What term is used to indicate the concentration of a substance that results in the death of half the test subjects in a study?

The term used to describe the concentration of a substance that leads to the death of half the test subjects in a study is referred to as LD50, which stands for "Lethal Dose 50." This metric is essential in toxicology as it provides a standardized measure of a substance's acute toxicity. The LD50 value is typically expressed in milligrams of substance per kilogram of body weight and represents the dose at which 50% of the test population (often animals in laboratory studies) is expected to die.

This term is critical for establishing safety guidelines and regulations for various chemicals, including pesticides, allowing applicators to understand the potential risks involved in using them. Understanding LD50 values helps in comparing the toxicities of various substances and informs decision-making regarding their safe application.

The other terms listed have different meanings: IC50 refers to the concentration needed to inhibit a biological process by half, primarily used in pharmacology; a CAS number is a unique identifier for chemical substances; and TC50 refers to the concentration that results in death of 50% of test subjects over a certain period, which may differ from immediate lethality. Hence, LD50 is the correct term for measuring acute toxicity.