Photodegradation of Ciprofloxacin, Clarithromycin and Trimethoprim: Influence of pH and Humic Acids.

In view of the rising relevance of emerging pollutants in the environment, this work studies the photodegradation of three antibiotics, evaluating the effects of the pH of the medium and the concentration of dissolved organic matter. Simulated light (with a spectrum similar to that of natural sunlight) was applied to the antibiotics Ciprofloxacin (Cip), Clarithromycin (Cla) and Trimethoprim (Tri), at three different pH, and in the presence of different concentrations of humic acids. The sensitivity to light followed the sequence: Cip > Cla > Tri, which was inverse for the half-life (Tri > Cla > Cip). As the pH increased, the half-life generally decreased, except for Cla. Regarding the kinetic constant k, in the case of Cip and Tri it increased with the rise of pH, while decreased for Cla. The results corresponding to total organic carbon (TOC) indicate that the complete mineralization of the antibiotics was not achieved. The effect of humic acids was not marked, slightly increasing the degradation of Cip, and slightly decreasing it for Tri, while no effect was detected for Cla. These results may be relevant in terms of understanding the evolution of these antibiotics, especially when they reach different environmental compartments and receive sunlight radiation.

The effect of Ultraviolet-B irradiation on the photodegradation of ciprofloxacin and norfloxacin as inhibitors of bacterial DNA replication and cell division in urea medium.

Ciprofloxacin hydrochloride and Norfloxacin are second-generation fluoroquinolone antibiotic against bacterial DNA gyrase, which reduces DNA strain throughout replication. As DNA gyrase is essential through DNA replication, subsequent DNA synthesis and cell division are inhibited. Direct photolysis of fluoroquinolones was studied by using UV irradiation in the presence or absence of other substances that generate free radicals. This study aimed to assess the effect of Ultraviolet B (UVB) irradiation in removing ciprofloxacin and norfloxacin by using a simulating model of wastewater contained urea at pH 4. A known concentration of ciprofloxacin and norfloxacin were prepared in an appropriate aqueous solution in presence or absence 0.2M urea and adjusted at pH 4. The dis-solved drugs were irradiated with UVB-lamp in a dark place for 60 minutes. The percent of removal and the rate of elimination (k) of each drug were calculated. The direct photolysis effect of UVB irradiation was observed with ciprofloxacin which amounted to 24.4% removal compared with12.4% removal of norfloxacin after 60 minutes of irradiation. The effect of UVB irradiation was enhanced by urea to reach 38.9% and 15% for ciprofloxacin and norfloxacin. The calculated k of ciprofloxacin has amounted to three folds of that of norfloxacin. Direct photolysis of ciprofloxacin and norfloxacin can be achieved simply by using a simulation model of 0.2 M urea and UVB irradiation at pH 4. UVB is highly effective in removing ciprofloxacin compared with norfloxacin by 2-3 folds.

Constructive Interfacial Charge Carrier Separation of a p-CaFe2O4@n-ZnFe2O4 Heterojunction Architect Photocatalyst toward Photodegradation of Antibiotics.

Charge dynamics across the interfacial junction of p-n heterostructures leading to effective charge separation along with notable photodurability are essential preconditions to achieve high photocatalytic activity. The p-CaFe2O4@n-ZnFe2O4 (CFO@ZFO) heterojunction has been successfully synthesized by a simple solution combustion method followed by the ultrasonication technique. XRD and HRTEM studies confirmed the effective interaction and formation of the CFO@ZFO heterojunction. The loading of CFO over ZFO selectively enhanced the intensity of the (111) plane of active ZFO, leading to greater crystallinity and a suitable heterojunction which triggers the photocatalytic reaction. The result shows that a 40% loading of CFO on ZFO makes it the flagship photocatalyst. The impedance and PL spectra of 40%CFO@ZFO confirmed the low electron-hole recombination in comparison to the neat materials. Bode phase analysis showed that the lifetime exciton in 40%CFO@ZFO is 1.35 times superior to that of pure ZFO. The heterostructure results in enhancement of the photocurrent in the anodic direction, i.e. 6.6 mA/cm2, which is nearly 2 times greater that of the neat materials. The 40%CFO@ZFO shows the best activity toward degradation of 20 ppm tetracycline and ciprofloxacin, i.e. 89.5% and 78%, respectively, in 1 h. The efficient charge separation at the interface, low charge transfer resistance, formation of heterostructures, and high value of synergy factor are collectively responsible for the best activity in 40%CFO@ZFO.

Enhancing photo-degradation of ciprofloxacin using simultaneous usage of eaq- and OH over UV/ZnO/I- process: Efficiency, kinetics, pathways, and mechanisms.

The aim of this study is to develop the process relies on the UV irradiation of ZnO and I-, i.e. UV/ZnO /I- (UZI), to create both oxidizer and reducer agents simultaneously for photo-degradation of the Ciprofloxacin (CIP). This paper shows that while applying UV irradiation, UV/ZnO and UV/I- for 20 min can lead to achieve 37.5%, 58.12%, and 61.4% photo-degradation of 100 mg L-1 CIP at pH 7, respectively. Moreover, the UZI treatment can provide 91.54% photo-degradation efficiency. The LC-MS analysis of the UZI effluent indicates that 10 min process was adequate to degrade CIP into simple ring-shaped metabolites while 15 min treatment, mostly of CIP intermediates were linear and biodegradable organic compounds. Furthermore, fourteen little fragments were identified in the CIP photo-degradation via UZI, during the photoreaction time of 2.5 to 20 min. Then, a pseudo first-order kinetics equation was utilized to model the observed photo-degradation process. Finally, the computational results show that the increased concentration of the CIP solution from 100 to 400 mg L-1 decreases the observed rate constant (kobs) from 0.4125 to 0.2189 min-1 while increases the photoreaction rate (robs) from 41.25 to 87.56 mg L-1 min-1.

The design of a sunlight-focusing and solar tracking system: A potential application for the degradation of pharmaceuticals in water.

Photolysis is considered one of the most important mechanisms for the degradation of pharmaceuticals. Photodecomposition processes to remove pharmaceuticals in water treatment presently use artificial UV light incorporated in advanced oxidation processes. However, UV lighting devices consume a substantial amount of energy and have high operational costs. To develop low energy treatment systems and make good use of abundant sunlight, a natural energy resource as a green technology is needed. As such, a system that combines sunlight focusing, solar tracking and continuous reaction was designed and constructed in the present study, and its application potential as a pharmaceutical water treatment option was tested. Two representative photolabile pharmaceuticals, ciprofloxacin and sulfamethoxazole, were chosen as the target pollutants. The results indicate that the sunlight-focusing system consisting of a UV-enhancing-coated parabolic receiver can concentrate solar energy effectively and hence result in a more than 40% improvement in the direct photolysis efficiency of easily photoconvertible ciprofloxacin. The sunlight-focusing coupled with a solar tracker (SFST) system can improve the sunlight-focusing efficiency by more than 2-fold, thus leading to the maximization of the efficient use of solar energy. Sulfamethoxazole, which is difficult to photoconvert, was successfully degraded by more than 60% compared to direct photolysis through the designed SFST system in the presence of persulfate. The treatment system exhibited good and consistent performance during clear and cloudy days of summer. It is proven that the UV-enhanced coated SFST system with the addition of persulfate indeed has development potential for application in the degradation of pharmaceuticals in water.

Improved ciprofloxacin removal by a Fe(VI)-Fe3O4/graphene system under visible light irradiation.

In this paper, Fe3O4/graphene (Fe3O4/GE) nanocomposites were prepared by a co-precipitation method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectra (UV-vis DRS). The composites were used in combination with Fe(VI) to construct a Fe(VI)-Fe3O4/GE system in order to degrade ciprofloxacin (CIP) in simulated water samples. The photocatalytic properties of Fe(VI)-Fe3O4/GE were evaluated under visible light irradiation. The concentration of CIP in solution was detected by high performance liquid chromatography (HPLC). A series of results showed that Fe(VI), as a good electron capture agent, could significantly improve the treatment performance. Major determining factors during CIP degradation were also investigated, in which solution pH of 9, Fe(VI) to Fe3O4/GE dosage ratio of 1:25 and GE content in the Fe3O4/GE nanocomposites of 10 wt% were found to be the best experimental conditions. The results demonstrated that the Fe(VI)-Fe3O4/GE system could offer an alternative process in water treatment in addition to the current Fe(VI)-UV/TiO2 process.

Photolytic degradation of ciprofloxacin in solid and aqueous environments: kinetics, phototransformation pathways, and byproducts.

Many lipophilic pharmaceuticals may be sorbed in solid phases, leading to different photochemical behaviors. This study investigated the photochemistry of ciprofloxacin in a solid-phase system and compared it to that in a water-phase system. Kaolinite was used as the model solid matrix. The photolysis of ciprofloxacin in kaolinite fits pseudo-first-order kinetics for thicknesses less than 199 µm, and the rate constants k p decreased from 0.0154 to 0.0016 min-1 as the thickness of the layer increased. Unlike the aqueous phase, two-step degradation processes were observed for all kaolinite layer thicknesses (14-199 µm), and the pseudo-first-order constant at the surface of the kaolinite layer was smaller than that in the water phase. Comparatively , a similar photolysis rate constant of ciprofloxacin in a kaolinite suspension was also observed, and it was an order of magnitude smaller than that of the direct photodegradation (0.035 min-1) in water. The results indicate that ciprofloxacin is likely more stable when it is adsorbed on kaolinite and that the half-lives of ciprofloxacin in kaolinite and a kaolinite suspension are 2-25 times longer than that in deionized water (20 min) under simulated sunlight. Direct photolysis is proposed to be the main photodegradation mechanism for ciprofloxacin in kaolinite, and the cleavage of a piperazine ring is the main degradation pathway. However, the interaction between ciprofloxacin and kaolinite reduces the direct photolysis and leads to a higher light stability. In association with the reduction in photolysis, the yields of norfloxacin and defluorinated byproduct decreased significantly. Consequently, the interaction increases the persistence of ciprofloxacin and thus the ecological risk to the environment.

Degradation of ciprofloxacin by 280 nm ultraviolet-activated persulfate: Degradation pathway and intermediate impact on proteome of Escherichia coli.

In this study, the degradation of ciprofloxacin (CIP) was explored using ultraviolet activated persulfate (UV/PS) with 280 nm ultraviolet light-emitting diodes (UV-LEDs), and the toxicological assessment of degrading intermediates was performed using iTRAQ labeling quantitative proteomic technology. The quantitative mass spectrum results showed that 280 nm UV/PS treatment had a high transformation efficiency of CIP ([CIP] = 3 µM, [S2O82-] = 210 µM, apparent rate constants 0.2413 min-1). The high resolution mass spectrum analyses demonstrated that the primary intermediates included C15H16FN3O3 (m/z 306.1248) and C17H18FN3O4 (m/z 348.1354). The former one was formed by the cleavage of piperazine ring, while the later one was generated by the addition of a hydroxyl on the quinolone backbone. The toxicological assessment demonstrated that 56 and 110 proteins had significant up regulations and down regulations, respectively, in the Escherichia coli exposed to degraded CIP compared to untreated CIP. The majority of up-regulated proteins, such as GapA, SodC, were associated with primary metabolic process rather than responses to stress and toxic substance, inferring that the moderate UV/PS treatment can reduce the antibacterial activity of CIP by incomplete mineralization. Consequently, these results provided a novel insight into the application of UV-LED/PS treatment as a promising removal methodology for quinolones.

Light-controlled active release of photocaged ciprofloxacin for lipopolysaccharide-targeted drug delivery using dendrimer conjugates.

We report an active delivery mechanism targeted specifically to Gram(-) bacteria based on the photochemical release of photocaged ciprofloxacin carried by a cell wall-targeted dendrimer nanoconjugate.

Degradation of ciprofloxacin in water by advanced oxidation process: kinetics study, influencing parameters and degradation pathways.

Gamma-radiation-induced degradation of ciprofloxacin (CIP) in aqueous solution and the factors affecting the degradation process have been investigated. The results showed that CIP (4.6 mg/L) was almost completely degraded at an absorbed dose of 870 Gy. The kinetic studies of aqueous solutions containing 4.6, 10, 15 and 17.9 mg/L indicated that the decomposition of CIP by gamma irradiation followed pseudo-first-order kinetics and the decay constant (k) decreased from 5.9 × 10(-3) to 1.6 × 10(-3) Gy(-1) with an increase in CIP initial concentration from 4.6 to 17.9 mg/L. The effect of saturation of CIP solution with N2, N2O or air on radiation-induced degradation of CIP was also investigated. The effects of radical scavengers, such as t-BuOH and i-PrOH, showed the role of reactive radicals towards degradation of CIP in the order of OH > e(aq)- . H. The apparent second-order rate constant of [Formula: see text] with CIP was calculated to be 2.64 × 10(9) M(-1) s(-1). The effects of solution pH as well as natural water contaminants, such as [HCO3-, CO3(2-), and NO2-, on CIP degradation by gamma-irradiation were also investigated. Major degradation products, including organic acids, were identified using UPLC-MS/MS and IC, and degradation pathways have been proposed.

[Radiolytic Decomposition of Ciprofloxacin Hydrochloride in Aqueous Solution Using γ Irradiation].

Effects of initial concentrations, pH values, different additives and composite pollutants on ciprofloxacin hydrochloride removal using γ irradiation were investigated. The experiments results showed γ irradiation could effectively remove ciprofloxacin hydrochloride; low initial concentration and strongly acidic condition were favorable for CIP removal using γ irradiation; the degradation of CIP was inhibited upon the addition of CO3(2-) and methanol, which indicated that the degradation of CIP might be mainly ascribed to *OH oxidation and the direct decomposition of CIP molecules induced by irradiation. BrO3- showed a synergistic effect with CIP in degradation of the composite pollutants when mixed together with CIP for γ irradiation, and the removal rates of both pollutants were improved. At an absorbed dose of 400 Gy, the removal rates of CIP and BrO3- were increased by 18.74% and 1.81%, respectively. The removal rates of TOC and COD were 15.22% and 61.44%, respectively, when the 100 mg x L(-1) CIP was degraded by γ irradiation at the absorbed dose of 6 000 Gy.

Radiolytic decomposition of ciprofloxacin using γ irradiation in aqueous solution.

Gamma irradiation-induced decomposition of ciprofloxacin (CIP) was elucidated with different additives, such as CO3 (2-), NO3 (-), NO2 (-), humic acid, methanol, 2-propanol, and tert-butanol. The results show that low initial concentration and acidic condition were favorable for CIP removal during γ irradiation. By contrast, radiolytic decomposition of CIP was inhibited with the addition of anions and organic additives. As a strong carcinogen, Cr(6+) was especially mixed with CIP to produce combined pollution. It is noteworthy that the removal of the mixture of CIP and Cr(6+) presented a synergistic effect; the degradation efficiency of the two pollutants was markedly improved compared to that of the single pollutant during γ irradiation. Based on the results of quantum chemical calculations and LC-MS analysis, we determined seven kinds of degradation intermediates and presented the CIP degradation pathways, which were mainly attributed to the oxidation process of hydroxyl radicals OH· and the direct decomposition of CIP molecules.

Decomposition reaction of the veterinary antibiotic ciprofloxacin using electron ionizing energy.

The application of electron ionizing energy for degrading veterinary antibiotic ciprofloxacin (CFX) in aqueous solution was elucidated. The degradation efficiency of CFX after irradiation with electron ionizing energy was 38% at 1 kGy, 80% at 5kGy, and 97% at 10 kGy. Total organic carbon of CFX in aqueous solution after irradiation with electron ionizing energy decreased 2% at 1 kGy, 18% at 5 kGy, and 53% at 10 kGy. The CFX degradation products after irradiation with electron ionizing energy were CFX1 ([M+H] m/z 330), CFX2 ([M+H] m/z 314), and CFX3 ([M+H] m/z 263). CFX1 had an F atom substituted with OH and CFX2 was expected to originate from CFX via loss of F or H2O. CFX3 was expected to originate from CFX via loss of the piperazynilic ring. Among the several radicals, hydrate electron (eaq(-)) is expected to play an important role in degradation of veterinary antibiotic during irradiation with electron ionizing energy. The toxicity of the degraded products formed during irradiation with electron ionizing energy was evaluated using microbes such as Escherichia coli, Pseudomonas putida, and Bacillus subtilis, and the results revealed that the toxicity decreased with irradiation. These results demonstrate that irradiation technology using electron ionizing energy is an effective was to remove veterinary antibiotics from an aquatic ecosystem.

Photolytic degradation of norfloxacin, enrofloxacin and ciprofloxacin in various aqueous media.

The photolytic degradation of norfloxacin, enrofloxacin and ciprofloxacin, fluoroquinolone antibacterials widely used in human and veterinary medicine, was investigated under simulated solar irradiation in different water matrices (river water and synthetic wastewater similar by composition to wastewater of pharmaceutical industry). The results showed that investigated fluoroquinolones degrade very quickly and photodegradation followed pseudo first order kinetics. The slowest photodegradation rate was observed in river water for all three fluoroquinolones. In the case of pharmaceutical mixture irradiation, no significant differences in rate constants were observed compared to single-component experiments. The structures of photodegradation products were determined and photodegradation pathways were suggested. Two main processes occurred primary from enrofloxacin depending on pH values: (I) cyclopropane ring cleavage at pH 4 and (II) oxidative photodegradation at pH 8. The structures of the photoproducts E-1 to E-6 are unknown and have not been reported for this fluoroquinolone. For ciprofloxacin two main processes were also identified depending on experimental conditions. Under acidic conditions (pH 4), reactions involved rather the quinolone ring (cleavage of the cyclopropane ring and fluorine solvolysis), while at pH 8 the side-chain reactions took place. The photodegradation pathway of norfloxacin somewhat differed from the previous two. There was no significant dependence on reaction conditions and there were no two different pathways. Determination and identification of photodegradation products were performed by liquid chromatography-mass spectrometry (LC-MS/MS). The obtained results are of importance for assessing the environmental fate of fluoroquinolones in aqueous media.

Ciprofloxacin in hospital effluent: degradation by ozone and photoprocesses.

There are several papers in the literature that have recorded satisfactory results for the degradation of different pharmaceuticals in aqueous solutions by means of oxidation processes; however, only a few of them relied on real samples in carrying out their investigations. This study examines the results of the performance of photo-induced oxidation, heterogeneous photocatalysis, ozonation and peroxone in degrading the fluoroquinolone antimicrobial ciprofloxacin (CIP) in a hospital effluent. The real samples were collected from the treatment system of the University Hospital of Santa Maria (HUSM). Liquid chromatography with fluorescence detection (LC-FLD) was used to monitor the decrease of the CIP concentration. As expected, photo-induced oxidation was much slower than the other processes in bringing about total CIP degradation. Both heterogeneous photocatalysis and peroxone led to almost complete CIP degradation after 60 min treatment. Ozonation showed the best performance: total degradation after 30 min treatment. This was an unexpected result in view of the greater capacity of the other two processes to generate hydroxyl radicals. However, this finding supports a result in the literature that has tended to be overlooked. The by-products formed during the application of the processes were found to be very similar. Moreover, on the basis of the data obtained from the literature, there is some evidence to suggest that the by-products are derived from the oxidation of the piperazine group.

Studies of the photooxidant properties of antibacterial fluoroquinolones and their naphthalene derivatives.

We synthesized and determined the production of reactive oxygen species (ROS) as 1O2, *-O2, *OH, H2O2 during the photolysis with UV-A light of three antibacterial quinolones and their naphthyl ester derivatives. Singlet oxygen and ROS dose-dependant generation from norfloxacin (1), enoxacin (2), ciprofloxacin (3) and their respective naphthyl ester derivatives 4-6 were detecting in cell-free systems by the histidine assay and by luminol-enhanced chemiluminescence (LCL). Both the electronic absorption and emission spectra were quantified and their photostability determined. The antibacterial activity in darkness and under irradiation of compounds 4, 5 and 6 was tested on E. coli and compared with their parent drugs.

Effect of selected metal ions on the photodegradation of ciprofloxacin in the solid phase.

The photodegradation of ciprofloxacin in the solid phase was investigated by using the chromatographic-densitometric method in the presence and absence of selected metal ions. It was shown that both ion concentration and ion type have an effect on the degradation process that leads to the generation of 2 new products with R(f) values of approximately 0.45 and 0.56, which are different from the R(f) of approximately 0.68 for ciprofloxacin. It was found that CU2+ and Fe3+ ions have the strongest effect on ciprofloxacin photodegradation compared with photodegradation carried out without these ions and also with photodegradations carried out in the presence of Zn2+, Cr3+, Ni2+, and Co2+ ions. To identify the photodegradation products, we used amine-specific chromatographic reactions, UV spectra recorded directly from the chromatograms, and proton nuclear magnetic resonance and IR spectroscopic methods. The chemical structures of the degradation products were found to be 7-[(2-aminoethyl)amino]-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acid and 7-amino-1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxoquinoline-3-carboxylic acid.

Partitioning and photodegradation of ciprofloxacin in aqueous systems in the presence of organic matter.

Ciprofloxacin is an extensively used antibiotic that has been reported to occur in surface water. Previous studies have indicated that ciprofloxacin photodegrades and sorbs to particulate organic material within aquatic systems. The first objective of the current study was to evaluate the influence of organic material on photodegradation rates of ciprofloxacin. Using a bench top experimental design, ciprofloxacin was added to experimental chambers that contained only water or water and fine particulate organic matter (FPOM) followed by exposure to ultraviolet light. Sorption to FPOM was rapid, reducing the amount of ciprofloxacin that was available for photodegradation. Thus, the presence of FPOM initially decreased the ciprofloxacin concentration in the aqueous compartment. However by the end of the 16 h test, 42% of the ciprofloxacin was recovered from the test system with FPOM present, while only 2% of the ciprofloxacin was recovered in systems that did not contain FPOM. The second objective of this study was to compare the sorption coefficients for ciprofloxacin between two types of organic material: FPOM, classified as amphipod processed leaves, and coarse particulate organic matter (CPOM), represented by intact leaf disks. Sorption to FPOM (log Kd of 4.54+/-0.09 l kg(-1)) was 1.6 orders of magnitude greater than sorption to CPOM (log Kd of 2.92+/-0.10 l kg(-1)) potentially resulting in differential toxicity among similar organisms that occupy these different niches and leading to different estimates of environmental fate and effects.

The effect of freeze-drying with different cryoprotectants and gamma-irradiation sterilization on the characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-glycolide) nanoparticles.

In the present study, the influence of freeze-drying with several cryoprotective agents and gamma (gamma)-irradiation sterilization on the physicochemical characteristics of ciprofloxacin HCl-loaded poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles was evaluated. Nanoparticles were prepared by W/O/W emulsification solvent evaporation followed by high-pressure homogenization. They were freeze-dried in the presence of 5.0% (w/v) mannitol, trehalose or glucose, with 5.0% (w/v) or 15.0% (w/v) dextran as cryoprotectants. The nanoparticles were irradiated at a dose of 25 kGy using a 60Co source. The following physicochemical properties of the formulations were investigated: the ratio of particle size before (initial) and after freeze-drying, the ease of reconstitution of the nanoparticle suspensions and the drug-release profiles of irradiated and non-irradiated nanoparticles. The antibacterial activity against Pseudomonas aeruginosa was measured. The freeze-drying process induced a significant increase in particle size when no cryoprotectant was employed. Similar results were observed when cryoprotectants were added to the formulation. Only when mannitol was used was no significant size increase measured. Moreover, for formulations with dextran, reconstitution after freeze-drying was difficult by manual agitation and particle size could not be determined because of aggregation. After gamma-sterilization no significant difference in mean particle size was observed, but reconstitution was more difficult and drug release was influenced negatively. Ciprofloxacin HCl incorporated in the nanoparticles was still effective against the micro-organism selected after freeze-drying and gamma-sterilization.

Antimicrobial activity of fluoroquinolone photodegradation products determined by parallel-line bioassay and high performance liquid chromatography.

The fluoroquinolones produce multiple photodegradation products. Little is known about these products, particularly whether any possess antimicrobial activity. To investigate this, we used the parallel-line bioassay to investigate discrepancies in zone of inhibition size in conjunction with high performance liquid chromatography (HPLC) analysis. A continuous flow photochemical reaction unit ('Beam-Boost') was used to partially photodegrade the fluoroquinolones ofloxacin, levofloxacin, ciprofloxacin and moxifloxacin (0.02 mM) by between 15 and 89%, as confirmed by HPLC. The concentration of residual parent fluoroquinolone in each irradiated sample was measured by HPLC and a non-irradiated control solution was prepared at the same concentration. These were compared by parallel-line bioassays using Escherichia coli, Enterobacter cloacae and Klebsiella oxytoca. With ofloxacin and levofloxacin, the zone size for the control solution was significantly less than that of the irradiated solutions, with >15% photodegradation in at least two of the indicator organisms, indicating that the photodegradation products possess antimicrobial activity. No difference was seen with ciprofloxacin at any level of photodegradation with any of the indicator organisms, nor with moxifloxacin at 30 and 54% photodegradation. A significant difference was observed with E. cloacae only, at 83% photodegradation.