United States Environmental Protection Agency Office of Research and Development National Exposure Research Laboratory FY02 Research Abstract Government Performance Results Act (GPRA) Goal 1 APM22 Significant Research Findings: A Modeling Analysis of Exposure of a Susceptible Subpopulation to PM of Ambient Origin Understanding human exposures to environmental pollutants is critical for the U.S. Environmental Protection Agency (EPA) to assess and manage human health risks. For particulate matter (PM), air pollution epidemiology studies have found statistically significant associations between PM concentrations and acute and chronic health outcomes. These epidemiology studies use PM measurements from stationary air monitoring sites within a community as a surrogate for personal exposure levels for the population. To better understand the relationship between personal exposures and stationary community measurements for PM, National Exposure Research Laboratory (NERL) has developed a research program to improve the data available for personal exposure to PM and to develop exposure models that predict population exposures to PM. Measurements of personal exposure to PM include contributions from both PM of ambient origin and indoor sources of PM. Modeling analyses are needed to estimate personal exposure to PM of ambient origin from the personal exposure measurement data. In addition, certain populations, such as the elderly or asthmatics, may be more at risk for health effects due to PM exposure. This effort addresses Research Area 1 of the National Research Council's Research Priorities for Airborne Particulate Matter. Research NERL is currently refining and evaluating a population exposure model for Approach PM, called the Stochastic Human Exposure and Dose Simulation (SHEDS- PM) model. The SHEDS-PM model estimates the population distribution of PM exposures by randomly sampling from distributions of ambient PM concentrations and exposure factors to estimate the distribution of PM exposures in various locations that people spend time in (such as in homes, in vehicles, outdoors, etc.). SHEDS-PM model output also includes estimates of the contribution from both PM of ambient origin and indoor sources of PM. An application of the SHEDS-PM model was implemented using measurement data from the NERL RTP PM Panel Study. The study included daily measurements of PM2 5 personal exposure, as well as indoor residential, outdoor residential, and ambient (central site) PM2 5 Scientific Problem and Policy Issues National Exposure Research Laboratory — November 2002 ------- concentrations, during a seven-day study period for each participant within each of the four seasons from June 2000 - May 2001. Daily measurements of ambient PM2 5 concentrations and residential air exchange rates and human activity pattern data obtained from daily diaries for each participant were used as input to the model. Additional model inputs, such as demographic data and residential characteristics, were matched to the NERL RTP PM Panel Study population. Results and The distribution of daily average total PM2 5 exposures predicted by the Implications SHEDS-PM model compared well with the measurements of personal PM2 5 exposures from the RTP PM Panel Study. The median total PM2 5 exposure (50th percentile) for the SHEDS-PM predictions was 20 |ig/m3 compared to 18 |ig/m3 for the personal PM25 exposure measurements. The median personal exposure to ambient PM2 5 predicted by the model was 9 |ig/m3 for the study population and ranged from 2-33 |ig/m\ The model results were compared to estimates of ambient PM2 5 exposures derived from analysis of 24-hr integrated personal PM2 5 measurement data collected during the study. This comparison was used to evaluate the SHEDS-PM model prediction of population exposures to ambient PM2 5 and indicated that the model results were generally consistent with the estimates derived from measurement data. This research effort is part of a ongoing research program to develop a scientifically robust exposure modeling system to analyze the relationship between PM sources, ambient air PM concentrations, and personal exposures and dose. The development of an improved, user-friendly PM exposure modeling system will give EPA better capability to set National Ambient Air Quality Standards (NAAQS) for PM. Case-study application of the modeling system will identify the major factors influencing PM exposures, including the relative contributions of outdoor and indoor PM concentrations to personal exposure and dose, as well as the effects of human activities, housing characteristics and seasonal factors (i.e. meteorology). These applications will also help NERL's human exposure measurement program prioritize and direct studies toward the data needed for reducing uncertainty in the model predictions. The greater understanding of personal exposure to PM obtained through application of this source-to-dose modeling system will also be valuable for improving the power of epidemiological studies of the impact of PM pollution on mortality and morbidity. This research project included collaboration between NERL's Human Exposure Measurements and Exposure Modeling Programs. The NERL RTP PM Panel Study was conducted through Contract #68-D-99-012 to the Research Triangle Institute and Assistance Agreement #CR-828186-01-0 to Shaw University. Assistance with the development of the SHEDS model Research Collaboration and Publications National Exposure Research Laboratory — November 2002 ------- program and application to the NERL RTP PM Panel Study was provided by ManTech Environmental Technology, Inc. under Contract #68-D-00-206. This research has recently been presented at an international conference: Burke, J., A. Rea, J. Suggs, R. Williams, J. Xue, H. Ozkaynak, "Ambient Particulate Matter Exposures: A Comparison of SHEDS-PM Exposure Model Predictions and Estimates Derived from Measurements Collected During NERL's RTP PM Panel Study." Presented at the 12th Conference of the International Society of Exposure Analysis (ISEA), Vancouver, BC, August 11-15, 2002. Future Research Future research will include further refinements and evaluation of the SHEDS-PM exposure model. In addition, the program's focus will transition to the various components of PM associated with health effects. A refined SHEDS-PM model will be used to predict exposure and dose (the magnitude, frequency and duration of) to various chemical species and/or size components of PM for the general population and susceptible sub- populations. Activities will focus on enhancing the model to include recent scientific advancements and developing new model inputs and algorithms as needed for case study applications. Questions and inquiries on NERL's human exposure and dose modeling research can be directed to: Haluk Ozkaynak, Ph.D. US EPA Office of Research and Development National Exposure Research Laboratory Ariel Rios Building (MC-8601-D) 1200 Pennsylvania Avenue, NW Washington, DC 20460 Phone: 202/564-1531 E-mail: ozkaynak.haluk@epa.gov Contacts for Additional Information National Exposure Research Laboratory — November 2002 ------- |