Residue level and dissipation pattern of spiromesifen in cabbage and soil from 2-year field study

Abstract

Spiromesifen is a new class of insecticide used for the control of whiteflies and mites which have developed resistance to the more commonly used neonicotinoids. Dissipation pattern of spiromesifen on cabbage was evaluated over 2 years by conducting supervised field studies as per good agricultural practices. Cabbage and soil samples were extracted and purified using modified QuEChERS method and analyzed through gas chromatography (GC). Confirmatory studies were carried out by liquid chromatography–tandem mass spectrometry (LC-MS/MS). The recoveries of spiromesifen from cabbage and soil were between 85.44 and 103.37 % with the relative standard deviation (RSD) between 3.2 and 9.4 % (n = 6). The limit of detection (LOD) and limit of quantification (LOQ) were 0.003 μg mL⁻¹ and 0.01 mg kg⁻¹, respectively. The measurement uncertainties (MUs) were within 9.9–14.9 %. Initial residues of spiromesifen on cabbage were 0.640 and 1.549 mg kg⁻¹ during 2013 and 0.723 and 1.438 mg kg⁻¹ during 2014 from treatments at standard and double doses of 125 and 250 g active ingredient (a.i.) ha⁻¹, respectively. Spiromesifen residue dissipation followed first-order rate kinetics, and it degraded within the half-lives of 2.9 and 3.9 days during 2013 and 3.2 and 4.5 days during 2014. The residue levels reached below the maximum residue limit (MRL; 0.02 mg kg⁻¹) within 15–17 days at the standard dose and 24–27 days at the double dose. The field soil analyzed at harvest (30 days) was free from spiromesifen residues. Metabolite spiromesifen-enol was not detected in any sample which was confirmed through LC-MS/MS analysis.