Which statement correctly describes LD50 and LC50?

• A. LD50 is the lethal dose for 50% of test animals; LC50 is the lethal concentration for 50% of test animals
• B. LC50 is the lethal dose for 50% of test animals; LD50 is the lethal concentration for 50% of test animals
• C. Both terms describe inhalation exposures only
• D. Both imply toxic effects at sublethal doses

Answer: (A)

In toxicology, LD50 and LC50 describe acute toxicity endpoints at the 50% mortality level. The difference is that LD50 uses dose (usually milligrams of substance per kilogram of body weight), while LC50 uses concentration (such as milligrams per liter of air) for inhalation or aquatic exposures. The statement that best fits is that LD50 is the lethal dose for 50% of test animals and LC50 is the lethal concentration for 50% of test animals. These metrics focus on lethal outcomes, not sublethal effects, and LD50 can come from oral or dermal routes (not just inhalation), whereas LC50 is tied to the concentration in the exposure medium. For example, an LD50 of 200 mg/kg means half the animals die at that dose, while an LC50 of 5 mg/L means half die at that air concentration during the test period.