Abiotic dealkylation and hydrolysis of atrazine by birnessite

Abstract

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and its degradation products are important contaminants of world water systems and have effects on aquatic life. These effects are modulated by the degradation of atrazine, which depends, in part, on its reactivity with soil minerals. We have studied the degradation reaction of atrazine on synthetic birnessite (delta-MnO2) in the aqueous phase using a batch reactor and a developed high-performance liquid chromatography method. The reaction was studied in the absence of light at 25 degrees C and between pH 2.3 to pH 8.3. The reaction rates increased with decreasing pH and increasing delta-MnO2 loading, and they did not follow simple first-order kinetics. The major products are hydroxylated and mono- and didealkylatrazine. Ammeline and cyanuric acid also were detected. The half-life (t 1/2) for the degradation of atrazine was approximately 16.8 d and independent of oxygen. Manganese(II) evolution was a minor product. The mechanism of dealkylation involved proton transfer to Mn(IV)-stabilized oxo and imido bonds, with no net oxidation and reduction. Oxidation was a secondary reaction. The proposed abiotic pathway for the transformation of atrazine on delta-MnO2 was identical to the reported biotic pathway. Thus, delta-MnO2, a common soil component, facilitated the efficient N-dealkylation and hydrolysis of the herbicide atrazine at 25 degrees C, possibly via a nonoxidative mechanisms. The N-dealkylation has been attributed strictly to a biological process in soils.