National Academies Press: OpenBook

Issues in Risk Assessment (1993)

Chapter: Selection of End Points

Suggested Citation:"Selection of End Points." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.

concept of dose-response assessment for ecological applications and then on the complexities that need to be addressed in practice. The group agreed immediately that for ecological assessments it is better to talk about stress-response than about dose-response relationships. Scientifically, the stress-response concept, as it applies to ecological risk assessment, is complex and involves many considerations that are absent from the usual understanding of dose-response relationships in human health risk assessment. The bulk of the session was devoted to identifying those considerations and discussing how assessments should be structured to address them.

Aspects of An Adequate Stress-Response Analysis for Ecological Risk Assessment
Selection of End Points

The group argued that end point definition is critical for ecological stress-response assessment. Responses can be assessed at all three hierarchical levels of ecological organization: population, community, and ecosystem. Because of the inherent linkages between the levels, it is important to assess how an effect at one level can affect the other levels. No standard methods exist for making those linkages. Because empirical studies of different levels of organization usually also involve different spatial and temporal scales, the decision about which levels to study must be made before studies are initiated.

Final end points must be expressed as measurable characteristics, such as minimal sustainable population or maximal damage that permits the continued viability of a complex ecosystem. Both structural end points and functional end points should be considered. Structural end points include descriptive characteristics of an ecosystem, such as abundance, species composition, and trophic structure. Functional end points include energy/material flows and other transformation processes (i.e., what the organisms do, as distinct from what they are). The choice of end points must be responsive to both technical and policy concerns, including the following:

  • Values (what do we really care about?),

Suggested Citation:"Selection of End Points." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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The scientific basis, inference assumptions, regulatory uses, and research needs in risk assessment are considered in this two-part volume.

The first part, Use of Maximum Tolerated Dose in Animal Bioassays for Carcinogenicity, focuses on whether the maximum tolerated dose should continue to be used in carcinogenesis bioassays. The committee considers several options for modifying current bioassay procedures.

The second part, Two-Stage Models of Carcinogenesis, stems from efforts to identify improved means of cancer risk assessment that have resulted in the development of a mathematical dose-response model based on a paradigm for the biologic phenomena thought to be associated with carcinogenesis.

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