Dissipation behavior of phorate and its toxic metabolites in the sandy clay loam soil of a tropical sugarcane ecosystem using a single-step sample preparation method and GC-MS

Abstract

The dissipation of phorate in the sandy clay loam soil of tropical sugarcane ecosystem was studied by employing a single-step sample preparation method and gas chromatography with mass spectrometry. The limit of quantification of the method was 0.01 μg/g. The recoveries of phorate, phorate sulfoxide, phorate sulfone, and phorate oxon were in the range 94.00-98.46% with relative standard deviations of 1.51-3.56% at three levels of fortification between 0.01 and 0.1 μg/g. The Half-life of phorate and the total residues, which include phorate, phorate sulfoxide and phorate sulfone, was 5.5 and 19.8 days, respectively at the recommended dose of insecticide. Phorate rapidly oxidized into its sulfoxide metabolite in the sandy clay loam soil. Phorate sulfoxide alone accounted for more than 20% of the total residues within 2 h post-application and it was more than 50% on the fifth day after treatment irrespective of the doses applied. Phorate sulfoxide and phorate sulfone reached below the detectable level on 105 and 135 days after treatment, respectively as against 45 days after treatment for phorate residues at the recommended dose. Thus, the reasonably prolonged efficacy of phorate against soil pests may be attributed to longer persistence of its more toxic sulfoxide and sulfone metabolites.