Characterizing Ecological Effects

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. 

Causality is the relationship between cause (one or more stressors) and effect (assessment end point response to one or more stressors). Without a sound basis for linking cause and effect, uncertainty in the conclusions of an ecological risk assessment will be high. Developing causal relationships is especially important for risk assessments driven by observed adverse ecological effects such as fish kills or long-term declines 

The injury, dysfunction, or other putative effect of the toxicant must be regularly associated with exposure to the toxicant and any contributory causal factors. 

Indicators of exposure to the toxicant must be found in the affected organisms. 

The toxic effects must be seen when normal organisms or communities are exposed to the toxicant under controlled conditions, and any contributory factors should be manifested in the same way during controlled exposures. 

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What are the criteria used to judge the importance of data when characterizing ecological effects ... 

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). 

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. 

Common Whole Mixtures There are few systematic studies of mixtures that are strictly based on the approach of the mixture of concern or similar mixtures as defined under human risk assessment of mixtures. Most ecological effect studies have more characteristics in common with a component-based or unique whole mixture approach than with the common mixture approach. A rare example of the common whole mixture approach in ecological risk assessment is the hydrocarbon block method. In this case, mixture effects are predicted on the basis of partial characterization of hydrocarbon mixtures. The hydrocarbon block method is used to determine the risks of a total hydrocarbon mixture on the basis of discriminating different chain length fractions of hydrocarbons, for each of which toxicities are known (King et al. 1996). 

Following construction of the conceptual model, problem formulation continues by developing a plan to implement the conceptual model of the ERA. The resulting analysis plan further characterizes the stressors, identifies specific ecological effects of concern, and identifies applicable data, as well as measures or models that can be used to quantitatively relate the stressors to the expected 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. 

The analysis phase develops profiles of environmental exposure and the effects of the stressor. The exposure profile characterizes the ecosystems in which the stressor may occur as well as the biota that may be exposed. It also describes the magnitude and spatial and temporal patterns of exposure. The ecological effects profile summarizes data on the effects of the stressor and relates them to the assessment endpoints. 

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. 

The third phase of the framework is risk characterization. Risk characterization uses the results of the exposure and ecological effects analyses to evaluate the likelihood of adverse ecological effects associated with exposure to a stressor. It includes a summary of the assumptions used, the scientific uncertainties, and the strengths and weaknesses of the analyses. In addition, the ecological significance of the risks is discussed with consideration of the types and magnitudes of the effects, their spatial and temporal patterns, and the likelihood of recovery. The purpose is to provide a complete picture of the analysis and results. 

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... 

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