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Definitions for the following terms were gathered from a variety of sources, which are listed in the References section.

absorption: The process of taking in, as when a sponge takes up water. Chemicals can be absorbed through the skin into the blood stream and then transported to other organs. Chemicals also can be absorbed into the blood after they are breathed in or swallowed.

acetaminophen: A synthetic chemical used as an analgesic and as an antipyretic.

acute exposure: A single exposure to a toxic substance that results in a severe response or death. Acute exposures are characterized as lasting no longer than a day, as compared with longer, continuing chronic exposure over a period of time.

Ames test: Mutagenic assay (a measure of mutagenic ability) that involves specially engineered strains of bacteria. Because of the relationship between mutagenicity and carcinogenicity, the test is used as a rapid and relatively inexpensive first screening of untested chemicals that are suspected of being carcinogens.

benzene: A clear, colorless liquid with a sweet odor that burns readily. Benzene is obtained from crude petroleum. Small amounts may be found in products such as paints, glues, pesticides, and gasoline.

caffeine: A bitter crystalline alkaloid found in coffee, tea, and kola nuts; it is a heart and central nervous system stimulant.

carbon monoxide: A colorless, odorless poison gas produced by incomplete combustion of organic matter. Carbon monoxide may be produced in lethal quantities in automobile exhaust, faulty home heating systems, improperly used portable gas stoves and heaters, improperly vented wood stoves and fireplaces, and in many industrial situations.

carcinogenic: Any substance that may produce cancer.

chemical: Any substance having a defined molecular composition.

chronic exposure: Exposure to toxic chemicals occurring over a long period of time (months to over one year).

collagen matrix barrier: An artificial "skin" used to test whether a chemical is likely to irritate, corrode, or burn human skin.

concentration: The amount of one substance dissolved or contained in a given amount of another. For example, sea water contains a higher concentration of salt than an equal amount of fresh water does.

dimethylmercury: The same as methylmercury, but containing two methyl radicals (CH3)2.

dosage: The amount of a toxicant, drug, or other chemical administered to, or taken by, an organism and expressed as some function of the organism and of time (mg/kg body weight/day).

dose: The total amount of a toxicant, drug, or other chemical that is administerd to, or taken by, an organism.

dose response: How an organism's response to a toxic substance quantitatively shifts as its overall exposure to the substance increases (e.g., a small dose of carbon monoxide may cause drowsiness; a large dose can be fatal).

EC50: Effective concentration; the dosage at which the desired response is present for 50 percent of the population.

element: A form of matter that cannot be broken down into simpler substances. Elements exist in nature as solids, liquids, or gases.

environment: The interdependent system of living and nonliving things.

experimental control: A group of experimental subjects that is not exposed to a chemical or treatment being investigated so that it can be compared with experimental groups that are exposed to the chemical or treatment.

exposure: Contact with a chemical by swallowing, breathing, or touching (such as with the skin or eyes). Exposure may be short term (acute) or long term (chronic).

A - E, F - O, P - Z