Using Si depletion in aerosol to identify the sources of crustal dust in two Chinese megacities

Depletion of Si in transported dust has been recognized for many years. It can be used to distinguish between transported and local dust in cities, although it rarely has been. Here we use the variations of the Si/Al ratio in 15 months of continuous PM_2.5 samples at Beijing (northern China) and Chongqing (southwestern China) to reveal the seasonal patterns of their dust sources. For both cities, peaks of concentration for Si and Al in PM_2.5 corresponded with minima of Si/Al, and could often be linked to pulsed air flow from deserts to the northwest. With significant depletion (up to 80%) and homogeneous distribution at urban and rural sites, Si/Al showed a clear seasonal evolution, which decreased from spring to summer, increased from fall to winter, and collapsed during Chinese Spring Festival, indicating the dominance of transported dust, local fugitive dust and firework influence, respectively. The low ratios implied that desert dust is a common source during spring at Chongqing, whereas its presence during cold season at Beijing was also more frequent than expected. Failing to recognize the depletion of Si may lead to an overestimate of desert dust by 15%–65% when using the average abundance of Al in crust (6%–8%), as in previous studies. The difference in Si/Al ratio between local and transported dust implies that >60% of the dust at Beijing came from outside the city during the springs of 2004–2006. This result can help resolve the contradictory findings on this topic that have been presented earlier.     

Degradation kinetics of anthracene by ozone on mineral oxides

To further understand the role of substrates on the heterogeneous reactions of polycyclic aromatic hydrocarbons, the reactions of ozone with anthracene adsorbed on different mineral oxides (SiO₂, α-Al₂O₃ and α-Fe₂O₃) and on Teflon disc were investigated in dark at 20 °C. No reaction between ozone and anthracene on Teflon disc was observed when the ozone concentration was ～1.18 × 10¹⁴ molecules cm^?3. The reactions on mineral oxides exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate constant (k_1,obs) displayed a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration. The adsorption equilibrium constants for ozone (K_O3) on SiO₂-1, SiO₂-2, α-Al₂O₃ and α-Fe₂O₃ were (0.81 ± 0.26) × 10^?15 cm³, (2.83 ± 1.17) × 10^?15 cm³, (2.48 ± 0.77) × 10^?15 cm³ and (1.66 ± 0.45) × 10^?15 cm³, respectively; and the maximum pseudo-first-order rate constant (k_1,max) on these oxides were (0.385 ± 0.058) s^?1, (0.101 ± 0.0138) s^?1, (0.0676 ± 0.0086) s^?1 and (0.0457 ± 0.004) s^?1, respectively. Anthraquinone was identified as the main surface product of anthracene reacted with ozone. Comparison with previous research and the results obtained in this study suggest that the reactivity of anthracene with ozone and the lifetimes of anthracene adsorbed on mineral dust in the atmosphere are determined by the nature of the substrate.     

多孔富铁填料曝气过滤除磷机理研究

采用多孔富铁填料的曝气过滤装置具有优良的除磷性能,理论分析研究了多孔富铁填料的除磷机理,通过铁细菌测定、电镜扫描、红外光谱分析等实验对其除磷机理进行了验证。结果表明,多孔富铁填料除磷为化学除磷过程,铁的形态转化中存在铁细菌的氧化作用,沉淀物以碱式磷酸铁为主。     

废弃轮胎制备中孔炭吸附材料工艺及性能研究

为了解决废弃轮胎造成的资源浪费和环境污染的问题,对以废弃轮胎橡胶为碳的前驱体原料,制备具有高吸附性能中孔炭材料工艺进行了系统的研究。通过XRD、扫描电镜以及比表面积分析,对制备的中孔炭微观结构和性能进行表征,讨论了炭化温度、碱炭比,以及活化温度和活化时间等工艺条件对制备中孔炭的产率、结构和性能的影响。结果表明,通过改变工艺条件制备的中孔炭的孔径分布可以在2~80 nm范围内进行调控。在500℃炭化温度,碱炭比为4∶1,900℃活化1 h的工艺条件下,制备的中孔炭的比表面积为473 m2/g,对甲基橙的最大吸附量达到254 mg/g。     

利用高炉水淬渣制作多孔吸声材料的研究

为了促进高炉炼铁水淬渣的二次利用,研究了以高炉炼铁水淬渣为原料,以硅微粉或水泥为粘结剂,采用压制成型方法制作的多孔吸声材料的吸声性能及力学性能。结果表明:用颗粒状的高炉炼铁水淬渣制作的多孔吸声材料具有良好的吸声性能,其平均吸声系数可以达到0.70以上;材料的抗压强度可以达到3.0 MPa以上。     

Cadmium tolerance in six poplar species

Selection of poplar species with greater Cd tolerance and exploiting the physiological mechanisms involved in Cd tolerance are crucial for application of these species to phyto-remediation. The aim of this study is to investigate variation in Cd tolerance among the six poplar species and its underlying physiological mechanisms. Cuttings of six Populus species were cultivated for 10 weeks before exposure to either 0 or 200 μM CdSO₄ for 20 days. Gas exchange in mature leaves was determined by a portable photosynthesis system. Cd concentrations in tissues were analyzed by a flame atomic absorbance spectrometry. Subsequently, Cd amount per plant, bio-concentration factor (BCF) and translocation factor (T _f) were calculated. Nonenzymatic compounds and activities of antioxidative enzymes in tissues were analyzed spectrophotometrically. Cd exposure caused decline in photosynthesis in four poplar species including Populus cathayana (zhonghua 1). Among the six species, P. cathayana (zhonghua 1) displayed the highest Cd concentrations in tissues, the largest Cd amount in aerial parts, the highest BCF in aerial parts and T _f under Cd exposure. Under Cd stress, increases in total soluble sugars in roots but decreases in starch in roots, wood, and leaves of P. cathayana (zhonghua 1) were found. Induced O ₂ ^?? and H₂O₂ production in roots and leaves, and increases in free proline, soluble phenolics, and activities of antioxidative enzymes were observed in P. cathayana (zhonghua 1). Based on results of this pot experiment, it is concluded that P. cathayana (zhonghua 1) is superior to other five species for Cd phyto-remediation, and its well-coordinated physiological changes under Cd exposure confer the great Cd tolerance of this species.     

Bioremediation of Cd and carbendazim co-contaminated soil by Cd-hyperaccumulator Sedum alfredii associated with carbendazim-degrading bacterial strains

The objective of this study was to develop a bioremediation strategy for cadmium (Cd) and carbendazim co-contaminated soil using a hyperaccumulator plant (Sedum alfredii) combined with carbendazim-degrading bacterial strains (Bacillus subtilis, Paracoccus sp., Flavobacterium and Pseudomonas sp.). A pot experiment was conducted under greenhouse conditions for 180 days with S. alfredii and/or carbendazim-degrading strains grown in soil artificially polluted with two levels of contaminants (low level, 1 mg kg^?1 Cd and 21 mg kg^?1 carbendazim; high level, 6 mg kg^?1 Cd and 117 mg kg^?1 carbendazim). Cd removal efficiencies were 32.3–35.1 % and 7.8–8.2 % for the low and high contaminant level, respectively. Inoculation with carbendazim-degrading bacterial strains significantly (P?<?0.05) increased Cd removal efficiencies at the low level. The carbendazim removal efficiencies increased by 32.1–42.5 % by the association of S. alfredii with carbendazim-degrading bacterial strains, as compared to control, regardless of contaminant level. Cultivation with S. alfredii and inoculation of carbendazim-degrading bacterial strains increased soil microbial biomass, dehydrogenase activities and microbial diversities by 46.2–121.3 %, 64.2–143.4 %, and 2.4–24.7 %, respectively. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed that S. alfredii stimulated the activities of Flavobacteria and Bradyrhizobiaceae. The association of S. alfredii with carbendazim-degrading bacterial strains enhanced the degradation of carbendazim by changing microbial activity and community structure in the soil. The results demonstrated that association of S. alfredii with carbendazim-degrading bacterial strains is promising for remediation of Cd and carbendazim co-contaminated soil.     

The residues, distribution, and partition of organochlorine pesticides in the water, suspended solids, and sediments from a large Chinese lake (Lake Chaohu) during the high water level period

The levels of organochlorine pesticides (OCPs) in the water, suspended solids, and sediments from Lake Chaohu during the high water level period were measured by a solid-phase extraction gas chromatograph–electron capture detector. The spatial distributions of the three phases and the water/suspended solids and sediment/water partition coefficients were analyzed. The results showed the following: (1) The mean contents of OCPs in the water, suspended solids, and sediments were 132.4?±?432.1 ng/L, 188.1?±?286.7 ng/g dry weight (dw), and 13.7?±?9.8 ng/g dw, respectively. The dominant OCP components were isodrin (85.1 %) for the water, DDTs (64.4 %) for the suspended solids, and both isodrin (48.5 %) and DDTs (31.8 %) for the sediments. (2) β-HCH was the primary isomer of HCHs in the water and sediments, and the proportions were 61.7 and 41.3 %; γ-HCH was the primary isomer in the suspended solids, accounting for 49.3 %; p,p′-DDT was the dominant content of DDTs in the water and suspended solids, whereas p,p′-DDD was the main metabolite of DDTs in the sediments. (3) The concentrations of contaminants in the water from the western lake were greater than those from the eastern lake, but the concentrations in the suspended solids from the western lake were less than those from the eastern lake. (4) There was no significant correlation between the water–suspended solids partition coefficient K _d and the n-octanol–water partition coefficient K _ow, and between the sediment–water organic-C weighted sorption coefficients K _oc and K _ow.     

Application of 15N–18O double stable isotope tracer technique in an agricultural nonpoint polluted river of the Yangtze Delta Region

One strategy to combat nitrate (NO₃-N) contamination in rivers is to understand its sources. NO₃-N sources in the East Tiaoxi River of the Yangtze Delta Region were investigated by applying a ¹⁵N–¹⁸O dual isotope approach. Water samples were collected from the main channel and from the tributaries. Results show that high total N and NO₃-N are present in both the main channel and the major tributaries, and NO₃-N was one of the most important N forms in water. Analysis of isotopic compositions (δ ¹⁸O, δD) of water suggests that the river water mainly originated from three tributaries during the sampling period. There was a wide range of δ ¹⁵N-NO₃ (?1.4 to 12.4 ‰) and a narrow range of δ ¹⁸O-NO₃ (3.7 to 9.0 ‰) in the main channel waters. The δ ¹⁵N and δ ¹⁸O-NO₃ values in the upper, middle, and lower channels along the river were shifted as 8.2, 3.5, and 9.5 ‰, and 9.0, 4.2, and 6.0 ‰, respectively. In the tributary South Tiao, the δ ¹⁵N and δ ¹⁸O-NO₃ values were as high as 9.5 and 7.0 ‰, while in the tributaries Mid Tiao and North Tiao, NO₃-N in most of the samples had relatively low δ ¹⁵N and δ ¹⁸O-NO₃ values from 2.3 to 7.5 ‰ and 4.7 to 7.0 ‰, separately. Our results also suggest that the dual isotope approach can help us develop the best management practice for relieving NO₃-N pollution in the rivers at the tributary scale.     

Effects of nitrogen application rate and a nitrification inhibitor dicyandiamide on methanotroph abundance and methane uptake in a grazed pasture soil

Methane-oxidizing bacteria (methanotrophs) in the soil are a unique group of methylotrophic bacteria that utilize methane (CH₄) as their sole source of carbon and energy which limit the flux of methane to the atmosphere from soils and consume atmospheric methane. A field experiment was conducted to determine the effect of nitrogen application rates and the nitrification inhibitor dicyandiamide (DCD) on the abundance of methanotrophs and on methane flux in a grazed pasture soil. Nitrogen (N) was applied at four different rates, with urea applied at 50 and 100 kg N ha^?1 and animal urine at 300 and 600 kg N ha^?1. DCD was applied at 10 kg ha^?1. The results showed that both the DNA and selected mRNA copy numbers of the methanotroph pmoA gene were not affected by the application of urea, urine or DCD. The methanotroph DNA and mRNA pmoA gene copy numbers were low in this soil, below 7.13?×?10³ g^?1 soil and 3.75?×?10³ μg^?1 RNA, respectively. Daily CH₄ flux varied slightly among different treatments during the experimental period, ranging from ?12.89 g CH₄ ha^?1 day^?1 to ?0.83 g CH₄ ha^?1 day^?1, but no significant treatment effect was found. This study suggests that the application of urea fertilizer, animal urine returns and the use of the nitrification inhibitor DCD do not significantly affect soil methanotroph abundance or daily CH₄ fluxes in grazed grassland soils.