Dissipation, residues and risk assessment of pyraclostrobin and picoxystrobin in cucumber under field conditions.

Pyraclostrobin and picoxystrobin are two representative pesticides of strobilurins used to treat cucumber downy mildew, which have raised issues of food safety and human health. A new formulation containing these two compounds is being prepared for marketing in China. The dissipation and residual levels of pyraclostrobin and picoxystrobin in cucumbers under field conditions were determined simultaneously by a validated method via liquid chromatography-tandem mass spectrometry (LC-MS/MS). The dissipation rules were described by first-order kinetics and the half-lives of pyraclostrobin and picoxystrobin were less than 8.2 days and 3.4 days. The highest terminal residue of pyraclostrobin was 0.014 mg kg-1 which was lower than maximum residue limit (MRL) in China (0.5 mg kg-1 ) and of picoxystrobin was 0.029 mg kg-1 , respectively. In the long-term intake risk assessment of pyraclostrobin and picoxystrobin for general population (18-79 years), the chronic risk quotient (RQc ) varied from 5.64% to 21.97%. The assessment of short-term risks included children (1-6 years) and adults (18-79 years) and in which the RQa values were 0.38% and 2.85%. Both results showed the intake risks of cucumber were acceptable. Pyraclostrobin and picoxystrobin degraded easily in cucumbers under open field conditions. The long-term and short-term risks caused by final residues of pyraclostrobin and picoxystrobin were insignificant. The recommended pre-harvest interval of 3 days was safe. The article will be helpful in rational use of these pesticides and MRL formulation of picoxystrobin on cucumber. © 2020 Society of Chemical Industry.