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3
Revision of 1983 Framework To Incorporate Ecological Risk Assessment
COMPONENTS OF THE 1983 FRAMEWORK
Risk Assessment in the Federal Government: Managing the Process (NRC, 1983), often called the "Red Book," proposed a conceptual framework for risk assessment that incorporates research, risk assessment, and risk management (Figure 3-1). Risk assessment was defined as "the characterization of the potential adverse health effects of human exposures to environmental hazards." The overall scheme and terminology proposed in the 1983 report entailed hazard identification, dose-response assessment, exposure assessment, and risk characterization. Hazard identification was defined as "the process of determining whether exposure to an agent can cause an increase in the incidence of a health condition," including "characterizing the nature and strength of the evidence of causation.'' Dose-response assessment was defined as "the process of characterizing the relation between the dose of an agent administered or received and the incidence of an adverse health effect … as a function of human exposure to the agent," accounting for exposure intensity, age, sex, lifestyle, and other variables affecting human health responses to hazardous agents. Exposure assessment was defined as "the process of measuring or estimating the intensity, frequency, and duration of human exposures to an agent currently present in the environment or of estimating hypothetical exposures that might arise from the release of new chemicals into the environment." Risk characterization was defined
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FIGURE 3-1 Elements of risk assessment and risk management.
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as "the process of estimating the incidence of a health effect under the various conditions of human exposure described in exposure assessment. It is performed by combining the exposure and dose-response assessments. The summary of effects of the uncertainties in the preceding steps are described in this step."
The 1983 report further defined points in the risk assessment process ("components") where inferences must be made and scientifically plausible options ("inference options") from which a risk assessor must choose regarding those components. The report did not, however, include in-depth discussion of scientific issues in health risk assessment. The 1983 committee's objectives were limited to addressing institutional and procedural issues: whether the analytic process of risk assessment should be cleanly separated from the regulatory process of risk management, whether a single organization could be designated to perform risk assessments for all regulatory agencies, and whether uniform risk assessment guidelines could be developed for use by all regulatory agencies. The general framework for health risk assessment developed by the 1983 committee (Figure 3-1) was intended to define the boundaries between risk assessment and risk management and to facilitate the development of uniform technical guidelines. The committee recommended that a board on risk assessment methods be established and assigned the tasks of assessing the scientific basis of risk assessment, establishing inference guidelines, evaluating agency experiences with risk assessment, and identifying research needs in risk assessment.
CONSISTENCY OF CASE STUDIES WITH THE 1983 FRAMEWORK
Most of the case studies fit reasonably well into the 1983 framework, although the relative emphasis on the four components of risk assessment varied considerably among the studies. The three case studies dealing with environmental chemicals provided the most obvious fits. All three included discussions of hazard identification, defined as determination of the physical, chemical, and toxic effects of the substances or stresses being examined. They differed substantially in their balance between data and models, but a fairly clean distinction could be drawn between exposure assessment (patterns of contamination in time and
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space, exposure, and doses) and dose-response assessment (quantitative relation of exposures to toxic effects).
The Georges Bank study appeared to be the most complete of the six. The determination of the qualitative effects of fishing on population and community dynamics is clearly analogous to the determination of contaminant effects and can legitimately be called "hazard identification." Estimates of fishing effort and models of the responses of populations to exploitation are equivalent to exposure and dose-response assessment of chemicals. The expression of outcomes in terms of likely future population sizes and yields carries risk characterization several steps further than was done in any of the contaminant studies.
The spotted owl study focused on only one aspect of the assessment process: estimation of basic demographic characteristics of spotted owl populations. However, other published work on the spotted owl (Dawson et al., 1986; Salwasser, 1986) available to the committee relates forest-cutting patterns to population dynamics and clearly includes exposure and dose-response assessments in the sense in which these terms are used in the Red Book framework.
The species introduction case study does not appear at first to fit the standard definition of a risk assessment. No scientific principles or decision criteria were presented at the workshop, although theoretical work was described in some of the breakout sessions. The consensus among participants in the workshop was that the procedure used by the U.S. Department of Agriculture (USDA) to evaluate proposed species introductions is not risk assessment. The committee believes, however, that USDA's process fits within the general definition of hazard identification as presented in the 1983 report. The objective appears to be to collect enough information to determine whether a proposed introduction constitutes a hazard to the environment. If no hazard is found, the introduction proceeds. The USDA process might more accurately be described as safety assurance.
One weakness in all the case studies was inadequate risk characterization. Only one of the case studies, the Georges Bank study, included any quantification of risks in terms that could be used for risk-benefit calculations, valuation studies, or other quantitative comparisons applicable to decision-making. Even in this case, the value of the assessment to decision-making is uncertain. During the plenary discussion, the author of the study emphasized that communication between scientists
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and managers is still inadequate and that fisheries management actions are often only marginally influenced by quantitative assessments.
The committee notes that risk characterization is the least-developed component of the 1983 framework. In the 1983 report, risk characterization is defined simply as an integration of exposure and dose-response information. It seems clear from the 1991 workshop that effective ecological risk characterization is more than an exercise in arithmetic. Many of the results presented at the workshop have no immediate relevance to decision-making and mean little or nothing to the public. The procedure used in pesticide registration, as described in the agricultural chemical case study, provides an excellent example. The method used is to compare doses that cause death or impairment of standard test birds with estimated exposures in typical applications. On the basis of the comparison, the risk manager is expected to make a decision about the environmental acceptability of the pesticide being considered. No attempt is made to account for interspecies differences, to assess the threat to the viability of wild avian populations, to estimate the fraction of the landscape that might be affected, or to quantify the value of the wildlife that might be lost.
Ecological risk assessments have no equivalent of the lifetime cancer risk estimate used in health risk assessment. The ecological risks of interest differ qualitatively between different stresses, ecosystem types, and locations. The value of avoiding these risks is not nearly as obvious to the general public as is the value of avoiding exposure to carcinogens. Because few risk managers are trained as ecologists, effective communication between risk managers and technical staff is essential in sound risk management decisions.
Approaches to hazard identification exemplified in the case studies were, on the other hand, substantially more diverse and in some cases more sophisticated than envisioned in the 1983 framework. The 1983 definition of this component was limited to scientific inferences about whether specific effects, such as cancer, were causally associated with specific chemical substances. Identification of ecological hazards also includes identification of specific species or ecosystems of interest, delineation of study areas, and determination of types of laboratory or field data on which an assessment will be based. These decisions reflect both scientific considerations (which systems are vulnerable? what kinds of effects are possible?) and management considerations (which species
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or ecosystems are to be protected? must costs be weighed against benefits? is the objective to protect the resource or to optimize exploitation of the resource?). The committee agrees with the consensus from the workshop that the initial phases of an ecological risk assessment involve a consideration of regulatory/legal mandates that goes well beyond the definition of hazard identification presented in the 1983 report.
INTEGRATION OF ECOLOGICAL RISK INTO THE 1983 FRAMEWORK
The committee believes that integration of ecological risks into the 1983 risk assessment framework is preferable to developing a de novo ecological risk assessment framework. Like health risk assessment, ecological risk assessment must be defined in broad terms if it is to be applicable to the full array of environmental problems that regulatory and resource management agencies must address. Moreover, any framework chosen for ecological risk assessment must be simple, flexible, and general, so that it will be understood by both scientists and the risk managers with whom scientists must communicate. The 1983 framework, by any measure, has been extraordinarily successful in communicating the broad features of health risk assessment throughout the scientific and regulatory communities. Although ecological risk assessment and human health risk assessment differ substantially in terms of scientific disciplines and technical problems, the committee believes that the underlying decision process is the same for both. The function of risk assessment is to link science to decision-making, and that basic function is essentially the same whether risks to humans or risks to the environment are being considered. Finally, the committee believes that prospects for integration of human and ecological concerns into comprehensive environmental policies protective of both will be enhanced if a common framework and terminology can be found that describes both kinds of risk assessments.
The committee agrees with the consensus at the workshop that the framework defined in the 1983 report is inadequate as written for application to ecological problems because the framework (1) does not account for legal mandates and other policy considerations that substantially influence the initial stages and focus of ecological risk assessments
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and (2) pays insufficient attention to the critical problem of effective communication with risk managers and the public. The opinion of the committee, however, is that these deficiencies are not unique to ecological risk assessment. Differences in the functions of different regulatory agencies clearly influence the types of data and inference guidelines used in health risk assessments, and effective risk communication is as important (and often as inadequately performed) in health as in ecological risk assessment.
DEFINITION OF FRAMEWORK COMPONENTS FOR ECOLOGICAL RISK ASSESSMENT
Hazard identification is redefined to be the determination of whether a particular hazardous agent is associated with health or ecological effects that are of sufficient importance to warrant further scientific study or immediate management action.
This change in definition is intended to account for the influence of regulatory mandates and other policy considerations on the conduct of risk assessments. Examples of such influences are restrictions on data acquisition or response time (e.g., premanufacture notification assessments under the Toxic Substances Control Act), standardized data requirements and regulatory criteria (pesticide registration under the Federal Insecticide, Fungicide, and Rodenticide Act), and the scoping provisions of the National Environmental Policy Act. Other aspects of hazard identification, such as investigation of cause-effect relationships and preliminary screening, would remain essentially unchanged.
Exposure-response assessment is defined as the determination of the relation between the magnitude of exposure and the probability of occurrence of the effects in question. Replacement of the term "dose" with a more general term is required, because "dose" has a distinctly medical connotation and cannot be effectively applied to nonchemical stresses, such as habitat change or harvesting. The "responses" addressed in ecological risk assessments include direct effects of exposure and the much broader indirect effects, such as secondary poisoning of raptors due to accumulation of pesticide residues in their prey and effects of harvesting on fish-community structure.
Exposure assessment is defined as the determination of the extent of
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exposure to the hazardous agent in question before or after application of regulatory controls. In the committee's view, the term "exposure" can legitimately be applied to nonchemical stresses, including physical stresses (such as habitat and UV radiation) and biological stresses (such as species introductions). The committee considered changes in terminology on the grounds that the term "exposure" is too closely associated with chemical risks. However, the alternative terms discussed (e.g., stress and stressor) were unsuitable because of conflicts with medical uses of the same or similar terms.
Risk characterization is defined as the description of the nature and often the magnitude of risk, including attendant uncertainty, expressed in terms that are comprehensible to decision-makers and the public. Extension of the definition provided in the 1983 report is needed to permit more explicit discussion of uncertainty, to facilitate expression of risks in management-relevant terms (including valuation), and to emphasize the importance of communication between scientists and managers. The committee believes that improved communication is as important for health risk assessment as it is for ecological risk assessment.
The revised framework is summarized in Figure 3-2. The relationships among the four components are unchanged from the Red Book: hazard identification is the initial step in an assessment. Exposure assessment and exposure-response assessment occur roughly in parallel and must be closely linked. The arrangement of those components in Figure 3-2, within a single box divided in half by a "permeable membrane," is intended to emphasize the ties between them. Risk characterization synthesizes the results of technical analyses and expresses them in a form suitable for valuation studies or other policy analyses that are carried out as part of risk management.
In addition to the four basic components, Figure 3-2 depicts two aspects of risk assessment that the committee wants to emphasize. As previously noted, it is essential to recognize that management considerations (e.g., regulatory constraints on the scope or time available for an assessment or legally prescribed definitions of acceptable or unacceptable uses) can shape the hazard identification step. The committee would also like to emphasize the need to create a connection between the results of today's risk assessments and the science base for future risk assessments. The risk assessment process should not end when a regulatory decision is made. Followup in the form of monitoring (where
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FIGURE 3-2 Extension of the 1983 NAS risk assessment paradigm to include ecological as well as human health risks.
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measurable effects have been predicted), validation studies, and basic research are needed to improve the data and models available to technical risk assessors whenever the same or a similar problem is encountered in the future.
Representative terms from entire chapter:
hazard identification
