Science Inventory



Zartarian, V, A H. Ozkaynak, J. Xue, W. G. Glen, AND E J. Furtaw Jr. MODELING AGGREGATE CHLORPYRIFOS EXPOSURE AND DOSE TO CHILDREN. Presented at ISEA 2000 Exposure Analysis in the 21st Century: Integrating Science, Policy and Quality of Life, Monterey Peninsula, CA, October 24-27, 2000.


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?


To help address the aggregate exposure assessment needs of the Food Quality Protection Act, a physically-based probabilistic model (SHEDS-Pesticides, version 3) has been applied to estimate aggregate chlorpyrifos exposure and dose to children. Two age groups (0-4, 5-9 years) and 3 time periods (<1 day, 1-7 day, 8-30 days) post-indoor crack and crevice application of chlorpyrifos were considered.

Time-location-activity diaries from the National Human Activity Pattern Survey for 1092 children were randomly sampled to generate a population of simulated children. For each location-activity combination in each child's diary, model input values were sampled from probability distributions: air, dust, soil, and surface residue concentrations; meal-specific food, beverage, and drinking water residues ingested; exposure factors; uptake factors; and pharmacokinetic rate constants. These inputs were combined to yield the children's daily exposure and dose time profiles for the inhalation, dietary and non-dietary ingestion, and dermal contact exposure routes. The daily time profiles were then aggregated across all routes and pathways. A simple pharmacokinetic component was incorporated to predict real-time metabolite concentrations in the blood compartment and eliminated urine. Two-stage Monte-Carlo sampling and initial sensitivity analyses were conducted to characterize variability and uncertainty in model outputs, and to identify the relative importance of routes, pathways, and model inputs.

Population distributions for route-specific and aggregate exposure and dose estimates for various exposure scenarios are presented. Modeled estimates for concentrations in urine of 3,5,6-trichloro-2-pyridinol (TCP), a metabolite of chlorpyrifos, compare well to measured children's levels in several studies, including EPA's NHEXAS. Results indicate that dermal contact with and non-dietary ingestion of residues from a recent pesticide application can be significant contributors to exposure and dose.

This abstract has been reviewed in accordance with the U.S. Environmental Protection Agency's peer and administrative review policies and approved for presentation and publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Record Details:

Product Published Date: 10/24/2000
Record Last Revised: 06/21/2006
Record ID: 60270