A Comparison of Toxicity Reference Values and their Derivation Methods: Implications for Ecological Risk Assessment. J. S. Podolsky, P. G. Newell, and O. B. Myers, Environmental Health Associates, Inc.
The derivation of toxicity reference values (TRVs) probably has the greatest influence on the outcome of ecological risk screening assessments because it is the basis for screening values used in the protection of wildlife from contaminants. Certain national laboratories (e.g., Oak Ridge, Sandia, and Los Alamos), federal agencies (e.g., U.S. Environmental Protection Agency), and environmental consulting companies (e.g., ENSR International) each have their own methods for developing TRVs for various chemical and ecological receptor combinations. Differences or similarities in TRVs among these organizations are influenced by the type of measured effect selected to represent the TRV, the application of uncertainty factors for contaminant exposure duration and effect level, the data pool from which the TRV is selected, the categorization of the age or life stage of the exposed organism, the use of biological and/or statistical significance in determining effect levels, and the selection of dose rate parameters used in TRV calculations. In some methods, additional steps are applied in the development of TRVs. Examples include calculating geometric means or specifying lower percentiles from frequency distributions for TRVs (approaches used by the Environmental Protection Agency). In other methods such as that of the Environmental Restoration Project at Los Alamos National Laboratory (LANL), an extensive primary literature review process was developed in order to select primary toxicity values that are the most applicable to the protection of long-term population health. Supporting details are provided to justify the reasoning for the selection, thus documenting the scientific basis of the resultant TRVs. The methods and TRVs used at LANL are compared to those from other organizations to assess the strengths and weaknesses of the different methods used to derive TRVs for ecological screening assessments.
This project is funded by the Los Alamos National Laboratory Environmental Restoration Project.
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