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Risk Assessment

Phase 3 - Risk Characterization

Phase 3 - Risk Characterization is the final phase of an ecological risk assessment. It is the culmination of all work done during the previous phases.

During risk characterization, the assessor uses the results of analysis to estimate the risk posed to ecological entities. The assessor then describes the risk, indicating the overall degree of confidence in the risk estimates, summarizing uncertainties, citing evidence supporting the risk estimates, and interpreting the adversity of ecological effects.

When estimating ecological risk, factors considered include:

  • Is the risk acute or chronic?
  • What is the severity of effects?
  • What is the time over which they occur?
  • Is the risk to one species or many species?
  • How many organisms are at risk?

Some approaches used to answer these questions and develop the risk estimate include:

  • Field observational studies (surveys)
  • Categorical rankings
  • Process models that rely partially or entirely on theoretical approximations of exposure and effects
  • Comparisons of exposure and effects data
Estimating Risk

Principles of Conducting Risk Characterizations

A good risk characterization will restate the scope of the assessment, express results clearly, articulate major assumptions and uncertainties, identify reasonable alternative interpretations, and separate scientific conclusions from policy judgments. EPA's risk characterization policy calls for conducting risk characterizations in a manner that is consistent with the following principles:

  • Transparency - The characterization should fully and explicitly disclose the risk assessment methods, default assumptions, logic, rationale, extrapolations, uncertainties, and overall strength of each step in the assessment.
  • Clarity - The products from the risk assessment should be readily understood by readers inside and outside of the risk assessment process. Documents should be concise, free of jargon, and should use understandable tables, graphs, and equations as needed.
  • Consistent - The risk assessment should be conducted and presented in a manner which is consistent with EPA policy, and consistent with other risk characterizations of similar scope prepared across programs within the EPA.
  • Reasonable - The risk assessment should be based on sound judgment, with methods and assumptions consistent with the current state-of-the-science and conveyed in a manner that is complete, balanced, and informative.

In order to achieve transparency, clarity, consistency, and reasonableness( or TCCR) in a risk characterization, these same principles need to have been applied in all of the previous steps in the ecological risk assessment which lead up to the risk characterization.

More information about risk characterization can be found in EPA's Risk Characterization Handbook (PDF) (189 pp, 8.90MB, About PDF).

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