Definition of the Term LD50

Definition: The median lethal dose of a substance, or the amount required to kill 50% of a given test population. LD50 is a measurement used in toxicology studies to determine the potential impact of toxic substances on different types of organisms. It provides an objective measure to compare and rank the toxicity of substances. The LD50 measurement is usually expressed as the amount of toxin per kilogram or pound of body weight. When comparing LD50 values, a lower value is regarded as more toxic, as it means a smaller amount of the toxin is required to cause death. The LD50 test involves exposing a population of test animals, typically mice, rabbits, guinea pigs, or even larger animals such as dogs, to the toxin in question. The toxins might be introduced orally, through injection, or inhaled. Because this testing kills a large sample of the animals, it is now being phased out in the United States and some other countries in favor of newer, less lethal methods. Pesticide studies involve LD50 testing, usually on rats or mice and on dogs. Insect and spider venoms can also be compared using LD50 measurements, to determine which venoms are the most deadly to a given population of organisms. Â   Examples: LD50 values of insect venom for mice: Honey bee, Apis mellifera - LD50 2.8 mg per kg of body weightYellowjacket, Vespula squamosa - LD50 3.5 mg per kg of body weight Reference: W.L. Meyer. 1996. Most Toxic Insect Venom. Chapter 23 in University of Florida Book of Insect Records, 2001. http://entomology.ifas.ufl.edu/walker/ufbir/.