A lower LD50 value indicates what about a chemical's acute toxicity?

• A. Higher toxicity
• B. Lower toxicity
• C. No toxicity
• D. Unknown

Answer: (A)

LD50 tells you the dose needed to kill half of the exposed population, so the smaller that dose, the more acutely toxic the chemical is. A lower LD50 means only a small amount is required to cause death in 50% of subjects, indicating higher acute toxicity. For example, a substance that causes death at 5 mg/kg is far more acutely toxic than one that causes death at 500 mg/kg. Conversely, a higher LD50 suggests the chemical is less acutely toxic because a much larger amount is needed to reach the same lethal effect. LD50 specifically measures acute lethality under defined conditions and does not assess chronic or other kinds of toxicity, so the idea that there is no toxicity or that toxicity is unknown isn’t what LD50 conveys.