Why is LD-50 used?

• A. To determine safe exposure levels in humans.
• B. To measure and compare how toxic different substances are.
• C. To assess environmental risk.
• D. To calculate dosage for treatments.

Answer: (B)

LD50 is a measure of acute toxicity used to compare how toxic different substances are. It represents the dose, per body weight, that would kill half the individuals in a standardized test population under defined conditions. Because it yields a single, comparable number, it lets scientists rank substances from most toxic to least toxic. A lower LD50 indicates higher toxicity, while a higher LD50 indicates lower acute toxicity. This is why it’s used to measure and compare how toxic different substances are. It’s not a direct indicator of safe human exposure, environmental risk, or therapeutic dosing, which depend on exposure scenarios, chronic effects, and clinical context.