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Environment
Environmental Risk Assessment (ERA) aims to assess the effects of stressors, usually chemicals, on the local environment. A risk is an integrated assessment of likelihood and severity of an undesired event. In ERA, the undesired event often depends on the chemical of interest and on the risk assessment scenario. This undesired event is usually a detrimental effect on organisms, populations or ecosystems. Current ERAs usually compare an exposure to a no-effect level, such as the Predicted Environmental Concentration/Predicted No-Effect Concentration (PEC/PNEC) ratio in Europe. Although this type of ratio is useful and often used in regulation purposes, it is only an indication of an exceeded apparent threshold. New approaches start to be developed in ERA in order to quantify this risk and to communicate effectively on it with both the managers and the general public.

Ecological risk assessment is complicated by the fact that there are many nonchemical stressors that substantially influence ecosystems, communities, and individual plants and animals, as well as across landscapes and regions. Defining the undesired (adverse) event is a political or policy judgment, further complicating applying traditional risk analysis tools to ecological systems. Much of the policy debate surrounding ecological risk assessment is over defining precisely what is an adverse event.