Science Inventory



Furtaw Jr., E J. OVERVIEW OF THE U.S. EPA NERL'S HUMAN EXPOSURE MODELING. Presented at Theories and Practies in Toxicology and Risk Assessment, Cincinnati, OH, April 15-18, 2002.


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?


Computational modeling of human exposure to environmental pollutants is one of the primary activities of the US Environmental Protection Agency's National Exposure Research Laboratory (NERL). Assessment of human exposures is a critical part of the overall risk assessment paradigm. In exposure assessment, we analyze the source-to-effects sequence of processes, in which pollutants are released from sources into the environment, where they may move through multiple environmental media, and to human receptors via multiple pathways. Exposure occurs at the environment-human interface, when pollutants are contacted in the course of human activities. Exposure may result in dose, in which chemicals enter the body through multiple portals of entry, primarily inhalation, ingestion, and dermal absorption. Within the body, absorbed pollutants are distributed to, metabolized within, and eliminated from various organs and tissues, where they may cause toxicologic responses or adverse health effects. NERL's modeling efforts are directed at improving our understanding of this sequence of processes, by characterizing the various factors influencing exposures and dose, and their associated variabilities and uncertainties. Modeling at NERL is one of three essential programmatic elements, along with Measurements and Methods Development. These are pursued interactively to advance our understanding of exposure-related processes. Exposure models are developed and run using the best currently available measurement data to simulate and predict population exposure and dose distributions, and to identify the most important factors and their variabilities and uncertainties. This knowledge is then used to guide the development of improved methods and measurements needed to obtain better data to improve the assessment and reduce critical uncertainties. These models and measurement results are tools that can be used in risk assessments and in risk management decisions in order to reduce harmful exposures. Current areas of NERL's exposure modeling emphasis include:

Pollutant concentrations in ambient (outdoor) air using the Third Generation Air Quality Modeling System's Community Multiscale Air Quality model (Models-3/CMAQ);

Air flow and pollutant concentrations at local and microenvironmental scales using computational fluid dynamics (CFD);

Human inhalation exposure to airborne particulate matter, air toxics, and multi-pathway exposure to pesticides, using the Stochastic Human Exposure and Dose Simulation (SHEDS) model;

Human and ecological exposure and risk assessments of hazardous waste sites using FRAMES-3MRA (Framework for Risk Analysis in Multi-media Environmental Systems-Multi-media, Multi-pathway, Multi-receptor Risk Assessment), one of many software programs available from NERL's Center for Exposure Assessment Modeling (CEAM);

Physiologically based pharmacokinetic modeling of pesticides and volatile organic compounds in the Exposure Related Dose Estimating Model (ERDEM).

A brief historical overview of NERL's evolution of human exposure models will be presented, with examples of the present state-of-the-science represented by SHEDS and FRAMES-3MRA.

This is an abstract of a proposed presentation and does not necessarily reflect the United States Environmental Protection Agency (EPA) policy. The actual presentation has not been peer reviewed by EPA. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Record Details:

Product Published Date: 04/15/2002
Record Last Revised: 06/21/2006
Record ID: 62215