Residues of the insecticides phorate and methomyl in mint hay and oil

Abstract Since mint oil is used as a flavouring agent for foods and cosmetics, pesticide residues in the oil are undesirable. The residual behaviour of two pesticides, phorate and methomyl, was studied as replacements for chlorinated hydrocarbon pesticides which leave residues in the oil. Phorate applications of 1.1 kg/ha resulted in oil residues of 0.24 mg/kg total phorate in Oregon samples and 1.69 mg/kg in Washington samples. Less than 1% of the residues in the hay distilled with the oil. Mint oil undergoes a 100‐ to 1000‐fold dilution in commercial use with a corresponding reduction of residues in the final product. No residues of methomyl were found in the oil, even with hay residues as high as 5.34 mg/kg. Residues in hay decreased to half of initial levels in 2 to 4 days, independently of use conditions. It was concluded that the proposed use of phorate or methomyl for control of mint pests does not present a residue hazard. Details of the analytical methods used are also presented.