LC50 refers to which toxicity measure?

• A. Lethal dose for 50% of test animals
• B. Lethal concentration for 50% of test animals
• C. Atmospheric concentration that kills half of a group of test animals after a specified exposure time
• D. The concentration that causes sublethal effects

Answer: (B)

LC50 is the median lethal concentration—the concentration of a substance in the exposure medium that kills 50% of exposed animals within a defined exposure period. It’s a measure of acute toxicity used for inhalation or aquatic scenarios, and it’s concentration-based rather than dose-based. The best description among the options is the lethal concentration for 50% of test animals, because it captures the idea of a concentration in the environment that yields 50% mortality after the specified exposure time. LD50 describes a dose rather than a concentration, and sublethal effects refer to outcomes that do not result in death, which LC50 by definition does not describe.