Why are uncertainty factors applied when deriving reference values from NOAEL/LOAEL?

• A. They remove uncertainty from data.
• B. They double the values to be safe.
• C. They account for interspecies variability, intraspecies variability, and data gaps.
• D. They are optional.

Answer: (C)

Uncertainty factors are protective safety margins used when turning study thresholds (NOAEL/LOAEL) into human reference values. They recognize that animals are not humans, and people are not a single uniform group. Differences in biology mean humans may respond differently to a chemical than the test species (interspecies variability) and among humans themselves (intraspecies variability). They also account for gaps or limitations in the data, such as missing endpoints, shorter study durations, or using a LOAEL instead of a NOAEL. By applying these factors, we derive conservative reference values like an RfD or an ADI, which helps ensure protection for all people, including sensitive subgroups. This isn’t about simply removing uncertainty or automatically doubling values, and these factors are standard rather than optional.