What is the term for the concentration of a chemical in air required to kill 50% of test animals?

The term that describes the concentration of a chemical in air required to kill 50% of test animals is known as LC50. This stands for "Lethal Concentration 50" and is specifically used in toxicology to indicate the concentration of a substance that is lethal to 50% of a population under controlled conditions. LC50 is important for assessing the risk posed by various chemicals, including pesticides, as it helps determine the potential hazard level to both the environment and human health when exposed to different concentrations.

In contrast, other terms provided refer to different measures of toxicity. LD50 indicates the lethal dose required to kill 50% of test animals when the substance is taken orally or through other forms of ingestion. TD50 refers to the toxic dose that causes a specified toxic effect in 50% of the test subjects, while EC50 denotes the effective concentration of a substance that produces 50% of its maximum effect, typically in a biological or ecological context. Therefore, in this context, LC50 is the correct choice for describing airborne concentrations that are lethal.