Ecological Risk Assessment for Pesticides: Technical Overview


This site describes the screening-level ecological risk assessment process that the U.S. Environmental Protection Agency (EPA) uses to evaluate the potential impact of pesticides to non-target organisms. A more detailed ecological risk assessment process for pesticides can be found at: Overview of the Ecological Risk Assessment Process.

Before a pesticide can be sold in the United States, EPA evaluates its safety to terrestrial and aquatic animals and plants based on a wide range of laboratory and field studies. These environmental studies, which are conducted mostly by pesticide manufacturers (registrants), examine:

  • ecological effects or toxicity of a pesticide and its breakdown products (degradation products) to various terrestrial and aquatic animals and plants that the pesticide is not intended to kill (non-target species) and

  • chemical fate and transport of a pesticide (how it degrades and where it goes) in soil, air, and water.

After EPA scientists review all the available information on toxicity, chemical fate and transport, and proposed use of a pesticide, they develop the following documents:

  • environmental exposure characterization that estimates the potential exposure of plants, animals, and water resources to pesticide residues in water, food, soil and air. This characterization includes information on how often, how long, and the amount of pesticide to which an organism may be exposed. It is based on environmental fate and transport data as well as modeling and monitoring information.

  • ecological effects characterization that describes the types of effects a pesticide can produce in an organism and how those effects change with varying pesticide exposure levels. This characterization is based on an ecological effects profile (assessment) that describes the available effects (toxicity) information for various plants and animals and an interpretation of available incidents information and effects monitoring data.

Finally, EPA scientists integrate the effects and exposure characterizations into a risk characterization that describes the ecological risk from the use of the pesticide or the likelihood of effects on aquatic and terrestrial animals and plants based on varying pesticide use scenarios.

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Ecological Risk Assessment Process

An ecological risk assessment tells what happens to a bird, fish, plant or other non-human organism when it is exposed to a stressor, such as a pesticide.

In scientific terms, an ecological risk assessment "evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors" (U.S. EPA's 1992 report: Framework for Ecological Risk Assessment). Undesirable events can include injury, death, or decrease in the mass or productivity of aquatic animals (e.g., fish and invertebrates), terrestrial animals (e.g., birds and wild mammals), plants, or other non-target organisms (e.g., insects), including endangered and threatened species.

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Framework for Ecological Risk Assessment

flow chart with components: problem formulation, exposure, effects, risk characterization, data, risk management, discussion with risk managersEPA's Guidelines for Ecological Risk Assessment, April 1998.
(Order 630R95002F (EPA/630/R-95/002F) from the National Service Center for Environmental Publications)

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Problem Formulation Phase

Problem formulation provides the foundation for the ecological risk assessment. It is an iterative process for generating hypotheses concerning why ecological effects occurred from human activities. The problem formulation articulates the purpose and objectives of the risk assessment and defines the problem and regulatory action. The quality of the assessment depends on rigorous development of the following products of problem formulation:

  1. Assessment endpoints that reflect management goals and the ecosystem they represent

  2. Conceptual model(s) that represents predicted key relationships between stressor(s) and assessment endpoint(s)

  3. Plan for analyzing the risk

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Analysis Phase

In this second phase of the risk assessment process, the risk assessors evaluate exposure to stressors (exposure characterization) and the relationship between stressor levels and ecological effects (ecological effects characterization). The risk assessor performs the following tasks:

  1. Selects the data that will be used and determines the strengths and weaknesses of the data

  2. Analyzes the sources of stressors, distribution in the environment, and potential or actual exposure to the stressors

  3. Examines stressor-response relationships and the relationship between measures of effect and assessment endpoints

During these analyses, the scientists evaluate the uncertainties in the exposure and effects characterizations. The products of the analysis phase are two profiles:

  1. Exposure profile based on environmental fate and transport data

  2. Ecological effects or stressor-response profile

The risk assessors and risk managers continue to interact throughout this phase.

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Risk Characterization Phase

The risk characterization is the final phase in which exposure and ecological effects characterizations are integrated into an overall conclusion (risk estimation). In this phase, the risk assessor compares the levels of exposure (estimated environmental concentrations) expected in the field to those levels that produce toxic effects in laboratory tests.

The integrated risk characterization includes the assumptions, uncertainties, and strengths and limitations of the analyses. It makes a judgment about the nature of and existence of risks.

When developing risk characterizations, EPA scientists follow the guidance presented in EPA's Risk Characterization Handbook (PDF) (189 pp, 2.08 MB, About PDF).

Risk assessors and risk managers continue their dialogue throughout this phase. After this phase is completed, risk assessors formally communicate and discuss their results with risk managers. In addition to the risk assessment report, risk managers consider other information, such as social, economic, political, and legal issues, in their decisions.

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Next Section: Problem Formulation