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Region 8

Ecological Risk Assessment

Ecological risk assessment seeks to estimate the effects of environmental contamination on the growth, reproduction, and survival of a variety of ecological receptors (e.g., birds, mammals, fish, plants) that may be exposed to chemicals in contaminated environmental media, now or in the future. The key components of the ecological risk assessment process are outlined below; click on a topic for more detailed information and related resources and guidance documents. General guidance and resources and examples of completed Region 8 ecological risk assessments are provided at the bottom of this page.

Site Conceptual Model: In this step, the risk assessor prepares a schematic diagram identifying the primary contamination sources at the site and the pathways by which contaminants may be moving from place to place or from medium to medium. Potential exposure pathways by which different ecological receptors might come into contact with contaminated media (e.g., direct contact with contaminated soil, ingestion of contaminated water, ingestion of contaminated soil or food) are also determined. This conceptual model is used to plan the ecological risk assessment and associated data collection activities.

Exposure Assessment: In this step, the risk assessor identifies which types of ecological receptors are likely to be exposed at a site and derives quantitative estimates of the magnitude of the exposure (i.e., the dose) for each receptor for each medium. In some cases, exposure assessment may involve the use of probabilistic risk assessment (PRA) methods and/or biomonitoring (collection of samples of environmental receptors and measuring chemical levels in their tissues).

Toxicity Assessment: In this step, the risk assessor compiles information on the dose levels, exposure durations, and exposure routes (oral, inhalation, dermal) that can cause adverse effects on the growth, reproduction, or survival of exposed receptors. The toxicity assessment for a chemical is usually based on data from laboratory studies, but may sometimes also utilize data from site-specific toxicity tests (e.g., fish may be exposed to site waters, benthic organisms may be exposed to site sediments, and plants may be grown in site soils).

Risk Characterization: In this step, the risk assessor combines the information on exposure and toxicity to estimate the likelihood and magnitude of adverse effects that might occur in each of the receptors selected for evaluation. When possible, this information is used to judge whether the effects are likely to result in an ecologically significant population-level impact.

Uncertainty Analysis: In this step, the risk assessor identifies the main sources of uncertainty in the risk estimates presented in the risk characterization step and evaluates the likely direction and magnitude of the error that may be introduced by the uncertainties. This may be done either in a qualitative discussion or may be performed quantitatively.

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General Guidance and Resources

Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments - Interim Final (OSWER 9285.7-25, June 1997)

Guidelines for Ecological Risk Assessment

ECO Update Bulletin Series

Issuance of Final Guidance: Ecological Risk Assessment and Risk Management Principles for Superfund Sites (PDF) (9 pp, 147 K, About PDF) (Memorandum, OSWER 9285.7-28 P, October 1999)

Oak Ridge National Laboratory's Ecological Risk Analysis Site (Guidance, Tools, and Applications)

Region 6 SLERAP Guidance

U.S. Fish & Wildlife Service

Ecological Assessment of Hazardous Waste Sites: A Field and Laboratory Reference (PDF) (299 pp, 1.2 MB, About PDF) (EPA/540/R-92/003, December 1991)

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Examples of Completed Region 8 Ecological Risk Assessments

Each ecological risk assessment is unique and must be adapted to the specific requirements and conditions of the site being evaluated. Thus, it is not possible to identify any single approach that is appropriate for all sites. The following sample ecological risk assessments illustrate some of the options and techniques that may be useful.

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