Residueanddissipationdynamicsof38%pyraclostrobin·boscalidSCinstrawberryandsoil

In order to evaluate the safety of 38% pyraclostrobin·boscalid suspension concentrate (SC) (mass fraction of active ingredient: 12.8% of pyraclostrobin, 25.2% boscalid) in agricultural products and environment, the residues and dissipation dynamics of the agent were investigated in field experiments in Beijing and Shandong for two years (2015 and 2016). The residues of pyraclostrobin and boscalid simultaneously in strawberry and soil were determined by a new high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis method. The samples were extracted by acetonitrile, purified by N-propyl ethylenediamine (PSA), measured by multiple reaction monitoring (MRM) using electrospray ionization and quantified via matrix matching external standard curve. At spiked levels of 0.015, 1.5 and 3.0 mg/kg, the average recoveries of pyraclostrobin in strawberry and soil samples were 97%-107% and 94%-106%, respectively, and RSDs were 1.8%-3.9% and 2.2%-4.1%, respectively. The limit of quantitation (LOQ) of pyraclostrobin in strawberry samples was 0.015 mg/kg. At spiked levels of 0.03, 3.0 and 6.0 mg/kg, the average recoveries of boscalid in strawberry and soil samples were 90%-101% and 92%-97%, respectively, and RSDs were 4.6%-13% and 2.9%-14%, respectively. The LOQ of boscalid in strawberry samples was 0.03 mg/kg. In the decline study, the dissipation equations of pyraclostrobin and boscalid in strawberry and soil samples fit the first-order kinetics equation, and the half-lives for the dissipation of these pesticides were 4.8-6.0 d and 5.1-11 d, respectively, in strawberry, while 3.4-10.0 d and 3.4-6.0 d, respectively, in soil. Following the recommended dosage of 38% pyraclostrobin o boscalid SC in strawberry (active ingredient: 228 and 342 g/hm²), the samples were applied for less than 4 times and collected 3, 5 and 7 d after the last application. The maximum final residue of pyraclostrobin in the strawberry was 0.13 mg/kg, which was below the maximum residual limit (MRL) (0.5 mg/kg) of EU. And that of boscalid was 0.78 mg/kg, which was lower than the MRL (3.0 mg/kg) of China. The safety interval of 38% pyraclostrobin. boscalid SC for strawberry is 3 days. The test results provide data support for the safe use of pesticides in strawberries and the food safety of agricultural products.