Characterization of Ecological Effects

The characterization of ecological effects is perhaps the most critical aspect of the risk assessment process. Several levels of confidence exist in our ability to measure the relationship between dose and effect. Toxicity measured under set conditions in a laboratory can be made with a great deal of accuracy. Unfortunately, as the system becomes more realistic and includes multiple species and additional routes of exposure, even the ability to measure effects is decreased. 

Evaluation of relevant effects data has long been left to professional judgment. The crucial factor is the relevance of the information to the endpoints selected during problem formulation. Criteria typically used to judge the importance of the data usually include the quality of the data, number of replicates and repeatability, relevance to the selected endpoints, and realism of the study compared to the ecosystem for which the risk assessment is being prepared. 

Toxicity data from several sources is usually compiled and compared. Generally, there are acute and chronic data for the stressor on one or several species. Toxicity data are usually limited to species and the species of interest, as an assessment endpoint may not have appropriate data available. This situation often occurs with threatened or endangered species since even a small-scale toxicity test involves relatively large numbers of animals to acquire data of sufficient quality. 

Field observations and controlled microcosm and large-scale tests can provide additional data on which to base the risk assessment. Only in these systems can an indication of the importance of indirect effects become apparent. Field research also has limitations. No two fields are alike, requiring extrapolation. It has been demonstrated by J.H. Brown (1994) and his coworkers that even fields started with as similar conditions as possible diverge in ways which are difficult to predict at the beginning of the experiment. 

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The second phase of ecological risk assessment, the analysis phase, includes two principal activities characterization of exposure and characterization of ecological effects (Figure 28.1). 

The ecological risk assessment was conducted in accordance with the USEPA guidance document Guidelines for Ecological Risk Assessment (USEPA, 1998) . A four-step assessment process was adopted problem formulation, exposure characterization, characterization of ecological effects and risk evaluation. 

The second phase of the framework is termed analysis and consists of two activities, characterization of exposure and characterization of ecological effects. The purpose of characterization of exposure is to predict or measure the spatial and temporal distribution of a stressor and its co-occurrence or contact with the ecological components of concern, while the purpose of characterization of ecological effects is to identify and quantify the adverse effects elicited by a stressor and, to the extent possible, to evaluate cause-and-effect relationships. 

Characterization of Ecological Effects Used Instead of Hazard Assessment... 

The framework uses characterization of ecological effects rather than hazard assessment for two reasons. First, the term "hazard" can be ambiguous because it has been used in the past to mean either evaluating the intrinsic effects of a stressor (U.S. EPA, 1979) or defining a margin of safety or quotient by comparing a toxicological endpoint of interest with an estimate of exposure concentration (SETAC, 1987). Second, many reviewers believed that hazard is more relevant to chemical than to nonchemical stressors. 

Use of the term characterization of ecological effects rather than hazard assessment... 

An uncertainty assessment is an integral part of the characterization of exposure. In the majority of assessments, data will not be available for all aspects of the characterization of exposure, and those data that are available may be of questionable or unknown quality. Typically, the assessor will have to rely on a number of assumptions with varying degrees of uncertainty associated with each. These assumptions will be based on a combination of professional judgment, inferences based on analogy with similar chemicals and conditions and estimation techniques, all of which contribute to the overall uncertainty. It is important that the assessor characterize each of the various sources of uncertainty and carry them forward to the risk characterization so that they may be combined with a similar analysis conducted as part of the characterization of ecological effects. 

The data used in characterization of ecological effects are analyzed to quantify the stressor-response relationship and to evaluate the evidence for causality. A variety of techniques may be used, including statistical methods and mathematical modeling. In some cases, additional analyses to relate the measurement endpoint to the assessment endpoint may be necessary. 

The results of the characterization of ecological effects are summarized in a stressor-response profile that describes the stressor-response relationship, any extrapolations and additional analyses conducted, and evidence of causality (e.g., field effects data). 

It is important to clearly describe and quantitatively estimate the assumptions and uncertainties involved in the evaluation, where possible. Examples include natural variability in ecological characteristics and responses and uncertainties in the test system and extrapolations. The description and analysis of uncertainty in characterization of ecological effects are combined with uncertainty analyses for the other ecological risk assessment elements during risk characterization. 

Evidence of causality. The degree of correlation between the presence of a stressor and some adverse effect is an important consideration for many ecological risk assessments. This correlation is particularly true when an assessor is attempting to establish a link between certain observed field effects and the cause of those effects. Further discussions of the evaluation of causal relationships may be found in the section on characterization of ecological effects (Section 3.2.2). 

Characterization of ecological effects — A portion of the analysis phase of ecological risk assessment that evaluates the ability of a stressor to cause adverse effects under a particular set of circumstances. 

Stressor-response profile — The product of characterization of ecological effects in the analysis phase of ecological risk assessment. The... 

Abstract The characterization of toxicological impact of chemicals and mixtures from environmental matrices is a critical point in the assessment of adverse effects induced in human and ecological targets. In fact, the toxicity of most of the environmental mixtures is still under investigation due to the possibility of synergic or antagonistic effects of the components. Moreover, in some cases, the toxicity of identified chemicals is not already well known and it could be an additional matter of concern. 

A number of EIA theorists believe in incorporating formal RA methods into EIA as a way to cope with uncertainties, especially in impact prediction where a formal framework for ecological risk assessment (EcoRA) is already developed. It includes three generic phases problem formulation, analysis, and risk characterization followed by risk management. The analysis phase includes an exposure assessment and an ecological effects assessment (see, e.g., US EPA (1998)). 

In formal EcoRA framework three phases of risk analysis are identified problem formulation, analysis, and risk characterization followed by risk management. The analysis phase includes an exposure assessment and an ecological effects assessment (see Figure 2). 

Ratte, H.T., Baird, D.J., Nahholz, J.V. and Sanderson, H. (2008) Extrapolation of effects measures across levels of biological organization in ecological risk assessment, in Extrapolation Practice for Ecotoxicological Effect Characterization of Chemicals, (eds K.R. Solomon, T.C.M. Brock, D. de Zwart, S.D. Dyer, L. Posfhuma, S.M. Richards, H. Sanderson, P.K. Sibley and P.J. van den Brink), CRC Press/Taylor and Francis/SETAC, Pensacola, FL,... 

In ecological effects characterization, relevant data are analyzed to evaluate stressor-response relationships and/or to provide evidence that exposure to a stressor causes an observed response. The characterization describes the effects that are elicited by a stressor, links these effects with the assessment endpoints, and evaluates how the effects change with varying stressor levels. The conclusions of the ecological effects characterization are summarized in a stressor-response profile. 

Guidance on the Application of Extrapolation Methods in Ecological Exposure and Effects Characterization of Chemicals... 

The basic features of ecological risk assessment schemes are very similar throughout the world. Usually, one focuses on effects (concentration or dose response information), exposure, and risk characterization. The following paragraphs summarize how extrapolation practices can be developed in such a way that a consistent pattern emerges. 

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