Endpoints for Regional Ecological RiskAssessments GI.ENN W. SlJTER II Environmental Sciences Division Oak Ridge National Laboratory Oak Ridge, Tennessee 37831-6038, USA ABSTRACT / Ecological risk assessments must have clearly defined endpoints that are socially and biologically relevant, accessible to prediction and measurement, and susceptible to the hazard being assessed. Most ecological assessments do not have such endpoints, in part because the endpoints of toxicity tests or other measurements of effects are used as assessment endpoints. This article distinguishes assessment and measurement endpoints in terms of their roles in risk as- sessments and explains how the criteria for their selection differ. It then presents critical discussions of possible as- sessment and measurement endpoints for regional ecological risk assessments. Finally, the article explains how endpoint selection is affected by the goal of the assessment. Generic goals for regional risk assessment include explanation of ob- served regional effects, evaluation of an action with regional implications, and evaluation of the state of a region. Cur- rently, population level assessment endpoints such as abun- dance and range are the most generally useful. For higher levels (ecosystems and regions), data are generally not available and the validity of models has not been demon- strated, and for lower level effects (physiological, and organ- ismal) are not relevant, However, landscape descriptors, ma- terial export, and other regional-scale measurement end- points show promise for regional assessments. Regional ecological risk assessment is concerned with describing and estimating risks to environmental resources at the regional scale or risks resulting from regional-scale pollution and physical disturbance (Hunsaker and others 1989). Examples include acid rain effects, ozone depletion, and pollution of a river basin by multiple-point and nonpoint pollution sources. Because of the apparent increase in the number of regional problems and the recognition of the value of a regional perspective in environmental regulation, the need for regional risk assessment is in- creasing. If regional assessments are to be performed efficiently and effectively, it is necessary to consider how each of the components of a risk assessment must be adapted to address regional-scale problems. The component addressed in this paper is the endpoints, those characteristics of valued environmental entities that are believed to be at risk. Ecological risk assessments begin with three activi- ties that define the nature of the problem to be as- sessed: choosing endpoints, describing the environ- ment, and describing the hazard. These are followed by a formal analysis of the problem which consists of exposure assessment, effects assessment, and integra- tion of the exposure and effects assessments to esti- mate the probability and level of effects. In a process called risk management, the results of the risk assess- ment are considered along with economic, technolog- ical, and political considerations to arrive at a decision. Each of these component processes should be coordi- nated. This article describes two different expressions KEY WORDS: Endpoints; Risk; Assessment;Regional; Landscape of endpoints, presents criteria for judging endpoints, presents endpoints that are potentially useful in re- gional risk assessments, judges them by the criteria, and discusses how the nature of the assessment problem affects endpoint choice. Types of Endpoints Some confusion has occurred in environmental risk assessment because the term endpoint has been used to describe two related but distinct concepts. To avoid this confusion, I have distinguished assessment end- points from measurement endpoints (Suter 1989) and that distinction has been adopted by the US Environ- mental Protection Agency's Ecotoxicity Subcommittee (Hinckley 1989). Assessment endpoints are formal ex- pressions of the actual environmental value that is to be protected. The output of a risk assessment is an estimated probability of occurrence of a dichotomous assessment endpoint (e.g., probability of extinction of a species) or an estimated relationship between proba- bility and magnitude of a scalar assessment endpoint (e.g., probability that the number of fishless lakes will be greater than X). These expressions of effects on as- sessment endpoints are the input to the risk-manage- ment process. Assessment endpoints must be valued by society, but they are not ultimate values. Rather, they are the highest values that can be assessed for- mally. In regional risk assessment, the ultimate value is the quality of life provided to the region's inhabitants, which is an indefinable function of the region's ability to provide food, clean water and air, aesthetic experi- ence, recreation, and other services without floods, Environmental Management Vol. 14, No. 1, pp. 9-23 9 1990 Springer-Verlag New York Inc.