Page 80 - FoodFocusThailand No.234 September 2025

STRONG QC & QA

The NOAEL (No-Observed-Adverse-Effect Level) refers
to the highest amount of dose of a chemical that does not
cause any toxicity or adverse effects, while the LOAEL
(Lowest-Observed-Adverse-Effect Level) is the lowest
amount of a chemical that produces toxicity or adverse
effects. In research literature, NOAEL or LOAEL values may
not always be presented as a dose-response graph, such
as in Figure 2, but may instead appear in tabulated results.
To determine the NOAEL, the parameter used to assess
toxicity must be considered, such as enzyme levels deviating
from the normal range. The doses or concentrations typically
increase step by step: for example, at Dose 1 and Dose 2,
no enzyme changes are observed, while at Dose 3, changes
occur. Thus, Dose 2 is identified as the NOAEL, and Dose
3 is the LOAEL. The NOAEL should always be used before
the LOAEL whenever available.
when using data from sub-chronic toxicity testing instead of
chronic studies, or when using a LOAEL in place of a NOAEL,
RfD or ADI = NOAEL ...........Equation 1 as shown in Table 1.
(mg/kg BW/day) (UFxMF) 3) Exposure Assessment is the evaluation of the extent
to which a chemical is taken into the body. This step is of
critical importance in risk assessment, as chemical toxicity will
The NOAEL or LOAEL is then applied to calculate not occur without exposure, and the severity of toxic effects
health-based guidance values, such as the Reference Dose depends on the amount of the chemical received. Therefore,
(RfD) or the Acceptable Daily Intake (ADI)—the amount of if the estimation of exposure is inaccurate, the resulting risk
a chemical that humans can ingest daily over a lifetime calculation will also be significantly erroneous. Three key
without any adverse health effects. The ADI can be calculated types of information are required in this step: 1) data on food
using Equation 1. consumption amounts, 2) data on the concentration of the
In cases where data are obtained from chronic toxicity chemical of interest in the relevant food or water, and 3) data
testing, the Uncertainty Factor (UF) is applied to address on the body weight of consumers by different age groups.
the uncertainty arising from the use of the NOAEL from Exposure can be calculated using Equation 2, with the unit
animal studies to calculate the Reference Dose (RfD) or of Consumption Daily Intake or Chronic Daily Intake (CDI)
Acceptable Daily Intake (ADI) for humans. The UF consists expressed in the same units as the Acceptable Daily Intake
of sub-factors: the first factor of 10 accounts for interspecies (ADI) or the Reference Dose (RfD), i.e., mg/kg bw/day.
variation (differences between animals and humans), and
Chemical concentration (mg/g) [
the second factor of 10 accounts for intraspecies variation [ Consumption amount (g/day) X
(differences among humans). Additionally, there may be
a Modifying Factor (MF), which reflects the completeness and CDI = ......Equation 2
reliability of the data used. This includes the appropriateness (mg/kg BW/day) Body weight (kg)
of the study design, the number of animals used, and
the quality and accuracy of pathological examinations. 4) Risk Characterization is the process of comparing
The MF typically ranges from 1 to 10, with a default value of the estimated chemical exposure obtained from Exposure
1. However, it may be assigned values such as 2, 5, or 10, Assessment (Step 3) with the reference value for a safe
depending on data quality and expert judgment based on level of exposure derived from Hazard Characterization
the available evidence. Moreover, the UF may be increased (Step 2), such as the Acceptable Daily Intake (ADI).

Table 1 Considerations in Determining the Uncertainty Factor
UF
Type of Study MF
NOAEL LOAEL

Chronic toxicity testing 10 X 10 10 X 10 X 10 1-10
According to expert judgment

Sub-chronic toxicity testing 10 X 10 X 10 10 X 10 X 10 X 10 1-10
According to expert judgment

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