• The importance of spatial variation in exposure for assessing risk to aquatic communities 
will be evaluated and discussed. This will include the general issue of the spatial extent 
of the area that WQC criteria are intended to protect. It will also include consideration of 
the effects of spatial and temporal variability at the sediment/water interface (drawing on 
results from project N3) and the implications of this to the integration of sediment and 
water column criteria. 
• The effects of physicochemical exposure conditions and of multiple routes of exposure 
will be addressed. Initial efforts will include general reviews of the importance of such 
factors and current abilities to address these effects. Later efforts will address 
developments from ongoing research regarding these effects, including results from 
project N4 on effects of dietary metals. 
• Exposure to multiple chemicals will be addressed. Existing literature which describes the 
effects of chemical mixtures will be reviewed, procedures appropriate for WQC 
development will be developed, and the significance of joint toxic action to common 
contamination scenarios will be examined. 
Products 
FY03 Journal articles evaluating methods for describing the relationship of toxic responses to 
time and concentration and their application to improved expressions of risk for WQC (part of 
APM 2A). 
Benefits of Products 
This work will provide OW with a prototype framework for criteria based on a more accurate and 
informative characterization of organismal-level risk, and will provide a more quantitative basis 
for deriving and evaluating criteria. This framework will address several of the limitations of 
current criteria and support incorporation of tools addressing other limitations, such as 
population-level effects and extrapolations among species and toxicity endpoints. Products will 
provide a technical basis for making changes to procedures for developing criteria. 
Project Title N2, Methods for Extrapolating Chemical Toxicity Data Across Endpoints, Ufe 
Stages, and Species Which Can Support Assessment of Risks to Aquatic Life for Chemicals 
with Limited Data 
Project Coordination and Resources (1.5 FTEs: GED-1.5) 
Objectives 
Ambient WQC have enabled the states to develop scientifically defensible standards and thereby 
reduce the amount of specific chemicals discharged into our nation’s surface waters. However, 
environmental managers must frequently perform risk analyses and make decisions regarding 
compounds for which WQC and the data necessary to derive them (EPA 1980) do not exist. 
Guidance is needed on comparative sensitivity relationships and on limits of extrapolation, and 
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