No-observed-adverse-effect level

No-observed-adverse-effect level (NOAEL) is a measure used in toxicology studies to denote the level of exposure of an organism, such as a human or animal, to a substance at which there are no observable adverse effects. It is usually derived from laboratory tests on animals and is used to establish safe levels for human exposure to the same substance.

Definition

The NOAEL is the highest experimental point that is without an adverse effect. It is used to study the effects of chemicals on health. The NOAEL is a part of the process of deriving acceptable daily intakes or tolerable daily intakes.

Use in Risk Assessment

In risk assessment, the NOAEL is used to determine the Reference Dose (RfD) or the Tolerable daily intake (TDI). The RfD or TDI is calculated by dividing the NOAEL by a safety factor. The safety factor is used to account for uncertainties in the data.

Limitations

The NOAEL has several limitations. It is dependent on the size of the study and the sensitivity of the measurements. It also does not account for individual variability in response to the substance.

See also

• Lowest-observed-adverse-effect level
• Threshold limit value
• Acceptable daily intake
• Tolerable daily intake

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