This paper outlines methods for developing a chemical-specific, species-specific Toxicity Reference Value (TRV), for use in evaluating potential impacts to terrestrial receptors from chemical exposure. The TRV is developed using laboratory toxicity data and uncertainty factors to extrapolate from the test animal species to the species of concern, and to adjust toxicity data to derive a chemical-specific, chronic no observed adverse effect level for the relevant endpoint or endpoints (i.e., the TRV).
Once the TRV is established and the chemical dose to the receptor is estimated, the Quotient Method (QM) can then be used to assess the potential for adverse impacts. Using the QM, a ratio of the estimated dose to the TRV is derived; summing the ratios for all chemicals with similar toxicity endpoints provides a Hazard Index (HI). The results of this screening approach can be used to make generalized predictions regarding the potential for adverse impacts to terrestrial receptors from chemical exposure, and the need for further field investigations or remediation at a site or facility. Use of this method in conjunction with results of field studies or bioassays will provide greater confidence in the results of the analysis.