Reactions of tet~Racycline antibiotics with chlorine dioxide and free chlorine

摘要

tet~Racyclines (TCs) are a group of widely used antibiotics that have been frequently found in the aquatic environment. The potential reactions of TCs with common water disinfection oxidants such as chlorine dioxide (C1O_2) and free available chlorine (FAC) have not been studied in depth and are the focus of this study. The oxidation kinetics of tet~Racycline, oxytet~Racycline, chlorotet~Racycline and iso-chlorotet~Racycline by ClO_2 and FAC are very rapid (with large apparent second-order rate constants K_(app) = 2.24 × 10~5-1.26 × 10~6 M~(-1)S~(-1) with C1O_2 and K_(app) = 1.12 × 10~4-1.78 × 10~6 M~(-1) S~(-1) with FAC at pH 7.0) and highly dependent on pH. Species-specific rate constants are obtained by kinetic modeling that incorporates pH-speciation of TCs and the oxidants (for FAC), and reveal that TCs primarily react with C1O_2 and FAC by their unprotonated dimethylamino group and deprotonated phenolic-diketone group. The modest difference in reactivity among the four TCs toward the oxidants is consistent with expectation and can be explained by structural influences on the two reactive moieties. Product evaluation shows that oxidation of TCs by C1O_2 leads to (hydr)oxylation and breakage of TC molecules, while oxidation of TCs by FAC leads to chlorinated and (hydrjoxylated products without any substantial ring breakage. Results of this study indicate that rapid transformation of TCs by oxidants such as C1O_2 and FAC under water and wastewater treatment conditions can be expected.