Reductive deactivation of some s-triazine herbicides: Prometryne, desmetryne and terbutryne

Abstract

The electrochemical behaviour (DC and DP polarography) of the methylthio-bis(alkyl-amino) s-triazine herbicides prometryne, desmetryne and terbutryne on mercury electrodes has been studied in the acidity range 2.25 M H2SO4 to pH 6.5. Two two-electron irreversible reduction processes wine found, complicated with adsorption, At pH values higher than the protonation pK of the triazine ring (ca. 4), this protonation reaction preceded the reduction processes. Reduction mechanisms are proposed for pH < pK and pH > pK. The products obtained in the electroreduction of dilute solutions of the above herbicides show a lower toxicological effect than that of the original compounds (lower aromatic character and cleavage of the -SCH3 group). Thus, electrochemical deactivation at pH ≤ 3.5 and at potentials around -1.10 V (vs. the Ag/AgCl/KClsat electrode) can be a valid method to deactivate these molecules. Finally, the reductive route can be an alternative environmental degradative process in waters under strong reductive conditions, with pH values equal or lower than 3.5 pH-units, and rich in carbonaceous materials on clays. In these ambients oxidative photolytic detoxification of herbicides cannot occur.