Combined effects of dissolved organic matter, pH, ionic strength and halides on photodegradation of oxytetracycline in simulated estuarine waters.

Estuarine waters of variable compositions are sinks for many micropollutants. The varying water properties can impact the photodegradation of organic pollutants. In this study, the combined effects of dissolved organic matter (DOM), pH, ionic strength, and halides on the photodegradation of the model organic pollutant oxytetracycline (OTC) were investigated. Suwannee River natural organic matter (SRNOM) was used as a representative DOM. The results showed that the observed photolysis rate constant (kobs) of OTC increased rapidly upon increase of pH. SRNOM induced a 11.0-17.9% decrease of the kobs for OTC. In the presence of SRNOM, the ionic strength and specific halide effects promote OTC photodegradation with a 39.2-84.2% and 7.1-28.8% increase of the kobs, respectively. The effects of SRNOM, ionic strength and halides on OTC photodegradation are pH-dependent. Direct photolysis half-lives (t1/2) of OTC were estimated in view of the more important role of direct photolysis compared to indirect photolysis. The estimated t1/2 values decreased from 187.4-206.6 d to 34.4-36.6 d as the pH increases in the Yellow River estuarine region. The results of this research demonstrate that the photodegradation rate of OTC increases rapidly in the gradient from river water to marine water in estuarine regions.

Nanocrystalline TiO2 Composite Films for the Photodegradation of Formaldehyde and Oxytetracycline under Visible Light Irradiation.

In order to effectively photodegradate organic pollutants, ZnO composite and Co-B codoped TiO2 films were successfully deposited on glass substrates via a modified sol-gel method and a controllable dip-coating technique. Combining with UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PL) analyses, the multi-modification could not only extend the optical response of TiO2 to visible light region but also decrease the recombination rate of electron-hole pairs. XRD results revealed that the multi-modified TiO2 film had an anatase-brookite biphase heterostructure. FE-SEM results indicated that the multi-modified TiO2 film without cracks was composed of smaller round-like nanoparticles compared to pure TiO2. BET surface area results showed that the specific surface area of pure TiO2 and the multi-modified TiO2 sample was 47.8 and 115.8 m²/g, respectively. By degradation of formaldehyde and oxytetracycline, experimental results showed that the multi-modified TiO2 film had excellent photodegradation performance under visible light irradiation.

Antibacterial activity of oxytetracycline photoproducts in marine aquaculture's water.

Oxytetracycline (OTC) is one of the most used antibiotics in aquaculture. The main concern related to its use is the bacterial resistance, when ineffective treatments are applied for its removal or inactivation. OTC photo-degradation has been suggested as an efficient complementary process to conventional methods used in intensive fish production (e.g.: ozonation). Despite this, and knowing that the complete mineralization of OTC is difficult, few studies have examined the antibacterial activity of OTC photoproducts. Thus, the main aim of this work is to assess whether the OTC photoproducts retain the antibacterial activity of its parent compound (OTC) after its irradiation, using simulated sunlight. For that, three Gram-negative bacteria (Escherichia coli, Vibrio sp. and Aeromonas sp.) and different synthetic and natural aqueous matrices (phosphate buffered solutions at different salinities, 0 and 21‰, and three different samples from marine aquaculture industries) were tested. The microbiological assays were made using the well-diffusion method before and after OTC has been exposed to sunlight. The results revealed a clear effect of simulated sunlight, resulting on the decrease or elimination of the antibacterial activity for all strains and in all aqueous matrices due to OTC photo-degradation. For E. coli, it was also observed that the antibacterial activity of OTC is lower in the presence of sea-salts, as demonstrated by comparison of halos in aqueous matrices containing or not sea-salts.

Quantitative assessment on the contribution of direct photolysis and radical oxidation in photochemical degradation of 4-chlorophenol and oxytetracycline.

In UV-254 nm/H2O2 advanced oxidation process (AOP), the potential degradation pathways for organic pollutants include (1) hydrolysis, (2) direct H2O2 oxidation, (3) UV direct photolysis, and (4) hydroxyl radical (HO(•)) reaction. In this study, the contribution of these pathways was quantitatively assessed in the photochemical destruction of 4-chlorophenol (4-CP), demonstrating pathways (3) and (4) to be predominantly responsible for the removal of 4-CP by UV/H2O2 in 50 mM phosphate buffer solution. Increasing reaction pH could significantly enhance the contribution of direct photolysis in UV/H2O2 process. The contribution of HO(•) oxidation was improved with increasing initial H2O2 concentration probably due to the increased formation of HO(•). Presence of sodium carbonate (Na2CO3) as in UV/H2O2/Na2CO3 system promoted the degradation of 4-CP, with carbonate radical (CO3 (•-)) reaction and direct photolysis identified to be the main contributing pathways. The trends in the contribution of each factor were further evaluated and validated on the degradation of the antibiotic compound oxytetracycline (OTC). This study provides valuable information on the relative importance of different reaction pathways on the photochemical degradation of organic contaminants such as 4-CP and OTC in the presence and absence of a CO3 (•-) precursor.

Effect of temperature, pH and illumination on abiotic degradation of oxytetracycline in sterilized swine manure.

Tetracyclines such as oxytetracycline (OTC) are widely used veterinary chemicals. They are often poorly absorbed with a significant fraction being excreted in manure that can subsequently result in environmental contamination. In many countries throughout South East Asia swine manure is not composted, but sun-dried. Using sunlight to heat manure has been suggested as an effective and low-cost strategy to reduce OTC contamination, but this has previously been unexplored. Such conditions have also been shown to reduce bacterial numbers in manure meaning abiotic OTC degradation processes may become more significant. This work investigated for the first time, the role of temperature, illumination and pH in the abiotic degradation of OTC in sterilized swine manure. OTC loss from laboratory-based experiments simulating conditions likely to be experienced in sun-drying were assessed using simple first order and availability-adjusted loss models. ANOVA results suggested that neither model was superior to the other. In addition, pH and light had little influence. Temperature was shown to be the main factor influencing OTC loss. Kinetic results showed reductions in OTC concentrations of 65 % after 100 h at 40°C based on the availability-adjusted loss model, regardless of pH and illumination. Such temperatures are likely to be attained during the process of sun-drying. Therefore this may be a useful and practical means of reducing OTC contamination in manure.

Evaluation of stability of oxytetracycline-HCl to sterilization levels of gamma radiation.

The effect of gamma irradiation at different dose levels (from 5 to 50 KGy) on the solid state of the antibiotic oxytetracycline-HCl was examined. The results obtained showed no effect on the biological activity of the compound, as investigated by the bioassay technique. The physicochemical properties of the antibiotic were not altered by irradiation dose levels up to 40 KGy. The UV-visible spectra of all irradiated samples showed no changes. The I.R. spectra of oxytetracycline, exposed to dose levels higher than 40 KGy, showed, however, definite destruction in the chemical structure of the antibiotic. HPLC separation of samples, irradiated at 45 KGy, showed the presence of new degradation products. Accordingly, sterilization of oxytetracycline by use of gamma irradiation could be considered safe and applicable, since sterilization doses are usually considered to be less than 30 KGy.