Which statement correctly describes LD50 and LC50?

• A. LD50 is a lethal dose; LC50 is a lethal concentration
• B. LD50 measures concentration; LC50 measures dose
• C. Both measure the same thing; no difference
• D. LD50 relates to toxicity in plants only

Answer: (A)

LD50 and LC50 both describe the exposure level that kills 50% of a test population, but they measure different things. LD50 is a lethal dose, typically expressed as milligrams of substance per kilogram of body weight (mg/kg), reflecting the amount delivered to the organism. LC50 is a lethal concentration, expressed as milligrams of substance per liter of air or water (mg/L) or in ppm, reflecting the concentration present in the environment that organisms are exposed to. So saying that LD50 is a lethal dose and LC50 is a lethal concentration precisely captures the distinction between dose to an organism and concentration in its surroundings. They’re not the same thing, and LD50 is not limited to plants.