LT50

LT50, short for lethal time 50, is a measure used in toxicology and related fields to express the exposure duration required to kill 50% of a test population under a specified set of conditions. Unlike LD50 or LC50, which express dose or concentration required to kill 50% of the population, LT50 is a time-based endpoint given a fixed dose or concentration. It is commonly reported for acute toxicity studies, sterilization processes, and pathogen inactivation experiments.

Determination involves exposing groups of organisms to a toxicant at defined concentrations and recording mortality over time to construct a survival or time-to-death curve. The LT50 is estimated from the curve as the time at which 50% mortality occurs, often using statistical methods such as probit or logistic regression, Weibull or log-logistic models, or Kaplan-Meier survival analysis. Values are typically temperature- and condition-dependent and may require standardization to enable comparisons.

Factors affecting LT50 include species and strain, age or life stage, exposure route, environmental conditions (temperature, humidity, pH, salinity), and the toxicant's properties (stability, bioavailability). LT50 values are used in risk assessment, regulatory toxicology, pesticide development, and sterilization protocols to compare relative lethality and to design effective control measures.

Limitations include variability between studies, ethical considerations in animal testing, and the challenge of extrapolating across species or conditions. LT50 provides a concise summary of time-to-lethality but should be interpreted alongside other metrics such as LD50/LC50, LT90, LT10, and full survival curves.