Photochemistry of Imidacloprid in Model Systems

Abstract

The photochemical behavior of the neonicotinoid insecticide imidacloprid was studied with regard to different chemical environments. Different model solvents simulated the structure moieties mainly occurring in waxes and cutin of the plant cuticle. Cyclohexane and cyclohexene substituted saturated and unsaturated hydrocarbon chains, whereas ethanol and 2-propanol were models for primary and secondary alcohol groups of cuticular components. After 5 h of irradiation, imidacloprid was completely degraded in all solvents. With 88-96 mol% 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine was formed as the main product, whereas 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-one was identified as minor product in the range 4-6 mol%. By contrast, besides the photoproducts formed in organic solvents, irradiation of the solid imidacloprid on a glass surface delivered a complex variety of unidentified photoproducts. The nucleophilic addition reaction of the main photoproduct, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine, with both cyclohexene oxide and methyl 9,10-epoxystearate as model compounds indicates that epoxidized cutin acids are possible reaction partners for the formation of plant cuticle bound residues of imidacloprid, which could explain the reported findings of nonextractable residues of imidacloprid in plants.

Bioavailability and release of nonextractable (bound) residues of chiral cycloxaprid using geophagous earthworm Metaphire guillelmi in rice paddy soil

“…Cycloxaprid (CYC) is one of the most effective neonicotinoids that have been developed for agricultural pest control (Schippers and Schwack, 2008;Shan et al, 2011;Shao et al, 2008Shao et al, , 2009Shao et al, , 2010Shao et al, , 2011aShao et al, , b, 2013. CYC is unique in having two enantiomers (Fig.…”

Comparative Phytotoxicity Assays of the Herbicide Alloxydim and Its Main Identified Photoproduct in Cereal and Broadleaves Crops

“…Because the plant cuticle represents a complex mixture of many compounds that may act as photosensitizers, quenchers, and potential reaction partners (Monadjemi et al 2012), model photoreactions in organic solvents simulating the natural constituents of cutin and plant waxes are often evaluated. These simple models, introduced by Schwack (Schippers and Schwack 2008;Schynowski and Schwack 1996), have proved to be the best practical way to study possible reaction pathways and product formation prior to studies in more complex natural environments. Furthermore, the resulting products can effectively be used as analytical standards for further studies in natural environments.…”

Residuos de Neonicotinoides y Espinosad en cera y polen : Determinación por LC-ESI-MS

“…Los resultados obtenidos para el estudio de la persistencia del nitenpyram en cera se muestran en la figura 13. estudios que indican que imidacloprida se degrada más fácilmente en presencia de luz. 151,156 Aunque no existe evidencia bibliográfica de la persistencia de este pesticida en cera, se pueden citar como referencia los tiempos Ác De los resultados obtenidos se desprende que para el caso de clotianidina, imidacloprida y sobre todo para acetamiprida y tiacloprida para conseguir eficacias similares a las conseguidas con menores cantidades de muestra se precisaban 2 limpiezas consecutivas.…”

“…Estudios que posteriormente demostraron que los metabolitos de dichos contaminantes persisten en la cera por lo menos durante siete años, que la movilización de los contaminantes se genera por intercambio de cuadros que los apicultores realizan dentro de la colmena y que las mismas abejas transportan contaminantes desde cuadros contaminados a cuadros nuevos, facilitando su movilización 148,149. En lo que se refiere a la persistencia de neonicotinoides en distintas matrices, se han encontrado algunos estudios que investigan la degradación de estos compuestos por efectos de la radiación solar en suelos,150 en grasas y cutículas de plantas151 o un trabajo más reciente que estudia la disipación de tiametoxam y tiacloprida en aguas residuales, lodos de depuradoras y soluciones surfactantes (tensoactivas), donde concluyen que bajo las mismas condiciones,…”