What describes the dose of a toxic chemical needed to kill 50% of an animal population?

The term that describes the dose of a toxic chemical needed to kill 50% of a given animal population is known as LD50, which stands for "Lethal Dose 50." This measurement is commonly used in toxicology to assess the toxicity of a substance. Specifically, it refers to the amount of a substance required to cause death in half of the test subjects (typically animals) exposed to it.

Understanding LD50 is crucial for evaluating the potential risks associated with exposure to various chemicals, including herbicides. The lower the LD50 value, the more toxic the chemical is considered, as it requires a smaller dose to achieve lethal effects in a population.

The other terms do not apply in this context: LC50 refers to the concentration of a chemical in the air or water required to kill 50% of a population, which is not applicable for a dose definition. LT50 deals with the time it takes for a specific percentage of the population to die, and AT50 is not a standard term used in toxicology for these measurements. Thus, LD50 is the correct and relevant measure in this scenario.