Objective of the study

Metabolism of the pesticide includes the processes of transport or translocation within the organism as well as transformation to metabolites or degradation products.

Metabolism studies are conducted to determine the qualitative metabolic fate of the active ingredient and elucidate its metabolic pathway. Many pesticides undergo change during and after application to livestock. The composition of the terminal residue must, therefore, be determined before the residue analytical methodology can be developed and residues quantified.

In metabolism studies, the pesticide is applied to fish in amounts and for durations of time that could occur in practice when the compound is used for pest control (i.e. the existing or intended good agricultural practices (GAPs)). In the case of fish in due course the animal is slaughtered. The animal commodities are then examined for content of total residues produced by administration of the compound.

Further information on studies on metabolism of residues in fish can be found in Chapters 3.2 and 5.3 of the JMPR Procedure Manual.

Worked examples on this topic are provided in Chapter 5 of the JMPR Training Manual.

Circumstances in which the study is required

These studies may be required where the pesticide is used in crops whose parts or products, also after processing, are fed to fish and where residues in feed may occur from the intended applications.

Results from fish bioaccumulation studies may be used if it can be shown scientifically that the results of these studies can be assumed to be equivalent.

Test organism or substrate

The study is conducted with a relevant fish species.

Test substance

The animals should be treated with radiolabelled active ingredient, preferably containing formulation ingredients typical of an end-use product as applied in the field.

Typical endpoints of the study

• Portion of extractable and non-extractable radioactivity in edible tissues, as % of total radioactive residues (TRR) and mg parent compound equivalent/kg sample material;
• Portion of characterised but not identified radioactivity in edible tissues and potential feed items;
• Identification of metabolites, described by their systematic chemical name – for all extractable residues at >10% TRR or at >0.05 mg/kg;
• Characterization of metabolites – for all extractable residues at <10% TRR or at 0.01- 0.05 mg/kg;
• Presence of metabolites in conjugated form, extractability of conjugated metabolites;
• Schematic diagram of the metabolic pathways in fish with a brief explanation of the distribution and chemical reactions involved.

Testing guidelines

The following testing guidelines may be used for determination of the nature of residues in fish:

• European Commission. Guidelines for Residue Data – Working document on the nature of pesticide residues in fish. (Technical Guidelines - Appendix J)