Determination of some insecticide and their toxic metabolites residues in maize silage

The aim of this study was to monitor the degradation of chlorpyrifos, deltamethrin and imidacloprid and transformation to their some metabolites [3,5,6-trichloro-2-pyridinol, diethyl phosphate, diethyl thiophosphate, chlorpyrifos-oxon, 3-phenoxybenzoic acid, 3-(4-hydroxyphenoxy)benzoic acid, imidacloprid-olefin, imidacloprid guanidine, 6-hydroxynicotinic acid and 6-chloronicotinic acid] during the 200-day fermentation period of maize silage. The effect of the fermentation process on the degradation of insecticides and the transforming to metabolites was investigated. The fermentation of lactic acid bacteria causes the acidic conditions in maize silage and insecticides can be metabolized by the microorganisms in the fermentation medium. In this study, each insecticide was applied separately under laboratory conditions to blank sample (maize plants grown without pesticides). A part of the maize plants spiked with insecticide were left to dry and the other part was ensiled in jars. Spiked insecticides and their metabolites were analyzed periodically using LC-MS/MS in samples to determine the effect of fermentation. Analytical method was verified according to the SANTE/12682/2019 Guideline. The LOD and LOQ values were between 2,76 mg/kg to 53,61 mg/kg and 9,19 mg/kg to 178,71 mg/kg, respectively. The recovery, repeatability RDSr and reproducibility RDSR values of compounds were calculated between 93,7-109,2%, 1-15%, and 1-13%, respectively. In silage samples, the degradation of chlorpyrifos, deltamethrin and imidacloprid was less with rates of 46, 45 and 30%, respectively, compared with the control samples (67, 55 and 61%). This study showed that the low pH in maize silage decelerate the degradation of insecticides, so pesticide residues can remain stable for longer in the silage environment compared to aerobic conditions.