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Managing Wastewater in Coastal Urban Areas
ization, involves the calculation or estimation of potential impacts based on hazard and exposure, i.e., risk is a function of exposure times hazard,
Risk = f [(exposure)(hazard)]
The process of determining risk to the environment from anthropogenic stresses involves a greater multiplicity of effects or endpoints, more complexity, and often more uncertainty than assessing human health risk. Also, ecological risk assessments involve various levels of biological organization and there is great regional variability among populations, communities, and ecosystems. For these and other reasons, a universally accepted methodology for ecological risk assessments has not been constructed yet.
Identify Hazards to Ecosystems and Human Health. The identification of hazards to ecosystems and human health should, in effect, take place within the goal-setting and domain definition processes. It is the identification of issues of concern and affected resources that point to the hazards of concern in the region.
Screen for Priority Issues. At this point in the process, the number of hazards identified may be too large to manage effectively. If so, two techniques may be used to narrow down the list of identified issues to one that contains the most significant hazards. It may be possible to screen the issues based on what is already known about their relative importance in the region. Some issues may be agreed upon as being less important than others. Initial efforts could then be focused on the ones of greatest concern with the understanding that those of less concern will be addressed at a later date.
A review of the issues may reveal that many of them have a common root cause. For example, regional-scale eutrophication, seagrass dieback, and nuisance algal blooms all result from excess nutrient enrichment. Thus, it may be appropriate to group these issues together in conducting a risk analysis on nutrient loadings.
Determine Dose-Response Relationships. The dose-response relationship is the one relation between the dose of an agent administered or received and the incidence of an adverse effect in the exposed population (NRC 1983). This step is perhaps one of the most important in the dynamic planning process because the results produced are useful in many ways. For example, once the dose-response relationship is determined, it is possible to establish exposure levels which will produce a particular level of response. This approach was taken in the setting of a goal of 40 percent reduction of nutrient loadings to the Chesapeake Bay (see Box 4.1). A general approach for assessing the dose-response relationship for nutrients and eutrophication is presented in Appendix A.