Residue behavior and dietary risk assessment of bifenthrin, thiamethoxam and clothianidin in wheat

A high efficient and simple method for residue analysis of bifenthrin, thiamethoxam and its metabolite clothianidin in wheat and straw was developed. The samples were extracted with acetic acid-acetonitrile, purified with anhydrous magnesium sulfate, primary secondary amine (PSA) and GCB, and detected by ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometry (UPLC-MS/MS). The results showed that there was a good linear relationship between the peak areas of bifenthrin, thiamethoxam and clothianidin and their mass concentrations in the range of 0.002 5-0.1 mg/L, with R² greater than 0.99. The recoveries of bifenthrin, thiamethoxam and clothianidin in wheat and straw were 93%-98%, 87%-98% and 87%-98%, respectively, and the relative standard deviations (RSDs) were 0.8%-4.8%, 0.6%-4.1% and 1.0%-3.3%, respectively, when the spiked levels were 0.01, 0.1, 0.5 mg/kg for wheat grain and 0.05, 0.5, 3 mg/kg for straw. The supervised residue trials were carried out in 12 main wheat producing areas in China according to "guideline for the testing of pesticide residues in crops". The 35% suspension concentrate of bifenthrin and thiamethoxam was sprayed once at the dosage of 150 g/hm² (active ingredient 52.5 g/hm²) at the beginning of wheat aphids bloom. The residual amounts of bifenthrin, thiamethoxam and clothianidin in wheat grains collected on day 14 and 21 after application verified the applicability of the MRL values, and the results of multi-point tests had higher reliability. The results of long-term and short-term dietary exposure risk assessment showed that the dietary exposure risks of bifenthrin, thiamethoxam and clothianidin residues in wheat were acceptable for children aged 1-6 years and the general population.