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An Overview of EPA's Human Exposure Panel Studies
Citation:
Sheldon, L S., R W. Williams, V R. Highsmith, C. E. Rodes, J P. Creason, AND D. B. Walsh. An Overview of EPA's Human Exposure Panel Studies. Presented at PM 2000 AWMA Conference, Charleston, SC, January 24-28, 2000.
Impact/Purpose:
The primary study objectives are:
1.To quantify personal exposures and indoor air concentrations for PM/gases for potentially sensitive individuals (cross sectional, inter- and intrapersonal).
2.To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts. These cohorts represent subjects of opportunity and relationships established will not be used to extrapolate to the general population.
3.To examine the inter- and intrapersonal variability in the relationship between personal exposures, and indoor, outdoor, and ambient air concentrations for PM/gases for sensitive individuals.
4.To identify and model the factors that contribute to the inter- and intrapersonal variability in the relationships between personal exposures and indoor, outdoor, and ambient air concentrations for PM/gases.
5.To determine the contribution of ambient concentrations to indoor air/personal exposures for PM/gases.
6.To examine the effects of air shed (location, season), population demographics, and residential setting (apartment vs stand-alone homes) on the relationship between personal exposure and indoor, outdoor, and ambient air concentrations for PM/gases.
Description:
In July 1997, the EPA Administrator issued new PM NAAQS that added PM2.5. The new standard is based largely on recent epidemiological investigations that indicated increased risks of mortality and morbidity are associated with higher concentrations of ambient particles. The new standard has been challenged largely due to inadequate information on toxicological mechanisms and actual human exposures to PM of ambient origin. In all of the epidemiological studies, ambient monitoring data were used as a surrogate for exposure. Previous studies with healthy individuals have shown poor correlations between ambient PM measurements and personal exposure.
The Clean Air Act mandates periodic reevaluations of the NAAQS. Thus the important scientific uncertainties associated with new standards must be addressed. For PM, this has required major new research initiatives. Congress requested an independent study by the National Research Council (NRC) to identify the most important research priorities and to develop a conceptual plan for PM research related to the new PM2.5 NAAQS. The NRC developed ten research recommendations. Two of the ten highest priority research activities are directed towards understanding PM exposures for susceptible subpopulations.
The PM Exposure Research Program for the National Exposure Research Laboratory (NERL) focuses directly on NRC Research Topic 1: Outdoor Measures versus Actual Human Exposure. Longitudinal panel studies are used to characterize interpersonal and intrapersonal variability in exposure to PM, and to describe the relationship between personal exposures to PM of ambient origin and ambient site measurements for susceptible subpopulations. This relationship is not clearly defined and represents a major uncertainty associated with the current standard. Specific objectives of the panel studies are:
1. To quantify personal exposures and indoor air concentrations for PM/gases for potentially
sensitive individuals;
2. To describe (magnitude and variability) the relationships between personal exposure, and indoor, outdoor and ambient air concentrations for PM/gases for different sensitive cohorts;
3. To examine the inter- and infra-personal variability in these relationships;
4. To identify and model the factors that contribute to the inter- and infra-personal variability in the relationships;
5. To determine the contribution of ambient concentrations to indoor air and personal exposures for PM/gases;
6. To examine the effects of airshed (location, season), population, and residential setting
(retirement center vs home) on these relationships.
Four projects are underway to evaluate different susceptible subpopulations, regions of the country, seasons, and housing stocks. Susceptible subpopulations will include COPD patients, individuals with cardiovascular disease, the elderly, asthmatics, and low SES elderly individuals. Three cooperative agreements have been awarded to Harvard University School of Public Health; New York University School of Medicine; and the University of Washington. NERL is conducting the fourth project which includes panel studies in Baltimore MD, Fresno CA, and RTP NC. An overview of the NERL project is given in Table 1.
The studies in Baltimore MD and Fresno CA have been completed and were conducted incollaboration with the U.S. EPA's National Health and Environmental Effects Research Laboratory. Generally, these studies have demonstrated the importance of housing type, house ventilation parameters, and personal behavior on exposure to total PM and PM of ambient origin. These studies confirmed that panel studies are feasible and that elderly populations will participate in personal PM monitoring studies over a long period of time (up to 28 days). Personal exposure monitoring and survey questionnaires were both practical and effective for understanding important exposure factors. Aggregate personal and residential PM measures showed high correlations with ambient site measures. Individual correlations showed more variability. Indoor/outdoor mass concentration ratios varied widely depending upon study site, season, residence and ventilation practices. Personal nepholometers provided valuable data on sources of personal exposure for PM. Concurrent real-time indoor and outdoor particle counts for different size fractions of PM were useful in evaluating penetration, decay, and emission parameters for PM. Results from these studies will be presented as various papers that address the program objectives. Results have also been used to refine the study design and approach for the studies in RTP. Data combined from all of the longitudinal panel studies will provide critical input for understanding and quantifying the relationship between personal exposure to ambient PM and ambient monitoring data.
This work has been funded wholly or in part by the U.S. Environmental Protection Agency under contract #68-DS-0040 to the Research Triangle Institute. It has be subjected to agency review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.