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
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
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