Which statement best describes LD50 and LC50 as toxicity measurements?

• A. They are the same measurement
• B. LC50 is the dose for 50% death by ingestion
• C. LD50 is the amount required to kill 50% by oral or dermal exposure; LC50 is the concentration in air that must be present to kill 50% of test animals
• D. They measure exposure time for 50% of population

Answer: (C)

LD50 and LC50 are acute toxicity measures that tell you what amount or concentration of a substance is needed to kill 50% of a test population, under specific conditions. LD50 refers to the dose of substance given by mouth or applied to the skin (oral or dermal exposure) and is usually expressed as mg of substance per kg of body weight. LC50 refers to the concentration of the substance in the air that, when inhaled, kills 50% of the test animals, and is expressed as mg per cubic meter of air or in ppm.

So, the best description is that LD50 is the amount required to kill 50% by oral or dermal exposure, while LC50 is the concentration in air required to kill 50% by inhalation. The other statements don’t fit because they either treat these as the same measurement, misstate LC50 as an ingestion metric, or imply they measure exposure time rather than lethal dose/concentration.