Stressor-response profile

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. 

Risk characterization A phase of the risk assessment process that integrates the exposure and stressor response profiles to evaluate the likelihood of adverse effects associated with exposure to the contaminants. 

The combining of exposure analysis with ecological effects data results in a stressor-response profile. This profile is an attempt to match ecosystem impacts at the levels of the stressor concentration under study. Relationships between the xenobiotic and the measurement endpoint are evaluated with a consideration of how this interaction affects the assessment endpoint. Rarely is this process straightforward. Often some model is used to specifically state the relationship between the measurement and assessment endpoint. When this relationship is not specifically stated it is then left to professional judgment. 

The stressor-response profile is in some ways analogous to a dose-response curve in the sense of a single species toxicity test expanded to the community and ecosystem level. Since many of the responses are extrapolations and based on models from the molecular to ecosystem level it is important to delineate the uncertainties, qualifications, and assumptions made at each step. 

One of the difficulties in the quantification of the stressor-response profile is that many of the extrapolations are qualitative in nature. Phylogenetic extrapolations are rarely quantified or assisted with structure-activity relationships. Quantification of population level effects is likewise difficult and in some cases probabilities of extinction have been used as the quantified variable, not a subtle population endpoint. 

Using information obtained from the exposure analysis, the exposure profile quantifies the magnitude and spatial and temporal patterns of exposure for the scenarios developed during problem formulation and serves as input to risk characterization. The exposure profile is only effective when its results are compatible with the stressor-response profile. For example, appraisals of potential acute effects of chemical exposure may be averaged over short time periods to account for short-term pulsed stressor events. It is important that characterizations for chronic stressors account for both long-term low-level exposure and possible shorter term, higher level contact that may elicit similar adverse chronic effects. 

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). 

Risk estimation consists of comparing the exposure and stressor-response profiles as well as estimating and summarizing the associated uncertainties. 

As noted earlier, the conceptual model is the product of the problem formulation phase, which, in turn, provides the foundation for the analysis phase and the development of the exposure and stressor-response profiles. If incorrect assumptions are made during conceptual model development regarding the potential effects of a stressor, the environments impacted, or the species residing within those systems, then the final risk assessment will be flawed. These types of uncertainties are perhaps the most difficult to identify, quantify, and reduce. 

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

The output of the analysis phase of an ecological risk assessment consists of an exposure profile and a stressor-response profile (Eigure 9.1). The profiles include estimates of uncertainty, which, as in human health risk assessments, are a constant and essential ingredient of ecological risk assessments. The exposure and effect profiles, together with their associated uncertainty estimates, set the stage for the final phase of the risk-assessment process. 

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