Poisons and toxins are molecules that are harmful to living organisms. it is important to note that virtually any substance can be harmful at high enough concentrations--as Paracelsus (1493-1541) said in the sixteenth century, "the dose makes the poison." In common usage, the word poison designates a substance that is harmful in relatively small quantities. There is no absolute limit for this designation, although it generally is reserved for substances that are lethal in adult humans at doses below 100 grams. Toxin is a synonym for poison.

Poisons include both naturally produced compounds and chemicals manufactured by humans. Natural poisons are produced by species of bacteria, fungi, protists, plants, and animals. Modern society produces and uses thousands of chemicals, including more than 65,000 manufactured in the United States. Many of these are poisonous, and their regulation is an important part of the work of the Occupational...