guidelines, and the specific nature and time line of products will be developed as part of this 
collaboration. 
Scientific Approach 
This project will use existing and developing information to evaluate and demonstrate procedures 
for more fully characterizing risks of nonbioaccumulative toxicants to aquatic organisms, and 
incorporating these risks into aquatic life criteria These efforts will address a variety of issues, 
identified and discussed as follows. For all these issues, initial efforts will describe general 
approaches, discuss the capabilities and limitations of current methods, and identify needed 
research efforts. 
• Improved descriptions of risk must start with methods which better describe individual- 
level concentration-response relationships than endpoints that address only a single level 
of effect under narrow exposure conditions (e.g., 96-hr LC50). A chemical will be 
selected (likely candidates: ammonia, copper) for which raw toxicity test data are 
available for a large number of tests and diverse aquatic species. Existing methods for 
describing the effects of exposure time series on toxicological response (Mancini 1983, 
Breck 1988, Erickson et al. 1989, Hickie et al. 1995, Meyer et al. Newman 1995) will be 
evaluated, refined, and tested using these data sets. Models and estimation procedures for 
describing fixed-duration concentration-response curves also will be evaluated. These 
methods will be used to develop procedures for describing risks, and their uncertainties, 
for individual-level endpoints as a function of exposure parameters in a manner useful for 
criteria development and application. 
• Efforts also will address better description of species-sensitivity distributions to allow 
criteria to address more than just a single level (i.e., the fifth percentile genus) in the 
range of available toxicity data. Methods for describing the distribution of toxic 
sensitivities among taxa (Kooijman 1987, Wagner and Lokke 1991, Aldenberg and Slob 
1993, Baker et al 1994, Solomon et al. 1996, Hall et al. 1998, Newman et al. 2000) will 
be reviewed and used to develop an aggregate, continuous measure of risk from the 
assemblage of available toxicity data, which can be applied to various exposure 
conditions and provide a more quantitative basis for specifying aquatic life criteria. 
Uncertainties in this analysis will be described to the extent possible and the effects of 
using limited data on the estimated risks and their uncertainties will be evaluated. 
• The use of population models in the recently developed saltwater DO criteria will be 
reviewed and the broader applicability of population models to criteria will be addressed 
in initial efforts. Subsequent work will, as appropriate, review advances in methods from 
other research in this plan (projects B1 and B3) and elsewhere, and ^xlate 
recommendations regarding assessment methods for aquatic life criteria. 
• Correlations of responses among taxa and endpoints will be discussed with regard to how 
criteria can address data gaps and limited data. Current work on interspecies 
extrapolation in project N2 will be summarized in initial products, and results of 
continued work in this project will be included in later efforts. 
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