Photodegradation study of some triazine-type herbicides

Abstract

Triazines are amongst the most widely used herbicides. Since triazines can be found in many environmental compartments, their fate in ecosystems and the characterization of their degradation pathways in the environment are to be determined. In this paper we report on a study intended to investigate the photodegradation of some triazine-type herbicides: atrazine, cyanazine, terbuthylazine and terbutryn. The rate of photodegradation process was determined, and degradation schemes were outlined for the compounds studied. Moreover, experiments with different degrading energies were carried out in order to gain information about the effect of total degrading energy on the photodegradation process. The most significant processes of photodegradation of triazines are the partial or complete loss of side-chains, or rather the substitution of the heteroatom-containing side-chain to hydroxyl-group. Besides consecutive processes, loss of the different side-chains takes place parallely also, thus, different metabolites will be formed having mixed side-chains, until the cyanuric acid and 2-amino-4,6-dihydroxy-1,3,5- s-triazine are formed by losing all the side-chains. The presence of the dimer products could be detected during the degradation of all triazines. This proves the radical character of processes occurring during the photodegradation. Increasing the degradation energy (15 to 125 W) has raised the degradation rate by 2–5, and the chlorine containing metabolite—which was still present in the completely degraded mixture during the low-energy experiments—has completely disappeared from the mixture, thus, the increased degrading energy is favorable to the formation of less dangerous, nature identical metabolites.