Little Pro on 2018-07-06
Margin of exposure(MOE) and margin of safety (MOS) are two very important concepts in chemical risk assessment. They are both used to characterize chemical exposure risks. In this article, we will summarize their definition, compare their difference and show you how to calculate them.
Margin of exposure (MOE) is the ratio of no-observed-adverse-effect level (NOAEL) obtained from animal toxicology studies to the predicted, or estimated human exposure level or dose. It is commonly used in human health risk assessment (i.e, assessing the safety of a cosmetic ingredient or a food impurity ).
For a chemical substance with health thresholds (i.e, not genotoxic and not carcinogenic), a MOE >= 100 is generally considered to be protective.
Sometimes, a higher MOE than 100 is needed when:
For genotoxic and carcinogenic compounds, you need to use the following equation to calculate the MOE since NOAEL values cannot be identified for those substances. In general a MOE >= 10,000 is considered to be protective. The approach below has been used by EFSA to assess genotoxic and carcinogenic impurities in food.
Unlike MOE, different experts may have different understandings of the margin of safety (MOS). There are 3 definitions. All of them are correct.
Definition 1: Margin of Safety (MOS) is the ratio of the lethal dose to 1% of population to the effective dose to 99% of the population (LD1/ED99). It is used to measure drug safety in pharma industry.
Definition 2: Margin of safety (MOS) is the ratio of no-observed-adverse-effect level (NOAEL) obtained from animal toxicology studies to the predicted, or estimated human exposure level or dose. It is equivalent to MOE. It is often used to assess the safety of cosmetic ingredients. For example, CFDA uses this appraoch.
For a chemical substance with health thresholds (i.e, not genotoxic and not carcinogenic), a MOS >= 100 is generally considered to be protective.
Definition 3: Margin of safety (MOS) is the ratio of derived reference dose (i.e, ADI, RfD, DNEL) to the predicted, or estimated human exposure level or dose. This definition is less common.
If 2 NOAEL values have been identified from long-term rat studies (10mg/kg bw/day for reproductive toxicity, 50mg/kg bw/day for dietary chronic toxicity), the lowest NOAEL(10mg/kg bw/d) will be used to calculate the MOE/MOS. If estimated human intake is 1mg/kg bw/d, then the MOE/MOS will be equal to 10. Since this value is <100, the chemical exposure risk is not likely to be acceptable.
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