Framework

Drs. Gentile and Harwell were leaders in the development of the US Environmental Agency’s framework for ecological risk assessment.  The concept of risk assessments became an organizing principle for US EPA in the mid-1980s, following the approach developed by the National Research Council’s panel on cancer risks to people from chemical exposures, known as the “Red Book” (NRC 1983).  The NRC framework combined hazard (the inherent ability of a chemical to cause harm) and exposure (the amount of chemical experienced by humans) into a probabilistic assessment of health risk.  However, it soon became apparent that this framework was inadequate to deal with ecological risk issues, for several reasons: a) there are many different types of ecological systems; b) each ecosystem has its own specific attributes of importance; and c) there are many different stressors, both natural and anthropogenic, where stressors are defined as any chemical, physical, and biological change that could affect an ecological system.  Thus, the NRC approach, which was designed to deal with only one system (humans) and one stressor (toxic chemicals) and one endpoint (cancers), was insufficient to address the complexities of ecological problems. 

Drs. Harwell and Gentile led a workshop of several dozen scientists from academia and government to develop the new ecorisk framework for US EPA (Harwell and Gentile 1992; Gentile et al. 1993). The central elements of this paradigm are: problem formulation, stress regime characterization, ecological effects characterization, analysis, and risk characterization.

Problem formulation identifies the stress regimes, ecosystem components of interest, selects ecological endpoints, and develops a conceptual model of stress-response relationships. Stress regime is more than exposure because it includes natural physical variability and time/space patterns of multiple natural and anthropogenic stressors.  A stressor is defined as any chemical, physical, or biological change that can affect an ecosystem.  Ecological effects characterization is more complicated than hazard because of the inherent diversity of ecosystems and extreme range of scales (time/space) that simultaneously operate in ecosystems.  Thus, evaluating ecological health requires a suite of ecological endpoints spanning organizational scales (species, population, community, ecosystem, and landscape) (Harwell et al. 1990).  The analysis phase is for development and testing of models, experiments, and data analyses to evaluate these relationships. Risk characterization  integrates stress and effects into a predictive and probabilistic statement of the risks and uncertainties which is used along with societal and economic factors by the decision-maker.

Harwell Gentile & Associates, LC, has applied this ecological risk assessment framework to several large-scale ecological risk assessments.  For example, we conducted two comparative risk assessments to evaluate the relative risks of spills of fuel oil vs. the emulsion fuel Orimulsion on Tampa Bay, Florida, and the Bay of Fundy, New Brunswick, Canada.  The comparative approach allowed decision-makers to see the ecological risk reductions associated with conversion of existing power plants to Orimulsion.  Another major ecological risk assessment has involved the Coeur d’Alene River basin, for which HGA developed a series of conceptual models to characterize the ecosystem and the exposure and effects risks from high levels of toxic metals resulting from mining operations. 

References Cited

Gentile, J.H., M.A. Harwell, W. van der Schalie, S. Norton, and D. Rodier.  1993. Ecological risk assessment: a scientific perspective. J. Hazardous Materials 35: 241-253.

Harwell, Mark A. and Jack Gentile.  1992.  Report of the EPA Ecological Risk Assessment Guidelines Strategic Planning Workshop, Miami, FL, May 1991.  US Environmental Protection Agency, Risk Assessment Forum, Washington, DC.

National Research Council (NRC). 1983. Risk Assessment in the Federal Government. National Academy Press, Washington, DC.

 

 

Conceptual Models

Conceptual models are used to illustrate the linkages among management (societal) actions, environmental stressors, and societal and ecological effects and provide the basis for developing and testing causal hypotheses.  These models, developed for a variety of landscape units and their drivers, stressors, and endpoints, are used to formulate hypotheses to explain historic, current, and future conditions.  They are also used as the basis for structuring management scenarios and analyses to project the temporal and spatial magnitude of risk reduction and system recovery.  Within the context of recovery, the conceptual models are used in the initial development of performance criteria for those stressors that are determined to be most important in shaping the landscape and to guide the use of numerical models used to develop quantitative performance criteria for scenario analyses.  The results are discussed within an ecosystem and adaptive management framework that provides the foundation for decision-making.

For more information see: Conceptual Model Development

 

© HGA, LC  2006-2007

 

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