Abiotic transformation of atrazine in aqueous phase by biogenic bixbyite-type Mn₂O₃ produced by a soil-derived Mn(II)-oxidizing bacterium of Providencia sp

Recently, biogenic Mn oxides (BioMnO_x) are considered as the promising degradation agents for environmental organic contaminants. However, little information is available for the degradation of atrazine by BioMnO_x. In this work, BioMnO_x, generated by a soil-derived Mn(II)-oxidizing bacterium, Providencia sp. LLDRA6, was explored to degrade atrazine. To begin with, collective results from mineral characterization analyses demonstrated that this BioMnO_x was biogenic bixbyite-type Mn₂O₃. After that, purified biogenic Mn₂O₃ was found to exhibit a much higher removal efficiency for atrazine in aqueous phase, as compared to unpurified biogenic Mn₂O₃ and LLDRA6 biomass. During the atrazine removal by biogenic Mn₂O₃, six intermediate degradation products were discovered, comprising deethylatrazine (DEA), hydroxylatrazine (HA), deethylhydroxyatrazine (DEHA), ammeline, cyanuric acid, and 5-methylhexahydro-1,3,5-triazine-2-thione (MTT). Particularly, the intermediate, MTT, was considered as a new degradation product of atrazine, which was not described previously. Meanwhile, Mn(II) ions were released from biogenic Mn₂O₃, and on the surface of biogenic Mn₂O₃, the content of hydroxyl O species increased at the expense of that of lattice and water O species, but the fundamental crystalline structure of this Mn oxide remained unchanged. Additionally, no dissociative Mn(III) was found to involve in atrazine degradation. In summary, these results demonstrated that both the non-oxidative and oxidative reactions underlay the degradation of atrazine by biogenic Mn₂O₃.