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 formati on of desaminometamitron. Photolysis rate was slower in the presence o f soils due to the screen effect of soil particles, although some diff erences observed between the 3 different soils indicated that soil org anic matter (SOM) may accelerate photolysis of metamitron. Photolysis studies with the colloidal fraction of the soils before and after orga nic matter elimination and with soil humic acids confirmed the photose nsitizing effect of humic acid on the phototransformation of metamitro n. Studies with model iron oxides (goethite and ferrihydrite) also sug gested that these soil components could accelerate metamitron degradat ion in aqueous medium. The Fe2O3-sensitizing effect is less significan t than that of the SOM and was not clearly developed in the natural cl ay fraction. Copyright (C) 1996 Elsevier Science Ltd