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Ecological Risk Assessment

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This information is provided for Natural Resource Trustees and the general public to facilitate their understanding of the Ecological Risk Assessment (ERA) process. CERCLA Section 104 requires EPA to remediate uncontrolled hazardous waste sites in ways that will protect both human health and the environment. As the first step to fulfill this mandate, the NCP requires that a baseline risk assessment "characterize the current and potential threats to human health and the environment" [40 CFR §300.430 (d)(4)]. The NCP also specifies that "environmental evaluations shall be performed to assess threats to the environment, especially sensitive habitats and critical habitats of species protected under the Endangered Species Act" [40 CFR §300.430 (e)(2)(i)(G)].

ERA has evolved from human health-based risk assessment to include evaluations of impacts to the environment. During the 1980s, risk assessment emerged as a prominent regulatory issue and consideration of ecological impacts began to influence regulatory and policy decisions.  The use of ecological information for decision-making expanded slowly through the 1980s as illustrated by the regulation of diazinon (a pesticide) due to potential impacts on bird populations.   In March 1989, the Agency released Risk Management Guidance for Superfund, Volume 2: Environmental Evaluation Manual, which was among the first documents to address ecological risk (EPA540-/1-89/001).  In 1992, the Agency published the Framework for Ecological Risk Assessment (EPA/63-R-92/001) as the first statement of principles for ERAs.   In April 1998, the Agency published the Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F), which supersedes the 1992 guidance.  These documents describe methods for conducting conventional single-species, chemical-based risk assessments, and techniques for assessing risk to ecosystems from multiple exposures (or stressors) and multiple effects (or endpoints) [ECO Update: Ecological Assessment of Superfund Sites: An Overview. EPA 9345.0-05I. Vol. 1, Number 2, December 1991].

ERAs are most often conducted by EPA during the Remedial Investigation/ Feasibility Study (RI/FS) phase of the Superfund response process. They are used to evaluate the likelihood of adverse ecological effects occurring as a result of exposure to physical (site cleanup activities) or chemical (releases of hazardous substances) stressors, which are defined as any physical, chemical, or biological entities that can induce adverse responses, at a site. These assessments often contain detailed information regarding the contact or co-occurrence of stressors (or agents) with the biological community at a site. Exposure profiles are developed to identify ecological receptors (tissues, organisms, populations, communities, and ecosystems), habitats, and pathways of exposure. The sources and distribution of stressors in the environment also are characterized. Other information contained in ERAs may include evaluations of individual species, populations of species, general trophic levels, communities, habitat types, ecosystems, or landscapes.

What Is Ecological Risk Assessment?

An ERA evaluates the potential adverse effects that human activities have on the living organisms that make up ecosystems. The risk assessment process provides a way to develop, organize and present scientific information so that it is relevant to environmental decisions. When conducted for a particular place such as a watershed, the ERA process can be used to identify vulnerable and valued resources, prioritize data collection activity, and link human activities to their potential effects. ERA results provide a basis for comparing different management options, enabling decision-makers and the public to make better informed decisions about the management of ecological resources.

The framework for ERA is described in the Framework for Ecological Risk Assessment (EPA/63-/R-92/001) and is discussed further in the Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F). The framework consists of three phases (problem formulation, analysis, and risk characterization) with analysis consisting of the following two parts: characterization of exposure and characterization of effects.

Problem formulation involves identifying goals and assessment endpoints, preparing a conceptual model, and developing an analysis plan. An assessment endpoint is an explicit expression of the environmental value (species, ecological resource, or habitat type) that is to be protected. Assessment endpoints relate to statutory mandates (protection of the environment), but must be specific enough to guide the development of the risk assessment study design at a particular site. Useful assessment endpoints define both the valued ecological resource and a characteristic of the resource to protect (reproductive success, production per unit area, areal extent). The conceptual model describes a series of working hypotheses of how the exposures might affect the ecological components of an environment. The ecosystem or ecosystem components potentially at risk and the relationships between assessment and measures of effects and exposure scenarios also are described in the conceptual model. Measures of effects are changes in attributes of assessment endpoints or their surrogates in response to the stressors to which they were exposed. Two additional types of measures are used since data other than those used to evaluated responses (i.e., measures of effects) is often required for an ERA: measures of exposures (which include the stressor and source measurements) and measures of ecosystems and receptor characteristics (which include water quality conditions, soil parameters, and habitat measures). The analysis plan specifies the data required to evaluate the impacts to the assessment endpoints and the methods that will be used to analyze the data.

The analysis phase involves creation of profiles to evaluate the exposure of ecological receptors to stressors and the relationships between stressor levels and ecological effects. Risk characterization is the process of estimating risk through integration of exposure and stressor- response profiles [Guidelines for Ecological Risk Assessment].

The framework for ERA is conceptually similar to the approach used for human health risk assessments, but is distinctive in its emphasis in three areas. First, ERA can consider effects beyond the individual or species level and may examine a variety of assessment endpoints, an entire population, community, or ecosystem. Second, the ecological values to be protected are selected from a wide range of possibilities based on both scientific and policy considerations. Finally, ERAs consider nonchemical stressors to the environment, such as loss of wildlife habitat [Guidelines for Ecological Risk Assessment]. ERA includes the following three general phases: (1) problem formulation, (2) analysis, and (3) risk characterization.

The Superfund Ecological Risk Assessment Process

EPA recently developed new guidance for conducting ERAs within the Superfund Program. This guidance, Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments (EPA 540-R-97-006, 1997), combines scientific methods and stakeholder input into the process for assessing site risks. ERAs conducted specifically for the Superfund Program refer to a qualitative and/or quantitative appraisal of the actual or potential impacts of contaminants from a hazardous waste site on plants and animals other than humans and domesticated species. A risk does not exist unless an exposure has the ability to cause one or more adverse effects, and that exposure co-occurs with or contacts an ecological component long enough and at a sufficient intensity to elicit the identified adverse effect. (See related information on the Superfund Risk Assessment Home Page)

The goal of the ERA process in the Superfund Program is to provide risk information that will assist risk managers at Superfund sites to make informed decisions regarding releases of hazardous substances. The specific objectives of the process are as follows: (1) to identify and characterize the current and potential threats to the environment from a hazardous substance release; and (2) to identify cleanup levels that would protect those natural resources from risk. The ERA process for Superfund is composed of the eight steps summarized below.

Step 1: Screening Level - Problem Formulation and Ecological Effects Evaluation

A problem formulation and ecological effects evaluation is part of this initial step. Though site-specific data will be limited, the following information should be available upon the completion of this step:

  • Description of the environmental setting, including habitat types, observed species and species likely to be present based on habitat types documented, and threatened, rare, and endangered species;
  • Description of contaminants known or suspected to exist at the site and the maximum concentrations present in each medium;
  • Contaminant fate and transport mechanisms that might exist;
  • Mechanisms of ecotoxicity associated with contaminants and categories of receptors that may be affected;
  • Complete exposure pathways that might exist; and
  • Screening ecotoxicity values equivalent to chronic No Observable Adverse Effects Levels (NOAELs) based on conservative assumptions.

Step 2: Screening Level - Preliminary Exposure Estimate and Risk Calculations

In the second step, risk is estimated by comparing maximum documented exposure concentrations with the ecotoxicity screening values developed in Step 1. Based on the outcome, the risk manager will decide either that the screening-level ERA is adequate to determine that ecological threats are negligible, or the process should continue to the more detailed ERA outlined in steps 3 through 7 below.

Step 3: Problem Formulation

Step 3, Problem Formulation, refines the screening-level problem formulation and, with input from stakeholders and other involved parties, expands on the ecological issues that are of concern at the particular site. The results of the screening assessment and additional site-specific information are used to determine the scope and goals of the baseline ERA and form the basis of the conceptual model, which is completed in Step 4. A conceptual model describes a series of working hypotheses of how an exposure might affect the ecological components of an environment.

Step 4: Study Design and Data Quality Objective Process

Step 4 completes the conceptual model, which was initiated in Step 3, by developing the measure of effect. The conceptual model is then used as the basis to develop the study design and data quality objectives (DQOs). The end products of Step 4 are the Work Plan (WP) and the Sampling and Analysis Plan (SAP). The WP documents the decisions and evaluations made during problem formulation and identifies additional research tasks needed to fully evaluate the risks to ecological resources. The SAP provides a detailed description of sampling and data-gathering procedures, as well as a description of the steps required to achieve the study objectives.

Step 5: Verification of Field Sampling Design

In this step, the sampling plan, exposure pathways, and measures of effects, are evaluated to verify that the SAP is appropriate for the site.

Step 6: Site Investigation and Data Analysis

Step 6, Site Investigation and Data Analysis, involves the collection of information to characterize exposures and ecological effects at the site. While much of the data for characterizing potential ecological effects will have been collected during the problem formulation stage, the site investigation provides evidence of existing ecological impacts and additional exposure- effects information response information. Both the site investigation and data analysis should be conducted according to the WP and SAP developed in Step 4.

Step 7: Risk Characterization

The Risk Characterization step integrates the results of the exposure profile and exposure-effects information (or stressor-response analysis), and is the final phase of the risk assessment process. Risk characterization includes two major components, risk estimation and risk description. Risk estimation involves integrating exposure profiles with the exposure-effects information and summarizing the associated uncertainties. Risk descriptions provide information important for interpreting the risk results and, in the Superfund Program, identifies a threshold for adverse effects on the assessment endpoints.

Step 8: Risk Management

The risk assessment should have established whether a risk is present and defined a range or magnitude of that risk. With this information, a site risk manager must integrate the risk assessment results with other considerations to make and justify risk management decisions. Other considerations in making risk management decisions include existing background levels of contamination, available cleanup technologies, and costs of alternative actions and remedy selections.

Ecological Risk Management Decisions at Superfund Sites

In October 1999 the Agency published Ecological Risk Assessment and Risk Management Principles for Superfund Sites (OSWER Directive 9285.7-28P). This final guidance intends to help Superfund risk managers from all regions make consistent ecological risk management decisions based on sound science, and to communicate site risks to the public. It provides risk managers with six principles to consider when making ecological risk management decisions. The guidance specifically declares that all ERAs should be performed according to the eight-step process described in Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments (EPA 540-R-97-006, 1997) and summarized above. The Risk Management Principles supplement the ERA guidance and will help remedial project managers and on-scene coordinators in planning ERAs of appropriate scope and complexity and in identifying response alternatives that are protective of the environment. By adhering to these principles, risk managers will be able to present a clear rationale for their ecological risk management actions as presented to the public in the proposed plan and the Record of Decision steps of the Superfund response process. In addition, the guidance provides a question and answer section to help guide risk managers and assessors through the eight-step ERA process. The guidance asks risk mangers to adhere to the six principles summarized below when scoping ecological risk assessments and when making ecological risk management decisions.

Principle 1: Superfund's Goal is to Reduce Ecological Risks to Levels that will Result in the Recovery and Maintenance of Healthy Local Populations and Communities of Biota

Superfund risk managers and risk assessors should select assessment endpoints and measures that (1) are ecologically relevant to the site and (2) include species that are exposed to and sensitive to site-related contaminants.

Principle 2: Coordinate with Federal, Tribal, and State Natural Resource Trustees

EPA recognizes that its response action may not lead to complete recovery of the ecosystem and that additional restoration activities by Natural Resource Trustees may be needed to bring natural resources back to their baseline condition within an acceptable timeframe. It is important that EPA and Trustees coordinate both EPA investigations of risk and Trustee investigations of resource injuries in order to make efficient use of Federal and State resources.

Principle 3: Use Site-specific Ecological Risk Data to Support Cleanup Decisions

Site-specific data should be collected and used, wherever practical, to determine whether or not site releases present unacceptable risks and to develop quantitative cleanup levels that are protective. Site-specific data includes plant and animal tissue residue data, bioavailability factors, and population- or community-level effect studies.

Principle 4: Characterize Site Risks

When evaluating ecological risks and the potential for response alternatives to achieve acceptable levels of protection, Superfund risk managers should characterize risk in terms of (1) magnitude, (2) severity, (3) distribution, and (4) the potential for recovery of the affected receptors.

Principle 5: Communicate Risks to the Public

Clearly communicate to the public the scientific basis and ecological relevance of the assessment endpoints used in the site risk assessment.

Principle 6: Remediate Unacceptable Ecological Risks

Superfund's goal is to eliminate unacceptable risks due to any release or threatened release. Contaminated media that may affect the ability of local populations of plants or animals to recover and maintain themselves in a healthy state at or near the site should be remediated to an acceptable level.

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