Assessing Multimedia/Multipathway Population Exposure to Multi-Pollutants Using a Mechanistic Source-to-Dose Modeling Framework
S.W. Wang, Y.C. Yang, and P.G. Georgopoulos (EOHSI, UMDNJ - R.W. Johnson Medical School and Rutgers University)
This study presents the implementation of a mechanistically consistent, source-to-dose modeling system, MENTOR (Modeling Environment for Total Risks Studies)/SHEDS (Stochastic Human Exposure and Dose Simulations), for assessing multimedia/multipathway/multiroute exposures to arsenic and Trichloroethylene (TCE) for the general population of Franklin County, Ohio. The MENTOR/SHEDS system uses a mechanistically consistent framework for source characterization, human activity patterns, etc. to conduct population exposure assessments of co-occurring pollutants. This is a distinction from typical studies, where different exposure factors and activity patterns could have been used for different pollutants.10,000 people were randomly selected from the entire county as the sample population that statistically reproduce the demographic characteristics of the target population. This study used the National Human Exposure Assessment Survey (NHEXAS) – Region V database [Whitmore et al., 1999] to extract the data for multimedia concentrations of arsenic and TCE as well as food consumption rates, while the USEPA’s Consolidated Human Activity Database (CHAD) [McCurdy et al., 2000] was used to provide the activity diaries and associated Metabolic Equivalent of Tasks (METS) values. The drinking water consumption rates were obtained by extracting the survey records in USDA’s Continuing Survey of Food Intakes by Individuals (CSFII) [Tippett et al., 1997] based on the demographic characteristics of the sample population.
The MENTOR/SHEDS system considers currently five exposure routes: inhalation, food intake, drinking water consumption, non-dietary ingestion, and dermal absorption. The simulations consist of the following steps: (1) Characterization of the multimedia background levels of contaminants through a combination of environmental model predictions and measurement studies; (2) Characterization of multimedia levels and temporal profiles of contaminants in various residential and occupational microenvironments using an extension of the SHEDS (Stochastic Human Exposure and Dose [Zartarian et al., 2000] Simulation) modeling methodology; (3) Selection of a fixed-size sample population that statistically reproduces essential demographics (age, gender, race, occupation, education) of the population unit used (e.g., census tract) in the assessment; (4) Development of activity event sequences for each member of the sample population by matching attributes to entries of USEPA's Consolidated Human Activity Database (CHAD); (5) Calculation of intake rates for the members of the sample population, reflecting/combining physiological attributes and activities pursued; (6)Combination of intake rates from multiple routes to assess exposures; (7) Estimation of target tissue doses (e.g., kidney, liver) with physiologically based pharmacokinetic modeling.
This work had been funded in part by the US Environmental Protection Agency under Cooperative Agreement # EPAR-827033 to the Environmental and Occupational Health Sciences Institute (EOHSI). The authors would also like to thank H. Ozkaynak, V. Zartarian, J. Xue, T. McCurdy, and J. Burke (USEPA) for their valuable inputs to this work. The viewpoints expressed in this work are solely the responsibility of the authors and do not necessarily reflect the views of the US Department of Energy, the US Environmental Protection Agency, or their contractors.