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Chlorinated persistent organic pollutants, including polychlorinated biphenyls (PCBs), represent a particularly serious environmental problem and human health risk worldwide. Leguminous plants and their symbiotic bacteria (rhizobia) are important components of the biogeochemical cycling of nitrogen in both agricultural and natural ecosystems. However, there have been relatively few detailed studies of the remediation of PCB-contaminated soils by legume-rhizobia symbionts. Here we report for the first time evidence of the reductive dechlorination of 2,4,4'-trichlorobiphenyl (PCB 28) by an alfalfa-rhizobium nitrogen fixing symbiont. Alfalfa (Medicago sativa L.) inoculated with wild-type Sinorhizobium meliloti had significantly larger biomass and PCB 28 accumulation than alfalfa inoculated with the nitrogenase negative mutant rhizobium SmY. Dechlorination products of PCB 28, 2,4'-dichlorobiphenyl (PCB 8), and the emission of chloride ion (Cl-) were also found to decrease significantly in the ineffective nodules infected by the mutant strain SmY. We therefore hypothesize that N2-fixation by the legume-rhizobium symbiont is coupled with the reductive dechlorination of PCBs within the nodules. The combination of these two processes is of great importance to the biogeochemical cycling and bioremediation of organochlorine pollutants in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

CoFe/C core-shell structured nanocomposites (CoFe@C) have been fabricated through the thermal decomposition of acetylene with CoFe2O4 as precursor. The as-prepared CoFe@C was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and thermogravimetric analysis. The results demonstrate that the carbon shell in CoFe@C has a poor crystallization with a thickness about 5-30 nm and a content approximately 48.5 wt.%. Due to a good combination between intrinsic magnetic properties and high-electrical conductivity, the CoFe@C exhibits not only excellent absorption intensity but also wide frequency bandwidth. The minimum RL value of CoFe@C can reach - 44 dB at a thickness of 4.0 mm, and RL values below - 10 dB is up to 4.3 GHz at a thickness of 2.5 mm. The present CoFe@C may be a potential candidate for microwave absorption application. [ABSTRACT FROM AUTHOR]

Purpose: A 7-month field experiment was conducted to investigate the polycyclic aromatic hydrocarbon (PAH) remediation potential of two plant species and changes in counts of soil PAH-degrading bacteria and microbial activity. Materials and methods: Alfalfa and tall fescue were grown in monoculture and intercropped for 7 months in contaminated field soil. Soil and plant samples were analyzed for PAHs. Plant biomass, densities of PAH-degradation soil bacteria, soil microbial biomass C and N, enzyme activities, and the physiological profile of the soil microbial community were determined. Results and discussion: Average removal percentage of total PAHs in intercropping (30.5%) was significantly higher than in monoculture (19.9%) or unplanted soil (−0.6%). About 7.5% of 3-ring, 12.3% of 4-ring, and 17.2% of 5(+6)-ring PAHs were removed from the soil by alfalfa, with corresponding values of 25.1%, 10.4%, and 30.1% for tall fescue. Intercropping significantly enhanced the remediation efficiency. About 18.9% of 3-ring, 30.9% of 4-ring, and 33.4% of 5(+6)-ring PAHs were removed by the intercropping system. Higher counts of soil culturable PAH-degrading bacteria and elevated microbial biomass and enzyme activities were found after intercropping. Soil from intercropping showed significantly higher ( p < 0.05) average well-color development obtained by the BIOLOG Ecoplate assay and Shannon-Weaver index compared with monoculture. Conclusions: Cropping promoted the dissipation of soil PAHs. Tall fescue gave greater removal of soil PAHs than alfalfa, and intercropping was more effective than monoculture. Intercropping of alfalfa and tall fescue may be a promising in situ bioremediation strategy for PAH-contaminated soils. [ABSTRACT FROM AUTHOR]

new liquid polyborosilazane precursor for Si-B-C-N ceramic was synthesized by co-condensation reaction of boron trichloride, organodichlorosilanes, and hexamethyldisilazane. The structure and properties of polyborosilazane were studied by means of Fourier transform-infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), rheology, and thermogravimetric analysis (TGA). The conversion of polymer to ceramic and the high-temperature behavior of the new polymer-derived ceramic were investigated by TG-MS, FT-IR, X-ray diffraction (XRD) and high-temperature TGA (HTGA). The ceramics showed good oxidative resistance and thermal stability with weight gain of 1.8 wt% at 1350 °C under air atmosphere and weight loss of 2.6% at 1900 °C under Ar atmosphere. [ABSTRACT FROM AUTHOR]

It was not unusual in soil and environmental studies that the distribution of data is severely skewed with several high peak values, which causes the difficulty for Kriging with data transformation to make a satisfied prediction. This paper tested an approach that integrates kriging and triangular irregular network interpolation to make predictions. A data set consisting of total Copper (Cu) concentrations of 147 soil samples, with a skewness of 4.64 and several high peak values, from a copper smelting contaminated site in Zhejiang Province, China. The original data were partitioned into two parts. One represented the holistic spatial variability, followed by lognormal distribution, and then was interpolated by lognormal ordinary kriging. The other assumed to show the local variability of the area that near to high peak values, and triangular irregular network interpolation was applied. These two predictions were integrated into one map. This map was assessed by comparing with rank-order ordinary kriging and normal score ordinary kriging using another data set consisting of 54 soil samples of Cu in the same region. According to the mean error and root mean square error, the approach integrating lognormal ordinary kriging and triangular irregular network interpolation could make improved predictions over rank-order ordinary kriging and normal score ordinary kriging for the severely skewed data with several high peak values. [ABSTRACT FROM AUTHOR]

Purpose: An in situ phytoremediation trial was developed in order to investigate the function of alfalfa during a 2-year bioremediation of an agricultural soil contaminated with polychlorinated biphenyls (PCBs). The study was conducted with the aim to better understand the application potential of PCB phytoremediation at field scale. Materials and methods: Two treatments were set up in this field study: (1) soil without planting as a control (CK), and (2) soil planted with alfalfa (P). Kinetics of soil PCB removal during the bioremediation treatment was determined using gas chromatography. Soil enzyme activities including dehydrogenase and fluorescein diacetate (FDA) esterase were detected by spectrophotometry. In addition, soil microbial community structures were investigated by using denaturing gradient gel electrophoresis (DGGE). Results and discussion: After the first and second years of remediation, planting alfalfa significantly decreased the initial soil PCB concentrations by 31.4% and 78.4%, respectively. Moreover, the presence of alfalfa significantly increased soil dehydrogenase and FDA esterase activities during the remediation. Changes in soil bacterial community structure and diversity were observed by PCR-DGGE fingerprinting. Planting alfalfa significantly increased soil bacterial diversity. Some well-known PCB-degrading bacteria such as Chloroflexi sp. may have contributed to the rhizoremediation of PCBs. Conclusions: Results of this field study suggest that alfalfa is a promising candidate for phytoremediation of PCB-contaminated agricultural soil. [ABSTRACT FROM AUTHOR]

Thirty typical soil profiles were sampled in Yangtze River Delta (YRD) region and analyzed for stable lead (Pb) isotopes and total concentrations of Pb and scandium (Sc). Pb isotopic compositions of A-horizon and C-horizon and Pb/Sc ratio were combined to estimate the amounts of endogenous and exogenous Pb accumulated in topsoil and identify possible sources. The results indicated that Pb exhibits a trend of accumulation in topsoil at regional scale. The isotopic composition of endogenous Pb is characterized by a narrow range of isotope ratios, varying with parent material, while that of exogenous Pb is characterized by a comparatively wide range of isotope ratios, varying with anthropogenic source. Coal combustion is probably the most important anthropogenic source of exogenous Pb in the soils of YRD region, as identified by isotopic ratio cross-plot combined with multi-elemental approaches. [ABSTRACT FROM AUTHOR]

We investigated the chemical fractions of Zn, Cd and Cu in soils collected from positions at different distances from a copper smelter and studied the relationships between distribution patterns of Zn, Cd and Cu, fractions and soil organic carbon (SOC), especially “black carbon” (BC), in contaminated soils. The relationships between soil particle size and concentrations of Zn and Cd in contaminated soil were also examined. Soil samples were collected from field sites at different distances from the copper smelter, air-dried and passed through 0.25-mm and 0.149-mm nylon mesh sieves. The SOC and BC were determined. Aqua regia and sequentially extracted Zn, Cd and Cu fractions in soil and the different sizes of soil particles, and metal concentrations (Zn, Cd and Cu) in BC were also determined. The soils were heavily contaminated by fly ash from the copper smelter. Concentrations of Zn, Cd and Cu in soil and SOC decreased with increasing distance from the smelter. Concentrations of Zn and Cd in the surface soil (0–15 cm) decreased from 27,017 to 892 mg kg−1 and from 18.7 to 1.04 mg kg−1, respectively. Soil BC and concentrations of Zn, Cd and Cu in the BC fraction showed significant and positive relationships with the corresponding aqua regia metal concentrations in soil. Soil Zn and Cd occurred predominantly in the exchangeable and reducible fractions, but residual and oxidisable fractions of Cu that were not considered mobile or bioavailable were predominant (>60%). Concentrations of Zn and Cd in the soil particle size fractions tended to increase with decreasing particle size. The Cd and Zn and BC were all derived from the fly ash of the smelter. Concentrations of Zn and Cd and BC in the soil decreased significantly with increasing distance from the smelter. Zinc and Cd in contaminated soils increased as particle size decreased, and were mainly in highly available exchangeable-, water- and acid-soluble, and reducible fractions. [ABSTRACT FROM AUTHOR]

total of 782 topsoil samples (0–20 cm) and 371 subsoil samples (20–40 cm) were collected from agricultural land in two rapidly industrialized areas with a large number of small rural industries in southeast China, Zhangjiagang City (ZJG) and Changshu City (CS), to measure soil chromium (Cr) concentrations. Kriging and cokriging were used to predict the spatial distribution of Cr in the topsoils and subsoils. Paired-samples t test and spatial distribution maps were used to compare the Cr concentrations in topsoils and subsoils. The mean Cr concentration in ZJG topsoils was significantly higher than that in ZJG subsoils and the mean Cr concentration in CS topsoils showed no significant difference from that in CS subsoils. The Cr concentrations in topsoils were higher than those in subsoils over most of the area of ZJG and part of CS, suggesting that Cr accumulation had occurred in these areas and extrinsic factors have an important role controlling the distribution of Cr in topsoils. Semivariogram/cross-semivariogram was used to evaluate soil Cr spatial variability. The Cr in ZJG topsoils, ZJG subsoils, and CS topsoils had moderate spatial dependence and the Cr in CS subsoils had strong spatial dependence. Cr in ZJG subsoils had longer effective range than Cr in ZJG topsoils, suggesting that the anthropogenic factors affecting Cr distribution in ZJG topsoils; and Cr in CS topsoils had longer effective range than Cr in CS subsoils, indicating that soil formation may be the major explanation for the decrease in the variation of Cr in topsoils. A significant correlation was found between the Cr in topsoils and Cr in subsoils, indicating that natural factors also play an important role as extrinsic factors that control the distribution of Cr in topsoils. [ABSTRACT FROM AUTHOR]

Carbon supplementation, soil moisture and soil aeration are believed to enhance in situ bioremediation of PAH-contaminated soils by stimulating the growth of indigenous microorganisms. However, the effects of added carbon and nitrogen together with soil moisture and soil aeration on the dissipation of PAHs and on associated microbial counts have yet to be fully assessed. In this study the effects on bioremediation of carbon source, carbon-tonitrogen ratio, soil moisture and aeration on an aged PAH-contaminated agricultural soil were studied in microcosms over a 90-day period. Additions of starch, glucose and sodium succinate increased soil bacterial and fungal counts and accelerated the dissipation of phenanthrene and benzo(a)pyrene in soil. Decreases in phenanthrene and benzo(a)pyrene concentrations were effective in soil supplemented with glucose and sodium succinate (both 0.2 g C kg-1 dry soil) and starch (1.0 g C kg-1 dry soil). The bioremediation effect at a C/N ratio of 10:1 was significantly higher (P<0.05) than at a C/N of either 25:1 or 40:1. Soil microbial counts and PAH dissipation were lower in the submerged soil but soil aeration increased bacterial and fungal counts, enhanced indigenous microbial metabolic activities, and accelerated the natural degradation of phenanthrene and benzo(a)pyrene. The results suggest that optimizing carbon source, C/N ratio, soil moisture and aeration conditions may be a feasible remediation strategy in certain PAH contaminated soils with large active microbial populations. [ABSTRACT FROM AUTHOR]

A protocol was developed to fractionate soil particles down to the nanocolloid scale by combining sieving, sedimentation, centrifugation, and cross-flow filtration (CFF). The validity of the method and the performance of the CFF system were tested by characterizing fractions using laser granulometry, electron microscopy, and chemical analysis. The 0.1-μm-pore-size membrane CFF system effectively retained nanocolloids (<0.1 μm) as shown by laser granulometry and observed directly by transmission electron microscopy. However, environmental scanning electron microscopy images of freeze-dried colloids were very different from their TEM counterparts, suggesting that sample preparation influenced microscopy imaging. Chemical analysis of Cu, Cd, and organic carbon in each fraction showed that the concentrations of these components increased as particle size decreased, indicating colloids and nanocolloids play an important role in retaining trace metals. Particle-size fractionation combined with chemical analysis and electron microscopy can provide insight into the nature and properties of nanocolloids in soil. [ABSTRACT FROM AUTHOR]

Microcosms were set up with a PAHscontaminated soil using biostimulation (addition of ground corn cob) and bioaugmentation (inoculated with Monilinia sp. W5-2). Degradation of polycyclic aromatic hydrocarbons and microbial community were examined at the end of incubation period. After 30 days, bioaugmented microcosms showed a 35 ± 0% decrease in total PAHs, while biostimulated and control microcosms showed 16 ± 9% and 3 ± 0% decrease in total PAHs, respectively. Bioaugmented microcosms also revealed 70 ± 8% and 72 ± 2% decreases in benzo[a]pyrene and anthracene, respectively, while the values for biostimulated and control microcosms were much lower. Detoxification of soils in bioaugmented microcosms was confirmed by genetic toxicity assay, suggesting important role of fungal remediation. Molecular fingerprint profiles and selective enumeration showed biostimulation with ground corn cob increased both number and abundance of indigenous aromatic hydrocarbons degraders and changed microbial community composition in soil, which is beneficial to natural attenuation of PAHs. At the same time, bioaugmentation with Monilinia strain W5-2 imposed negligible effect on indigenous microbial community. This study suggests that fungal remediation is promising in eliminating PAHs, especially the part of recalcitrant and highly toxic benzo[a]pyrene, in contaminated soil. It is also the first description of soil bioremediation with Monilinia sp. [ABSTRACT FROM AUTHOR]

An assessment of exposure to mercury in Changchun city has been undertaken. We estimated Hg exposure to members of the general population based on currently available information and our research. We also studied the Hg concentrations in scalp hair of adults. Adults have an estimated intake of all Hg species via all routes of 6.780 μg day−1 (excluding dental amalgam), which equates to an absorbed dose of 1.718 μg day−1. Fish consumption was the most important exposure route (12% of intake, 43% of absorbed dose). Furthermore, air, cereals and vegetables were important exposure routes, and these exposure were estimated for absorbed dosed at 0.296, 0.209 and 0.318 μg day−1, respectively. The mean Hg concentration in hair was 0.448 μg g−1 (range 0.092–10.463 μg g−1). Hg concentration in the hair of males was 0.422 μg g−1 (0.105–2.665 μg g−1), and was 0.474 μg g−1(0.092–10.463 μg g−1) in the hair of females. Neither place of residence nor age had any significant effect on hair Hg concentrations. [ABSTRACT FROM AUTHOR]

Polychlorinated biphenyls (PCBs) were determined in surface soil samples from Zhejiang Province, east China. Concentrations of total PCBs ranged widely from 7.50 to 263 ng kg−1 with a mean value of 45.4 ng kg−1 (dry matter basis). In general, concentrations in soil samples from the southern part of the test area and especially from some sites near hills tended to be higher than those from other sites. The prevailing winds may have been the main factor influencing the spatial distribution of PCBs in soils. Other factors may have included the distribution of residential areas and land use variables. In this paper we also discuss the relationships between OCPs and PCBs in soils and relationships between these and land use variables as revealed by correlation analysis. [ABSTRACT FROM AUTHOR]

A survey was conducted on the accumulation and spatial distribution of PAHs in surface soils under different land use patterns in a valley in the Yangtze Delta region with an area of 10 km2 containing 15 small copper- and zinc-smelting furnaces. Sixty-five topsoil (0–20 cm) samples were collected and 16 PAHs were determined. The average amount of all the 16 PAHs ranged from 0 to 530 μg kg−1 (oven dry basis), with a mean concentration of 33.2 μg kg−1. Benzo[a]pyrene and indeno[1, 2, 3, -cd]pyrene were the two main PAHs present at high concentrations, while pyrene and fluorene had very low concentrations. PAH concentrations were higher in uncultivated than in cultivated soils, and areas of woods and shrubbery had the␣lowest soil PAH contents. The average PAH-homologue concentrations ranked as follows: 5-rings >> 3-rings, 4-rings > 6-rings >2-rings. Much higher concentrations of PAHs were found in the southern part of the sampling area, perhaps due to deposition of airborne particles by the southeasterly winds in winter and spring. We conclude that the small smelting furnaces were the dominant source of PAHs that accumulated in the soils and the southeasterly winds led to the spatial distribution of PAHs in the topsoils. Land vegetation cover and soil utilization patterns also affected the accumulation and distribution of soil PAHs. [ABSTRACT FROM AUTHOR]

Effects of benzo[a]pyrene (B[a]P) on ryegrass ( Lolium perenne L.) growth, plant accumulation and dissipiation of B[a]P in a red sandy soil (Hapli-Udic Argosol) were studied in a pot experiment. The plants were grown for 61 days in soil spiked with B[a]P at 0, 12.5, 25 and 50 mg kg−1. Control pots without plants were also set up. Soil extractable B[a]P, plant shoot and root biomass, and concentrations of B[a]P in plant shoots and roots were determined. Ryegrass biomass was increased by addition of B[a]P and root B[a]P concentrations were significantly correlated with B[a]P application rate, but no such correlation was found for shoot B[a]P concentrations. This indicates that B[a]P enhanced the growth of the ryegrass. The extractable B[a]P concentration in the planted soil was significantly lower than that in the unplanted control soil at the rate of 50 mg B[a]P kg−1. This indicates that ryegrass may help to dissipate B[a]P in soil at concentrations over 50 mg kg−1 soil although the mechanism for this is not understood. [ABSTRACT FROM AUTHOR]

The extraction of K+ and SiO2 from silicate minerals by Bacillus mucilaginosus in liquid culture was studied in incubation experiments. B. mucilaginosus was found to dissolve soil minerals and mica and simultaneously release K+ and SiO2 from the crystal lattices. In contrast, the bacterium did not dissolve feldspar. B. mucilaginosus also produced organic acids and polysaccharides during growth. The polysaccharides strongly adsorbed the organic acids and attached to the surface of the mineral, resulting in an area of high concentration of organic acids near the mineral. The polysaccharides also adsorbed SiO2 and this affected the equilibrium between the mineral and fluid phases and led to the reaction toward SiO2 and K+ solubilization. These two processes led to the decomposition of silicate minerals by the bacterium. [ABSTRACT FROM AUTHOR]

The mobility of phenanthrene (PHE) in soils depends on its sorption and is influenced by either the existing soil humus or exogenous humic substances. Exogenous humic acids (HAs) were added to soil to enhance the amount of soil organic carbon (SOC) by 2.5, 5.0, and 10.0 g kg−1. PHE desorption of the treated soils was determined at two pH levels (3.0 and 6.0) and temperatures (15 and 25 °C). Soil PHE adsorption was related to pH and the type and quantity of added HAs. Humic acid (HA) and fulvic acid (FA) derived from peat had different effects on adsorption of PHE. Adsorption increased at first and then decreased with increasing quantity of exogenous FA. When the soil solution pH (in 0.005 M CaCl2) was 4.5 or 3.0, the turning points were 2.5 g FA kg−1 at pH 3.0 and 5 g FA kg−1 at pH 4.5. When soil solution pH was 6, the amount of adsorbed PHE was enhanced with increasing exogenous HAs (HA or FA) and amount of adsorption by soil treated with FA was higher than with HA. Adsorption of PHE in the FA treatment at 10.0 g kg−1 was lower than the controls (untreated soil or treatment with HAs at 0 g kg−1) when the soil solution pH was 3.0. This suggests that FA adsorbed by soil was desorbed at low pH and would then increase PHE solubility, and PHE then combined with FA. PHE adsorption was usually higher under lower pH and/or lower temperature conditions. PHE sorption fitted the Freundlich isotherm, indicating that exogenous humic substances influenced adsorption of phenanthrene, which in turn was affected by environmental conditions such as pH and temperature. Thus, exogenous humic substances can be used to control the mobility of soil PAHs under appropriate conditions to decrease PAH contamination. [ABSTRACT FROM AUTHOR]

A comparison of structure and pattern of the soil seed bank was made between active and stabilized sand dunes in northeastern Inner Mongolia, China. The objective of this paper was to determine the significance of seed bank in vegetation restoration of sand dunes. The results showed that (1) average seed density decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune; (2) horizontally, along the transect from interdune lowland to ecotone and to sand dune top, a ‘V’ shaped pattern was presented in the active dune system, and a reverse ‘V’ shaped pattern in the stabilized sand dune system; (3) vertically, the proportion (accounting for the total seeds) of seeds found in 0–20 mm soil profile decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune. The same order was also found in 20–50 mm and 50–100 mm soil profiles; (4) the Sokal and Sneath similarity indices in the species-composition between soil seed bank and above-ground vegetation were ranked as: the stabilized sand dune (24%) > the interdune lowland of active sand dune (21%) > the interdune lowland of stabilized sand dune (18%) > the active sand dune (5%); and (5) vegetation restoration of active sand dunes depends on the dispersal of seeds from nearby plant communities on the interdune lowlands. Much effort must be made to preserve the lowlands, as lowlands are the most important seed reservoir in the active sand dune field. [ABSTRACT FROM AUTHOR]

Catalytic synthesis of di(methylphenyl)methane (CH3C6H4CH2C6H4CH3, DMPMs) from toluene and formaldehyde were investigated over various solids acids. At 140 °C and toluene/HCHO = 5/1, the conversion of HCHO over zeolite (Hβ, H-mordenite, HX, HY and HZSM-5) is limited, while heteropolyacids (H3PW12O40, H4SiW12O40 and H3PMo12O40) exhibited higher activity and DMPMs selectivity. The best yield of DMPMs reached 81.5% (conversion of HCHO nearly 100%). H3PW12O40 could be recovered by simply drying and the recycle-used catalyst remained its activity and structure in five runs. [ABSTRACT FROM AUTHOR]

Two-phase composites consisting of (1 - x) Al2O3 and xTi3SiC2 (x=0-1) were prepared by spark plasma sintering (SPS). Sintered densities larger than 98% of theoretical density were achieved when the specimens were sintered at 1300°C for 5 mm (in vacuum, at pressure 30 MPa). When content of Ti3SiC2 increased up to 30 wt%, composites were found to be machinable—they could be drilled easily using conventional Fe-Mo-W drills or gravers. The mechanical properties of the (1 - x) Al2O3-xTi3SiC2 composites were evaluated. The bending strength, Vickers hardness of the specimens had the following ranges: 428 ± 10.2 (x = 0) to 673 ± 15.4 Mpa (x = 1) (bending strength at room temperature); 19.9 (x = 0) to 4.0 GPa (x = 1) (Vickers hardness). [ABSTRACT FROM AUTHOR]