A TDI is an estimate of the amount of a substance in air, food or drinking
water that can be taken in daily over a lifetime without appreciable health
risk. TDIs are calculated on the basis of laboratory
toxicity data to which uncertainty
factors are applied.
TDIs are used for substances that do not have a reason to be found in food (as
opposed to substances that do, such as additives, pesticide residues or
veterinary drugs in foods- see ADI).
For most kinds of toxicity, it is generally believed that there is a dose
below which no adverse effect will occur. For chemicals that give rise to such
toxic effects, a tolerable daily intake (TDI) should be derived as follows,
using the most sensitive endpoint in the most relevant study, preferably in
As TDIs are regarded as representing a tolerable intake for a lifetime, they
are not so precise that they cannot be exceeded for short periods of time.
Short-term exposure to levels exceeding the TDI is not a cause for concern,
provided the individual’s intake averaged over longer periods of time does not
appreciably exceed the level set. The large uncertainty factors generally
involved in establishing a TDI (see below) serve to provide assurance that
exposure exceeding the TDI for short periods is unlikely to have any deleterious
effects upon health. However, consideration should be given to any potential
acute effects that may occur if the TDI is substantially exceeded for short
periods of time.