Systemic insecticides, their degradation products and metabolites in the environment. Quantification methodologies in environmental samples relevant for toxicological and ecotoxicological studies

Systemic insecticides are widely used for pests control and their success is due to their ability of protect the whole plant from roots to the upper leaf. In particular, seeds coating technique is very popular and it is applied to many crops (e.g. corn). However, the use of high amount of Active Ingridient (AI) for seeds coating is causing concern about negative effects to non-target animals. Pollinators insects are exposed to contaminated pollen and nectar, but also herbivore insects are exposed through contaminated leaf. In addition, these insecticides can leach from fields and contaminate wild plants or waterbodies. Therefore, also aquatic species are exposed to insecticides pollution and vertebrates like birds and small mammals could be exposed through coated seeds, seedling and insects. The aim of this study was to develop an UHPLC-HRMS method for the identification of insecticides and their degradation production in corn guttation drops. Particular attention was posed to metabolites, because few information are available in the literature about their presence in relevant matrix for eco-toxicological studies. In addition, some metabolites may have greater toxicity if compared with their parent compounds. In particular, neonicotinoids imine metabolites are characterised by an inversion of selectivity between insects and mammals. Therefore, they can be more toxic for mammals if compared to the neonicotinoids AI. Several metabolites were identify in corn guttation and an extraction procedure based on QuEChERS strategy coupled with a target UHPLC-MS2 method was developed and validated for the quantification of these compounds in corn leaf. High concentration of neonicotinoids thiamethoxam and thiacloprid were observed in corn seedling. In addition, high concentration of the thiamethoxam metabolite clothianidn was observed. Concerning the carbamate methiocarb, the AI was observed only at low concentration, but its metabolites were present at ug/g level. Particularly interesting was the presence of methiocarb sulfoxide, because this metabolite is more toxic of the parent compounds for some species. In conclusion, guttation analysis with UHPLC-HRMS is a powerful technique in order to assess the presence of insecticides metabolites in plants treated with systemic AI. However, UHPLC-MS2 still provide better performance for quantitative analysis, in particular for complex matrices as corn leaf. Therefore, HRMS and MS2 are complementary technique useful to provide levels of contamination and exposure.