Determination of Quizalofop-p-ethyl in onion spices: Weed control efficiency, residual profile, and food safety assessment under field conditions

Abstract Monitoring for pesticide residues in onion (Allium cepa L.) is important to protect consumer health and to ensure food safety. A field experiment was conducted for two consecutive seasons with quizalofop ethyl (5% EC) @ 50 and 100 g a.i. ha-1 to evaluate weed control efficiency and to determine terminal residues. Double the recommended dose (100 g a.i. ha-1) produced higher weed control efficiency (88.53-95.13 %), lower weed density (4.15-7.73 m-2), and weed dry weight. A rapid, sensitive, and analytical method was developed using high-performance liquid chromatography with excellent linearity (r2 > 0.99). Accuracy of the method in terms of average recoveries ranged from 94.4 to 99.9 % at spiking levels of 0.04, 0.20 and 0.40 mg kg-1 with intra and inter-day precision expressed relative standard deviation RSD (%) between 0.1-2.3 and 1.7-3. The limit of quantification for quizalofop-p-ethyl was established at 0.04 mg kg-1 with signal to noise (S/N) ratio ≥10. The method was successfully applied and initial quantified residues were in the range of 2.5-4.4 mg kg-1 irrespective of seasons and doses. Finally, the presence of targeted herbicide residues in harvested samples was confirmed by liquid chromatography tandem mass spectrometry (LC-MS/MS) under optimized operating conditions. The herbicide dissipated to the lowest validated level (0.04 mg kg-1) between 10-15 days with half-life values (DT50) of 1.5-1.6 days. Dietary risk assessment assured harvested onions were safe for consumption at the recommended dose.