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The Environment and Human Health

Author(s): Nancy P. Moreno, PhD

The Dose Makes the Poison

Toxicology is the branch of science that studies the effects of poisons on living organisms. And there is a lot to study, because too much of any substance can cause harm. In the 1500s, the Swiss physician, Paracelsus, accurately observed that the “dose,” or amount of exposure, to a toxin determines whether the toxin will have a harmful effect, and how severe the effect will be. “Dose” refers specifically to the amount of a substance that is eaten, inhaled or absorbed through the skin. Obviously, rapid exposure to large amounts of toxins, such as after a major chemical spill, can be harmful. But exposure to relatively low doses of chemicals or radiation over long periods of time also can contribute to the development of disease. 


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