Soil degradation of metazachlor and quizalofop-p-ethyl herbicides on TLC plates under natural solar light and dark conditions

The degradation of the herbicides metazachlor (MTZ) and quizalofop-p-ethyl (QZE) was investigated in three different loamy (L) soils on thin-layer chromatography plates under natural solar light and dark conditions. Both herbicides degraded significantly faster under sunlight irradiation. The degradation rate of MTZ followed single first-order kinetics, and the determined half-life under sunlight and dark conditions were 18 and 78 days in L soil, 13 and 39 days in silty loam (SL) soil and 15 and 64 days in silty clay loam (SCL) soil, respectively. For QZE, first-order multi-compartment kinetic model fitted better for the description of the degradation rates. The half-life of the herbicide was determined at 0.6 and 2.9 days in L soil, 0.8 and 3.5 days in SL soil and 1.0 and 3.9 days in SCL soil, under sunlight and dark conditions, respectively. The putative degradation products (DPs) of herbicides have been determined by liquid chromatography time-of-flight mass spectrometry. MTZ oxalic acid was identified as the probable major DP of MTZ in the studied soils under sunlight conditions. For QZE three putative DPs were identified in all soils: quizalofop-p-acid and demethylated-quizalofop-p-acid under sunlight and dark conditions, while hydroxy-quizalofop-p-ethyl was detected only in samples under sunlight exposure.