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A TIERED APPROACH TO PERFORMING UNCERTAINTY ANALYSIS IN CONDUCTING EXPOSURE ANALYSIS FOR CHEMICALS
Citation:
OZKAYNAK, H. A. A TIERED APPROACH TO PERFORMING UNCERTAINTY ANALYSIS IN CONDUCTING EXPOSURE ANALYSIS FOR CHEMICALS. Presented at 17th Annual Conference of the International Society of Exposure Analysis, Durham, NC, October 14 - 18, 2007.
Impact/Purpose:
The overall objective of this research is to develop, apply, and evaluate a human exposure model for predicting population exposures to the components of particulate matter (PM) identified as potential toxic agents contributing to adverse health effects.
Description:
The WHO/IPCS draft Guidance Document on Characterizing and Communicating Uncertainty in Exposure Assessment provides guidance on recommended strategies for conducting uncertainty analysis as part of human exposure analysis. Specifically, a tiered approach to uncertainty analysis is recommended. A tiered approach refers to a process in which the exposure or risk assessment uncertainties progress systematically from a relatively simple to more complex. An important feature of a tiered analysis is that the uncertainty analyses may be refined in successive iterations. Lowest-tier analyses are often performed in screening-level regulatory and preliminary research applications. Intermediate-tier analyses are often considered during regulatory evaluations when screening-level analysis either indicates a level of potential concern or is not suited for the case at hand. The highest-tier analyses are often performed in response to regulatory compliance needs or for informing risk management decisions on suitable alternatives or trade-offs. According to the WHO/IPCS draft Guidance Document, Tier 0 uncertainty analyses incorporates appropriate conservative assumptions or default safety factors. Higher-tier assessments (i.e., Tiers 1-3) do not require the quantification of every uncertainty and are targeted on the uncertainties which have most influence on the assessment outcome. These begin with qualitative approaches (Tier 1), and progressing to deterministic (Tier 2) or probabilistic approaches (Tier 3). Some Tier 3 analyses may separate contributions of variability and uncertainty to overall assessment uncertainties. However, uncertainties may be treated at different tiers within a single exposure assessment depending on the particulars of that assessment. This presentation will provide further details on the recommended approaches for conducting tiered uncertainty analyses for exposure assessment along with illustrative examples.