EPA-Expo-Box (A Toolbox for Exposure Assessors)
Screening-Level and Refined
When conducting a tiered exposure assessment, after each iteration, the question is asked,
Is this level of detail or degree of confidence good enough to achieve the purpose of the assessment?
If the answer is no, successive iterations continue until the answer is affirmative, new input data are generated, or, as is the case for many assessments, the available data, time, or resources are depleted.
(U.S. EPA, 1992) Guidelines for Exposure Assessment
EPA’s Exposure Assessment Guidelines recommend completing exposure assessments iteratively using a tiered approach to “strike a balance between the costs of adding detail and refinement to an assessment and the benefits associated with that additional refinement” (U.S. EPA, 1992). In other words, an assessment using basic tools (e.g., simple exposure calculations, default values, rules of thumb, conservative assumptions) can be conducted as the first phase (or tier) of the overall assessment (i.e., a screening-level assessment). The exposure assessor or risk manager can then determine whether the results of the screening-level assessment warrant further evaluation through refinements of the input data and exposure assumptions (e.g., include site-specific data) or by using more advanced models (e.g., probabilistic models that use distributions of data in place of point estimates).