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Population Exposure and Dose Model for Air Toxics: A Benzene Case Study

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Abstract: The EPA's National Exposure Research Laboratory (NERL) is developing a human exposure and dose model called the Stochastic Human Exposure and Dose Simulation model for Air Toxics (SHEDS-AirToxics) to characterize population exposure to air toxics in support of the National Air Toxics Program. SHEDS-AirToxics uses a probabilistic approach to predict the distribution of exposure and dose for a specified population. The model estimates this distribution by simulating the time series of exposure and dose for individuals that demographically represent the population of interest. U.S. census data are used to build the simulation population, and human-activity-pattern data are assigned to each simulated individual to account for interaction with their immediate environment. Each individual's inhalation exposure and dose profile is estimated from the time spent in each location, the concentration in that location, and the activity-specific inhalation rate while in that location. The model also can estimate exposure and dose from ingestion of food containing air toxic residues and from dermal absorption of chemicals while bathing. A daily-averaged exposure and dose for each individual can then be calculated and combined to provide a distribution of exposure and dose for the population.

A case-study application of the model was conducted to estimate benzene exposures for the population of Houston, Texas. Modeled ambient benzene concentrations used as input to the model were produced by EPA's Office of Air Quality Planning and Standards (OAQPS) using the ISC model for all major point, area, and mobile sources in the Houston area. Model inputs for estimating indoor and in-vehicle benzene concentrations were obtained from analysis of available measurement study data. Preliminary results from the case study indicate that benzene exposure and dose varied significantly across the population due to variability in microenvironmental concentrations and the impact of certain activities (e.g., commuting, smoking). The SHEDS-AirToxics inhalation exposure results will also be compared with outputs generated for Houston using OAQPS's Air Pollutant Exposure (APEX) model.

Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.
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Citation:Graham, S. E., and J. M. Burke. Population Exposure and Dose Model for Air Toxics: A Benzene Case Study. Presented at International Society of Exposure Analysis 14th Annual Conference, Philadelphia, PA, October 17-21, 2004.
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Contact: Liz Hope - (919) 541-2785 or hope.elizabeth@epa.gov
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Division: Human Exposure & Atmospheric Sciences Division
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Branch: Exposure Modeling Research Branch
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Product Type: Abstrct/Oral
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Presented: 10/19/2004
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Related Entries:
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Bullet Item Air Toxics Human Exposure Modeling
spacer Relationship Reason:   A Project of the Product
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Last Updated on Monday, October 22, 2007
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