In toxicology, what is the related measure used specifically for inhalation exposure called?

• A. LC50
• B. LD50
• C. TD50
• D. ED50

Answer: (A)

LC50 is the concentration of a substance in air that kills 50% of exposed animals during a defined exposure period. This inhalation-specific metric directly reflects how much of the substance people or animals would breathe in, rather than how much would be absorbed per body weight. It is typically expressed in mg/m3 or ppm and is time-dependent (for example, a 4-hour LC50).

LD50, by contrast, refers to the lethal dose per body weight for ingestion or other non-inhalation routes, not the concentration in air. TD50 denotes the dose that produces a toxic (often non-lethal) effect in 50% of subjects for a specific endpoint, while ED50 is the dose that produces 50% of the maximal pharmacologic effect. These latter two are not specific to inhalation exposure.