Development of Uncertainty Factors for Nonhuman Receptors

Abstract

A baseline human public health evaluation is required under the National Contingency Plan as a part of the Remedial Investigation/ Feasibility Study process. For the protection of aquatic organisms, many of the priority pollutants have Ambient Water Quality Criteria promulgated or pending, but few have criteria to protect terrestrial receptors. Contaminant levels judged to be acceptable may be determined following methods used to develop human values from literature sources. Part of this process involves the determination of uncertainty factors for which USEPA (1985) presents a step-wise approach to use in public health evaluations. This paper describes a similar step-wise approach to develop uncertainty factors to be applied to literature-cited toxicity values for aquatic and terrestrial organisms. When compared with the methodology used by USEPA (1986) for the assessing the risk to terrestrial animals, notably livestock, this method results in levels 2 to 4 orders of magnitude smaller than those developed by the regulatory risk criteria approach as specified in the Federal Insecticide, Fungicide, and Rodenticide Act for pesticide evaluation. For aquatic organisms, the values are similar or only differ by approximately one order of magnitude, with the method described here representing the more conservative approach.