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APPLICATION AND EVALUATION OF AN AGGREGATE PHYSICALLY-BASED TWO-STAGE MONTE CARLO PROBABILISTIC MODEL FOR QUANTIFYING CHILDREN'S RESIDENTIAL EXPOSURE AND DOSE TO CHLORPYRIFOS
Xue, J, V Zartarian, A H. Ozkaynak, S V. Liu, G. Glenn, AND L. Smith. APPLICATION AND EVALUATION OF AN AGGREGATE PHYSICALLY-BASED TWO-STAGE MONTE CARLO PROBABILISTIC MODEL FOR QUANTIFYING CHILDREN'S RESIDENTIAL EXPOSURE AND DOSE TO CHLORPYRIFOS. Presented at International Society of Exposure Analysis 14th Annual Conference, Philadelphia, PA, October 17-21, 2004.
The primary objective of this research is to produce a documented version of the aggregate SHEDS-Pesticides model for conducting reliable probabilistic population assessments of human exposure and dose to environmental pollutants. SHEDS is being developed to help answer the following questions:
(1) What is the population distribution of exposure for a given cohort for existing scenarios or for proposed exposure reduction scenarios?
(2) What is the intensity, duration, frequency, and timing of exposures from different routes?
(3) What are the most critical media, routes, pathways, and factors contributing to exposures?
(4) What is the uncertainty associated with predictions of exposure for a population?
(5) How do modeled estimates compare to real-world data?
(6) What additional human exposure measurements are needed to reduce uncertainty in population estimates?
Critical voids in exposure data and models lead risk assessors to rely on conservative assumptions. Risk assessors and managers need improved tools beyond the screening level analysis to address aggregate exposures to pesticides as required by the Food Quality Protection Act of 1996. Thus, there is a need for developing probabilistic aggregate and cumulative source-to-dose models for assessing realistic multimedia, multipathway exposure and risk to pollutants and populations of concern. The aggregate Stochastic Human Exposure and Dose Simulation model for multimedia, multipathway pollutants (SHEDS-Pesticides) is a physically-based probabilistic model designed to estimate likely values of human exposure and dose to selected multimedia/multipathway pollutants. SHEDS-Pesticides combines actual human activity data (from national time/activity diary surveys and videography studies) with residue and concentration measurements in media contacted, exposure factors, and dose factors. The model then predicts, for user-specified cohorts, exposures and doses incurred via eating contaminated foods or drinking water, inhaling contaminated air, touching contaminated surface residues, and ingesting residues from hand- or object- to-mouth activities. To illustrate model capabilities, an aggregate case study for young children and chlorpyrifos was conducted, and model predictions were evaluated using measured chlorpyrifos data from the National Human Exposure Assessment Survey (NHEXAS) Minnesota Children's study. Three post-application time periods (<1,1-7, 8-30 days) were considered for indoor residential crack and crevice applications and outdoor liquid and granular turf applications. Non-dietary ingestion and dermal contact were found to be the most important routes for shorter post-application time periods (<7 days); inhalation and dietary ingestion were most important for longer time periods (>7 days). Despite current data limitations and model assumptions, the model predictions of exposure and dose compared well with the Minnesota Children's data, and provided useful insights to the relative importance of exposure routes and critical model inputs.
Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.