TDI / TWI / TMI – daily, weekly or monthly: the tolerable intake of toxins is clearly defined
The Tolerable Daily Intake (TDI) is the estimated quantity of any given substance which can be ingested every day of a person’s entire life without having any tangible effects on his or her health. The TDI is comparable to the ADI (Acceptable Daily Intake), but it is only used in connection with the intake of substances which were not deliberately added, such as contamination in food and feed.
Whether or not a health risk exists due to the intake of a substance with a certain hazard potential depends on the quantity ingested (exposure). As long as the daily intake of an environmental contaminant does not exceed the tolerable quantity, a health risk is practically excluded. The presence of an environmental contaminant with a certain hazard potential does not therefore necessarily lead to the expectation of a health risk.
Determining TDI by adding a safety factor
To determine the TDI, the “No Observed Adverse Effect Level” (NOAEL) is taken from tests with animals or epidemiological data. This value is then divided by a safety factor (usually 100) which is intended to take into account the different levels of sensitivity between humans and animals and between individuals within the human population. The TDI can also be determined using the benchmark dose model or physiology-based pharmacokinetic model.
Depending on intake habits and the pharmacokinetic and pharmacodynamic properties of the substance to be assessed, it can also make good sense to establish a threshold value over a period of one week (TWI, Tolerable Weekly Intake) or one month (TMI, Tolerable Monthly Intake). In this way, undesired effects will not necessarily result if the TDI is exceeded once within the space of a week or a month over a person’s entire lifetime, whereas regularly exceeding the monthly threshold value will.