Residue Behavior and Risk Assessment of Pyraclostrobin and Thifluzamide in Cowpea

A rapid and sensitive analytical method for determination of pyraclostrobin and thifluzamide in cowpea was established based on QuEChERS sample preparation and liquid chromatography–tandem mass spectrometry (LC–MS/MS). Average recoveries of pyraclostrobin and thifluzamide on cowpea were 100%–105% and 99%–105% with RSDs of 1%–5% and 2%–6%, respectively. The storage stability tests showed degradation rates of < 20% for samples stored at − 18℃ within 12 weeks. The field trials at eight locations in China showed that the residues of pyraclostrobin in cowpea at 3 and 5 days after spraying were 0.081–0.49 mg/kg and 0.029–0.48 mg/kg, and the residues of thifluzamide were 0.12–0.46 mg/kg and 0.047–0.50 mg/kg, respectively, which were all lower than the corresponding maximum residue limits in China. The dissipation of both pyraclostrobin and thifluzamide in cowpea were fast with half-lives (T 1/2 ) of 1.5–2.3 days and 1.7–2.4 days. This study provided risk assessment data for establishment of good agricultural practice in cowpea plant.