This section provides summary information on pesticide residue definitions. More details can be found in the JMPR Manual (chapter 5.12) and the JMPR Training Manual (chapter 6), which also provide worked examples.

A pesticide residue is any specified substance in food, agricultural commodities, or animal feed resulting from the use of a pesticide. The term includes any derivatives of a pesticide, such as conversion products, metabolites, reaction products, and impurities considered to be of toxicological significance.

Although metabolites, degradation products and impurities are included in the definition of pesticide residues, this does not necessarily mean that metabolites or degradation products should always be included in the residue definition.

Residue definitions are required to clearly establish the compound or compounds of interest to:

1. estimate dietary intake risks associated with the presence of residues in food or feed commodities;

and

2. provide the basis for monitoring of compliance with maximum residue limits (MRLs).

The basic requirements for the definition of residues are different, depending on the purpose of the residue assessment.

1. The residue definition for dietary intake estimations and risk assessment should include metabolites and degradation products of toxicological concern, irrespective of their source, where present in significant concentrations.
   
   
2. The residue definition for monitoring of compliance with MRLs, on the other hand, should be:

• based on a single compound whenever possible, which is preferably recoverable with multi-residue methods;
  
  
• enable unambiguous identification of source of residues, to allow for effective monitoring of compliance with MRLs and enforcement of the registered Good Agricultural Practice (GAP)
  
  
• the same for all commodities, if possible, to facilitate routine monitoring.

The requirements for these two residue definitions are not always compatible and for certain pesticides it may be necessary to establish separate residue definitions for MRL enforcement and dietary risk assessment purposes.

It should be stressed that a residue definition characterized as a single compound does not reduce the data requirements. Complete information on the total residue composition and the relative ratio of residue components is needed to determine whether a single compound can be used, and this information is also needed for risk assessment purposes.

Residue definitions are set by JMPR and also by major registrars. Although there may be differences among these definitions, there is a tendency towards international harmonization. Therefore, residue definitions established by reputable bodies can generally also be used by registrars in developing countries, as long as the established residue definition is representative of the intended use.

In general, the residue definition of a pesticide can be considered representative of its intended use if residue metabolism studies have been conducted in each type of crop category for which use is proposed.

Crops can be considered to belong to one of five group for crop metabolism studies:

• root crops (root and tuber vegetables, bulb vegetables)
  
  
• leafy crops (Brassica vegetables, leafy vegetables, stem vegetables, hops)
  
  
• fruits (citrus fruit, pome fruit, stone fruit small fruits, berries, grapes, banana, tree nuts, fruiting vegetables, persimmon)
  
  
• pulses and oilseeds (legume vegetables, pulses, oilseeds, peanuts, legume fodder crops, cacao beans, coffee beans)
  
  
• cereals (cereals, grass and forage crops)

One crop from a group will cover the entire group for purposes of metabolism in those crops within the group.

In order to extrapolate metabolism of a pesticide to all crop groupings, metabolism studies on a minimum of three representative crops (from the five different crop categories) should be conducted. If the results of these three studies indicate a comparable metabolic route, then additional studies will not be needed on crops in the other two groups.

A residue definition for farm animals may be required whenever a pesticide is applied directly to livestock, to animal premises or housing, or where significant residues remain in crops or commodities used in animal feed, in forage crops, or in any plant parts that could be used in animal feeds. Animal groups that may have different metabolism, and thus different residue definitions, are rats, ruminants and poultry.

Different residue definitions may sometimes apply for crops and for animals. For example, if the major residue in animal commodities is a specific animal metabolite, a definition which includes that metabolite is needed for regulatory monitoring. However, the animal metabolite is not required in the residue definition for crop commodities if it is not found in the crops. Separate definitions would then be proposed for commodities of plant and animal origin.

In many cases, the residue definition established by JMPR and/or by reputable registration authorities can be used by a developing country and there will be no need to set a local definition.

The residue definition used by a reference country or JMPR is representative of the intended use in the local situation if:

• it has been established based on metabolism studies conducted in the same crop group (see above)

or

• it has been established based on metabolism studies conducted in three different crop groups, even if the crop group relevant the local situation was not included in those studies.

If, alternatively, there is a need to set a local residue definition, the registrar should refer to the JMPR manual for further guidance.