Lethal dose of a toxic substance or radiation is the dose required to kill half the members of a tested population after a specified test duration. LD50 figures are frequently used as a general indicator of a substance's acute toxicity. LD50 are expressed in mg or Bq per kg of species (animal, human), and can correspond to different type of contamination (inhalation, oral or dermal). European Commission (directive 2001/59/EC) proposed a classification into 4 categories.
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