LC/LD50

LC50 and LD50 are the median lethal concentration and median lethal dose, the exposure that kills 50% of a test population. LC50 applies to a concentration in water or air (mg/L or ppm) over a fixed exposure, typically 96 hours for fish; LD50 applies to a dose administered to the organism (mg/kg body weight). Both are acute-toxicity endpoints derived from dose-response curves. A lower value means higher toxicity. They anchor hazard classification under the GHS and feed PNEC derivation, where the lowest acute value is divided by an assessment factor, usually 1,000, to set a screening no-effect concentration.