Conservatism in maximally exposed individual (MEI) predictive exposure assessments: a first-cut analysis

The United States Environmental Protection Agency (USEPA) sometimes applies exposure assessment models based upon the concept of a hypothetical "maximally exposed individual" (MEI) as a means of dealing with uncertainty. This concept has been described in the benzene NESHAPS rule, the proposed RCRA Corrective Action Rule, and the Clean Air Act reauthorization debate. This paper describes a first-cut analysis of the level of conservatism of the current MEI approach relative to a central estimate of exposure of the most exposed population around a source. The inherent level of conservatism of the current MEI model, which appears to be at least one order of magnitude, is usually left unstated. The significance of this conservatism is described along with some proposals for future research.