Poisons and Toxins Health Article

Poisons and Toxins

Substances that cause illness or death in living things.

A poison is a chemical that causes some dysfunction, or toxic reaction, in a person or other living thing. By definition, a toxin is a poisonous chemical of biological origin, produced by a microorganism, plant, or animal. In common usage, however, the words poison and toxin are often used interchangeably. The study of poisons is called toxicology.

Individuals differ in their tolerance of potentially toxic chemicals, and children are much more sensitive to poisons than adults. Individuals who are extremely sensitive to poisoning by a particular chemical are said to be hypersensitive to that chemical. People are exposed daily to potentially toxic chemicals in the environment through food, medicine, water, and the atmosphere.

Toxicity

All chemicals have the potential to be toxic when the dose (or exposure) is large enough to affect the functioning of the organism. The Swiss physician and alchemist Paracelsus (1493-1541) wrote, "Dosage alone determines poisoning." Exposure to poisoning may be by ingesting (swallowing), inhaling, or injecting the substance; the poison may also be absorbed through the skin. Even benign household products can be toxic in large doses, especially to children. Smaller exposures to chemicals may be referred to as contamination, while larger exposures are referred to as poisoning; in an environmental context, the term pollution is used to describe the presence of chemicals.

Acute toxicity

Biochemical responses to exposure to chemicals range from mild irritation to loss of function, tissue damage, or death. When there is obvious tissue damage, illness, or death after a short-term exposure to a large dose of some chemical, the condition is referred to as acute toxicity. One index of acute toxicity is known as the LD₅₀, which is based on the dose of chemical that is required to kill one-half of a laboratory population of organisms during a short-term, controlled exposure. Even seemingly harmless substances—such as table sugar—can be toxic in high doses.

Some examples of acute toxicity levels for laboratory rats (measured in milligrams [mg] of chemical per kilogram [kg] of body weight) are shown in the table below

Chronic toxicity

When toxic effects of chemicals develop after a longer period of exposure to smaller concentrations than are required to cause acute poisoning, they are referred to as chronic toxicity. In humans, chronic toxicity may take the form of increased rate of birth defects and spontaneous abortions (miscarriages), cancer, and organ damage. Because of their relatively indeterminate nature and long-term lags in development, chronic toxicities are much more difficult to diagnose than acute toxicities.:

In the home

For children, household chemicals pose the greatest threat for poisoning. Substances such as art supplies; cleaning and laundry products; cosmetics, medications, and vitamin supplements; and garden and automotive chemicals are all potentially hazardous, especially to young children.

In the environment

Many poisonous chemicals—such as metals and other elements—are present naturally in the environment, causing natural "pollution" in areas where minerals containing toxic elements, such as copper, lead, selenium, or arsenic are concentrated. The soil may contaminate plant material in areas, such as the semi-arid regions of the western United States, where the soil contains high concentrations of selenium. This element is absorbed by plants, causing them to become extremely poisonous to cattle that might eat their toxic foliage.

Other naturally occurring toxins are biochemicals that are synthesized by plants and animals as part of their system of defenses. Some of the most toxic chemicals known to science, such as tetrodotoxin, synthesized by the Japanese globe fish (Sphdroides rubripes), occur in nature. Other examples of deadly biochemicals are snake and bee venoms and mushroom poisons.

See also Lead Poisoning

Books

Freedman, B.

Environmental Ecology. 2nd ed. San Diego: Academic Press, 1995.

Klaassen, C, M. Amdur, and J. Doull. Cassarett and Doull's Toxicology: The Basic Science of Poisons. 4th ed. Boston: Little, Brown, 1991.

Lerner, Carol. Dumb Cane and Daffodils: Poisonous Plants in the House and Garden. New York: Morrow Junior Books, 1990.

Smith, R. P. A Primer of Environmental Toxicology. Philadelphia: Lea & Febiger, 1992.