Ecological Risk Assessment

An ecological risk assessment is an approach at understanding environmental problems that uses a fundamental research approach. The goal is to evaluate actual and predicted effects of contaminants on animal and plant populations and their habitats or communities. In ecological risk assessment the impact of contaminants on humans and domestic animals is not considered. The phases of an ecological risk assessment are: problem formulation, analysis, and risk characterization. The analysis phase includes development of an exposure assessment and development of an ecological effects assessment.

Problem Formulation, also known as Response Assessment, begins with the recognition that there is something wrong in the environment. Some evidence that the quality of life or ecological health is "not what it should be" is noted, such as when recreational fishers note that the number of fish caught is declining. This response leads to a review of existing data about the affected site. It identifies the characteristics of the contaminant, the ecosystem at risk, and the effects to the ecosystem. During this phase particular parts (types of plants or animals) of the ecosystem are identified for analysis and the measurements (expected response) are established.

The Analysis Phase includes an exposure assessment and an ecological effects assessment. An exposure assessment identifies and quantifies stressors that are causing the problem by examining physical and chemical measurements and observing biotic indices (key species that indicate the health of a particular ecosystem). Human activities that might affect the environment are also considered. When the stressor is a contaminant, the movement of the contaminant through the environment helps identify the receptors (species) that are exposed and the concentrations of exposure. The susceptibility of a receptor to a contaminant is determined by: properties of the contaminant, the route of exposure into the organism (absorption, ingestion, inhalation) and the behavior and patterns of the receptor.

The ecological effects assessment links the concentrations of contaminants to adverse effects in receptors. This toxicity testing is sometimes known as the "dose-response" curve. It is a measure of the amount of the contaminant and the degree of effect. Field studies can provide evidence of the link between these two factors. Toxicity tests can evaluate the effects of the contamination on the survival, growth and reproduction of the organisms.

Risk characterization compares the results of the exposure assessment with the results of the ecological effects assessment. The conclusions lead to a numeric probability of harm. The severity is described along with the degree of uncertainty of these conclusions. The risk is described numerically and descriptively.

For the other risk-related pages, please see:

  • Steps of Assessment. This page describes detailed descriptions of the steps in risk assessment, with emphasis on human health risk assessment.
  • Risk Assessment Standards This page provides a discussion on standards for risk assessment based on the American Society for Testing and Materials.
  • Risk Management This page provides information about plans for managing and/or preventing risk.
  • Risk Communication This page provides information about communicating with communities facing contaminated sites.
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