Spinach or amaranth contains highest residue of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin on six leaf vegetables upon open field application.

To select representative leaf vegetables which may contain the highest residue, field experiments of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin on six crops including pakchoi, rape, crown daisy, amaranth, spinach, and lettuce were designed and conducted. In this study, a high-performance liquid chromatograph and electrospray ionization tandem mass spectrometer with multiple reaction monitoring was used to simultaneously determine metalaxyl and fluazifop-P-butyl residue in various samples, and a gas chromatograph with electron capture detector was used to detect chlorpyrifos and lambda-cyhalothrin. The limits of quantification (LOQ) of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin were in the range of 0.001-0.01 mg kg(-1) for all samples, and the average recoveries of all pesticides ranged from 67.6 to 119.1% at spiked levels of 0.01-0.1 mg kg(-1). In supervised field trials, the half-lives of metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin were in the range of 1.11-3.79 days, 1.11-2.27 days, 1.13-5.17 days, and 1.77-6.24 days. It was also found that all pesticide residues in spinach and/or amaranth were higher than others after application. It is recommended that spinach or amaranth can be selected as a representative crop of leaf vegetables in studying systemic fungicide, insecticides, and herbicides with similarity as metalaxyl, fluazifop-P-butyl, chlorpyrifos, and lambda-cyhalothrin.