Types of HBGVs

The "history" of HBGVs starts with the Acceptable Daily Intake (ADI). This concept was introduced in 1961 in Europe and was taken over by WHO/JECFA. Its unit is milligram or microgram per kg body weight of the consumer per day. So the unit demonstrates that it refers to the consumer, and not to the concentration in food or feed. This HBGV is derived for chemical substances or groups of substances that are intentionally added to food or feed, such as additives, pesticides and veterinary drugs (i.e. the residues). Sometimes it is called a "Provisional" ADI, to stress that it is based on very limited data and that it might be subject to an update in the near future.

A similar type of HBGV is the Reference Dose (RfD). The RfD is quite compliant to the ADI; it is derived using the same procedure, on the basis of the same data. It has the same unit as the ADI. This term is mostly used in North America (e.g. in the IRIS database of US-EPA).

Another well known HBGV is the Acute Reference Dose (ARfD). This guidance value is to be used in cases of acute exposure; most experts in exposure assessment use it for a single intake e.g. from one meal. It is mostly used in evaluations of pesticides. Its unit is milligram or microgram per kg body weight of the consumer. There is no unit for time here.

Another HBGV used in exposure assessment of chemicals in food or feed is the Tolerable Daily Intake (TDI). It is similar to the ADI but refers to contaminants and toxins whereas ADIs refer to residues. The term Tolerable is used here to express that we "tolerate" the contaminant rather than "accept" its presence, in contrast to residues. Besides of a Tolerable Daily Intake, one can also find the Tolerable Weekly Intake (TWI) or even a Tolerable Monthly Intake (TMI). Such HBGVs underline that the chronic exposure is more relevant than a short term intake. JECFA uses also the additonal term Provisional for most TDIs.

ADIs, TDIs, and RfDs are the HBGVs to be used in exposure assessments of chemicals in food or feed. Other types of values do also exist (e.g. AOEL, UL, AR, ..) but these do not point to maximal permissible exposure from food, but for the workplace, or refer to an optimal intake of nutrients.