The study of the harmful effects of chemicals on humans and the environment is called "toxicology." The term "toxicity" is used to describe the pattern of harmful effects that a chemical can produce. Over four hundred years ago, a European doctor named Paracelsus established the basic premise of toxicology: |
 "All substances are poisons; there is none which is not; the dose differentiates a poison from a remedy." - Paracelsus, 1493-1541 |
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This statement says that everything can be toxic if the dose is high enough. For some highly toxic chemicals only a very small amount is needed to produce harm. For others a large amount may be necessary to produce harm. This difference in the amount of chemical needed to produce the same level of effect is called "potency." |
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