Principle

The exact pesticide use details are key input parameters for dietary risk assessment as well as for the establishment of MRLs. These are referred to as the Good Agricultural Practice (GAP) of the pesticide.

GAP in the use of pesticides includes the officially recommended or nationally authorized uses of pesticides under actual conditions necessary for effective and reliable pest control. It encompasses a range of levels of pesticide applications up to the highest authorized use, applied in a manner which leaves a residue which is the smallest amount practicable.

To establish an MRL, the regulator will identify the likely scenarios which may lead to the highest residues in food or feed, which is often referred to as the critical GAP or maximum GAP. Dietary risk assessment is done for the critical GAP.

When a residue assessment is bridged from a reference country to a local situation, one of the steps in the assessment is a comparison of GAPs between the two situations. If the proposed GAP for the local situation is similar or less critical than the GAP in the reference country, residue levels in the local situation will likely also be similar or lower than in the reference country.

Applicability

Comparison of GAPs can be done if the two cases to be compared concern the same pesticide active ingredient and the same commodity or commodity group.

Data requirements

The following data are needed to compare GAPs between a reference country and a local situation.

1. GAP table (or information) of the registered use in the reference country.
2. GAP table (or information) of the proposed use in the local situation.

The key parameters in a GAP table are:

• Crop (according to the Codex classification of food and animal feeds [Standard CAC/MISC 4]) and/or use situation
• Product name
• Type of use (e.g. field, greenhouse, indoor)
• Pest or group of pests
• Formulation type (according to CropLife International formulation codes) & concentration
• Application method (e.g. high volume spraying, granule drilling, low volume application) and kind of application (e.g. broadcast, aerial spraying, between plants – indicate type of equipment)
• Minimum and maximum number of applications (per year or per season) & minimum application interval.
• Minimum and maximum application rate per treatment (as kg a.i./hectolitre & litres of water/ha & kg a.i./ha)
• Minimum pre-harvest interval (PHI)

An example of a GAP table, as recommended by OECD, can be found here. {link to separate document A07-01-01-#1 – GAP table example}

Assessments

The parameters in the GAP tables are compared, and it is assessed whether the proposed GAP for the local situation is similar, more, or less critical than the in the reference country.

From the point of view of residue levels on agricultural commodities, GAP parameters are considered similar in the following cases.

• Application rate. Application rates may be considered similar if they do not deviate more than 25%
• Pre-harvest interval. Pre-harvest intervals may be considered similar if they do not deviate more than 25%
• Number of treatments. When a large number of applications are made in trials (more than 5 or 6) earlier treatments should not be considered to contribute greatly to the final residue unless the compound is persistent or the treatments are made with unusually short intervals.

Formulation type. In many situations different formulations would cause no more variation than other factors, and data derived with different formulations would be considered comparable. The most common formulation types which are diluted in water prior to application, such as EC, WP, water dispersible granules (WG), suspension concentrates (SC) and soluble concentrates (SL) can be considered similar.

In establishing comparability of residue trials data in which more than one of the first three parameters, i.e. application rate, number of treatments or PHI, deviate from the reference, consideration should be given to the combination effect on the residue value which may lead to an underestimation or overestimation of the residue level. Generally, trials should not be used where two critical parameters of GAP deviate. For example, a trial result should not be considered similar if both the application rate is lower (e.g. 0.75 kg/ha in the local situation; 1 kg ai/ha in the reference country) and the PHI is longer (perhaps 18 days in the local situation, 14 days in the reference), as these parameters could combine to underestimate the residue.

More guidance on similarity of GAPs in the JMPR Manual, in particular Chapter 6.2.

Interpretation of the outcome

If the proposed GAP for the local situation is similar or less critical than the GAP in the reference country, residue levels in the local situation will likely also be similar or lower than in the reference country. In the bridging procedure between the residue assessments, a comparison of diets {link to A07-01-02-#2}. is then the next step.

If, on the other hand, the proposed GAP is more critical, then residue levels following the proposed use may be higher, and dietary risks may be greater than in the reference country. In such a case, residue levels resulting from the proposed use {link to A07-02-02-#1}.should be estimated more precisely.