Photolysis of metamitron in water in the presence of soils and soil components

The herbicide metamitron (4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one) photodegrades rapidly in aqueous solution leading to the formation of desaminometamitron. Photolysis rate was slower in the presence of soils due to the screen effect of soil particles, although some differences observed between the 3 different soils indicated that soil organic matter (SOM) may accelerate photolysis of metamitron. Photolysis studies with the colloidal fraction of the soils before and after organic matter elimination and with soil humic acids confirmed the photosensitizing effect of humic acid on the phototransformation of metamitron. Studies with model iron oxides (goethite and ferrihydrite) also suggested that these soil components could accelerate metamitron degradation in aqueous medium. The Fe2O3-sensitizing effect is less significant than that of the SOM and was not clearly developed in the natural clay fraction.