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EPA EcoBox

EPA EcoBox Tools by Receptors - Receptors in ERA

Planning and Problem Formulation Phase: Identifying Receptors of Concern

During the planning and problem formulation phase, potential ecological receptors are identified. Identification of receptors arises from a review of the fate, migration, and potential release of stressorsHelpstressorsAny physical, chemical, or biological entity that can induce an adverse response (synonymous with agent). in terrestrial and aquatic environments (U.S. EPA, 1991). Selection of receptors is a component of establishing the “assessment endpointsHelpassessment endpointsAn explicit expression of the environmental value to be protected, operationally defined as an ecological entity and its attributes.” and “measures of effectHelpmeasures of effectA change in an attribute of an assessment endpoint or its surrogate in response to a stressor to which it is exposed.” in the study design. Assessment endpoints include two elements: identification of the specific receptor that is to be protected (e.g., species, community, ecosystem), and a characteristic about the receptor of concern that is important to protect (e.g., survival, growth, reproduction) (U.S. EPA, 1998). See the Phases of ERAs Tool Set of EPA EcoBox for additional discussion and tools related to the planning and problem formulation phase of ERA. See the Stressors Tool Set of EPA EcoBox for identifying and evaluating stressors.

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Analysis Phase: Characterizing Exposures and Effects to Receptors

After identifying potentially exposed receptors, risk assessors can focus on receptors known or likely to occur in a particular habitat (U.S. EPA, 1991; 1998). During the analysis phase—which comprises exposure assessment and effects assessment—exposure pathways and receptors likely to be exposed to stressors are characterized, exposure levels are measured or estimated, and effects for each stressor/receptor combination likely to occur are characterized. There may be a large number of different ecological receptors present at a site, and it is generally not feasible or practicable to evaluate risk quantitatively for each receptor. Instead, a limited number of receptors might be selected based on the endpoints of concern and specific characteristics of the area being studied (U.S. EPA, 2008). Ideally an ERA will have representative organisms from multiple trophic levelsHelptrophic levelsEach step along a food chain; an organism's feeding level.. See the Exposure Pathways (Media) and Effects Tool Sets for information on characterizing exposure pathwaysHelpexposure pathwaysThe physical course a chemical takes from the source to the organism exposed. and potential effects to receptors in an ERA.

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Risk Characterization: Quantifying Effects to Receptors and Exposure Factors

The risk characterization phase quantifies the links between exposure and effects to ecological receptors and characterizes the types, extent, and severity of these risks (U.S. EPA, 1991; 1998). Uncertainties associated with potential receptor risks are also described. The stressor-effects assessment relates stressor levels to effects on ecological receptors using documented known effects that may be based on a literature review, toxicity tests, and/or field studies. Effects to ecological receptors might include altered survival, growth, reproduction, or development. See the Effects Tool Set for details on estimating risks to ecological receptors in an ERA.


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Resources that provide information related to receptors and exposure factors in ecological risk assessments are provided below.

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