assessing photo-induced PAH toxicity and thus extrapolations are required to assess risks, project 
B4 will contribute to APG 4. Project B4 also will provide the key aquatic life related 
contribution to APG 5. The determination of the extent to which populations of aquatic 
organisms, including fish during early life stages, are reduced due to photo-induced toxicity 
across the broad range of PAH contamination in aquatic ecosystems will require achievement 
and application of a highly advanced PBT risk assessment capability. This PBT risk problem 
will provide a uniquely challenging test of PBT risk assessment methodologies because, although 
concentrations of complex mixtures of PAHs in organisms may be sufficiently described as a 
steady-state condition, the timing of UV exposure required for photo-activation is highly variable 
in time and space as well as being subject to habitat conditions and organismal/species behavior. 
Project Title NL Improved Risk Characterization Methods for Developing Aquatic Life 
Criteria for Nonbioaccumulative Toxicants 
Project Coordination and Resources (4.0 FTEs: AED-1.5, GED-0.5, MED-2.0) 
Objectives 
Current WQC incorporate only limited information regarding the magnitude and time- 
dependency of the responses of aquatic organisms to toxic chemicals. They address only one 
point (the fifth percentile) in the distribution of toxic effects concentrations among tested species. 
No uncertainty estimates are made and the importance of untested species and endpoints is not 
assessed. Assessments are not made at ail in the absence of certain minimum datasets. The 
spatial variation of exposure, especially between sediment and water column, is not addressed. 
Except for recent efforts regarding sediment assessments, the effects of multiple stressors are 
generally not considered nor are the consequences of toxic effects on populations as a result of 
exposure of individuals. These limitations result in a weakly defined definition of risk associated 
with criteria conditions and an inability to quantify how risk would change with exposures above 
or below criteria concentrations. 
Methods do exist for more completely addressing many of these issues, albeit with some 
uncertainty, and thus providing a more meaningful statement of risk. However, this will require 
adoption of more comprehensive risk assessment framework for criteria. A major short term 
objective of this project will be to describe a methodological fi'amewoik for such risk 
characterization that could be used to improve criteria derivation. Current and possible 
methodologies for the components of this framework will be described, identifying where 
improvements to criteria are possible with current knowledge and where research efforts are 
needed. This effort will provide APM (2A) under APG 2. 
The longer term objective of this project will be to further test, refine, and describe this 
framework and its component methodologies, based on results of research conducted in other 
projects in this program and elsewhere. In particular, we will address application of methods for 
population-level assessments and for extrapolation of toxicological information among endpoints 
and exposure conditions (APG 3 and APG 4). Products will consist of reports which synthesize 
new information and update descriptions of risk assessment methods relevant to aquatic life 
criteria. Much of this work will be pursued in collaboration with OW efforts to update WQC 
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