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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Screening-Level and Refined


In advance of undertaking an exposure assessment, it is necessary to define the problem. Thoughtful planning, scoping, and problem formulation at the beginning of the project is necessary to describe the specific problem that triggered the assessment and define the question(s) it is intended to answer. This process considers cross-disciplinary issues, including critical windows of susceptibility based on lifestages and toxicological endpoints. Effectively articulating the problem allows the exposure assessor to select the right approach for the situation with the goal being to use the simplest approach possible to answer the question(s), which in turn saves resources. (See discussion of Problem Formulation in the Approaches Tool Set.)

In many cases, the assessment process is iterative, and a screening-level assessment might be followed by one or more assessments in which the quality of inputs and results are refined as shown in the figure below.

Example Application of Tiered Approach to Exposure Assessment
Example Application of Tiered Approach to Exposure Assessment (U.S. EPA, 2004)

As emphasized in the Guidelines for Exposure Assessment (U.S. EPA, 1992), after each iteration, the exposure assessor determines whether the outcome of the iteration meets the needs of the assessment. If the level of exposure estimated by a screening-level exposure assessment is of potential concern, some of the following refinements might make sense.

  • Collect site-specific measured data for environmental properties or stressor concentrations.
  • Refine exposure parameters to reflect site-specific conditions more accurately or use higher-precision sampling or analysis techniques.
  • Use more complex models. For example, replace a box model for fate and transport with one that estimates dispersion, deposition, and other movement of a stressor in environmental compartments.
  • Employ probabilistic approaches to reduce uncertainty and better characterize both uncertainty and variability.

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Tools for Planning, Scoping, and Problem Formulation

The tools below provide guidance on planning, scoping, and problem formulation.

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Tools for Conducting Screening-Level or Refined Assessments

The tools below provide guidance on conducting screening-level or refined (i.e., higher tiered) assessments.

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