Guoguang Liu

Diclofenac photodegradation under simulated sunlight: Effect of different forms of nitrogen and Kinetics

A synthetic non-steroidal anti-inflammatory drug diclofenac is one of the most frequently detected pharmaceuticals in various water samples. One of the most important degradation processes relating to diclofenac is its photodegradation in the aquatic environment. This paper studies the kinetic model for diclofenac degradation in water and the variation of the photodegradation of diclofenac in the presence of different forms of nitrogen changes with different pE values in the aquatic environment under simulated sunlight. The results demonstrate that degradation pathways proceed via pseudo first-order kinetics in all cases and the photodegradation of diclofenac is the sum of the degradation by direct photolysis and self-sensitization. NO(3)(-) and NO(2)(-) have inhibiting effects on the photodegradation of diclofenac. The different forms of nitrogen changes with different pE values and this has a significant influence on the photodegradation of diclofenac. The results show that when NH(4)(+) and NO(2)(-) coexist in the aquatic environment, the inhibiting effect on the photodegradation diclofenac is less than the sum of the partial inhibiting effects. The results indicated that NO(2)(-) had an obvious antagonistic action for NH(4)(+). When NO(3)(-) and NO(2)(-) coexisted in the aquatic environment, a similar antagonistic action between NO(3)(-) and NO(2)(-) was observed.

Oxidation of diclofenac by aqueous chlorine dioxide: Identification of major disinfection byproducts and toxicity evaluation

Diclofenac (DCF), a synthetic non-steroidal anti-inflammatory drug, is one of the most frequently detected pharmaceuticals in the aquatic environment. In this work, the mechanism and toxicity of DCF degradation by ClO2 under simulated water disinfection conditions were investigated. Experimental results indicate that rapid and significant oxidation of DCF occurred within the first few minutes; however, its mineralization process was longer than its degradation process. UPLC-MS and (1)H NMR spectroscopy were performed to identify major disinfection byproducts that were generated in three tentative degradation routes. The two main routes were based on initial decarboxylation of DCF on the aliphatic chain and hydroxylation of the phenylacetic acid moiety at the C-4 position. Subsequently, the formed aldehyde intermediates were the starting point for further multistep degradation involving decarboxylation, hydroxylation, and oxidation reactions of CN bond cleavage. The third route was based on transient preservation of chlorinated derivatives resulting from electrophilic attack by chlorine on the aromatic ring, which similarly underwent CN bond cleavage. Microtox bioassay was employed to evaluate the cytotoxicity of solutions treated by ClO2. The formation of more toxic mid-byproducts during the ClO2 disinfection process poses a potential risk to consumers.

Photoelectrocatalytic degradation of triclosan on TiO2 nanotube arrays and toxicity change.

Triclosan, one of the most widely used disinfectants, has been found to be toxic to animals and human beings. In this paper, triclosan was degraded on TiO2 nanotube arrays, using a photoelectrocatalytic (PEC) process under UV illumination, with Na2SO4 as the supporting electrolyte. The effect of bias potential was investigated and the results showed that 0V was the most appropriate potential for the degradation of triclosan. In 30min, 78.7% of triclosan had degraded during the PEC process. Intermediate analysis showed that 2,7-dichlorodibenzodioxin (DCDD) had formed during the degradation. The toxicity change during the PEC process was investigated using a luminescent bacteria test, with the results demonstrating that the toxicity of the reaction liquid decreased at the beginning and subsequently increased to a stable level. The indications were that some intermediates such as 2,7-dichlorodibenzodioxin was more toxic and stable than triclosan in the solution.

Photodegradation of salicylic acid in aquatic environment: effect of different forms of nitrogen.

Salicylic acid (SA), as an extensively used compound, can be detected in a great variety of environmental water samples. Photodegradation is important in many ways. The present study concerns the environmental behavior of SA under simulated sunlight. A kinetic model was used for SA degradation in water, and the variations of the photodegradation of SA in the presence of different initial concentrations, different oxygen levels, different forms of nitrogen and different pE values in the aquatic environment were determined. Experiments demonstrated that the photodegradation process had pseudo-first-order reaction kinetics. The photodegradation rate decreased with increasing initial concentration and increased with increasing oxygen level. The NO(3)(-) and NO(2)(-) ions promoted photodegradation of SA, but increases of NH(4)(+) concentration had no effect. The form of nitrogen depends on pE, which therefore has a significant influence on the photodegradation of SA. When the pE value increased gradually, there was a transformation of NH(4)(+) to NO(2)(-) and then to NO(3)(-). The photodegradation rate of SA first increased, then decreased and finally increased again. When NO(2)(-) and NH(4)(+) coexisted, the photodegradation rate was almost the same as it was in the presence of NO(2)(-) alone. When NO(2)(-) and NO(3)(-) coexisted, the promoting effect on the photodegradation SA was less than the sum of the partial promoting effects. The results indicated that NO(2)(-) had an obvious antagonistic action on NO(3)(-) when NO(3)(-) and NO(2)(-) coexisted in the aquatic environment.

Quantifying interactions between propranolol and dissolved organic matter (DOM) from different sources using fluorescence spectroscopy

Beta blockers are widely used pharmaceuticals that have been detected in the environment. Interactions between beta blockers and dissolved organic matter (DOM) may mutually alter their environmental behaviors. To assess this potential, propranolol (PRO) was used as a model beta blocker to quantify the complexation with DOM from different sources using the fluorescence quenching titration method. The sources of studied DOM samples were identified by excitation–emission matrix spectroscopy (EEMs) combined with fluorescence regional integration analysis. The results show that PRO intrinsic fluorescence was statically quenched by DOM addition. The resulting binding constants (log Koc) ranged from 3.90 to 5.20, with the surface-water-filtered DOM samples claiming the lower log Koc and HA having the highest log Koc. Log Koc is negatively correlated with the fluorescence index, biological index, and the percent fluorescence response (Pi,n) of protein-like region (PI,n) and the Pi,n of microbial byproduct-like region (PII,n) of DOM EEMs, while it is correlated positively with humification index and the Pi,n of UVC humic-like region (PIII,n). These results indicate that DOM samples from allochthonous materials rich in aromatic and humic-like components would strongly bind PRO in aquatic systems, and autochthonous DOM containing high protein-like components would bind PRO more weakly.

Decoration of TiO2/g-C3N4 Z-scheme by carbon dots as a novel photocatalyst with improved visible-light photocatalytic performance for the degradation of enrofloxacin

A novel visible-light-driven carbon dot (CDs)/TiO2/g-C3N4 photocatalyst was successfully synthesized by doping CDs in TiO2 nanoparticles and the surface of g-C3N4 nanosheets via a facile hydrothermal process and was confirmed by characterization methods. UV-vis diffuse reflectance spectra (DRS) revealed that CDs/TiO2/g-C3N4 showed obvious additional absorption in the 370–450 nm region. DMPO spin-trapping ESR spectra demonstrated the existence of O2˙− and ·OH. The photocatalytic activity of the CDs (1.0 wt%)/TiO2/g-C3N4 was remarkably enhanced as compared to that of the single components (TiO2 and g-C3N4) and double component (TiO2/g-C3N4) towards the degradation of enrofloxacin (ENX) under visible-light irradiation. About 91.6% of ENX was decomposed by CDs (1.0 wt%)/TiO2/g-C3N4 in 1 h, which is nearly 3.95 times, 4.82 times, and 1.69 times that for TiO2, g-C3N4, and TiO2 (90.0 wt%)/g-C3N4, respectively. Scavenging experiments revealed that O2˙− and ·OH played key roles during the photocatalytic degradation of ENX. This study provides a simple and convenient method to modify materials with enhanced photocatalytic performance, and the CDs/TiO2/g-C3N4 catalyst is efficient, stable, and reusable for environmental practical applications.

A sulfate radical based ferrous–peroxydisulfate oxidative system for indomethacin degradation in aqueous solutions

The degradation of indomethacin (IM) by ferrous ion-activated potassium peroxydisulfate (Fe2+/PDS) was investigated. We aimed to determine the optimal conditions for the removal of IM under different concentrations of Fe2+and PDS, evaluate the effects of operational parameters (solution pH, humic acid (HA), N2 bubbling and persulfate species), and propose the degradation mechanism of IM by the Fe2+/PDS system. The sequential addition of Fe2+ led to an improvement in the IM degradation and TOC removal efficiency. When the molar ratio of IM/PDS/Fe2+ was 1 : 1.5 : 2, the IM was almost completely degraded. Restrictions to the degradation efficiency of IM were caused by increasing the solution pH, bubbling with nitrogen, or through the addition of HA. A low concentration of Cl− had no effect on the reaction, while a high concentration led to a dramatic inhibitory effect. In addition, quenching experiments revealed that SO4˙− was the major active radical for the degradation of IM by ferrous ion-activated peroxydisulfate. Based on the identification of transformation products by liquid chromatography-mass spectrometry (LC-MS/MS), the pathways of the ferrous–peroxydisulfate oxidative system for the degradation of IM were tentatively proposed.

Photodegradation of diclofenac in seawater by simulated sunlight irradiation: The comprehensive effect of nitrate, Fe(III) and chloride

Diclofenac is one of the most frequently detected pharmaceuticals in various aquatic environments. The photodegradation of diclofenac in the absence/presence of nitrate, Fe(III) and chloride, especially their interactions, were systematically studied. Under the study conditions, photodegradation rate was decreased with increasing nitrate, Fe(III) and chloride concentrations. Nitrate has an synergistic action for Fe(III). Nitrate and chloride have antagonistic effect. An antagonistic action is present between nitrate, Fe(III) and chloride. Moreover, a simple linear model which very well describes the results is given.

Investigation of the interaction between the fate of antibiotics in aquafarms and their level in the environment

China is the largest freshwater aquaculture producer and antibiotics consumer in the world, and rivers in China are generally polluted by antibiotics. However, there is little information available regarding the linkage of antibiotics in aquaculture and the aquatic environment. Therefore, this study investigated the fate of antibiotics in several open water culture-based freshwater aquafarms, including integrated livestock/fish systems and non-integrated fish ponds, and explored the contamination profiles of antibiotics in the Beijiang River. Then the study tried to clarify the two-way interaction of antibiotics in aquaculture and the environment. The results showed that, when compared with the effluent from livestock farms and wastewater treatment plants, the contribution of antibiotics from non-integrated fish pond water without livestock sewage input was limited, while that of effluent from the integrated livestock/fish system was quite high. The total concentrations of antibiotics detected in the aquafarm source water were similar to those in the upper river water and generally higher than those in the corresponding fish pond water, implying that the occurrence of antibiotics in intensive aquafarms can mainly be attributed to the antibiotic residues in nearby river water. Overall, the results underscore the need to develop a sewage infrastructure for the treatment of effluent from integrated livestock/fish aquafarms, and suggest that open water culture-based fish farms should be located far from seriously contaminated sections of rivers.

Analysis of azole fungicides in fish muscle tissues: Multi-factor optimization and application to environmental samples

Azole fungicides have been reported to be accumulated in fish tissue. In this study, a sensitive and robust method using high-performance liquid chromatography-tandem mass spectrometry combined with ultrasonic extraction, solid-liquid clean-up, liquid-liquid extraction and solid-phase extraction (SPE) for enrichment and purification have been proposed for determination of azole fungicides in fish muscle samples. According to the results of non-statistical analysis and statistical analysis, ethyl acetate, primary secondary amine (PSA) and mixed-mode cation exchange cartridge (MCX) were confirmed as the best extraction solvent, clean-up sorbent and SPE cartridge, respectively. The satisfied recoveries (81.7-104%) and matrix effects (-6.34-7.16%), both corrected by internal standards, were performed in various species of fish muscle matrices. Method quantification limits of all azoles were in the range of 0.07-2.83ng/g. This optimized method was successfully applied for determination of the target analytes in muscle samples of field fish from Beijiang River and its tributaries. Three azole fungicides including climbazole, clotrimazole and carbendazim were detected at ppb levels in fish muscle tissues. Therefore, this analytical method is practical and suitable for further clarifying the contamination profiles of azole fungicides in wild fish species.