LC50

LC50, short for lethal concentration 50%, is the concentration of a toxicant in air or water at which 50% of a tested population is expected to die within a specified exposure period. It is a common metric in toxicology, especially for aquatic organisms and inhalation hazards. In aquatic toxicology, LC50 is expressed as concentration in water (for example mg/L) and is typically determined over 24 to 96 hours. For inhalation toxicity, LC50 is expressed as concentration in air (often mg/m3) and reflects mortality after a defined exposure duration.

Determination: Acute toxicity tests expose groups of organisms to a range of concentrations to observe mortality. Data are analyzed with probit or logistic regression to estimate the concentration that causes 50% mortality, with confidence limits. Tests may use static, semi-static, or flow-through exposure conditions.

Factors: LC50 values depend on species, developmental stage, and environmental conditions such as temperature, salinity, pH, dissolved oxygen, and the presence of solvents or formulation. Because of this, LC50 is not directly comparable across species or contexts.

Interpretation and use: A lower LC50 indicates higher acute toxicity. LC50 values inform regulatory hazard classifications, risk assessments, and comparisons of substances. They are often used alongside other metrics such as LC50 over different time periods (e.g., 24, 48, 96 hours) and nonlethal endpoints (EC50, NOEC, LOEC) to build a broader toxicological profile.

Limitations: LC50 reflects short-term, acute toxicity under specific test conditions and does not capture chronic effects, sublethal impacts, bioaccumulation, or variability in real-world exposures.