Wenwen Gong

Seasonal variation and sediment-water exchange of antibiotics in a shallower large lake in North China.

The occurrence of four antibiotics, including oxytetracycline (OTC), tetracycline (TC), norfloxacin (NOR) and ofloxacin (OFL), in surface water, overlying water, pore water and sediment samples were studied in the Baiyangdian Lake from February to November in 2009. The total concentrations of these antibiotics ranged among 17.73-281.82, 22.98-258.45, 22.43-198.95 ng L(-1) and 131.65-750.27 ng g(-1) in surface water, overlying water, pore water and sediments, respectively. Seasonal variation might be impacted by the frequency of different pattern of antibiotics and the water temperatures of different seasons, where the higher concentrations appeared at different seasons. In addition, the regions with significant sewage discharge or human agricultural activities exhibited high concentrations of antibiotics in water and sediments. The highest accumulation rates of the four antibiotics ranged from 11.27 to 29.71%, which indicated that these compounds exhibited strong adsorption to the sediment. However, higher concentrations of antibiotics in pore water and even overlying water may result in the release of these compounds from the sediment acting as a secondary contaminant source in a certain time period, especially for TC. The pseudo-partitioning values of fluoroquinolones (FQs) ranged from 4493 to 47,093 L kg(-1) and were much higher than those of tetracyclines (TCs), which ranged from 277 to 1880 L kg(-1) indicating that the FQs are prone to accumulation in the sediment.

The use of carbon black to catalyze the reduction of nitrobenzenes by sulfides.

Using carbon black (CB) as catalyst, the reduction of nitrobenzenes (NBs) to anilines by sulfides at room temperature was studied. In the reactions, CB serves as an intermedium to accelerate the reduction of NBs by sulfides. In the presence of 0.3g/L CB and 3.0 mM sulfides at pH 7.0 and 25°C, our results showed that CB-catalyzed reduction of NBs were pseudo-first order. The reduction rate constant of nitrobenzene was 0.0367 h(-1) in the presence of CB-1, which was 10 times more than the reduction rate constant in the absence of CB-1. Other experiments of different CB samples produced by different methods and different raw materials indicated that some active oxygenated functional groups on CB surface should be the reactive sites and play the dominant role in catalyzing the reduction of NBs. The catalytic reactions of different NBs by sulfides indicated that the reduction rate constants of chloronitrobenzenes to chloroanilines were greater than those of methylnitrobenzenes to methylanilines. And due to the effect of different substituent positions, the nitro group with meta substituent was reduced most easily while the nitro group with ortho substituent was reduced most difficulty.

Reduction of nitrobenzene with sulfides catalyzed by the black carbons from crop-residue ashes

In this paper, three types of black carbons (BCs) named R-BC, W-BC, and C-BC were derived from rice straw ashes, wheat straw ashes, and corn straw ashes, respectively. Under room temperature and in an anaerobic aqueous solution, these three types of BCs could catalyze the reduction of nitrobenzene (NB) by sulfides rather than only act as the superabsorbent. The catalytic activities of BCs derived from different crop-residue ashes were very different and in the order of R-BC > W-BC > C-BC, since the reaction rate constants (kobs) of NB with the BCs in the presence of 3 mM sulfides were 0.0186, 0.0063, and 0.0051 h−1, respectively. The key catalytic active sites for NB reduction were evaluated, with four types of modified BCs and two types of tailored graphite as the model catalysts. The results indicated that BCs probably had two types of active sites for NB reduction, the microscopic graphene moieties and the surface oxygen functional groups. Since the sulfides and BCs often coexist in the environment, this BC-catalyzed reduction technology of NACs may be applied as an in situ remediation technique without the need for reagent addition.

Abiotic reduction of trifluralin and pendimethalin by sulfides in black-carbon-amended coastal sediments

Dinitroaniline herbicides such as trifluralin and pendimethalin are persistent bioaccumulative toxins to aquatic organisms. Thus, in-situ remediation of contaminated sediments is desired. This study investigated whether black carbons (BCs), including apple wood charcoal (BC1), rice straw biochar (BC2), and activated carbon (BC3), could facilitate abiotic reduction of trifluralin and pendimethalin by sulfides of environmentally-relevant concentrations in anoxic coastal sediments. The reduction rates of trifluralin and pendimethalin increased substantially with increasing BC dosages in the sediments. This enhancing effect was dependent on BC type with the greatest for BC3 followed by BC1 and BC2, which well correlated with their specific surface area. The pseudo-first order reduction rate constants (kobs) for BC3-amended sediment (2%) were 13- and 14 times the rate constants in the BC-free sediment. The reduction rates increased with increasing temperature from 8 to 25°C in the BC-amended sediment, following the Arrhenius relationship. Finally, through molecular modeling by density functional theory and reaction species identification from mass spectra, molecular pathways of trifluralin and pendimethalin reduction were elucidated. In contrary to the separate sequential reduction of each nitro group to amine group, both nitro groups, first reduced to nitroso, then eventually to amine groups.

The kinetics and QSAR of abiotic reduction of mononitro aromatic compounds catalyzed by activated carbon

The kinetics of abiotic reduction of mono-nitro aromatic compounds (mono-NACs) catalyzed by activated carbon (AC) in an anaerobic system were examined. There were 6 types of substituent groups on nitrobenzene, including methyl, chlorine, amino, carboxyl, hydroxyl and cyanogen groups, at the ortho, meta or para positions. Our results showed that reduction followed pseudo-first order reaction kinetics, and that the rate constant (logkSA) varied widely, ranging between -4.77 and -2.82, depending upon the type and position of the substituent. A quantitative structure-activity relationship (QSAR) model using 15 theoretical molecular descriptors and partial-least-squares (PLS) regression was developed for the reduction rates of mono-NACs catalyzed by AC. The cross-validated regression coefficient (Qcum(2), 0.861) and correlation coefficient (R(2), 0.898) indicated significantly high robustness of the model. The VIP (variable importance in the projection) values of energy of the lowest unoccupied molecular orbital (ELUMO) and the maximum net atomic charge on the aromatic carbon bound to the nitro group (QC(-)) were 1.15 and 1.01, respectively. These values indicated that the molecular orbital energies and the atomic net charges might play important roles in the reduction of mono-NACs catalyzed by AC in anaerobic systems.

Adsorption of potentially toxic metals on negatively charged liposomes: equilibrium isotherms and quantitative modeling

We investigated the adsorption behaviour of ten potentially toxic metals (Ni, Co, Cd, Fe, Ba, Sr, Cr, Hg, Ag and Zn) on negatively charged liposome vesicles composed of phosphatidyl choline (PC), phosphatidyl glycerol (PG) and cholesterol. The adsorption data for selected metal ions closely fit the Freundlich isotherm. Most metal ions (except Cr3+ and Cd2+) were strongly adsorbed by liposomes (n > 1) and the ionic covalent index significantly affected the Freundlich adsorption intensity. We used multivariate statistical methods, including principal components analysis regression and partial least squares regression, to elucidate the adsorption relationships between 18 physical and chemical properties and their respective Freundlich isotherm constants (KF). The cross-validated correlation efficient (Qcum2) and correlation coefficient (RY2) of the model were 0.76 and 0.91, respectively. High Qcum2 and RY2 values indicated that the predictive model was both precise and robust. According to the VIP value, parameters like ionic polarisation, ion charge and ionisation potential played crucial roles in predicting KF.

Assessing the Mutagenic Potential of Surface Sediments from Beijing Guanting Reservoir to Salmonella typhimurium

Mutagenicity of organic extracts from Beijing Guanting Reservoir sediments was investigated with TA98 and TA100 of Salmonella typhimurium. TA98 and TA100 were employed to detect frameshift mutation and base-pair substitution mutation, respectively. For TA100, no positive result was found, while TA98 was more sensitive and pro-mutagenic frameshift mutagens were mainly detected in sediments. Sediments from northern and southern Guanting Reservoir were at potential mutagenic risk. No mutagenicity was found in the sediments from the entrance of the tributaries, but strong mutagenicity was observed in the sediments from the outlet of the reservoir. Chemical analysis was also performed, and poor correlation was found between mutagenicity and organochlorine pesticides (OCPs). However, significant positive correlation was found for polycyclic aromatic hydrocarbons (PAHs) (r = 0.603–0.946), which showed that PAHs were dominated for the tested mutagenicity in the sediments. Polychlorinated biphenyls (PCBs) might induce mutagenicity or promote the mutagenicity of other substances.