LOAEL definition.

• A. LOAEL is the lowest exposure level with adverse effects.
• B. LOAEL is the highest exposure with no adverse effects.
• C. LOAEL is the same as LD50.
• D. LOAEL is the exposure at maximum tolerated dose.

Answer: (A)

The main idea is to identify the threshold at which adverse effects first appear in a toxicology study. LOAEL stands for the Lowest Observed Adverse Effect Level: it is the smallest exposure level at which any adverse effect has been observed in the test population, based on the endpoints being examined. This is determined from dose–response data, and it can vary depending on what effects are being watched and which species are studied. For example, if a study shows no harm at a certain dose but just above that dose small adverse effects appear, that dose is the LOAEL. This differs from the NOAEL, which is the highest dose at which no adverse effects are observed. It also differs from LD50, which refers to the dose that kills 50% of the population and uses a lethality endpoint, not general adverse effects. And it’s not the same as the maximum tolerated dose, which is about the highest dose that can be given without unacceptable toxicity.