Xianfei Huang

Heavy-metal pollution and potential ecological risk assessment of sediments from Baihua Lake, Guizhou, P.R. China

Baihua Lake, a man-made reservoir, is one of the five drinking water sources for Guiyang City in Chinas southwestern province of Guizhou. In the present research, the distribution and accumulation characteristics of heavy metals (Pb, Cd, As, Cu and Zn) for the sediment of this lake were analyzed by examination of 10 recently collected samples. A method based on toxic-response factor was applied to assess the potential ecological risk of these heavy metals to the water body. For comparison, the two sets of reference data representing the pre-industrial and the local baseline pollution levels were employed to derive the accumulating coefficients for the heavy metals under study. The calculated potential ecological risk indices show that the lake was polluted by heavy metals and both cadmium and arsenic loadings were critical factors responsible for the ecological hazards posed to Baihua Lake by the five elements.

A Theoretical Study on Reductive Debromination of Polybrominated Diphenyl Ethers

Recent progress has been made in the reductive debromination of polybrominated diphenyl ethers (PBDEs) by nanoscale zero-valent iron (nZVI). To better understand the mechanism of this reaction, seven selected BDE congeners and their anions were investigated at the density functional theory (DFT) level using four different methods, including B3LYP/6-31G(d), B3LYP/6-31+G(d), B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p). The cleaved C–Br bonds observed in the equilibrium structures of anionic PBDEs were adopted as the probe of the susceptible debromination position of PBDEs in the presence of nZVI, and the proposed major reaction pathways based on our calculations can satisfactorily conform to the reported experimental results. The debromination preference is theoretically evaluated as meta-Br > ortho-Br > para-Br. In addition, both the calculated frontier orbital energies and adiabatic electronic affinities were found to be highly related to their experimental reductive debromination rate constants. The highest linear regression coefficient was observed in the case using the energy of lowest unoccupied molecular orbital as the molecular descriptor obtained from B3LYP/6-31G(d) (R2 = 0.961, n = 7) or B3LYP/6-31G(d,p) (R2 = 0.961, n = 7). The results clearly showed the evidence of an electron transfer mechanism associated with this reductive debromination reaction.

Electron-induced reductive debromination of 2,3,4-tribromodiphenyl ether: a computational study

To better understand the mechanism of the electron induced elimination of the bromide anion, we examined at the B3LYP/6-31+G(d) level electron capture by 2,3,4-tribromodiphenyl ether (BDE-21) followed by the release of the bromide anion and a radical. Both the geometry and energy of the BDE-21 neutral and its possible anionic states were studied. A significant relationship was found between the total energy and the length of the C-Br bonds by the analysis of the potential energy surface for the anionic states. Debromination preference for the bromine substituted positions was theoretically evaluated as meta-Br > ortho-Br > para-Br. The reaction profiles of the electron-induced debromination of BDE-21 demonstrated that, in general, the presence of a solvent makes the electron induced reductive debromination of BDE-21 significantly more advantageous, and the stabilization effect of the solvent on the reaction intermediates would make the electron attachment and dissociation relatively effective in comparison with the results from the gas-phase calculations.

Excited States and photodebromination of selected polybrominated diphenyl ethers: computational and quantitative structure--property relationship studies.

This paper presents a density functional theory (DFT)/time-dependent DFT (TD-DFT) study on the lowest lying singlet and triplet excited states of 20 selected polybrominateddiphenyl ether (PBDE) congeners, with the solvation effect included in the calculations using the polarized continuum model (PCM). The results obtained showed that for most of the brominated diphenyl ether (BDE) congeners, the lowest singlet excited state was initiated by the electron transfer from HOMO to LUMO, involving a π–σ* excitation. In triplet excited states, structure of the BDE congeners differed notably from that of the BDE ground states with one of the specific C–Br bonds bending off the aromatic plane. In addition, the partial least squares regression (PLSR), principal component analysis-multiple linear regression analysis (PCA-MLR), and back propagation artificial neural network (BP-ANN) approaches were employed for a quantitative structure-property relationship (QSPR) study. Based on the previously reported kinetic data for the debromination by ultraviolet (UV) and sunlight, obtained QSPR models exhibited a reasonable evaluation of the photodebromination reactivity even when the BDE congeners had same degree of bromination, albeit different patterns of bromination.

Theoretical study on the radical anions and reductive dechlorination of selected polychlorinated dibenzo-p-dioxins.

For the effective use of remediation technologies for PCDDs contamination, it is essential to study the reactivity and dechlorination pathways of these compounds. In this study, density functional theory (DFT) calculations (B3LYP/6-31+G(d), B3LYP/6-311+G(d,p)) were performed to investigate the neutrals and different anionic states of selected PCDD congeners. The calculated adiabatic electron affinities and frontier orbital energies of the PCDD congeners (in gas-phase and in solution) are significantly correlated with the reported dechlorination rate constants, showing that this kind of reductive cleavage reaction is kinetically controlled by the electron transfer step. The predicted major dechlorination pathways of 1,2,3,4-TeCDD and its daughter products based on the energies of the anionic states were found to be satisfactorily consistent with the reported experimental results. Simulation of the 1,2,3,4-TeCDD dechlorination process showed that not only the dechlorination regioselectivity but also the reactivity of the PCDDs played an important role in the distribution of dechlorinated products. An exponential correlation was found between the sum of the concentration of the PCDD congeners and the reaction time in the simulation, indicating that the time required for the conversion of the PCDD congeners to the fully dechlorinated product (dibenzo-p-dioxin) might not be significantly dependent on the initial concentration of 1,2,3,4-TeCDD.

Occurrence and Implications of SEM-AVS for Surface Sediments from Baihua Lake, China

The concentrations of acid volatile sulfide (AVS) and simultaneous extracted metals (SEMs, including SEMCu, SEMCd, SEMPb, SEMZn, SEMNi, SEMHg, SEMAs and SEMCr) in 17 superficial sediment samples were determined to better understand their spatial distribution in Baihua Lake, Guizhou Province, in southwest China. The SEMs/AVS ratio was employed to assess the bioavailability of the eight cationic metals. The SEMs/AVS ratio was significantly lower than 1.0, indicating that AVS in the sediments was sufficient to shield the eight selected heavy metals; thus the eight heavy metals showed no significant bioavailability to the benthic organisms. In addition, a preliminary study on the crystal composition in the sediments from Baihua Lake before and after SEMs’ extraction by X-ray diffraction analysis partly confirmed the efficiency of the cold-acid purge-and-trap technique.

Vertical Profile of Acid Volatile Sulfide (AVS) and Risk Assessment of Sediments from Baihua Lake, China

Acid volatile sulfide (AVS), simultaneously extracted metals (SEMs), and total concentrations of trace elements (Cu, Cd, Pb, Zn, Ni, Hg, As, and Cr) were studied in sediment cores from Baihua Lake in southwest China. The molar ratios of SEMs to AVS for all samples were lower than 1.0 except for the 25- to 30-cm layer of the sample collected at location YPZ, indicating that the heavy metals were currently not significantly bioavailable as a whole to benthic organisms. Based on the sediment quality guidelines and the potential ecological risk assessment, Hg presented a high ecological risk for the water body.

Heavy Metal Pollution and Ecological Assessment around the Jinsha Coal-Fired Power Plant (China)

Heavy metal pollution is a serious problem worldwide. In this study, 41 soil samples and 32 cabbage samples were collected from the area surrounding the Jinsha coal-fired power plant (JCFP Plant) in Guizhou Province, southwest China. Pb, Cd, Hg, As, Cu and Cr concentrations in soil samples and cabbage samples were analysed to study the pollution sources and risks of heavy metals around the power plant. The results indicate that the JCFP Plant contributes to the Pb, Cd, As, Hg, Cu, and Cr pollution in nearby soils, particularly Hg pollution. Cu and Cr in soils from both croplands and forestlands in the study area derive mainly from crustal materials or natural processes. Pb, Cd and As in soils from croplands arise partly through anthropogenic activities, but these elements in soils from forestlands originate mainly from crustal materials or natural processes. Hg pollution in soils from both croplands and forestlands is caused mainly by fly ash from the JCFP Plant. The cabbages grown in the study area were severely contaminated with heavy metals, and more than 90% of the cabbages had Pb concentrations exceeding the permissible level established by the Ministry of Health and the Standardization Administration of the People’s Republic of China. Additionally, 30% of the cabbages had As concentrations exceeding the permissible level. Because forests can protect soils from heavy metal pollution caused by atmospheric deposition, close attention should be given to the Hg pollution in soils and to the concentrations of Pb, As, Hg and Cr in vegetables from the study area.

Spatio‐temporal Distribution and Chemical Speciation of Iron and Manganese in Sediments from Lake Aha, China

This paper reports an investigation on pollution and potential risk on elements of iron (Fe) and manganese (Mn) in sediments from Lake Aha, which is a drinking‐water source for Guiyang City, the capital of Guizhou Province in southwestern China. In the present research, chemical speciation of Fe and Mn in sediments from the lake was studied based on the sequential extraction procedure developed by Tessier et al.. The results obtained from the study are as follows. The average values of total Fe were 47617 mg/kg and 70325 mg/kg in sediments from the lake in summer and winter respectively, and its speciation consisted mainly of residual and Fe‐Mn oxides fractions. The amounts of total Fe and the distribution of its speciation in the sediments should be affected by effluents from a large quantity of deserted coal mines in the lake basin in summer and winter. The average values of total Mn were 7996 mg/kg and 1753 mg/kg in summer and winter respectively, and its speciation is primarily comprised of carbonate ...

Distribution, fraction and risk assessment of vanadium in surface sediments from a Chinese karstic lake: a case study of Hongfeng Lake

The distribution characteristics of vanadium and its fraction based on the Tessier sequential extraction method were studied in surface sediment samples collected from Hongfeng Lake. The results of this study indicated that the total amount of vanadium in the sediment samples ranged from 124.0 to 213.0 mg/kg. The average percentages of exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual were 2.79, 2.75, 30.40, 2.89 and 59.32, respectively. The concentrations of the different vanadium fractions decreased in the order of residual > bound to Fe-Mn oxides > bound to organic matter > exchangeable ≈ bound to carbonates. Furthermore, assessment using the enrichment factors (EF), the ratio of secondary to primary phase (RSP) and the secondary phases enrichment factor (SPEF) methods showed that the risk of vanadium in sediments especially from sites TLHJC and TX from Hongfeng Lake was generally high.