Define NOAEL and LOAEL and explain how they are used to derive reference doses.

• A. NOAEL is the lethal dose for 50% of animals; LOAEL is the dose that kills all animals.
• B. NOAEL and LOAEL indicate the average observed response and are used for statistical power.
• C. NOAEL is the highest dose/exposure at which no adverse effects are observed; LOAEL is the lowest dose at which adverse effects are observed; they serve as Points of Departure to derive reference values like RfD or TDI.
• D. NOAEL is the dose causing some effect; LOAEL is the dose with no effect.

Answer: (C)