The degree to which a substance (a toxin or poison) can harm humans. Exposure to toxic or poisonous substances causes harm to human health and in more extreme cases can lead to serious injury or death. Toxicity is an intrinsic property of a chemical and cannot be modified. Even the slightest exposure to a highly toxic substance can result in serious health problems. However, correct medical first aid treatment following exposure can mitigate the consequences.
Generally there are three defined types of toxicity which relate to the nature of the substance:
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Chemical
This relates to specific chemical compounds. The toxicity of such compounds or mixture of compounds is measured in terms of the exposure time needed to cause an effect.
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Biological
This relates to the effects of viruses and bacteria. Measuring the toxicity of such compounds is more complicated because it depends on the effectiveness of the immune system of the person exposed.
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Physical
This relates to compounds that on their own are not specifically toxic, but which can be directly responsible for potentially life threatening consequences, for example the inhalation of dust from coal and asbestos.
DEGREES OF TOXICITY
Toxicity can be defined as acute, sub-acute or chronic:
- A substance with acute toxicity is sufficient to cause harm almost immediately after exposure.Substances commonly called poisons have extreme acute toxicity;
- A substance with sub-acute toxicity will only start to show symptoms after repeated exposure in doses too small to cause an immediate acute effect; or
- A substance has chronic toxicity if its effects only appear after repeated exposure over a period of ime. Examples are substances which are carcinogenic (cancer inducing) such as benzene.
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