Dissipation kinetics and dietary risk assessment of metrafenone in greenhouse-grown tomatoes and cucumbers using LC-MS/MS

Abstract

This study investigates the dissipation kinetics, terminal residues, and dietary risk assessment of metrafenone in tomatoes and cucumbers cultivated under greenhouse conditions in the Khubash governorate, Najran region, Saudi Arabia. Residue analysis was performed using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with acetonitrile-based extraction. The method demonstrated excellent linearity (R ² = 0.9981 and 0.9946 for tomatoes and cucumbers, respectively), low limits of detection (LOD: 0.0002 mg kg^-1 and 0.0003 mg kg^-1, respectively), and limits of quantification (LOQ: 0.0025 mg kg^-1 for both matrices). Recovery rates ranged from 93.6% to 98.1% and 92.7% to 99.7% for tomatoes and cucumbers, respectively, with relative standard deviations (RSDs) below 6%, ensuring method accuracy. Precision analysis demonstrated intra-day (RSD_r) and inter-day (RSD_R) repeatability below 16% for both matrices, confirming the method's repeatability. Matrix effects were minimal, with values of -6.71% and -4.15% for tomatoes and cucumbers, respectively, indicating negligible signal suppression. The dissipation followed first-order kinetics, with half-lives of 1.93-1.96 days and 1.61-1.67 days, respectively. The pre-harvest interval (PHI) was estimated at 1.18-1.56 days for tomatoes and 1.37-2.68 days for cucumbers. Terminal residues varied based on application rates and spray frequency, with some exceeding maximum residue limits (MRLs) at early intervals before declining to safe levels. Chronic dietary risk assessment confirmed that the chronic hazard quotient (HQc) values remained significantly below the safety threshold of 100%, indicating no significant health risks. These findings provide essential data for determining appropriate PHIs and ensuring food safety compliance in commercial crop production.

Fig. 1. Chemical structure of metrafenone.

Fig. 2. Optimization of metrafenone MS/MS parameters.

Fig. 3. Matrix matched calibration of metrafenone in tomato (A) and cucumber (B) sample extracts.

Fig. 4. Representative LC-MS/MS chromatograms of metrafenone in blank and spiked tomato and cucumber sample extracts.

Fig. 5. Dissipation of metrafenone in tomato (A) and cucumber (B) at 100 and 200 g a. i. per ha, (n = 3, error bars represent ± standard deviation).