-dose response-

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Five centuries ago, the physician and alchemist Paracelsus said that:

“All substances are poisons: there is none which is not a poison.

The right dose differentiates a poison and a remedy.”

Paracelsus (1493-1541)

By this, he meant essentially that a substance in too great an amount can be dangerous, yet in an extremely small amount can be relatively harmless. Every chemical element has a spectrum of possible effects on a particular organism. For example, selenium is required in small amounts by living things but may be toxic or increase the probability of cancer in cattle and wildlife when it is present in high concentrations in the soil. Copper, Chromium and manganese are other chemical elements required in small amounts by animals but toxic in higher amounts.


From these, we can know the effect of a certain chemical on an individual depends on the dose. This concept is termed dose response. Dose dependency can be represented by a generalized dose-response curve such as that shown in Figure 1.

When various concentrations of a chemical present in a biological system are plotted against the effects on the organism, two things are apparent:

· Relatively large concentrations are toxic and even lethal (points D, E and F in Figure 1).

· Trace concentrations may be beneficial for life (between points A and D); and the dose-response curve forms a plateau of optimal concentration and maximum benefit between two points (B and C). Points A, B, C, D, E and F in Figure 1 are important thresholds in the dose-response curve. Unfortunately, the amounts at which points E and F occur are known only for a few substances, for a few organisms, including people; and the very important point D is all but unknown. Doses that are beneficial, harmful, or lethal may differ widely for different organisms and are difficult to characterize.

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