What Is Toxicity?

Toxicity refers to the ability of a substance to induce harmful effects. In general, all substances are toxic or poisonous; however, at normal levels, these substances are considered allowable or safe. Hence, toxicity is the level above the allowable limit. For instance, salt, if taken at normal levels, is safe, but if consumed at excessive amounts, salt may damage your kidneys and other organs.

There are two general types of toxicity according to the site affected. Furthermore, there are important factors that influence toxicity, the dosage level being the most critical.

Definition

• Toxicity refers to the hazardous effect of a substance to a living system. The substance may be of synthetic (drugs, chemical solutions) or natural (waste products) origin. The living system may include simple life forms such as single-celled bacteria as well as complex life forms including humans, plants and animals.

History

• The first considered toxicity-related description in the Western literature is the biological weapon or poison from the "many-headed" sea serpent, Hydra, used in poisoning Hercules's arrows. The knowledge on toxicity and poisonous substances is attributed to the earliest humans, who devised "poisonous" weapons using plant extracts and animal venom for hunting food.

  Further toxicological studies have led to the establishment of safety standards, maximum allowable dosages, and detailed toxicity levels of substances, which are the scientific bases of medical treatments, environmental and health care systems.

Principle

• The principle behind toxicity is based on the prescient statement of Philippus Theophrastus Aureolus (Paracelsus), a Swiss physician and alchemist, that "all substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy."

Factors

• There are important factors in determining the toxicity of a substance. These factors, according to Dr. Emily Monosson, a toxicologist and an editor of the Encyclopedia of Earth, include "dosage, exposure route, form and innate chemical activity, species, age, sex, ability to be absorbed, metabolism, distribution within the body, excretion and presence of other chemicals." These factors may have significant impact on toxicity; however, the most critical factor is dosage.

Types

• Toxicity, in general, is classified according to the site affected by the toxicant (toxic substance). The toxic effect may occur at only one site and this is called organ specific toxicity. Some of the common organ specific toxicity includes hepatotoxicity (liver), immunotoxicity (immune system), neurotoxicity (nervous system) and nephrotoxicity (kidney). On the other hand, if the toxic effect occurs on multiple organs or parts, it is called systemic toxicity. The systemic toxicity may be developmental (developing fetus), carcinogenic (abnormal cell growth), acute (occurs immediately) and chronic (occurs gradually or over time).