Residue behavior and dietary risk assessment of tebuconazole and pyraclostrobin in corn

A high efficient and simple methods for residue analysis of tebuconazole and pyraclostrobin in corn and stover (forage) were developed. The samples were extracted with acetonitrile, purified with primary secondary amine (PSA) and C₁₈, and detected by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that all the correlation coefficient of calibration curves were over 0.99 in ranged of 0.0025 to 0.1 mg/L. At three spiked concentration levels, the average recoveries of the tebuconazole varied from 75% to 101% with the relative standard deviations (RSDs) ranging from 1.3% to 6.0%; the average recoveries of the pyraclostrobin varied from 76% to 101% with the RSDs ranging from 2.1% to 8.4%. The 30% suspension concentrate (SC) of tebuconazole· pyraclostrobin was sprayed at 180 g a.i./ha for 3 times on corn. The residue of tebuconazole and pyraclostrobin in corn were less than 0.01 mg/kg at day 21 and 28 after the last application, which were below the maximum residue limits (MRLs) for tebuconazole and pyraclostrobin in the Codex Alimentarius Commission (CAC), European Union (EU) and Environmental Protection Agency (EPA). For general population, the national estimated daily intake of tebuconazole was 0.154 5 mg, accounting for 8.2% of the acceptable daily intake. The national estimated daily intake of pyraclostrobin was 0.45 mg, accounting for 24.0% of the acceptable daily intake. Thus, the dosage of 180 g a.i./ha for tebuconazole· pyraclostrobin 30% SC was recommended on corn with the preharvest interval at 21 days, and maximum application of three times with a 7-day interval between the sprays.