CD included with the printed report and on our website). The individual sections on each of the seven priority MSATs and a summary of diesel studies are provided here as well for the convenience of readers who wish to download a particular section after reviewing the entire report.