In 1989, the Committee on Risk Assessment Methodology was convened within the Board on Environmental Studies and Toxicology of the Commission on Life Sciences, National Research Council (NRC) to identify and investigate important scientific issues in risk assessment. The committee was asked to consider changes in the scientific foundation of risk assessment that have occurred since the 1983 report, Risk Assessment in the Federal Government: Managing the Process, and to consider applications of risk assessment to noncancer end points.
This report addresses one of the first issues selected by the committee: The development of a conceptual framework for ecological risk assessment, defined as the characterization of the adverse ecological effects of environmental exposures to hazards imposed by human activities. Adverse ecological effects include all environmental changes that society perceives as undesirable. Hazards include unintentional hazards, such as pollution and soil erosion, and deliberate management activities, such as forestry and fishing, that often are hazardous either to a managed resource itself or to other components of the environment. The committee believes that a general framework analogous to the human health risk assessment framework described in the NRC's 1983 report is needed to define the relationship of ecological risk assessment to environmental management and to facilitate the development of uniform technical guidelines. A framework for ecological risk assessment could, for example, be used for the following:
Evaluation of the consistency and adequacy of individual assessments.
Comparison of assessments for related environmental problems.
Explicit identification of the connections between risk assessment and risk management.
Identification of environmental research topics and data needs common to many ecological risk assessment problems.
Ecological risk assessment is an extraordinarily diverse field whose practitioners include ecologists, fish and wildlife biologists, toxicologists, and pollution-control engineers. Many of the practices in these different fields have grown somewhat independently for many decades, and it was not clear to the committee whether diverse traditions could be united by a common conceptual framework. The committee chose to investigate the feasibility issue by conducting a workshop in which six case studies representing different types of current assessments would be examined with respect to their consistency with a common framework. The six case studies were:
Assessing the effects of tributyltin on Chesapeake Bay shellfish populations.
Testing agricultural chemicals for effects on avian species.
Predicting the fate and effects of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).
Quantifying the responses of northern spotted owl populations to habitat change.
Regulating species introductions.
Harvesting the Georges Bank multispecies fishery.
A workshop on ecological risk assessment was held on February 26-March 1, 1991, at Airlie House, Warrenton, Virginia. The workshop summary (Appendixes C-H) contains summaries of the plenary presentations, case studies and discussions, and breakout sessions. The workshop summary provides much of the supporting information for the conclusions and recommendations presented.
A consensus emerged at the workshop that an ecological version of the 1983 framework is desirable and feasible, but no specific endorsement of a particular framework was sought or obtained. Workshop
participants noted several deficiencies in the 1983 framework that prevent direct application to ecological risk assessment. On reviewing the written materials produced at the workshop, the committee concluded that those deficiencies are relevant to health risk assessment as well. The committee chose to respond by modifying the 1983 framework to account for these perceived deficiencies. The committee believes that with modifications, a single framework can accommodate human health and ecological risk assessment.
The committee was not charged with conducting an in-depth analysis of scientific issues in ecological risk assessment or to recommend specific technical guidelines. Many such issues were identified at the workshop, and discussion summaries included in Appendices C-H should provide valuable material for future expert committees charged with evaluating the scientific basis of ecological risk assessment and developing inference guidelines.
Chapter 2 of this report defines the broad uses of ecological risk assessment and its relevance to environmental decision-making at the levels of the individual program, the agency, and society at large. Chapter 3 presents the unified health/ecological risk assessment framework developed by the committee. Chapter 4 highlights key scientific problems limiting the application of ecological risk assessment. The committee's conclusions and recommendations are presented, respectively, in chapters 5 and 6.
For readers interested in further information on topics discussed in this report and its appendices, three of the case studies presented at the workshop were subsequently published in Environmental Science and Technology (Fogarty et al.; 1992, Huggett et al., 1992; Kendall, 1992). After the workshop, the U.S. Environmental Protection Agency published a ''Framework for Ecological Risk Assessment" (EPA, 1992) that is similar in concept to the framework recommended in this report, although slightly different in terminology and definitions.