Ecological risk assessment endpoints

It is essential to define the assessment scenario within which the assessment endpoint will be assessed. The assessment scenario should specify the spatial, temporal, and ecological boundaries within which the endpoint is assessed, since these have substantial implications for the structure of the assessment model and the scope of the input data. The assessment scenario should also describe those aspects of the ecosystem that are relevant to the assessment, that is, those aspects that have an influence on the mechanisms of exposure and effects that will be assessed. This step is important in all ecological risk assessments it places the assessment activity into the real context of an ecosystem, helps to prevent construction of inappropriate models, and helps with interpretation and communication of results. 

USEPA] US Environmental Protection Agency. 2003. Generic ecological assessment endpoints (GEAEs) for ecological risk assessment. Risk Assessment Forum. Washington (DC) USEPA. 

Suter, G. W., II. Endpoints for regional ecological risk assessments. Environ. Manag. 14 19-23, 1990. 

Ingersoll, C.G., Ankley, G.T., Baudo, R., Burton, G.A., Lick, W., Luoma, S.N., MacDonald, D.D., Reynoldson, T.F., Solomon, K.R., Swartz, R.C. and Warren-Hicks, W. (1997) Work group summary report on an uncertainty evaluation of measurement endpoints used in sediment ecological risk assessments, Chapter 18, EPA/600/A-96/097, U.S. Environmental Protection Agency, National Biological Service, Corvallis, OR, USA. 

Reynoldson, T.B., Thompson, S.P. and Milani, D. (2002b) Integrating multiple toxicological endpoints in a decision-making framework for contaminated sediments, Human and Ecological Risk Assessment 8, 1569-1584. 

Clements WH. 1997. Ecological significance of endpoints used to assess sediment quality. In Ingersoll CG, Dillon T, Biddinger GR, editors. Ecological risk assessments of contaminated sediments. Pensacola (FL) SETAC Press, p 123-134. 

Ecological risk assessment of chemical mixtures thus has to deal with a variety of field phenomena, a possible range of assessment endpoints, and a variety of assessment approaches. Moreover, there exists a huge variety in the regulatory questions and problem formulations addressed in ecological risk assessment of chemical mixtures. Examples include the protection of specific species against well-defined mixtures (like PCBs and PAHs), the protection of an undefined concept like the ecosystem, and retrospective assessments for highly or diffusely contaminated systems. 

There is much dissimilarity between the fields of human and ecological risk assessment, but many of the differences are not typical for mixtures. Examples are differences in assessment endpoints (individuals vs. species or communities), in exposure routes and media (oral, inhalatory, and dermal for humans vs. aquatic or terrestrial for ecosystems), and in the level of mechanistic understanding (generally larger in human than in ecological studies). 

Analysis of effects A phase in an ecological risk assessment in which the relationship between exposure to contaminants and effects on endpoint entities and properties is estimated along with associated uncertainties. 

Landis, W.G., G.B. Matthews, R.A. Matthews, and A. Sergeant. 1994. Application of multivariate techniques to endpoint determination, selection, and evaluation in ecological risk assessment. Environ. Toxicol. Chem. 13 1917-1927. 

Perhaps a more useful means of quantifying structural data is to use a similarity measurement. These are reviewed by Ludwig and Reynolds (1988) and form the basis of multivariate clustering and ordination. Similarity measures can compare the presence of species in two sites or compare a site to a predetermined set of species derived from historical data or as an artificial set comprised of measurement endpoints from the problem formulation of an ecological risk assessment. The simplest similarity measures are binary in nature, but others can accommodate the number of individuals in each set. Related to similarity measurements are distance metrics. Distance measurements, such as Euclidean distance, have the drawbacks of being sensitive to outliers, scale, transformations, and magnitudes. Distance measures form the basis of many classification and clustering techniques. 

The remainder of this section details the potential application of multivariate methods in the selection of endpoints and in the evaluation of exposure and effects of stressors in ecosystems. Particular reference is made to the application of these methods to the current framework for ecological risk assessment. Examples of the use of multivariate methods in detecting effects and in selecting important measurement variables are covered using both field surveys and multispecies toxicity tests. 

Discuss an assessment baseline and measurement endpoints as analysis of ecological risk assessment. 

Schematic of the framework for ecological risk assessment (U.S. EPA1992). Especially important is the interaction between exposure and hazard and the inclusion of a data acquisition, verification, and monitoring component. Multivariate analyses will have a major impact on the selection or assessment and measurement endpoints and will play a major role in the data acquisition, verification, and monitoring phase.

The conceptual model of the risk assessment is the framework into which the data are placed. Like the selection of endpoints, the selection of a useful conceptual model is crucial to the success or failure of the risk assessment process. In some cases a simple single species model may be appropriate. Typically, models in ecological risk assessment are comprised of many parts and attempt to deal with the variability and plasticity of natural systems. Exposure to the system may come from many different sources. The consideration of organisms at risk depends upon the migratory and breeding habits of numerous organisms, many rare and specialized. 

The distinctive nature of the framework results primarily from three differences in emphasis relative to previous risk assessment approaches. First, ecological risk assessment can consider effects beyond those on individuals of a single species and may examine population, community, or ecosystem impacts. Second, there is no one set of assessment endpoints (environmental values to be protected) that can be generally applied. Rather, assessment endpoints are selected from a very large number of possibilities based on both scientific and policy considerations. Finally, a comprehensive approach to ecological risk assessment may go beyond the traditional emphasis on chemical effects to consider the possible effects of nonchemical stressors. 

The next three sections of this report are arranged to follow the framework sequentially Section 2 describes problem formulation this section is particularly important for assessors to consider when specific assessment endpoints are not determined a priori by statute or other authority. Section 3 and Section 4 discuss analysis and risk characterization, respectively. Section 5 defines the terms used in this report, and Section 6 provides literature references. The lists of ecological risk assessment issues at the end of Section 1 to Section 4 highlight areas for further discussion and research. EPA believes that these... 

Good communication between the risk assessor and risk manager is important to ensure that ecologically relevant assessment endpoints reflect policy goals and societal values. Societal concerns can range from protection of endangered or commercially or recreationally important species to preservation of ecosystem attributes for functional reasons (e.g., flood water retention by wetlands) or aesthetic reasons (e.g., visibility in the Grand Canyon). 

Ankley, G.T. (1995) Laboratory v. field measurement endpoints a contaminated sediment perspective. In Ecological Risk Assessment of Contaminated Sediments, Ingersoll, C.G., Dillon, T. and Biddinger, G.R. (eds), pp. 115-122. SETAC Press, Pensacola, FL. 

The use of NOECs and LOECs has been questioned as they have some major limitations. Their values depend very much on the concentrations that have been selected in the test set-up. Large concentration steps will result in a large difference between NOEC and LOEC. Moreover, poor test design (e.g. low number of replicates) will result in increased variance of effects and the acceptance of the null hypothesis. As a consequence, the toxicity of a chemical may be underestimated. Statistical measurement endpoints obtained from ecotoxicity testing may be used to derive predicted no effect concentration (PNEC) levels that are employed in ecological risk assessment for chemicals. 

The extrapolation of test data includes uncertainty, in particular, if measurement and assessment endpoints are not identical. However, this source of variation is even more pronounced when using chemical concentrations for the prediction of field effects. It has to be emphasised that the use of bioassays represents one line of evidence, which together with chemical analysis and/or biological field data should be used for a reliable ecological risk assessment. 

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