Risk assessment is a general approach established for independent, neutral, science-based evaluation of the probable likelihood of harm (response) from exposure (dose of stressor) to deleterious elements in the environment. Risk assessment is borne out of the need to manage risks of any such negative occurrence in order to protect public health and our ecosystems. While ecological risk assessment is not entirely new, it definitely lags behind human health risk assessment. However, the growing public awareness and concern about the consequences of major environmental events of our times at both local and global levels, for example, acid precipitation, global warming, biodiversity loss, ozone depletion, etc., has created renewed interest and urgency for appropriate approach for predicting these human-induced stressors in both terrestrial and aquatic ecosystems. Consequently, risk-assessment methodologies, particularly for ecological systems, are constantly evolving and improving upon methods used in the past.
'Dose' is defined as the quantity of an agent to which an entity is exposed to in the environment. Since these agents - biological, chemical, or physical - exert stress on the entity receiving them, they are termed stressors. A stressor is thus aptly defined as a substance or condition that causes stress on an entity in an ecosystem, whereas a 'response' is the deleterious effect(s) manifested in the entity as a result of exposure to the stressor. Dose-response from an ecological context is the quantity of exposure to a stressor (chemical, physical, or biological agent) and the resulting changes in function or health (response) of a designated entity receiving the agent. A graphical representation of such a relationship is a stressor dose-response curve which is slightly different from the classical dose-response curves and models used for human health risk assessment.
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