166 research outputs found
Occurrence and Removal of Polychlorinated Biphenyls (PCBs) in Urban Stormwater
Polychlorinated biphenyls (PCBs) are a group of chlorinated organic compounds. They are persistent in the environment and can threaten the health of humans and wildlife. Urban stormwater runoff is considered as an important source of PCBs to aquatic environments. The objective of this study is to provide information on the occurrence and removal of PCBs in stormwater; specifically, the occurrence, concentrations, and biological transformations of stormwater PCBs were studied together with their removal. Concentrations of 209 PCB congeners were determined in surface stormwater sediments collected from various roadway sites and bioretention media. The total PCB concentrations ranged from 8.3 to 57.4 ng/g dry weight (dw), with a mean value of 29.2 ng/g dw. Land use had an impact on the concentration of PCBs, where higher stormwater sediment PCB concentrations were found in dense urban areas (average: 39.8 ± 10.5 ng/g) compared to highways passing through greenspace (average: 18.0 ± 0.4 ng/g). PCB sorption tended to increase with the concentration of total organic carbon (TOC) and smaller particle size (< 75 µm) of stormwater particulate matter. In bioretention core samples, PCB concentrations decreased with bioretention media depth (from 30.0 ± 2.0 ng/g at the surface to 21.2 ± 4.8 ng/g at 40 cm depth), and with distance from the stormwater entrance (from 38.4 ± 2.3 ng/g at the entrance to 33.2 ± 2.9 ng/g at 3 m distance). A non-Aroclor congener, PCB 11, was detected in all samples, likely originating from yellow road paint. Putative organohalide respiring bacteria within Chloroflexi and aerobic PCB degrading bacteria containing the functional genes encoding for biphenyl dioxygenase (bphA) and ring cleavage (bphC) were detected in some of the stormwater sediments and bioretention media. The presence of such bacteria and a higher level of ortho-chlorinated biphenyls indicated the potential of PCB biotransformation in these samples. The performance of an on-campus bioretention indicated that bioretention is effective in removing PCBs from stormwater, with 64–92% reduction of dissolved PCB concentrations. Overall, urban stormwater is an important environmental source of PCBs. Bioretention has the potential to remove PCBs from stormwater via adsorption and biotransformation
Frustrated Altermagnetism and Charge Density Wave in Kagome Superconductor CsCr3Sb5
Using first-principles density-functional calculations, we investigate the
electronic structure and magnetism of the kagome superconductor CsCrSb.
At the ambient pressure, its ground state is found to be
altermagnetic spin-density-wave (SDW) pattern, with an averaged effective
moment of 1.7 per chromium atom. The magnetic long range order is
coupled to the lattice structure, generating 4 structural modulation.
However, multiple competing SDW phases are present and energetically very
close, suggesting strong magnetic fluctuation and frustration. The electronic
states near the Fermi level are dominated by Cr-3d orbitals, and flat band or
van Hove singularities are away from the Fermi level. When external pressure is
applied, the energy differences between competing orders and the structural
modulations are suppressed by external pressure. The magnetic fluctuation
remains present and important at high pressure because the non-magnetic phase
is unstable up to 30 GPa. In addition, a bonding state between Cr-3d and
Sb-p quickly acquires dispersion and eventually becomes
metallic around 5 GPa, leading to a Lifshitz transition. Our findings strongly
support unconventional superconductivity in the CsCrSb compound above 5
GPa, and suggest crucial role of magnetic fluctuations in the pairing
mechanism
Effect of Soy Lecithin, Glucose Oxidase, and Transglutaminase on Dough Rheology and Quality Properties of Steamed Bread Enriched with Potato Pulp
This study aimed to assess the effect of soy lecithin (Soy L, 0.2%–1.0%), glucose oxidase (GOX, 0.3–1.5 U/g), and transglutaminase (TG, 0.3–1.5 U/g) on dough elongation properties and texture qualities of steamed bread. The optimum formulation of steamed bread prepared from wheat flour (50%) and potato pulp (50%) was investigated. Results showed that Soy L and GOX significantly (P < 0.05) affected the specific volume and hardness of steamed bread, whereas TG significantly (P < 0.05) affected the resistance to extension and extensibility of dough, as well as the springiness and cohesiveness of steamed bread. The optimum formulation consisting of 0.65% Soy L, 0.92 U/g GOX, and 0.96 U/g TG increased the viscoelasticity and fermentation characteristics of dough and improved the specific volume, texture, and porosity of steamed bread enriched with potato pulp
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Cloning, Heterologous Expression, and Characterization of a βκ-Carrageenase From Marine Bacterium Wenyingzhuangia funcanilytica: A Specific Enzyme for the Hybrid Carrageenan–Furcellaran
Carrageenan is a group of important food polysaccharides with high structural heterogeneity. Furcellaran is a typical hybrid carrageenan, which contains the structure consisted of alternative beta-carrageenan and kappa-carrageenan motifs. Although several furcellaran-hydrolyzing enzymes have been characterized, their specificity for the glycosidic linkage was still unclear. In this study, we cloned, expressed, and characterized a novel GH16_13 furcellaran-hydrolyzing enzyme Cgbk16A_Wf from the marine bacterium Wenyingzhuangia fucanilytica CZ1127. Cgbk16A_Wf exhibited its maximum activity at 50 degrees C and pH 6.0 and showed high thermal stability. The oligosaccharides in enzymatic products were identified by liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) and nuclear magnetic resonance (NMR) spectroscopy. It was confirmed that Cgbk16A_Wf specifically cleaves the beta-1,4 linkages between beta-carrageenan and kappa-carrageenan motifs from non-reducing end to reducing end. Considering the structural heterogeneity of carrageenan and for the unambiguous indication of the specificity, we recommended to name the furcellaran-hydrolyzing activity represented by Cgbk16A as beta kappa-carrageenase instead of furcellaranase
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