Junfeng Niu

Distribution and speciation of heavy metals in sediments from the mainstream, tributaries, and lakes of the Yangtze River catchment of Wuhan, China

A comparative study of the heavy metal (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) concentrations in sediments collected from the mainstream, tributaries, and lakes of the Yangtze River catchment of Wuhan, China, was conducted. Compared with the maximum background values in Wuhan Province soils, Cd was the metal with the highest contamination level, especially in the mainstream, followed by Zn and Cu. In a few samples from tributaries and lakes, the Hg concentration was very high compared to background levels. The concentrations of As and Ni in all sites fluctuated close to background levels. Partitioning of speciation of each heavy metal in sediments was similar for samples taken from the mainstream, tributaries, and lakes. Compared to the other metals studied, Cd, Cu, Zn, and Pb had higher bioavailability in the three zones, which means they pose a higher ecological risk. Significant correlations among group a (Zn, Cu, and Pb, r>0.9) and group b (Cr and Ni, r=0.978) in the mainstream; Hg, Cu, Cd, and Pb in lakes (r>0.9); and Cu and Pb (r>0.9) in tributaries were observed using Cluster and correlation analysis. However, a low correlation between As and the other elements in the three zones was shown. Overall, 63.6% of samples from the mainstream, 75.0% from tributaries, and 88.9% from lakes exhibited low and moderate ecological risk of heavy metals, and the potential ecological risks in the mainstream and tributaries were higher than those in lakes.

Electrochemical degradation of perfluorooctanoic acid (PFOA) by Ti/SnO2-Sb, Ti/SnO2-Sb/PbO2 and Ti/SnO2-Sb/MnO2 anodes.

Electrochemical decomposition of environmentally persistent perfluorooctanoic acid (PFOA) in aqueous solution was investigated over Ti/SnO(2)-Sb, Ti/SnO(2)-Sb/PbO(2), and Ti/SnO(2)-Sb/MnO(2) anodes. The degradation of PFOA followed pseudo-first-order kinetics. The degradation ratios on Ti/SnO(2)-Sb, Ti/SnO(2)-Sb/PbO(2), and Ti/SnO(2)-Sb/MnO(2) anodes achieved 90.3%, 91.1%, and 31.7%, respectively, after 90 min electrolysis at an initial 100 mg/L PFOA concentration at a constant current density of 10 mA/cm(2) with a 10 mmol/L NaClO(4) supporting electrolyte solution. The defluorination rates of PFOA on these three anodes were 72.9%, 77.4%, 45.6%, respectively. The main influencing factors on electrochemical decomposition of PFOA over Ti/SnO(2)-Sb anode were evaluated, including current density (5-40 mA/cm(2)), initial pH value (3-11), plate distance (0.5-2.0 cm), and initial concentration (5-500 mg/L). The results indicated that PFOA (100 mL of 100 mg/L) degradation ratio and defluorination ratio achieved 98.8% and 73.9%, respectively, at the optimal conditions after 90 min electrolysis. Under this optimal condition, the degradation rate constant and the degradation half-life were 0.064 min(-1) and 10.8 min, respectively. The intermediate products including short-chain perfluorinated carboxylic acids (PFCAs, C(2) ≈ C(6)) and perfluorocarbons (C(2) ≈ C(7)) were detected by electrospray ionization (ESI) mass spectrum. A possible electrochemical degradation mechanism of PFOA including electron transfer, Kolbe decarboxylation, radical reaction, decomposition, and hydrolysis was proposed. The electrochemical technique could be employed to degrade PFOA from contaminated wastewater as well as to reduce the toxicity of PFOA.

Characterization, ecological risk assessment and source diagnostics of polycyclic aromatic hydrocarbons in water column of the Yellow River Delta, one of the most plenty biodiversity zones in the world.

As one of the most active regions of land-ocean interaction among the large river deltas in the world, the Yellow River Delta (YRD) gains increasing concern on its ecological and environmental conditions. However, few studies on polycyclic aromatic hydrocarbons (PAHs) have been reported for this area. In this study, the distribution characteristics, probabilistic risk and possible sources of PAHs were investigated in the water column of the YRD. The PAH concentrations were found to be at relatively low or medium levels (121.3 ng L(-1) in water and 209.1n g g(-1) in suspended particulate matter (SPM) on average), and the result of probability risk assessment additionally elucidated low PAH ecological risk in the YRD. The PAH composition showed that low and moderate molecular PAHs were the major species in water phase, whereas the SPM showed a different proportion of each PAH composition. An interesting result was found that low-ring PAHs and salinity in this land-ocean interaction area had a positive relationship (R=0.609). For PAH source identification, both diagnostic ratios of selected PAHs and principal component analysis (PCA) with multiple linear regression (MLR) analysis were studied, suggesting mixed sources of pyrogenic and petrogenic deriving PAHs in the YRD.

Adsorption of phosphorus on sediments from the Three-Gorges Reservoir (China) and the relation with sediment compositions.

The adsorption of phosphorus (P) on four sediment samples (CunTan, XiaoJiang, DaNing and XiangXi) from the Three-Gorges Reservoir on the Yangtze River in China was studied systematically in batch experiments. A sequential chemical extraction experiment was conducted to clarify the effect of sediment composition on P adsorption. The results showed that P adsorption on four sediment samples mainly occurred within 6h. P adsorption kinetics can be satisfactorily fitted by both power function and simple Elovich model. A modified Langmuir model may describe well the P adsorption on all the samples in our study. Theoretically, the maximum adsorption amount (Q(max)) was 0.402mg-P/g for XiaoJiang sediment, 0.358mg-P/g for DaNing sediment, 0.165mg-P/g for CunTan sediment, and 0.15mg-P/g for XiangXi sediment. The sediment compositions such as organic matter, metal hydroxides, calcium and clay content showed influences on the P adsorption. Wherein, organic matter and metal hydroxides were the main factors affecting the P adsorption. The maximum P adsorption capacity (Q(max)) enhanced with the increase of the content of (Fe+Al+Ca). Compared the zero-equilibrium P concentration (EPC(0)) values obtained by the modified Langmuir models with actual P concentrations in water, all the sediments studied in this paper except for XiaoJiang showed a trend of releasing P as a source role, which could enhance the risk of eutrophication occurrence in the Three-Gorges Reservoir.

Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-Doped Modified Porous Nanocrystalline PbO2 Film Electrode

The Ce-doped modified porous nanocrystalline PbO(2) film electrode prepared by electrodeposition technology was used for electrochemical mineralization of environmentally persistent perfluorinated carboxylic acids (PFCAs) (~C(4)-C(8)), i.e., perfluorobutanoic acid (PFBA), perfluopentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoheptanoic acid (PFHpA), and perfluorooctanoic acid (PFOA) in aqueous solution (100 mL of 100 mg L(-1)). The degradation of PFCAs follows pseudo-first-order kinetics, and the values of the relative rate constant (k) depend upon chain length k(PFHpA) (4.1 × 10(-2) min(-1); corresponding half-life 16.8 min) ≈ 1.1k(PFOA) ≈ 2.5k(PFHxA)≈ 6.9k(PFPeA) ≈ 9.7k(PFBA). The carbon mineralization indices [i.e., 1 - (TOC(insolution)/TOC(inPFCA,degraded))] were 0.49, 0.70, 0.84, 0.91, and 0.95 for PFBA, PFPeA, PFHxA, PFHpA, and PFOA, respectively, after 90 min electrolysis. The major mineralization product, F(-), as well as low amount of intermediate PFCAs with shortened chain lengths were detected in aqueous solution. By observing the intermediates and tracking the concentration change, a possible pathway of electrochemical mineralization is proposed as follows: Kolbe decarboxylation reaction occurs first at the anode to form the perfluoroalkyl radical, followed by reaction with hydroxyl radicals to form the perfluoroalkyl alcohol which then undergoes intramolecular rearrangement to form the perfluoroalkyl fluoride. After this, the perfluoroalkyl fluoride reforms perfluorinated carboxylic with shorter chain length than its origin by hydrolysis. This electrochemical technique could be employed to treat PFCAs (~C(4)-C(8)) in contaminated wastewater.

Mechanism of Reductive Decomposition of Pentachlorophenol by Ti-Doped β-Bi2O3 under Visible Light Irradiation

The reductive decomposition of pentachlorophenol (PCP) by photocatalysis with Ti-doped beta-Bi(2)O(3) was investigated under visible light (lambda > 420 nm) irradiation. The results indicated that hydroxyl radical (*OH) and singlet oxygen ((1)O(2)) could not be detected with electron spin resonance (ESR) on the photocatalyst under light irradiation. An electron scavenger weakened the photocatalytic activity of the photocatalyst for the decomposition of PCP; however, scavengers of reactive oxygen species (ROS) enhanced the activity. The decomposition intermediates of PCP detected by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) suggested the existence of phenol, cyclohexanone, cyclohexanol, glycol, and propylene. All the evidence suggested that reductive dechlorination was the major route in the decomposition of PCP, during which the photogenerated electron under visible light irradiation acted as reductant. The reliability of the proposed reductive mechanism was further verified by comparing the reduction potential (E(re)) of PCP with the conduction band potential (E(cb)) of the photocatalyst. The decomposition pathway of PCP with electron reduction under visible light irradiation was also investigated.

Photolysis of Enrofloxacin in aqueous systems under simulated sunlight irradiation: Kinetics, mechanism and toxicity of photolysis products.

Photolysis of Enro in water was investigated under simulated sunlight irradiation using a Xenon lamp. The results showed that Enro photolysis followed apparent first-order kinetics. Increasing Enro concentration from 5.0 to 40.0 mg L⁻¹ led to the decrease of the photolysis rate constant from 1.6 × 10⁻² to 3.0 × 10⁻³ min⁻¹. Compared with the acidic and basic conditions, the photolysis rate was faster at neutral condition. Both of nitrate and humic acid can markedly decrease the photolysis rate of Enro because they can competitively absorb photons with Enro. The electron spin resonance and reactive oxygen species scavenging experiments indicated that Enro underwent self-sensitized photooxidation via OH and ¹O₂. After irradiation for 90 min, only 13.1% reduction of TOC occurred in spite of fast photolysis of 58.9% of Enro, indicating that Enro was transformed into intermediates without complete mineralization. The photolysis of Enro involved three main pathways: decarboxylation, defluorination, and piperazinyl N⁴-dealkylation. The bioluminescence inhibition rate using Vibrio fischeri increased to 67.2% at 60 min and then decreased to 56.9% at 90 min, indicative of the generation of some more toxic intermediates than Enro and then the degradation of the intermediates. The results will help us understand fundamental mechanisms of Enro photolysis and provide insight into the potential fate and transformation of Enro in surface waters.

Degradation of pentachlorophenol and 2,4-dichlorophenol by sequential visible-light driven photocatalysis and laccase catalysis.

Chlorophenols (CPs) can be degraded by visible-light driven photocatalysis or laccase catalysis. However, previous and present studies have shown that neither of the two methods was efficient when being used individually. Low degradation rates were observed for the degradation of pentachlorophenol (PCP) by laccase-catalysis and that of 2,4-dichlorophenol (2,4-DCP) by photocatalysis. To remove CPs more completely, a sequential photolaccase catalytic system was designed to degrade PCP and 2,4-DCP mixture in water at the optimal pH value. The results showed that photocatalysis prior to laccase-catalysis (PPL) is a better approach than laccase-catalysis prior to photocatalysis (LPP), eliminating CPs more efficiently and generating lower toxic products. The identified intermediate products consisted of adipic acid, hexanediol, glycol, propylene glycol, hydroquinol, and phthalandione. Based on the products identified, the sequential degradation process was proposed, including the interlace reactions involving quinoid oxidation, reductive dechlorination, and no-enzyme polymerization. Upon reaction optimization, a piston flow reactor (PFR) was designed to treat the continuous feeding of simulated wastewater containing PCP and 2,4-DCP. After a 128 h period of treatment, 87.4-99.5% total concentration of CPs were removed (PPL removed 99.7% PCP and 99.2% 2,4-DCP; LPP removed 95.9% PCP and 78.9% 2,4-DCP).

Role of living environments in the accumulation characteristics of heavy metals in fishes and crabs in the Yangtze River Estuary, China.

Correlation of heavy metals in the tissues of typical organisms (i.e., fishes and crabs) and those in their living environments (i.e., surface water, bottom water, and sediment) in Yangtze River Estuary has been qualitatively and quantitatively analyzed. Metal levels followed the trend: sediments > Eriocheir sinensis > Eriocheir leptognathus > benthic fish > pelagic fish > bottom water > surface water. Tissues in fishes and crabs of different species and sizes had diverse metal bioaccumulation characteristics, which was significantly affected by environment factors and their living habits. Metal levels in legs of crabs, and heads and skins of fishes showed significant correlations with those in their living environments. Collichthys lucidus is an effective bioindicator for assessing metal levels in water. No significant health risk was identified by the estimated daily intake and target hazard quotients analyses.

In situ encapsulation of laccase in microfibers by emulsion electrospinning: preparation, characterization, and application.

Laccase from Trametes versicolor was successfully in situ encapsulated into the poly(D,L-lactide) (PDLLA)/PEO-PPO-PEO (F108) electrospun microfibers by emulsion electrospinning. The porous morphology of electrospun microfibers was observed with scanning electron microscope, and the core-shell structure of microfibers and existence of laccase in microfibers were proved by laser confocal scanning microscopy micrograph. In this study, fibrous porosity and core-shell structure are advantageous to the activity and stability preservation of immobilized laccase. The activity of immobilized laccase could retain over 67% of that of the free enzyme. After 10 successive runs in the enzyme reactor, the immobilized laccase could also maintain 50% of its initial activity. Crystal violet dye was successfully degraded by the PDLLA/F108-laccase electrospun microfiber membranes. It was observed that the immobilized laccase possessed a broadening pH range of catalysis activity compared to free laccase.