LD50 is defined as

• A. The concentration that kills 50% of the organisms
• B. The time to death for 50% of test subjects
• C. The amount of a chemical that kills 50% of the animals in a test population
• D. The dose causing death in all exposed individuals

Answer: (C)

LD50 measures how much of a chemical is needed to kill half of a test population under defined conditions. It’s a dose, not a concentration, and is usually reported as milligrams of substance per kilogram of body weight, taking into account factors like route of exposure and species. This focuses on the amount required to cause death, not how concentrated the substance is in the environment or how long it takes for death to occur. The idea of all exposed individuals dying would describe a 100% mortality threshold, which is different from the 50% point LD50 represents.