Recommendations for Estimating Transport Between Environmental Compartment (Fugacity) for Existing chemicals, including HPV chemicals

EPA strongly recommends the use of the EQC level III model, downloadable from the Trent University web site  for estimating transport between environmental compartments (fugacity) for chemicals for which there are measured values for many of the required inputs (i.e. p/chem property and half-life inputs), including existing chemicals, and HPV chemicals.

The Trent University model defaults should be used, or if they are not, the values that are used in place of the defaults should be provided in the remarks field along with an explanation. The physical/chemical properties and half-lives used in the model in estimating the distributions and media concentrations (using the correct units) should be reported with the model results. EPA does not believe that the environmental media concentration results from this analysis are useful for quantitative risk assessment.

The EPA believes that the EQC model is suitable for chemicals (such as in the HPV Challenge program) where users will have measured values for many of the required inputs (i.e. p/chem property and half-life inputs). In addition, it is widely accepted and has been thoroughly discussed in the peer-reviewed scientific literature; is downloadable free from the Trent University web site; is transparent and user-friendly; and has reasonable default settings.

EPA further recommends that the level III model be used rather than the level II model. Level III provides the most realistic results for environmental distribution, since it does not assume attainment of equilibrium distribution of the chemical across environmental compartments as does a level II model. Level III assumes steady state is attained such that inputs equal outputs, but not achievement of thermodynamic equilibrium-this is more realistic where releases are relatively constant over time.

EPA has an interest in developing guidance for using the EQC Level III and related models to estimate overall environmental persistence and the potential for l10 long range transport (LRT). Such guidance would be of value not only in assessments on chemicals and in the implementation of national and international efforts to identify and control persistent, bioaccumulative and toxic (PBT) substances.