International Association for Impact Assessment

Risk Assessment in EIA

Edited By: Bridget

Overview & History

The fundamental principles associated with risk assessment studies were enunciated in the 1970s, with the planning and conduction of such studies moving toward maturity in the subsequent decades. Early risk assessments focused on human health and traditionally encompasses components on hazard (risk) identification, dose-response assessment, exposure assessment, and risk characterization. Environmental impact assessment (EIA) studies were also initiated in the 1970s, with their primary focus in the initial decade toward impacts on physical/ chemical and ecological components of the environment. Human health risks were often not addressed or only marginally considered in EIA studies; however, water resources development project EIAs in developing countries often focused on disease transmission and resultant health impacts as a consequence of construction worker carriers and the enhancement of mosquito breeding conditions.

Risk assessment studies in many countries were initially directed toward regulatory issues such as establishing environmental quality standards, and on the carcinogenic effects of synthetic chemicals on humans. In more recent years the emphases have been expanded toward ecological risks and noncarcinogenic effects on humans. Adaptations of classical risk assessment studies have also been directed toward environmental problem assessments and remediation needs. Remedial action programs for uncontrolled hazardous waste sites, called Superfund sites in the United States, have incorporated risk assessment principles in the comparison of alternatives and decision making associated therewith.

Increased attention is now being given to ecological risks in relation to contaminant assessments and environmental management programs. Ecological risk assessment has been defined as a process that evaluates the probability or likelihood that adverse ecological effects will occur (or have occurred or are occurring) as a result of exposure to stressors from various human activities. Such effects can occur on non-human ecological components ranging from organisms, to populations and communities, to ecosystems. Stressors can be chemical, physical, biological, or radiological in nature, with the major portion of current interest related to the use and/or current or previous disposal of industrial chemicals or pesticides. A given ecological risk assessment study could be narrow (one ecological component, one stressor, and one human activity) or comprehensive (multiple ecological components, multiple stressors, and multiple activities).

Both human health risk assessment and ecological risk assessment within the EIA process can be accomplished using one to several of the following approaches: 

(1) addressing actual or perceived risks using a descriptive or qualitative approach;

(2) calculation or determination of a relative risk index based on information on several selected factors;

(3) relative comparisons of the perceived risks of the alternatives being evaluated; and/or

(4) a quantitative, probabilistic approach focused on actual risks of the alternatives being evaluated.

Risk assessment considerations can include human health and/or ecological risks, and combinations thereof. Such considerations can be focused on only one aspect of the project being addressed (e.g., use of pesticides in vegetation management), or on one phase (e.g., construction or operation or decom-missioning), or on the entirety of all aspects and phases.

It is timely to incorporate risk assessment tools in the EIA process. The possibilities range from the determination of relative risk indices for single issues such as the choice of pesticides or herbicides in forestry or range management plans, to the use of environmental pathways modeling and risk calculation for industrial plant and/or waste site emissions, to the use of quantitative probabilistic calculations for industrial or power plant accidents or for highway/railway accidents and associated chemical spills. The potential benefits of the inclusion of risk assessment include: 

(1) the encouragement for integrated thinking (such as for environmental transport pathways and associated health/ecological effects) by the interdisciplinary teams conducting EIA studies;

(2) the opportunity to focus attention on risk reduction activities such as waste minimization, pollution prevention, and mitigation measures; and

(3) the inclusion of emphases on emergency response measures in the event of accidents and associated environmental perturbations.


Special thanks to Larry Canter for providing initial content for this IAIA Wiki topic.

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