Dongbin Wei

Photosonochemical degradation of Phenol in water

The combination of ultrasound (US) and photochemistry has been used to degrade an aqueous solution of phenol. It was considerably more effective than ultrasound or ultraviolet (UV) light alone. Based on the results of total organic carbon (TOC) removal, it was shown that the synergistic action of ultrasound and ultraviolet light existed. Identification of the first intermediates of the reaction (hydroquinone, catechol, benzoquinone and resorcin) indicates that OH radicals are involved in the photosonochemical degradation mechanisms. The effects of parameters such as pH, saturating gases, and Fe2+ on the photosonochemical degradation have been studied. The experimental results have shown that lower pH and higher concentration of dissolved oxygen favor the phenol degradation and that the presence of Fe2+ enhanced TOC removal of phenol solutions.

Photodegradation and toxicity changes of antibiotics in UV and UV/H2O2 process

The photodegradation of three antibiotics, oxytetracycline (OTC), doxycycline (DTC), and ciprofloxacin (CIP) in UV and UV/H(2)O(2) process was investigated with a low-pressure UV lamp system. Experiments were performed in buffered ultrapure water (UW), local surface water (SW), and treated water from local municipal drinking water treatment plant (DW) and wastewater treatment plant (WW). The efficiency of UV/H(2)O(2) process was affected by water quality. For all of the three selected antibiotics, the fastest degradation was observed in DW, and the slowest degradation occurred in WW. This phenomenon can be explained by R(OH,UV), defined as the experimentally determined OH radical exposure per UV fluence. The R(OH,UV) values represent the background OH radical scavenging in water matrix, obtained by the degradation of para-chlorobenzoic acid (pCBA), a probe compound. In natural water, the indirect degradation of CIP did not significantly increase with the addition of H(2)O(2) due to its effective degradation by UV direct photolysis. Moreover, the formation of several photoproducts and oxidation products of antibiotics in UV/H(2)O(2) process was identified using GC-MS. Toxicity assessed by Vibrio fischer (V. fischer), was increased in UV photolysis, for the photoproducts still preserving the characteristic structure of the parent compounds. While in UV/H(2)O(2) process, toxicity increased first, and then decreased; nontoxic products were formed by the oxidation of OH radical. In this process, detoxification was much easier than mineralization for the tested antibiotics, and the optimal time for the degradation of pollutants in UV/H(2)O(2) process would be determined by parent compound degradation and toxicity changes.

Biodegradation of di-n-butyl phthalate by an isolated Gordonia sp. strain QH-11: Genetic identification and degradation kinetics

Di-n-butyl phthalate (DBP) is one of the most widely used phthalic acid esters (PAEs), which have shown increasing environmental concerns worldwide. A bacterial strain designated as QH-11, was isolated from activated sludge and found to be capable of utilizing DBP as carbon and energy sources for growth. 16S rRNA and gyrb gene sequence analysis revealed that strain QH-11 was most closely related to Gordonia sp. Kinetics studies of DBP degradation by the strain QH-11 revealed that DBP depletion curves fit with the modified Gompertz model (R(2)>0.98). Meanwhile, substrate utilization tests showed that strain QH-11 could utilize other common PAEs and also the main intermediate product phthalic acid (PA). A gene encoding the large subunit of the phthalate dioxygenase, which is responsible for PA degradation, was successfully detected in strain QH-11. Furthermore, the results of reverse transcription quantitative PCR demonstrate that mRNA expression level of phthalate dioxygenase increased significantly after strain QH-11 was induced by DBP and PA.

A carbohydrate modified fluoride ion sensor and its applications.

A new fluorescent probe for the detection of F(-) (TBA(+) and Na(+) salts) has been developed, which is based on a desilylation triggered chromogenic reaction in water. This probe exhibits excellent F(-) ion selectivity as well as significant color changes visible to the naked eye at the concentration of 1.5 mg L(-1), the WHO recommended level of F(-) ions in drinking water. This new carbohydrate modified probe can be used directly in aqueous medium without using organic co-solvents. Furthermore, the probe presents high sensitivity and selectivity for the imaging of F(-) ions in HepG2 cells.

Progressive study and robustness test of QSAR model based on quantum chemical parameters for predicting BCF of selected polychlorinated organic compounds (PCOCs).

Systematic analyses on the effects of chemical structures of 31 polychlorinated organic compounds (PCOCs) on their bioconcentration behavior in rainbow trout (Oncorhynchus mykiss) were conducted using quantitative structure-activity relationship (QSAR) techniques. The cluster analyses of individual variables as well as the quality control chart of QSAR model implies the existence of outliers, while the simulation model excluding such samples showed an extreme robustness even if it was tested with different methods. Furthermore, the quantum chemical parameters entering into QSAR model were used to describe the bioconcentration pathways, and the results indicated that bioconcentration behaviors of selected compounds were complicated processes involving permeation stages as well as bio-chemical reaction stages.

Genotoxicity of quinolones: Substituents contribution and transformation products QSAR evaluation Using 2D and 3D models

The genotoxicity of 21 quinolones antibiotics was determined using SOS/umu assay. Some quinolones exhibited high genotoxicity, and the chemical substituent on quinolone ring significantly affected genotoxicity. To establish the relationship between genotoxicity and substituent, a 2D-QSAR model based on quantum chemical parameters was developed. Calculation suggested that both steric and electrostatic properties were correlated well with genotoxicity. Furthermore, the specific effect on three key active sites (1-, 7- and 8-positions) of quinolone ring was investigated using a 3D-QSAR (comparative molecular field analysis, CoMFA) method. From our modeling, the genotoxicity increased when substituents had: (1) big volume and/or positive charge at 1-position; (2) negative charge at 7-position; and (3) small volume and/or negative charge at 8-position. The developed QSAR models were applicable to estimate genotoxicity of quinolones antibiotics and their transformation products. It is noted that some of the transformation products exhibited higher genotoxicity comparing to their precursor (e.g., ciprofloxacin). This study provided an alternative way to understand the molecule genotoxicity of quinolones derivatives, as well as to evaluate their potential environmental risks.

Prediction of mixture toxicity with its total hydrophobicity

Based on the C18 Empore disk/water partition coefficient of a mixture, quantitative structure-activity relationships (QSARs) are presented, which are used to predict the toxicity of mixed halogenated benzenes to P. phosphoreum. The predicted toxicity of 10 other related mixtures based on the QSAR model, agree well with the observed data with r2 = 0.973, SE = 0.113 and F = 287.785 at a level of significance P < 0.0001. The joint effect of these chemicals is simple similar action and the toxicity of the mixtures can be predicted from total hydrophobicity and is independent of hydrophobicity of the components or the ratio of the individual chemicals.

Characterization of dissolved organic matter fractions and its relationship with the disinfection by-product formation

Dissolved organic matter (DOM) has been identified as precursor for disinfection by-products (DBPs) formation during chlorination. Recently, it has been demonstrated that the characteristics of DOM influence the DBPs formation mechanism. A study was, therefore, initiated to investigate the effects of DOM fractions on DBPs formation mechanism. In the chlorination process, organic acids are dominant precursors of total thihalomethanes (TTHM) because of the v(c-o) and unsaturated structures. Furthermore, the TTHM formation of organic acids was affected by pH more greatly. Based on the fluorescence spectroscopy analysis, DOM fractions contained several fluorescence substances. During chlorination, humic acid-like substances were found to exhibit high chlorine reactivity and hydrophobic organics decomposed to smaller molecules faster than hydrophilic organics even at lower chlorine dosages. Unlike hydrophobic fractions, hydrophilic organics showed no toxicity following chlorination, suggesting that the toxic structures in hydrophilic organics showed high chlorine reactivity during chlorination.

Photosonochemical degradation of trichloroacetic acid in aqueous solution

The degradation of trichloroacetic acid (TCA) was studied with ultraviolet (UV) photolysis, ultrasound (US) sonolysis and their combination. It was found that the degradation in the combined processes was more significant than in the UV photolysis or sonolysis alone. The effects of pH and dissolved gases on the rate of photosonochemical degradation of TCA were investigated and the degradation kinetics, mechanism and possible degradation products were discussed in detail.

Transformation mechanism of benzophenone-4 in free chlorine promoted chlorination disinfection.

The UV-filter BP-4 (2-hydroxy-4-methoxybenzophenone-5-sulfonic acid) has been frequently observed in the environment, showing high potentials to invade drinking water, swimming water, or wastewater reclamation treatment systems. With the help of high performance liquid chromatography-high resolution mass spectrometry and nuclear magnetic resonance spectroscopy, 10 new products from free chlorine-promoted BP-4 disinfection have been disclosed and their possible transformation routes have been investigated. The first route is chlorine substitution of BP-4 and its transformation products, forming mono-, di-, and tri-chlorinated BP-4 analogs. The second is Baeyer-Villiger-Type oxidation, converting diphenyl ketone to phenyl ester derivatives. The third is ester hydrolysis, generating corresponding phenolic and benzoic products. The fourth is decarboxylation, replacing the carboxyl group by chloride in the benzoic-type intermediate. The fifth is desulfonation, degrading the sulfonic group through an alternative chlorine substitution on the benzene ring. Orthogonal experiments have been established to investigate the species transformed from BP-4 at different pH values and free available chlorine (FAC) dosages. The reaction pathways are strongly dependent on pH conditions, while an excessive amount of FAC eliminates BP-4 to the smaller molecules. The initial transformation of BP-4 in chlorination system follows pseudo-first-order kinetics, and its half-lives ranged from 7.48 s to 1.26 × 10(2) s. More importantly, we have observed that the FAC-treated BP-4 aqueous solution might increase the genotoxic potentials due to the generation of chlorinated disinfection by-products.