Which statement best describes LD50?

• A. It is a measure for a specific route of exposure
• B. It is a measure that applies to all routes equally
• C. It is used only for inhalation
• D. It is used only for dermal exposure

Answer: (A)

LD50 is the dose of a substance that would kill 50% of a defined test population under a specific exposure condition. The key point is that this dose is tied to the route by which the substance enters the body. Absorption, metabolism, and distribution differ greatly between ingestion, dermal contact, and inhalation, so the amount needed to reach lethal effects changes with the route. That’s why LD50 is described as a measure for a specific route of exposure. It isn’t interchangeable across routes, and it isn’t limited to inhalation or dermal exposure. When evaluating toxicity, you compare LD50 values only within the same route to make meaningful comparisons.