The present study investigates the occurrence of pymetrozine residues in cauliflower samples obtained from six cauliflower‐producing areas of China during fixed time periods in 2017 and estimates the dietary risk of pymetrozine in cauliflower. A liquid chromatography with tandem mass spectrometry method was developed and validated to detect pymetrozine in cauliflower. The samples were extracted using 20 mL of acetonitrile and purified with dispersive solid‐phase extraction using C18 as sorbent. The limit of quantification of pymetrozine was 0.008 mg/kg in cauliflower. The recoveries of the analyte were 82.04–95.18% with RSD <8.45%. The calibration curves for pymetrozine showed good linearities in the concentration range 0.004–2.0 mg/L with determination coefficients (R2) >0.999. Pymetrozine dissipated rapidly in cauliflower with a half‐life of <4 days. The terminal residues of pymetrozine were <0.008–0.0881 mg/kg in cauliflower at 7, 10 and 14 days after spraying from six sites. The routine washing process removed about half amount of the pymetrozine in cauliflower; the reduction ratios were 51.0–52.8%. The dietary risk assessment indicated that pymetrozine did not exhibit obvious dietary health risks in cauliflower when good agricultural practices were implemented.

In this study, a modified quick, easy, cheap, effective, rugged and safe method coupled with gas chromatography with electron capture detection was established to determine dimethachlon residues in paddy soil, rice husk, rice straw, brown rice and cooked rice. The limits of quantification of dimethachlon were 0.01 mg/kg for paddy soil, brown rice and cooked rice and 0.02 mg/kg for rice straw and rice husk. The mean recoveries were in the range 78.59-104.7% with relative standard deviation values of <10% for dimethachlon in the five matrices. For field experiments, the final residues of dimethachlon in paddy soil were < 0.05 mg/kg and were < 1.21 mg/kg in rice straw from six sites. The final residues of dimethachlon in the brown rice at 21, 28 and 35 days after spraying from six sites were 0.08-7.58 mg/kg, and 0.16-30.1 mg/kg in rice husk. Our six test sites covered the main rice-producing areas of China. The routine rice cooking process of a Chinese family could apparently increase the removal of dimethachlon in rice compared with brown rice, and the reduction ratios were > 96%.