Boîte à outils pour l’homologation des pesticides

#709 Residues in rotational crops

Objective of the study

Metabolism and residue studies conducted in rotational crops (also referred to as rotational crops) are typically required for uses of pesticides where a food or feed crop may be planted after the harvest of a pesticide treated crop (or in some cases replanting of crops after failure of the pesticide treated crop).

The following studies are generally conducted:

1. Metabolism in rotational crops (confined rotational crop study)

The main objectives of metabolism studies in rotational crops are to:

  • provide an estimate of the total terminal residues in the relevant portion of crops at harvest of rotational crops following treatment of the preceding crop as proposed;
  • identify the major components of the total terminal residue;
  • indicate the distribution of residues between relevant crop parts;
  • to quantify the major components of the residue;
  • to decide on the necessity of field residue trials in rotational crops (limited field studies).

 

2. Magnitude of residues in rotational crops (field rotational studies)

Field studies of residues in rotational crops are performed to determine the amount of pesticide residues which maybe accumulated into rotational crops via soil uptake following realistic agricultural practices.

These data may be used to:

  • establish crop rotation restrictions, i.e., the time from application to a time when rotational crops can be planted based on residue accumulation;
  • provide information for assessing the overall significance of the residues for dietary risk assessment;
  • determine whether maximum residue limits (MRLs) will be needed in rotational crops.

Further information on studies on residues in rotational crops can be found in Chapter 3.5 of the JMPR Procedure Manual.

Worked examples on this topic are provided in Chapter 3 of the JMPR Training Manual


Circumstances in which the study is required

1. Metabolism in rotational crops

Metabolism studies in rotational crops should be conducted if the parent compound or soil metabolites are persistent in soil or significant concentrations of metabolites in soil occur.

Studies on rotational crops are generally not required for uses of pesticides on permanent or semi-permanent crops including, but not limited to, the following commodities or crop groups: asparagus, avocado, banana, berries crop group, citrus fruit crop group, coconut, cranberry, dates, fig, ginseng, globe artichoke, grapes, guava, kiwi fruit, mango, mushrooms, olives, papaya, passion fruit, pineapple, plantain, the pome fruits crop group, rhubarb, the stone fruits crop group, and the tree nuts crop group

2. Magnitude of residues in rotational crops

If the metabolism studies indicate that residues of the active substance or of relevant metabolites or breakdown products either from plant or soil metabolism may occur (> 0,01 mg/kg), limited field studies and, if necessary, field trials should be carried out.

Studies are normally not be required in the following cases:
• no metabolism studies on rotational crops are to be performed; or
• metabolism studies on rotational crops show that no residues of concern are to be expected in rotational crops.


Test conditions

1. Metabolism in rotational crops

The study should normally be performed using a sandy loam soil.

Rotational crops studied should be representative of each of the following crop groupings:

  • root and tuber vegetable, e.g., radish, beets or carrots;
  • small grain, e.g., wheat, barley, oats or rye;
  • leafy vegetable, e.g., spinach or lettuce.

Where possible, crops should include those expected in the rotational schedule on the label, if known.

2. Magnitude of residues in rotational crops

The study uses a typical end-use product applied to a field plot, after which suitable rotational crops are grown to assess the amount of pesticide residue taken up into rotational crops under actual field conditions.


Test substance

1. Metabolism in rotational crops

The soil is treated with radiolabelled pesticide active ingredient, preferably containing formulation ingredients typical of an end use product as applied in the field.

2. Magnitude of residues in rotational crops

Residue field trials for rotational crops are conducted with a typical end product (formulation).


Typical endpoints of the study

1. Metabolism in rotational crops

Identity and levels of parent and metabolites occurring in rotational crops (is the composition of the residue the same as in direct plant metabolism?).

Levels of total radioactive residues occurring in rotational crops.

2. Magnitude of residues in rotational crops

Residue levels of the pesticide (and relevant metabolites) expressed as mg a.i./kg substrate.


Testing guidelines

The following testing guidelines may be used for crop field trials: