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Issues in Risk Assessment
should be comprehensive, detailed, and flexible enough "to consider unique scientific evidence in particular instances." Finally, the 1983 report recommended establishment of a "Board on Risk Assessment Methods." Some of the suggested functions of the board are now being carried out by CRAM.
Michael Slimak: U.S. Environmental Protection Agency Activities In Ecological Risk Assessment
Michael Slimak, deputy director of EPA's Office of Ecological Processes and Effects Research, presented an overview of EPA's past and present activities in ecological risk assessment. Dr. Slimak identified five major problems that have made these assessments difficult to perform in a consistent way:
The need to consider multiple species and levels of biological organization;
The diversity and multiplicity of end points (e.g., mortality and biochemical cycling);
The simultaneous actions of multiple stressors, such as pollution and habitat loss;
The difficulty of relating ecological changes to societal values;
The multiplicity of regulatory mandates under which EPA operates.
Dr. Slimak defined ecological risk assessment as a "probabilistic statement of the 'outcome' [effects] associated with an ecological receptor being exposed to some form of stress." He then described some of the agency's approaches to assessing exposures and outcomes, focusing on two generic classifications: predictive or "bottom-up" assessments for single chemicals, as exemplified by the regulation of pesticides and toxic chemicals, and holistic or "top-down" assessments, such as assessments of wetland loss, effects of acid deposition, and global climate change. Most of EPA's attention has been devoted to predicting ecological effects of single chemicals from laboratory toxicity-test data. Although relatively elaborate guidelines and procedures have been developed for this purpose, the predictive approach has inherent weaknesses
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that have long been recognized. Recently, water quality regulation has moved toward a top-down approach based on measurement of community integrity from field data.
Many of the problems facing EPA are not amenable to the predictive approach, either because they involve stresses other than toxic chemicals or because they involve direct observation of adverse ecological changes. Examples discussed by Dr. Slimak include explanation of dolphin-stranding incidents, a reported worldwide amphibian decline, and performance of ecological assessments at Superfund sites. Such studies involve difficult scientific problems. The National Acidic Precipitation Assessment Program's assessment of the relationship of sulfur dioxide deposition to aquatic resource quality (NAPAP, 1991) best demonstrates problems encountered by EPA.
For the last 5 years, EPA has been conducting an ecological risk assessment research program focused on developing better predictive models for single-chemical assessments. A major new initiative, the Environmental Monitoring and Assessment Program (EMAP), will attempt to measure ecosystem quality on regional and national scales through a nationwide monitoring program. The results will be used to determine the success of EPA's regulatory programs and to support future risk assessments.
The EPA Risk Assessment Forum has initiated the development of guidelines for ecological risk assessment analogous to the existing guidelines for health risk assessment. A series of risk assessment colloquia was held during 1990. The proceedings were summarized and published in early 1991 in a report entitled Issues in Ecological Risk Assessment . A "framework document," intended to provide the conceptual basis for detailed guidelines, is now being reviewed (EPA, 1992a). A strategy for subject-specific guidelines structured around ecosystem types, levels of biological organization, end points, and stressors is being developed simultaneously. Case studies illustrating current practice are being developed and a report containing case studies will be announced in the Federal Register (EPA, 1992b).
Dr. Slimak closed his presentation by raising issues for consideration at the CRAM workshop:
The amenability of ecological risk assessments to biostatistical treatment;
End point identification and selection;
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Ecological values;
The relationship of the 1983 paradigm to regulatory processes;
The relationship between risk assessment and risk management.
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Issues in Risk Assessment
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