What is the primary measure of how poisonous a substance is after acute exposure known as?

The primary measure of how poisonous a substance is after acute exposure is referred to as acute toxicity. Acute toxicity specifically relates to the harmful effects that occur soon after a single exposure or multiple exposures in a short span of time. This can be determined through various methods, including lethal dose (LD50) studies, which determine the dose required to kill half of a test population, thereby providing a clear indication of the substance's immediate risk or danger.

Chronic toxicity, on the other hand, relates to the adverse effects resulting from long-term exposure to a substance, typically showing different outcomes than acute toxicity. Topical toxicity examines the potential harm of a substance when it comes into direct contact with the skin, which can be a specific aspect of acute toxicity but does not encompass the broader measure intended in the question. Environmental toxicity assesses the effect of substances on ecosystems, which is distinct from how poisonous the substance is to living organisms following acute exposure. Therefore, the correct answer accurately identifies the key concept of measuring immediate toxicity in a relevant context.