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PT12 Methods in Risk Assessment
(PT185) A tiered approach for deriving toxicity reference values for ecological risk assessment.
Newell, P1, Podolsky, J1, 1 Environmental Health Associates Inc., Albuquerque, New Mexico, USA
ABSTRACT- The Risk Reduction and Environmental Stewardship Remediation Program at the Los Alamos National Laboratory has developed a tiered approach for deriving toxicity reference values (TRVs) used in ecological risk assessments (ERAs). This tiered approach is used to derive oral food, oral drinking water and inhalation TRVs for terrestrial wildlife, as well as oral/dermal and seed/root uptake TRVs for terrestrial invertebrates and plants, respectively. A tiered approach is valuable because 1) it takes advantage of the breadth of toxicity data available for developing ecologically relevant TRVs and 2) it is a mechanism for assigning a confidence rating to each TRV. By maximizing the amount of toxicity data deemed usable for TRV derivation, the toxicity data gaps in an ERA are minimized, which improves the comprehensiveness of the assessment. The confidence rating of a TRV can also aid in the uncertainty analysis of a chemical of potential ecological concern (COPEC) in an ERA because it is a measurement of the pedigree of the TRV. The following tiers listed in the order of preference are used to derive the TRVs: 1) a nationally accepted TRV such as a United States Environmental Protection Agency (US EPA) Ecological Soil Screening Level (Eco-SSL) TRV; 2) a TRV equal to the geometric mean of ecologically relevant primary toxicity values (PTVs) derived based on firsthand review of the literature; 3) a Critical Study (CS) TRV for the most protective ecologically relevant endpoint derived based on firsthand review of the literature; and 4) a CS TRV derived using ecologically relevant PTVs or TRVs reported by a secondary data source such as Oak Ridge National Laboratory or US EPA Region 6. The details behind the rationale for the four tiers and the confidence rating associated with the values are presented, as well as a comparison of the TRVs from each tier for several chemical-ecological receptor pairs.
Key words: risk, toxicity, assessment, wildlife
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