Toxicity 36
Toxicity 36 : Toxicity is the degree to which a substance can damage an organism. Toxicity can refer to the effect on a whole organism or on a part of this organism, such as a cell (cytotoxicity) or an organ (organotoxicity). Depending on the timeframe, there is: (1) acute toxicity = harmful effects through a single or short-term exposure to a substance or mixture; (2) chronic toxicity = harmful effects of repeated or continuous exposure to a substance or mixture. Toxic effects are dose-dependent. T. is therefore measured by a quantity of a substance required to achieve a given effect. This can be expressed by a "lethal dose" LD50, the dose that kills 50 per cent of the exposed population, expressed usually in milligrams (mg) per kilo bodyweight or by an "incapacitating dose" ID50 that incapacitates 50 per cent of the exposed population. For exposure to an aerosol or vapour the dose can be expressed by multiplying time and concentration. The result is the "concentration time" Ct (expressed as mg. min/m3). The term LCt50 is often used to denote the vapour or aerosol exposure (Ct) necessary to cause death in 50% of the population exposed
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