Project Title BL Framework for Development and Application of Population Risk~Based 
Criteria for Fish and Wildlife Exposed to Persistent Bioaccumulative Toxicants 
Project Coordination and Resources (3.0 FTEs: AED-1.5, MED-1.5) 
Objectives 
The primary goal of this project is to describe and demonstrate a framework for assessing 
ecological risks and developing risk-based WQC criteria for fish and wildlife populations 
exposed to PBTs, as required by APGl. Currently, national WQC or contaminated sediment 
screening levels are not available for protection of fish and wildlife exposed to PBTs. However, 
ecological risk assessment methodologies, with PBT doses based on residues in tissues of 
organisms, have been under development and extensively discussed for at least a decade (Cook 
et al. 1992). Recently, scientific experts have favorably reviewed the state of the models and 
methods for risks to fish and wildlife populations associated with early life stage toxicity from 
bioaccumulated PBTs. For example, the residue-based, additive toxicity equivalence approach 
for dioxin-like chemicals that act through an aryl hydrocarbon receptor (AhR) mediated 
mechanism of action was examined in great detail in 1998 and found to be ready for application 
in ecological risk assessments (EPA 2001). The fundamental purpose of this project is to insure 
that appropriate chemical residue-based toxicity data and models are effectively used, in 
conjunction with bioaccumulation and population dynamics models, to determine site-specific 
water quality conditions required to sustain populations of aquatic organisms and aquatic- 
dependent wildlife. A general risk assessment framework and associated methods will be 
developed for all PBTs based on the principles contained in EPA’s Guidelines for Ecological 
Risk Assessment (EPA 1998). Also, the PBT framework and associated methods will allow 
probabilistic and spatially explicit representations of population level risks to the extent possible 
and beneficial. 
Scientific Approach 
This project will function as a framework for a continuing development and application of risk- 
based water quality criteria for PBTs. The framework will be based on the conceptual model for 
bioaccumulative toxicants (Figure 11). Three major groups of PBTs that must be addressed are 
halogenated organics, of which the chlorinated organics are preponderant (Carey et al. 1998); 
PAHs which are ubiquitous contaminants of aquatic ecosystems with potential for increased 
aquatic life exposures in the future associated with increasing rates of fossil fuel production and 
combustion (Neff 1979); and organometallic compounds such as methyl mercury which are a 
particular concern for wildlife connected to aquatic food webs (EPA 1997). 
Initially, the conceptual model for risk assessments and criteria development involving 
determination of safe loadings of PBTs to aquatic systems (Figure 11) will be applied to existing 
data and models for chlorinated aromatic chemicals that act through an AhR mediated toxicity 
mechanism in vertebrates. This class of chemicals includes polychlorinated biphenyls (PCBsX 
polychlorinated dibenzo dioxins (PCDDs), and polychlorinated dibenzo furans (PCDFs) for 
which residue-based ELS toxicity data and a mixture toxicity model are available. Thus, 
ecological risk assessment tools and approaches will be described and demonstrated for risk 
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