United States Environmental Protection Agency (USEPA) framework for ecological risk assessment (Cont.)

conceptual model and analysis plan, developed during the "Problem

formulation" phase, provide the basis for this "Analysis phase." A

characterization of exposure must be conducted during this phase. This

characterization can be quantitative or qualitative, depending on the

stressor and the scope of the assessment. Exposure is defined as "contact

or co-occurrence of stressors with ecological receptors." Exposure can be

analyzed by describing "the source and releases of stressors, the spatial

and temporal distribution of the stressor in the environment, and the

extent and pattern of contact or co-occurrence between the stressor and

receptor." Intensity, time, and space are three important factors to

consider when estimating exposure. After these factors are taken into

consideration in an exposure analysis, an exposure profile should be

written to convey the "likelihood that exposure will occur."

Also in the "Analysis Phase," the assessor should identify the ecological

effects of interest and conduct an ecological response analysis. The

analysis should show how the magnitude of ecological effects changes

with varying stressor levels, present evidence that the stressor causes the

effect (show "causality"), and link the effects to the assessment end

points. Stressor-response relationships can be difficult to assess,

especially if multiple stressors are present. However, if the assessor can

repeatedly demonstrate cause-effect relationships between the stressor and

the effect, then he or she has strong evidence for causality. The document

also includes several considerations when linking effects to assessment

end points. Judgment approaches, empirical approaches and process-

based approaches are presented as general categories of methods to

extrapolate effects to assessment end points. The most useful

extrapolation approach depends on the parameters outlined in the analysis

plan and the conceptual model used. At the end of the ecological response

analysis, a stressor-response profile is written to present the results,

rationale, and uncertainty of the analysis.

d. Risk characterization phase. The third phase of an ecological risk

assessment is "risk characterization." The three components of this phase

are risk estimation, risk description, and reporting results. The purpose of

risk estimation is to "determine the likelihood of adverse effects to

assessment end points [identified in the "Problem formulation" phase] by

integrating exposure and effects data [from the "Analysis phase"] and

evaluating any associated uncertainties." The authors outline the

advantages and disadvantages of six approaches for conducting a risk

estimate. A risk estimate approach should be chosen based on the amount

of data available, the scope of the assessment, and usefulness for risk

management. The results of the risk estimate as well as the degree of

confidence in the estimate should be included in the risk characterization

report.

The goals of the risk description component of this third phase are to

make conclusions "about risks to the assessment endpoints," to evaluate

the "lines of evidence supporting or refuting the risk estimate(s)," and to

interpret the "adverse effects on the assessment end point." Examples of

Appendix A Summary of Federal, State, and Regional Guidance