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

The electrochemical behaviour (DC and DPpolarography) of the methylthio-bis(alkylamino) s-triazine herbicides prometryne, desmetryne and terbutryne on mercury electrodes has been studied in the acidity range 2.25MH2SO4 to pH 6.5. Two two-electron irreversible reduction processes were found, complicated with adsorption. At pH values higher than the protonation pKof 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. Proucavano je elektrohemijsko ponasanje (DC i DP polarografija) prometrina desmetrina i terbutrina (metiltio-bis(alkilamino) s-triazinskih herbicida) na zivinoj elektrodi u sumpornoj kiselini u oblasti pH 2,25?6,5. Uocene su dve ireverzibilne dvoelektronske redukcije, pracene adsorpcijom. Pri pH vrednostima ve}im od pK protonacije triazinskog prstena (oko 4) ova reakcija protonacije prethodi procesu redukcije. Predlozeni su mehanizmi reakcije pri pH < pK i pri pH > pK. Proizvodi elektroredukcije razblazenih rastvora ovih herbicida imaju manji toksikoloski efekat od polaznih jedinjenja (manji aromaticni karakter i otcepljivanje ?SCH3 grupe). Prema tome, elektrohemijska redukcija pri pH ?3,5 i pri potencijalima oko ?1,10 V (vs. Ag/AgCl, KClsat) moze biti dobra metoda za deaktivaciju ovih molekula. Najzad, redukcija moze biti alternativan degradacioni proces u prirodi u vodi u jacim redukcionim uslovima, pri pH ?3,5 i u prisustvu karbonizovanih materijala u glini. U takvim uslovima oksidativna fotoliticka detoksifikacija ne moze da se odigrava.