Ecological risk assessment is a broad framework for estimating the likelihood and severity of potential impacts to the structure, functioning, components or processes of ecological systems (ecosystems); such assessments are used routinely by many countries. Typically, these assessments follow the general ecotoxicology paradigm, identifying and assessing the exposure--and effects of--human and other populations to such stressors as contaminants or pathogens or habitat change. The approach has been formalized by the United States’ Environmental Protection Agency among other bodies. Significantly, the approach applies equally well to analysis of the potential ecological effects of invasive species and biological control agents.
Ecological Risk Terms
Here are some important terms in ecological risk assessment:
- Hazard: A situation that could potentially lead to ecological harm.
- Stressor: The component or components of a system that may lead to a hazard or undesirable outcome.
- Receptor: The component or components of a system that may be negatively influenced by a stressor.
For example, non-target impacts are a possible hazard from the introduction of biological control agents. In this case, the population of biological control agent itself is the stressor, and the non-target species of concern are the receptors.
Pollutant risk assessments are always directed at such particular assessment endpoints as response of growth or fecundity to toxicity. These endpoints are focused typically on effects of chemical contaminants on individuals. However, since the scale of impacts of interest are usually population-level effects (i.e., changes in abundance), ecological models are often used to perform the necessary extrapolation from the measurement endpoint (e.g., a toxic, teratogenic or developmental effect) to the assessment endpoint (the ecological characteristic or feature that is to be protected from risk, such as the abundance of some sensitive species).
Phases of Ecological Risk Assessment
There are four phases recognized in the process of ecological risk assessment, as follows:
- Problem formulation: In this phase, one identifies the features of the system, the stressors and receptors present in the system, and the endpoints that will be considered. In addition, one must carefully formulate a conceptual model of the system, and specify questions and objectives.
- Exposure analysis: In this phase, the mechanisms of contact between stressor(s) and receptor(s) are characterized, and the magnitude and frequency of contact are assessed. The result of this phase is a quantitative estimate of the probability of some harm being done. For many risk assessments, exposure analysis will include a GIS component or some other spatially-explicit analysis.
- Effects analysis: In this phase, the effects of stressors on receptors are estimated, often based on such endpoints as toxicity thresholds or exposure-response relationships. The result of this phase is a quantitative estimate of the severity of the harm that might arise. Also, the effects analysis phase includes the process of hazard identification, and may conclude with hazard identification for some types of discrete endpoints.
- Risk characterization: Finally, the effects and exposure analyses are integrated to obtain an estimate of the probability of a negative effect on the receptor. In addition, it is important to assess uncertainty, confidence in the results, the ecological significance of any risks identified, and future information (that is. the results of stated research) needs.
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- Walker, R., W. G. Landis, and P. Brown. 2001. Developing a regional ecological risk assessment: A case study of a Tasmanian agricultural catchment. Human and Ecological Risk Assessment 7:417-425.