there is a need to establish a residue-based toxicity framework with associated models. This 
framework is intended to improve aquatic ecological risk assessments and criteria 
development/application. In so doing, it can also be used to design, conduct, and report results 
for a long term PBT aquatic risk research program. The framework, like the framework for non- 
bioaccumulative toxicants, should be upxlated periodically and revised as new research improves 
and expands the methods, models, and data available for effectively applying the conceptual 
model. These jjeriodic improvements need to be reported to OW and other interested Program 
Offices in a context that emphasizes integration into the framework and practical applications of 
the resulting risk assessment methodology. Project B1 {Framework for Development and 
Application of Population Risk-Based Criteria for Fish and Wildlife Exposed to Persistent 
Bioaccumulative Toxicants) serves this need. The initial products under project B1 will address 
APG 1. Subsequent improvements to the framework and validation efforts will concentrate on 
population level impacts and thus address APG 3. As for project Nl, work in this project will in 
large part be in conjunction with OW efforts to update W(^ guidelines. The nature and time 
line of additional products will be defined as these collaborative efforts develop during FY03. 
As discussed in the Research Needs subsection for bioaccumulative toxicants, BAFs and models 
are essential for application of the residue-based toxicity approach. Although basic models and 
approaches are available for predicting bioaccumulation throughout aquatic food webs, improved 
capabilities are needed. Prime examples are the need to incorporate the effects of chemical 
metabolism into predictions of whole organism chemical elimination rates, the need to predict 
site-specific bioaccumulation with minimum data sets, and the need to extend bioaccumulation 
models to allow tissue residue predictions for vertebrates during the embryo and subsequent early 
stages of development. Project B2 {Incorporate Chemical Metabolism Rates and Site-specific 
Bioavailability into Bioaccumulation Models Structuredfor Practical Assessments of Risks to 
Fish and Wildlife Exposed to PBTs) is intended to advance the state of knowledge and risk 
assessment capabilities for all five of the major gaps identified under the Bioaccumulation Model 
Path. In so doing, project B2 will ultimately share with project B4 a goal of development of a 
model for fish ELS bioaccumulation of chemicals with significant metabolism potential such as 
PAHs. Although influencing APG 3 and APG 5, project B2 will primarily address APG 4. 
(Note : Because of resource reductions after the initial preparation of this plan, this project will 
not be pursued at this time.) 
Projects B3 and B4, although focused on specific PBTs, will provide products needed to fill 
important gaps associated with both the toxicity model and the population model paths of the 
conceptual model. Exposure to methyl mercury arguably creates the most widespread and 
intractable PBT risk problem for piscivorous birds. Project B3 {Multiple Stressor Risks to 
Common Loon and Other Piscivorous Bird Populations) will provide population models that are 
capable of evaluating relative risks of multiple stressors, including habitat alterations, in response 
to APG 3. Project B3 will also advance methods for interspecies extrapolation of dose-response 
relationships through development of PBTK/TD models in support of APG 4, and extend the 
population model to assessment of risks to wildlife from multiple stressors across spatially 
diverse landscapes in support of APG 5. Project B4 {Risks to Fish Populations from PAHs in 
Natural Systems) inherently addresses complex chemical mixture modeling issues with 
complexity added in association with the need to model photo-activation of PAHs in tissues of 
organisms, including early life stages of fish. Since data will probably always be limited for 
97 
