Basic Toxicological Terms and Definitions

Toxicology has been defined in various ways. It is “the basic science of poisons” according to the preeminent text on the subject. In Webster’s Dictionary, it is “a science that deals with poisons and their effect and with the problems involved (as clinical, industrial, or legal)”. In Dorland’s Medical Dictionary, it is “the scientific study of poisons, their actions, their detection, and the treatment of conditions produced by them.”

“The dose makes the poison”: often recognized as the most basic tenet of toxicology, and usually attributed to Paracelsus in the early 1500s. What he actually said has been reported to be, “Poison is in everything, and no thing is without poison. The dosage makes it either a poison or a remedy.” This is an important point. In great enough quantities oxygen and water can be deadly. On the other hand, if the dose of very toxic chemicals a person gets is small enough, there will not be adverse effects.

Adverse or Toxic Effect: Not all effects of chemical exposures can be classified as “adverse” or “toxic”. Some exposures can cause measureable changes in physiological parameters, but are not great enough to compromise normal functioning and may in fact be beneficial to the organism. In contrast, adverse effects are those that have abnormal, harmful, or undesirable effects and cause anatomical or functional damage, irreversible physical changes, or increases the susceptibility to other biological, chemical, or environmental stresses.

Dose-Response Relationship: With some exceptions, the magnitude or frequency of a “response” (usually some type of adverse health effect in an individual or a group of organisms or people) will increase as the dose of chemical administered increases. The shape of the dose-response curve is a good descriptor of the toxicity of a chemical.

Carcinogen: a substance that can cause cancer. Contrary to public opinion, not every chemical causes cancer. In fact, the number of chemicals for which there is sufficient human evidence for carcinogenesis is quite small compared to the number of chemicals in the world. Some examples of known human carcinogens include arsenic, benzene, chromium +6, nickel, tobacco smoking, and vinyl chloride.

Mutagen: a substance that can cause genetic mutations. Since cancer is a disease that can be caused by changes in DNA, many mutagens are also carcinogens. Testing for mutagenicity is an approach used to identify possible carcinogens.

Teratogen: a substance that can cause physical defects in the developing embryo, in other words, birth defects. Many drugs have been implicated as teratogens (thalidomide, diethylstilbesterol, valproate, etc.). Lifestyle factors like tobacco smoking, cocaine use, and alcohol consumption in pregnant women are also linked to birth defects. Environmental chemicals associated with teratogenic effects include lead, mercury, polychlorinated biphenyls (PCBs), and toluene.

Litigen: a substance that can cause litigation. Some examples are asbestos, benzene, mold, and silica (this is meant as a joke, but there’s some truth to it as well).