DEFINITION OF TOXICITY AND CLASSIFICATION OF TOXINS
Toxicity can be defined as “the capacity of a substance to cause adverse health effects (injury, hazard) on a living organism.” The type of toxicity that occurs can be local effects such as skin irritation, or general effects such as in impaired coordination, behavioral changes, organ structure changes or death. The toxicity of a chemical substance is related to the amount, or dose, taken into the organism. Paracelsus stated this evidence in the 15th century using the following phrase: “All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.” Thus, the amount of a chemical a person is exposed to is important in determining the extent of toxicity that will occur. In toxicity tests, a wide variety of the doses of the same chemical are administered and the effects are examined by plotting the results on dose-response curves. The response of living organisms to the same chemical differs according to factors such as strains, species, age, sex and nutritional status. This can be observed from Figure 2.1, which shows the dose-response relations of two different species for the same chemical.