The U.S. Environmental Protection Agency particulate matter health effects research centers program: a midcourse report of status, progress, and plans - Research Review

Environmental Health Perspectives, June 15, 2003 by Morton Lippmann, Mark Frampton, Joel Schwartz, Douglas Dockery, Richard Schlesinger, Petros Koutrakis, John Froines, Andre Nel, Jack Finkelstein, John Godleski, Joel Kaufman, Jane Koenig, Tim Larson, Dan Luchtel, L-J. Sally Liu, Gunter Oberdorster, Annette Peters, Jeremy Sarnat, Constantinos Sioutas, Helen Suh, Jeff Sullivan, Mark Utell, Erich Wichmann, Judith Zelikoff

In 1998 Congress mandated expanded U.S. Environmental Protection Agency (U.S. EPA) health effects research on ambient air particulate matter (PM) and a National Research Council (NRC) committee to provide research oversight. The U.S. EPA currently supports intramural and extramural PM research, including five academically based PM centers. The PM centers in their first 2.5 years have initiated research directed at critical issues identified by the NRC committee, including collaborative activities, and sponsored scientific workshops in key research areas. Through these activities, there is a better understanding of PM health effects and scientific uncertainties. Future PM centers research will focus on long-term effects associated with chronic PM exposures. This report provides a synopsis of accomplishments to date, short-term goals (during the next 2.5 years) and longer-term goals. It consists of six sections: biological mechanisms, acute effects, chronic effects, dosimetry, exposure assessment, and the specific attributes of a coordinated PM centers program. Key words: acute effects, biological mechanisms, chronic effects, criteria pollutants, dosimetry, exposure assessment, infrastructure, morbidity, mortality, particulate matter. Environ Health Perspect 111:1074-1092 (2003). doi:10.1289/ehp.5750 available via http://dx.doi.org/[Online 9 January 2003]

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Over the past 15 years, an ever-increasing number of epidemiologic studies have shown significant associations between the mass concentration of ambient air particulate matter (PM) and adverse respiratory and cardiovascular health effects. These effects include PM concentration-related excess rates of daily and annual mortality, hospital admissions, emergency room and clinician visits for respiratory and cardiac diseases, increased use of medications, and time lost from work and school. By the mid-1990s, the evidence for these associations was sufficiently compelling for the U.S. Environmental Protection Agency (U.S. EPA) to propose revised and more stringent National Ambient Air Quality Standards (NAAQS) for PM (NAAQS 1997). Their form and stringency were endorsed by the U.S. EPA Clean Air Scientific Advisory Committee (CASAC), a group of external scientific advisors whose charter was established by the Clean Air Act Amendments of 1977 (1991).

The revised PM NAAQS, promulgated in July 1997, retained with minor modification the previous daily maxima and annual average PM NAAQS for PM whose aerodynamic diameters were < 10 [micro]m (P[M.sub.10]). It also established new PM NAAQS for particles with aerodynamic diameters < 2.5 [micro]m (P[M.sub.2.5]), as excess mortality was found to be more strongly associated with P[M.sub.2.5] than with P[M.sub.10].

The U.S. EPA (and CASAC) acknowledged that the database supporting the judgments that P[M.sub.2.5] and P[M.sub.10] exposures were likely causal factors for adverse health effects was not fully supported by, or consistent with, available knowledge of the underlying biological mechanisms. Among the likely factors for discrepancies between observations in human populations and corresponding observations in controlled animals and human studies are the following:

* Epidemiologic observations of adverse effects had largely been confined to subpopulations who may have been especially susceptible because of underlying preexisting disease or who were very young or very old. In contrast, because of practical and ethical considerations, most human clinical studies had examined effects in small groups of healthy individuals of intermediate ages. Similarly, most previous animal studies focused on healthy and younger animals and used exposures to concentrations that were much higher than those encountered in ambient air.

* Toxicological studies have been limited, as the most active components of PM remain a matter of speculation. Subsequent studies would need to use more realistic ambient mixtures, e.g., concentrated ambient air particles (CAPs) or laboratory-generated surrogates that focus on specific particle characteristics such as particle size [e.g., ultrafines (diameters less than 0.1 [micro]m)] and/or chemistry [e.g., metals, polycyclic aromatic hydrocarbons (PAHs), quinones]. In addition, it is possible that responses may require a mixture of PM components and/or the simultaneous or sequential exposure to gaseous pollutants in the ambient air mixture [e.g., S[O.sub.2], N[O.sub.2], [O.sub.3], CO, and volatile organic compounds (VOCs)].

* No laboratory-based toxicological studies have been conducted involving chronic or even subchronic exposures to ambient air PM mixtures at concentrations at the upper end of the range of current U.S. ambient air concentrations.

As a result of the remaining scientific uncertainties, in 1998 Congress directed the U.S. EPA to substantially increase its level of funding on PM health effects research. It also mandated that a National Research Council (NRC) committee (i.e., the Committee on Research Priorities for Airborne Particulate Matter) be established to provide scientific oversight for the PM research. In the first of its three reports, the NRC Committee on Research Priorities for Airborne Particulate Matter recommended a multiyear research program that included the establishment of academically based research centers to create a comprehensive and integrated particle health effects research program. The PM centers were intended to foster interdisciplinary collaborations within and among institutions with extensive experience in air pollution health effects research. Research that arose through these collaborations were in turn intended to help the U.S. EPA address scientific issues about PM health effects in a timely and effective manner.