Phototransformation of imidacloprid on isolated tomato fruit cuticles and on tomato fruits

Imidacloprid, a neonicotinoid insecticide, is widely used in plant protection to prevent crop losses. The objective of this study was to show the photochemical fate of imidacloprid on plant surfaces by irradiation experiments on isolated tomato fruit cuticles and tomato fruits (Lycopersicon esculentum Mill.). Imidacloprid spiked samples were irradiated both under sunlight simulator and natural sunlight conditions for 24 h, which resulted in recoveries of 23% and 24%, respectively, if isolated cuticles were studied. On whole tomato fruits, recoveries were 33% and 71%, respectively. Similar results were obtained on cuticles spiked with the formulation Confidor and irradiated under natural sunlight. However, on tomato fruits the application of Confidor resulted in a higher loss (56%) of imidacloprid. During all irradiation experiments both on cuticles and whole fruits, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine was generally formed at 10–14 mol%, but different other photoproducts were also detected in low amounts, whereas N-nitrosoimidacloprid was only detected under natural sunlight conditions. Rapid photodegradation of imidacloprid could be demonstrated in all experiments. The identified photoproducts, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine and N-nitrosoimidacloprid, are possible reaction partners for plant cuticle constituents to form cuticle bound residues.