Photolysis of chlortetracycline in aqueous solution: kinetics, toxicity and products.
The aqueous photodegradation of the widely used antibiotic chlortetracycline (CTC) was investigated under simulated sunlight. The quantum yield of photodegradation increased from 3.3 x 10(-4) to 8.5 x 10(-3) within the pH range of 6.0 to 9.0. The presence of Ca2+, Fe3+, and NO(-3) enhanced the photodegradation of CTC, whereas Mg2+, Mn2+, and Zn2+ inhibited the degradation with the order Mn2+ > Zn2+ > Mg2+ at pH 7.3. The monovalent cations (Na+ and K+) had negligible effect on the photolysis of CTC. Fulvic acid (FA) decreased the photodegradation of CTC due to light screening effect. Hydrogen peroxide (H2O2) was formed concurrently with direct photodegradation of CTC. The generation rate of H2O2 increased from 0.027 to 0.086 micromol/(L x min) when the pH ranged from 6.0 to 9.0. The CTC solution was about three-fold more toxic to the Photobacterium phosphoreum bacteria after irradiation, suggesting that the photoproducts and H2O2 formed in the CTC solution exhibited high risk on the bacteria. By LC-ESI(+)-MS, the photoproducts of CTC were identified. The direct photodegradation of CTC was involved in hydroxylation and N-demethyl/dedismethyl processes. The main photoproducts included the iso-CTC analog containing hydroxyl groups (m/z 511.4 and 495.4), and the N-demethyl/dedismethyl products of the photoproduct m/z 495.4 (m/z 481.3 and 467.4). In addition, the photochemical dechlorination of CTC led to tetracycline (m/z 445.5).
State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. ychen@mail.hust.edu.cn
Yong
Y
Chen
Hua
H
Li
Zongping
Z
Wang
Tao
T
Tao
Dongbin
D
Wei
Chun
C
Hu
D001578:Benzopyrans / Q000737:chemistry; D002751:Chlortetracycline / Q000737:chemistry* / Q000633:toxicity; D006861:Hydrogen Peroxide / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry; D010776:Photobacterium / Q000187:drug effects; D010782:Photolysis; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000633:toxicity
D001578:Benzopyrans; D008670:Metals; D009566:Nitrates; D014874:Water Pollutants, Chemical; D006861:Hydrogen Peroxide; D002751:Chlortetracycline; C005023:fulvic acid