This initial and perhaps most important part of the assessment defines the nature and scope of the ERA, describes the sources of potential risk (stressors), identifies the undesired ecological impacts (endpoints), considers the nature of the ecological impacts in relation to the stressors, and produces a conceptual model of the overall assessment. Thus, problem formulation essentially encapsulates the entire ERA process. Performing this step requires collaboration among risk managers and risk assessors to define the assessment objectives and develop the corresponding conceptual model. This model should be viewed as dynamic and subject to change throughout the ERA in relation to modifications to the objectives and the development of new data and information.
The initial interactions between risk managers and risk assessors might also involve other organizations and concerned members of the public (stakeholders). Initial discussions can help ensure that all important aspects of the assessment are identified, included as part of the problem formulation, and represented in the conceptual model. Such interactions can also ensure that the kinds of results produced by the ERA can be used effectively in the process of risk management and decision making.
Following construction of the conceptual model, problem formulation continues by developing a plan to implement the conceptual model. 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.
Upon completion of risk estimation, risk managers, risk assessors, and stakeholders may reconvene to discuss the nature and interpretation (e.g., conclusions, assumptions, caveats) of the results in the context of the overall assessment objectives. Possible outcomes of these interactions include revisions to the conceptual model, collection of new data, and subsequent iterations of risk estimation. Once the requirements of risk managers and decision makers are fulfilled and documented, the process ends.
Following the problem formulation, the ERA continues with analyses that characterize exposure to the stressor(s) and the ecological effects of concern. The subsequent derivation of functional relationships between exposure and effects sets the stage for risk estimation.
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