What does LC50 mean?

• A. Lethal concentration that is lethal to 50% of a group of test animals after a single dose
• B. Lethal dose to 50% of animals after multiple exposures
• C. Lethal concentration that is safe for humans
• D. Lethal dose for 50% after two weeks

Answer: (A)

LC50 refers to the concentration of a toxicant in air or water that will kill 50% of a test population during a defined short exposure. The emphasis is on concentration, not the amount of chemical per body weight, and it reflects acute toxicity from a single exposure period. A lower LC50 means the chemical is more acutely toxic, because a smaller environmental concentration causes mortality in half the test animals. It’s determined by testing several concentrations and estimating the point at which 50% die, often reported with units like mg/L or mg/m³.

This isn’t about a lethal dose after multiple exposures, nor about a concentration “safe for humans,” and it doesn’t specify a two-week duration. Those ideas relate to different concepts or time frames.