APM 4A FY02 Interspecies correlation estimations (ICEs) for acute toxicity to aquatic 
organisms (GED). 
APM 4B FY02 Time-concentration-effect models for use in predicting chronic toxicity 
from acute toxicity data (GED). 
APM 4C FY03 Acute-to-chronic estimation (ACE) user guide and software (GED). 
APM 4D FY06 Report evaluating importance of dietary route of exposures to aquatic risk 
assessments for metals (MED). 
APG 5 FY08 Provide approaches for evaluating the relative and cumulative risks from toxic 
chemicals, with respect to risks from nonchemical stressors, on populations of aquatic life and 
aquatic-dependent wildlife at various spatial scales. 
APM 5 A FY05 Report regarding assessment of risks to aquatic organisms from 
combined exposure to polycyclic aromatic hydrocarbon (PAHs) mixtures and ultraviolet 
(UV) radiation in natural systems (MED). 
APM 5B FY06 Approaches for addressing spatial scale issues in assessing risks of 
multiple stressors to wildlife populations in spatially-diverse landscapes (AED, MED). 
Critical Path 
Defining critical research paths needed to improve aquatic risk assessments and criteria 
development for toxic chemicals should start with consideration of the problem formulation that 
should be part of any good risk assessment (Figure 8). There needs to be clear definition of the 
assessment problem, including the ecological effects (assessment endpoints) and exposure 
scenarios of concern, and better conceptual models which define the logical structure of the 
assessments. These conceptual models should identify critical toxicological endpoints to be used 
in the assessment (i.e., measurement endpoints) and how these are to be related to the assessment 
endpoints, based on knowledge of the dynamics of the ecosystem(s) of concern. There also 
should be specification of how assessments might be tiered initially, basing evaluations on 
limited data to determine whether risks might be significant, and adding data as needed to make 
more definitive assessments. 
With better definition of the conceptual model, the needs of the other phases of a risk assessment 
can be better identified. Methods are needed so that the exposure profiles (Figure 8) can 
describe, in sufficient detail, the distribution of the toxicant(s) relative to the biological receptors. 
This would include evaluation of the temporal and spatial variability of exposure and the 
chemical’s speciation and partitioning to the extent needed to determine the distribution of 
toxicological responses. Response profiles (Figure 8) need to provide good organism-level 
response models and linkages between organism response and population/community responses. 
When limited toxicological data are available, methods for extrapolating among species and 
endpoints also will be needed. Methods must support risk characterizations which describe a 
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