- LD50 (Lethal Dose 50%): The dose of a substance that is lethal to 50% of a test population. - NOAEL (No Observed Adverse Effect Level): The highest dose at which no adverse effects are observed. - LOAEL (Lowest Observed Adverse Effect Level): The lowest dose at which adverse effects are observed. - Benchmark Dose (BMD): A dose or exposure level that produces a predetermined change in response rate of an adverse effect.