Chemical Management

Risk Assessment on chemicals-For Better Understanding-4

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NOAEL (No Observed Adverse Effect Level) and TDI (Tolerable Daily Intake)

What is NOAEL (No Observed Adverse Effect Level)?

The highest exposure of a chemical, determined in toxicity tests etc., having no adverse effect (e.g., onset of sickness) even when the chemical is taken (exposed) daily for the rest of one’s life. In practice, mice, rats or other animals are forced to take a chemical for a certain period of time. This test is repeated several times at varying dose levels. The highest dose level causing no adverse effect in these tests is adopted as NOAEL (No Observed Adverse Effect Level).

Usually, NOAEL is expressed in the amount of a chemical taken daily per kg body weight (e.g., mg/kg/day).

The graph which showed NOAEL(No Observed Adverse Effect Level)

NOAEL is determined by the toxicity tests etc. listed below.

Long-term toxicity*1 Toxicity appearing following a long-term continued exposure (repeated exposure)
Reproductive and developmental toxicity Toxicity exerting adverse effects on parent’s reproductive function and fetuses
Carcinogenicity*2 Potential of causing cancer of various types
Respiratory tract irritation Potential of causing respiratory tract allergies (asthma, etc.)
  1. *1: Also called “repeated dose toxicity”
  2. *2: In some cases there is no NOAEL for carcinogenicity.

→See “Methods and threshold levels for carcinogenicity assessment”

What is TDI (Tolerable Daily Intake)?

Image illustration of a young family

The highest exposure of a chemical having no adverse effect (e.g., onset of sickness) on humans even when the chemical is taken (exposed) daily for the rest of one’s life. NOAEL (No Observed Adverse Effect Level), determined by toxicity studies etc., is divided by UFs (product of Uncertainty Factors)*3 to convert it to human NOAEL.

Usually, NOAEL is expressed in the amount of a chemical taken daily per kg body weight
(e.g., mg/kg/day).

*3: See “UF (Uncertainty Factor)”

TDI (Tolerable Daily Intake)= NOAEL (No Observed Adverse Effect Level)
UFs (product of Uncertainty Factors)

The graph which showed TDI(Tolerable Daily Intake)=NOAEL(No Observed Adverse Effect Level)/UFs(product of Uncertainty Factors)

ADI (Acceptable Daily Intake) and RfD (Reference Dose) are also used as terms having the same meaning as TDI.

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*”Initial Risk Assessment Report” of the NEDO Project achieved the NOAEL determined by a reference survey on long-term toxicity, reproductive and developmental toxicity, carcinogenicity and so on.

Initial Risk Assessment Report

Related Terms

  • LOAEL (Lowest Observed Adverse Effect Level)
  • NOEC (No Observed Effect Concentration)
  • LOEC (Lowest Observed Effect Concentration)

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