The aim of these studies is to demonstrate the time period for which stability during freezing has been shown in representative commodities from plant origin (raw and processed) and animal origin.
Freezer storage stability studies should include sufficient starting material and should have a sufficiently high concentration of residue to allow for any observed decline during storage to be quantified. Samples could either be obtained from crops treated or animals dosed with the pesticide (samples with incurred residues) or from the fortification of control (untreated) commodities with known amounts of each component of the residue definition. With residues being incorporated in the sample matrix, studies using incurred residue samples represent a more realistic scenario than studies with fortified samples. Freshly fortified control samples of the stored commodities should be analysed at each of the time points when aged/stored commodities are removed from frozen storage for analysis, to allow differentiation of procedural losses and losses due to storage. Control samples used for concurrent recovery (= procedural recovery) determinations should be of the same commodity type as the commodity studied in the storage stability study. At least two sampling intervals (time zero and other) should be used. Duplicate samples of every commodity at each time point for all components of the residue definitions need to be analysed, while for Day zero a minimum of five independent samples is recommended.
Reports on freezer storage stability studies should include a detailed description of the commodities that were stored); the test chemical(s); the experimental design and storage conditions; freezer storage stability results and reporting of the data; statistical analysis; quality control measures/precautions taken to ensure the validity of these operations.