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Initiative to Revise the Ecological Assessment Process for Pesticides
About Ecological Risk Assessment
This site describes the assessment process that the U.S. Environmental Protection Agency (EPA) uses to evaluate the potential impact of pesticides to non-target organisms. 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:
environmental exposure characterization that estimates the potential exposure of plants, animals, and water resources to pesticide residues in water, food, 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.
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.
This assessment process combines all the information from the toxicity tests (ecological effects), the exposure information, assumptions, and uncertainties in a way that helps the risk assessor understand the relationships between the ecological effects and the stressors (pesticides) and helps support decision-making.
In determining whether a pesticide will harm the environment and wildlife, EPA conducts an ecological risk assessment for each pesticide active ingredient and major degradation products.
Ecological risk assessment consists of three major phases: problem formulation, analysis, and risk characterization. These three phases are described in the following section under Framework for Ecological Risk Assessement.
In developing its ecological risk assessments, the Office of Pesticide Programs follows the framework that was developed by EPA's Risk Assessment Forum. This framework can be found in EPA's February 1992 report Framework for Ecological Risk Assessment, which was later updated as the Agency's Guidelines for Ecological Risk Assessment (April 1998).
For most risk assessments, EPA uses a deterministic approach or the quotient method to compare toxicity to environmental exposure. In the deterministic approach, a risk quotient (RQ) is calculated by dividing a point estimate of exposure by a point estimate of effects. This ratio is a simple, screening-level estimate that identifies high- or low-risk situations.
Calculation of risk quotients are based upon ecological effects data, pesticide use data, fate and transport data, and estimates of exposure to the pesticide. In this method, the estimated environmental concentration (EEC) is compared to an effect level, such as an LC50 ( the concentration of a pesticide where 50% of the organisms die.)
With the publication of the "EPA Framework for Ecological Risk Assessment" and subsequent guidance from the Scientific Advisory Panel (SAP), EPA has moved towards developing new, more sophisticated methodologies for conducting probabilistic or refined risk assessments (RRA).
In a refined risk assessment, EPA incorporates probabilistic tools and methods to predict the magnitude of the expected impact of pesticide use on non-target organisms as well as the uncertainty and variability involved in these estimates.
A refined or probabilistic risk assessment produces a distribution or range of values instead of one fixed value. The assessment becomes more refined as the levels increase, presenting increasingly focused effects and exposure scenarios. Because the results of the refined risk assessment show the range of possible environmental impacts and which ones are most likely to occur, they provide a better basis for decision-making.