Behavior of Thiamethoxam and Clothianidin in Young Oilseed Rape Plants before Flowering, Monitored by QuEChERS/LC–MS/MS Protocol

Abstract

Nitro-substituted neonicotinoid insecticides have been widely used until recently to control a range of important agricultural pests. Growing concerns about thiamethoxam’s toxicity to pollinators have led to its use being restricted or to it even being banned in some countries. Nevertheless, in Asia, Africa, Southeast Europe, and South America thiamethoxam is still used. Although thiamethoxam has been intensively studied all over the world, its dissipation dynamics have not been studied in depth. The subject of the present study was to (1) develop and validate a QuEChERS/LC-MS/MS protocol for the determination of thiamethoxam and its main metabolite clothianidin in samples of young oilseed rape plants with high chlorophyll content, and (2) make a comparison of the degradation behaviors of thiamethoxam and clothianidin in two crops of winter oilseed rape, cultivated on soils with different pH. For determination of thiamethoxam and clothianidin in plant material with high chlorophyll content, a QuEChERS/LC–MS/MS protocol enabling the detection of low levels of compound concentrations was developed. The proposed clean-up protocol provided recoveries within the range of 92–98% for the compounds under analysis. Precision, calculated as relative standard deviation, was below 20%. Satisfactory linearity of the method was obtained in the concentration range under analysis (0.001–1.0 mg kg−1). Differences in degradation of both insecticides, depending on the physico-chemical properties of the soil, were observed. Thiamethoxam and clothianidin residues disappeared in plants very quickly, and they were not detected below the limit of quantitation in oilseed rape at the flowering stage.