LD50 and LC50 describe the dose or concentration required to kill what percentage of test animals?

• A. Lethal concentration/dose to kill 50 percent of test animals
• B. Lethal concentration/dose to kill 100 percent of test animals
• C. A measure of the taste threshold for the chemical in test animals
• D. Lower values indicate higher toxicity

Answer: (A)

LD50 and LC50 pinpoint the amount or concentration of a substance needed to cause death in a defined proportion of a test population. Specifically, LD50 is the lethal dose per body weight (often mg/kg) that kills 50% of the animals, while LC50 is the lethal concentration in the environment (such as in air or water) that kills 50% under defined exposure conditions. This 50% mortality endpoint is what these metrics describe. The idea of 100% lethality would be LD100/LC100, not LD50/LC50, and a measure of taste threshold is unrelated to what these toxicology metrics quantify. It’s also true that lower LD50/LC50 values mean higher toxicity, but the question is about what these measures describe, which is the dose or concentration needed to kill half of the test subjects.