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 that indicates the concentration of a substance that results in the death of half the test subjects in a study is known as LD50, which stands for "Lethal Dose 50." This measurement is commonly used in toxicology to assess the acute toxicity of a substance. It provides crucial information about the potential hazards of chemicals, allowing researchers and health professionals to gauge the risks associated with exposure to various substances. The LD50 value is typically expressed in terms of milligrams of substance per kilogram of body weight (mg/kg) and is essential for determining safe dosage levels in both human and environmental health contexts.

Other terms like IC50, which signifies the concentration required to inhibit a biological process by half, are more relevant in pharmacological contexts rather than lethal outcomes. CAS numbers serve as unique identifiers for chemical substances, and TC50, similar to LD50 but less commonly used, refers to the concentration that produces toxicity in 50% of the subjects without specifying lethality. Thus, LD50 is the most appropriate term for measuring the lethal outcome of a substance.