Addressing Variability and Uncertainty in Residual Risk Analysis. D. A. Amaral, EC/R Incorporated, 1129 Weaver Dairy Road, Chapel Hill, NC 27514; M. G. Dusetzina, US EPA/OAQPS (MD-15), Research Triangle Park, NC 27711; and B. S. Perkovich, EC/R Incorporated, 1129 Weaver Dairy Road, Chapel Hill, NC 27514
The EPA Risk Characterization Policy emphasizes the need to include a discussion of variability and uncertainty when drawing conclusions from the integration of hazard and dose-response with exposure assessment. The Policy recommends separate treatment of variability and uncertainty in risk assessment. The analysis of residual risk in the secondary lead smelter source category case study addressed variability and uncertainty using sensitivity analysis and two-dimensional Monte Carlo simulation. This paper describes the representation of variability and uncertainty in the risk model developed for the refined residual risk assessment of secondary lead smelters. It examines the selection of probability distributions to represent variability and uncertainty in the model input parameters, emission processes, dispersion and deposition, inhalation, dermal contact, and ingestion through the food chain. Data used in the analysis were derived from sources such as the background information document (BID) developed for regulating the secondary lead smelter source category, the 1997 Exposure Factors Handbook, and State air permits. The paper presents the results of the sensitivity and two-dimensional Monte Carlo analysis for total cancer and noncancer risks, and for cancer and noncancer risks from the HAPs contributing most significantly to the total risk. The results are compared with the point estimates calculated using defaults given in EPA guidance.
Funded by the U. S. EPA under Contract 68-D6-60065.
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