LD50 is the dose of a substance that kills what?

• A. Dose of a substance that kills 50% of a test population
• B. The time to degrade a compound
• C. The concentration required to neutralize a toxin
• D. The average lethal dose in humans

Answer: (A)

LD50 is a standard toxicology measure that tells you how much of a substance is likely to cause death in half of a test group under defined conditions. It’s usually expressed as the dose per body weight (for example, mg of substance per kg of body weight) and depends on factors like species, route of exposure, and the observation period. This makes it useful for comparing acute toxicity between substances. It does not describe how long a compound lasts in the environment (that would be degradation half-life), nor the amount needed to neutralize a toxin, nor the average lethal dose in humans—it's an experimentally determined value based on a specific test population and setup. So the correct interpretation is that LD50 is the dose that kills 50% of a test population.