Dr. Linke Ge

National Marine Environmental Monitoring Center,

Linghe Street 42, Shahekou District, Dalian 116023,

P. R. China

Tel: +86-411-8470 2024 (Office), 158 4096 3916 (Mobile)

E-mail: lkge@mail.dlut.edu.cn, lkge@nmemc.gov.cn

 

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²   Publications and Abstracts

1. Linke Ge, Jingwen Chen, Xiaoxuan Wei, Siyu Zhang, Xianliang Qiao, Xiyun Cai, Qing Xie. Aquatic photochemistry of fluoroquinolone antibiotics: Kinetics, pathways, and multivariate effects of main water constituents. Environmental Science & Technology, 2010, 44 (7): 2400-2405.

 

Abstract  The ubiquity of fluoroquinolone antibiotics (FQs) in surface waters urges insights into their fate in the aqueous euphotic zone. In this study, 8 FQs (ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin, enrofloxacin, gatifloxacin and balofloxacin) were exposed to simulated sunlight and their photodegradation was observed to follow apparent first-order kinetics. Based on the determined photolytic quantum yields, solar photodegradation half-lives for the FQs in pure water and at 45° N latitude were calculated to range from 1.25 min for enrofloxacin to 58.0 min for balofloxacin, suggesting that FQs would intrinsically photodegrade fast in sunlit surface waters. However, we found freshwater and seawater constituents inhibited their photodegradation. The inhibition was further explored by a central composite design using sarafloxacin and gatifloxacin as representatives. Humic acids (HA), Fe(III), NO₃^-, and HA−Cl^- interaction inhibited the photodegradation, as they mainly acted as radiation filters and/or scavengers for reactive oxygen species. The photodegradation product identification and ROS scavenging experiments indicated that the FQs underwent both direct photolysis and self-sensitized photo-oxidation via ·OH and ¹O₂. Piperazinyl N⁴-dealkylation was primary for N⁴-alkylated FQs, while decarboxylation and defluorination were comparatively important for the other FQs. These results are of importance towards the goal of assessing the persistence of FQs in surface waters.

 

 

2. Linke Ge, Jingwen Chen, Xianliang Qiao, Jing Lin, Xiyun Cai. Light-source-dependent effects of main water constituents on photodegradation of phenicol antibiotics: Mechanism and kinetics. Environmental Science & Technology, 2009, 43 (9): 3101-3107.

 

Abstract  Thiamphenicol and florfenicol are two phenicol antibiotics commonly used in aquaculture. Photodegradation experiments on these phenicols were performed in aqueous solutions under irradiation of different light sources. We found under UV−vis irradiation (λ > 200 nm), they photodegraded the fastest in seawater, followed by pure water and freshwater, whereas under solar or simulated sunlight (λ > 290 nm), they photodegraded in freshwater only. The effects of Cl^- (the dominant seawater constituent), humic acids (HA, main constituents in freshwater) and other water constituents on the photodegradation of the antibiotics as a function of different light sources were studied so as to interpret the light-source-dependent effects of different waters. Under UV−vis irradiation, Cl^- was found to promote singlet oxygen (¹O₂) formation and accelerated the photodegradation of phenicols, whereas the phenicols did not photolyze under simulated solar irradiation, irrespective of Cl^-. In contrast, the presence of HA inhibited phenicol photolysis under UV−vis irradiation through competitive photoabsorption, but HA photosensitized degradation under simulated solar irradiation. Under UV−vis irradiation, the wavelength-averaged (200−290 nm) quantum yields for thiamphenicol and florfenicol in pure water were 0.022 ± 0.001 and 0.029 ± 0.001, respectively. Their photolytic half-lives in freshwater were 186 ± 17 h and 99 ± 16 h, respectively. UV−vis photodegradation intermediates were identified by HPLC-MS/MS, and degradation pathways were proposed. These involve photoinduced hydrolysis, dechlorination, self-sensitized photo-oxidation process via ¹O₂, and chlorination. These results are of importance towards the goal of assessing the persistence of phenicols in wastewater treatment and the environment.

 

 

3. Linke Ge, Siyu Zhang, Qing Xie, Jingwen Chen. Progress in studies on aqueous environmental photochemical behavior of antibiotics. Science China Chemistry, 2010, 40 (2): 124-135.

 

Abstract  Antibiotics are emerging pollutants that are ubiquitous in the aqueous environment. They have recently received increasing concerns due to their pseudo-persistence and potential to induce bacterial resistance. Photochemical degradation is a central factor in determining the fate of antibiotics. This paper reviews the current research progress on the aqueous environmental photochemical behavior of antibiotics. Their direct, indirect and self-sensitized photodegradation kinetics are introduced. The effects of pH and aqueous dissolved matter on the photodegradation kinetics of antibiotics are highlighted, and the photodegradation pathways and mechanisms are summarized for some important antibiotic classes. Furthermore, the photoinduced toxicities of some antibiotics are discussed. Finally, the research prospects about the aqueous photochemical behavior of antibiotics are proposed.

Keywords: antibiotics, photodegradation, influencing factors, photochemical behavior

 

 

4. Linke Ge, Jingwen Chen, Siyu Zhang, Xiyun Cai, Zhuang Wang, Chunling Wang. Photodegradation of fluoroquinolone antibiotic gatifloxacin in aqueous solutions. Chinese Science Bulletin, 2010, 55(15): 1495-1500.

 

Abstract  Fluoroquinolone antibiotics (FQs) are frequently detected as emerging pollutants in aqueous environments. In this study, kinetics, influencing factors and mechanisms on the photodegradation of gatifloxacin, a representative FQ, were investigated. The photodegradation follows the pseudo-first-order kinetics. Gatifloxacin photodegrades with a quantum yield of (5.94 ± 0.95) × 10^{-3 in pure water and undergoes direct photolysis as well as self-sensitized photodegradation. The FQ photodegrades slower in freshwater and seawater than in pure water, which is attributed to the integrative effects of pH and the aqueous dissolved matter (e.g., humic acids and NO}₃^-) on the photodegradation. A toxicity test using Vibrio fischeri revealed the formation of hazardous photoproducts.

Keywords: gatifloxacin, photodegradation, influencing factors, reactive oxygen species

 

 

5. Linke Ge, Jingwen Chen, Xianliang Qiao, Ying Wang, Xiyun Cai, Siyu Zhang. Concerntration-dependent photodegradation kinetics of florfenicol in pure water. Organohalogen Compounds, 2009, 71: 2378-2381.

 

Abstract  Florfenicol is a phenicol antibiotic widely used in aquaculture. The photodegradation kinetics of florfenicol in pure water was studied as a function of different initial concentrations (C₀). It was found that the kinetics was impacted by C₀ and a linear plot of the initial rate (r_i) divided by C₀ (-r_i·C₀^-1) vs C₀ was obtained with a negative slope. The photolysis was enhanced by N₂ sparging, but was inhibited by air sparging, which indicated that the observed photolytic rate constant (k) of florfenicol was decreased when self-sensitized photodegradation via ¹O₂ was involved. Upon increasing C₀, the contribution of the self-sensitized photodegradation increased and the contribution of direct photoysis decreased. Thus, the observed k was decreased by increasing C₀.

 

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