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EPA ExpoBox

Exposure Assessment Tutorials

Risk Assessment Training and Experience (RATE)

The Risk Assessment Training and Experience (RATE) Program modules were developed to cover scientific subject matter and methodologies considered to be essential knowledge and skills for EPA’s Integrated Risk Information System (IRIS) Chemical Managers and risk assessors within and outside of the Agency.

RATE modules were developed on the topics of general risk assessment, human health risk assessment, the IRIS process, specific IRIS methodologies, including use of Benchmark Dose (BMD) and physiologically-based pharmacokinetic (PBPK) models.

Modules on exposure assessment were also developed and are provided in the Toolbox. RATE modules may be updated as necessary in the future, and new modules may be developed for additional subjects should stakeholder needs and interests exist.

The available exposure modules, along with brief descriptions of their content, are shown in the table below.

Module Number Title RATE Training Description
EXA 401 (ZIP, 3 files, 2.28MB) General Concepts of Exposure Assessment This module provides the basic concepts and principles of human exposure assessment. The various components of an exposure assessment and key terminology are introduced. Fundamentals that are covered include: intake, uptake, and dose; applied, potential, internal, and biologically effective dose; acute, average daily dose, and average lifetime dose; and dermal, oral, and respiratory dose.

This module familiarizes participants with EPA’s Exposure Assessment Guidelines and other key exposure assessment resources.
EXA 402 (ZIP, 3 files, 3.91MB) Approaches for Quantifying Exposure Selecting the approach for quantifying exposure/dose, as well as determining the appropriate type and scope of the study are important first steps in planning an exposure assessment.

This module is designed to explore the various approaches that may be used to measure or model exposure, including point-of-contact measurements, scenario evaluation methods, and dose reconstruction approaches. The purpose and utility of these approaches as well as their strengths and weaknesses are covered. The types (e.g., deterministic or probabilistic) and scope (e.g., single or multiple chemicals; national-scale, or specific location or industry) are introduced. The use of exposure descriptors in the exposure assessment planning process is also covered.
EXA 403 (ZIP, 3 files, 3.47MB) Developing Exposure Scenarios and Calculating Dose Exposure scenarios are sets of facts, assumptions and inferences about how exposure takes place that aids the exposure assessor in evaluating, estimating or quantifying exposure. This module provides the necessary tools for developing assessment-specific exposure scenarios. Factors that are considered include: the source(s) of contaminant release, identification of contaminants, transport of contaminants from source to site of exposure, which exposure media are impacted, potentially exposed populations, and all exposure routes and pathways.

This module also provides interactive exercises for scenario development and introduces some standard scenarios used in EPA program offices and/or in published exposure assessments.
EXA 404 (ZIP, 3 files, 2.71MB) Fate and Transport This module provides an overview of the factors that are important when assessing the fate of contaminants, starting from their point of release until they reach "receptors" at the "site of exposure." Potential pathways of movement from source to receptor, and concept of transfer of contaminants between media (e.g., air to soil, soil to plant, water to fish, etc.) are described.

Concepts of partitioning and first order degradation are also presented, and common parameters such as Henry’s Constant, octanol water (or octanol air, or organic carbon, and other) partition coefficients are defined. The module concludes with paper and calculator exercises on partitioning and first-order decay.
EXA 405 (ZIP, 3 files, 4.6MB) Monitoring and Modeling Strategies This module provides an overview of means to assess sources and exposure media through the use of monitoring and modeling. With regard to monitoring, different study designs are described, depending on objectives, resources, geographic extent, and other factors. Concepts of laboratory quality are presented, including the important concept of the detection limit and how to handle "censored" data.

A simple paper and calculator exercise is used to show the impact of different assumptions for non-detects in calculating a survey mean. The modeling portion of this module discusses model types, limitations, and calibration/validation.
EXA 406 (ZIP, 4 files, 3.32MB) Obtaining and Using Exposure Factor Data This module is designed to familiarize participants with the selection and use of exposure factors data. It reviews key sources of data on human behaviors and characteristics that affect exposure to environmental contaminants (e.g., Exposure Factors Handbook and Child-specific Exposure Factors Handbook).

The types of factors that are covered include: ingestion of water and other select liquids; non-dietary ingestion via hand-to-mouth and object-to-mouth contact; soil and dust ingestion; inhalation rates; dermal exposure factors (i.e., skin surface area and adherence of solids to the skin); body weight; intake of fruits, vegetables, fish and shellfish, meats, dairy products, and fats, and grain products; intake of home-produced foods; total food intake; human milk intake; activity factors; use of consumer products; life expectancy; and residential characteristics.
EXA 407 (ZIP, 3 files, 3.7MB) Assessing Uncertainty and Variability in the Context of Exposure Assessment Characterizing uncertainty and variability a fundamental component of the exposure and risk assessment process. This module explores the concepts of uncertainty and variability within the context of exposure assessment. The module covers the difference types of variability and uncertainty, and explores methods for analyzing, coping with, and reducing uncertainty and variability.
EXA 408 (ZIP, 3 files, 2.05MB) Interpreting Biomonitoring Data and Using Pharmacokinetic Models in Exposure Assessment This module discusses biomonitoring data in general, but with a focus on what is offered by National Health and Nutritional Examination Surveys (NHANES) data. Simple pharmacokinetic modeling approaches are described, which can be used in conjunction with these data to better understand exposure. One model is the "creatinine correction" model, used to relate a urine measurement to a daily intake as a way to "back calculate" intake doses of the contaminant.

Another model is the simple 1-compartment first-order model. This model is applied to contaminants which bioaccumulate in the body, with elimination (or degradation) half-lives in the body on the order of years. This model can be used in either a "forward" or "backward" mode, with the latter mode appropriate to use in conjunction with biomonitoring data.
EXA 409 (ZIP, 4 files, 3.69MB) Case study - Lead Contamination and Local Exposure This exercise is aimed at applying some of the concepts in an interactive format, using a hypothetical data for a lead manufacturing facility where soil and drinking water well contamination has been discovered. The class is broken up into four groups: the manufacturers, the environmental agency with regulatory jurisdiction, the local health department, and citizens/activists, and are tasked to gather more information and prepare a presentation stating their position at a town hall meeting.

Topics that can be explored by the groups in their presentations include: environmental fate (how can the lead get into the wells?), natural background exposures, validity of the monitoring data, severity of the problem (including modeling of blood levels based on water levels), remediation and further data gathering requirements, drinking water restrictions and testing, and other topics.

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