Huei-An Chu's final Doctoral Dissertation Defense 12/1
| November 29, 2005 | |
| Huei-An Chu’s final Doctoral Dissertation Defense is this Thursday, December 1st at 3:30pm in the Miller Hall conference room.A Framework of Risk-Based Decision Making by Characterizing Variability and Uncertainty Probabilistically: Using Arsenic in Drinking Water as an Example
Risk-based regulatory decisions generally apply a margin of safety meant to guard against underestimation of risk in the face of inter-subject variability and uncertainty. Since these two components often are unknown or only vaguely characterized, the decisions involved usually employ conservative default assumptions concerning the margin of safety, resulting in regulatory limits that may be more (or less) health protective than necessary if variability and uncertainty could be characterized probabilistically. As a result, it remains impossible in most cases to determine the degree of protectiveness inherent in a standard. For example, arsenic MCLs continue to provoke debates because of the variability and uncertainty issues in risk assessment. These issues are: (1) Limitations in the data concerning the risk at low doses of arsenic; (2) Uncertainty about the appropriate mathematical models for estimating the risk at low doses based on data obtained at higher doses; (3) Identification of any sensitive subpopulation unprotected under new MCLs because of variability of health effects within the population; and (4) Lack of a methodology to quantify probabilistically the appropriate margin of safety. At present, we can only get a vague idea that lowering maximum containment levels (MCLs) result in larger margins of safety, but at the expense of greater compliance costs. If the magnitude of this margin of safety is not taken into account, it is possible that an MCL may be established based on a significantly larger margin of safety than is necessary, reasonable or consistent with that applied to other contaminants. Thus an unnecessarily expensive treatment policy may be selected. In this study, a new framework of probabilistic risk-based decision making was developed. A meta-analysis was conducted for bladder cancer from arsenic in drinking water by combining several epidemiological studies from various regions (such as Taiwan, US, India, Chile and Finland). Meta-analysis was used to resolve the discrepancies among epidemiological data and get a reasonable generalized dose-response relationship and its distribution. Then the results of the meta-analysis were incorporated into the framework to characterize the margin of safety through variability and uncertainty analyses. The final product of this study is to develop a method of probabilistic risk assessment that better deals with variability and uncertainty issues. This risk assessment methodology can help decision-makers make optimization determinations on regulatory limits for a contaminant that adequately protect human health with an ample margin of safety at a more reasonable cost than currently is the case. Committee Members: For further information please contact Rebecca Riggsbee Lloyd by email at Rebecca_Lloyd@unc.edu |
