Xunchang Fei

Binding of PFOS to serum albumin and DNA: insight into the molecular toxicity of perfluorochemicals.

BackgroundHealth risk from exposure of perfluorochemicals (PFCs) to wildlife and human has been a subject of great interest for understanding their molecular mechanism of toxicity. Although much work has been done, the toxigenicity of PFCs remains largely unknown. In this work, the non-covalent interactions between perfluorooctane sulfonate (PFOS) and serum albumin (SA) and DNA were investigated under normal physiological conditions, aiming to elucidate the toxigenicity of PFCs.ResultsIn equilibrium dialysis assay, the bindings of PFOS to SA correspond to the Langmuir isothermal model with two-step sequence model. The saturation binding number of PFOS was 45 per molecule of SA and 1 per three base-pairs of DNA, respectively. ITC results showed that all the interactions were spontaneous driven by entropy change. Static quenching of the fluorescence of SA was observed when interacting with PFOS, indicating PFOS bound Trp residue of SA. CD spectra of SA and DNA changed obviously in the presence of PFOS. At normal physiological conditions, 1.2 mmol/l PFOS reduces the binding ratio of Vitamin B2 to SA by more than 30%.ConclusionThe ion bond, van der Waals force and hydrophobic interaction contributed to PFOS binding to peptide chain of SA and to the groove bases of DNA duplex. The non-covalent interactions of PFOS with SA and DNA alter their secondary conformations, with the physiological function of SA to transport Vitamin B2 being inhibited consequently. This work provides a useful experimental method for further studying the toxigenicity of PFCs.

Binding of bisphenol A and acrylamide to BSA and DNA: Insights into the comparative interactions of harmful chemicals with functional biomacromolecules

The interactions between bisphenol A (BPA)/acrylamide (AA) and bovine serum albumin (BSA)/deoxyribonucleic acid (DNA) was investigated by the equilibrium dialysis, fluorophotometry, isothermal titration calorimetry (ITC) and circular dichroism (CD). The bindings of BPA and AA to BSA and DNA responded to the partition law and Langmuir isothermal model, respectively. The saturation mole number of AA was calculated to be 24 per mol BSA and 0.26 per mol DNA-P. All the reactions were spontaneous driven by entropy change. BPA stacked into the aromatic hydrocarbon groups of BSA and between adjacent basepairs of DNA via the hydrophobic effect. The interactions of AA with BSA and DNA induced the formation of hydrogen bond and caused changes of their secondary structures. At normal physiological condition, 0.100 mmol/l BPA reduced the binding of vitamin B(2) to BSA by more than 70%, and 2.8 mmol/l AA by almost one half. This work provides an insight into non-covalent intermolecular interaction between organic contaminant and biomolecule, helping to elucidate the toxic mechanism of harmful chemicals.

Transmembrane transports of acrylamide and bisphenol A and effects on development of zebrafish (Danio rerio).

Acrylamide (AA) and bisphenol A (BPA) are two kinds of pollutants with different structures and polarities. AA found in fried and toasted starchy foods can cause developmental and reproductive toxicity and BPA has neuro-, immuno- and developmental toxicities. Their transports in zebrafish (Danio rerio) embryos were determined and their toxicity characteristics observed. Approximately 70% of AA was concentrated on the outer membrane surface probably via hydrogen bonds and van der Waals forces, but only 0.3% of AA entered the cytoplasm. In contrast, over 10% of the BPA adsorbed to the cells entered the cytoplasm via the membrane by lipid-water partition. The hydrophilic AA and hydrophobic BPA used different cell transport pathways; AA accumulated on the outer membrane surface whereas BPA readily reached the cytoplasm. AA caused acute and indirect toxicity in developing cells, including serious malnutrition and axial malformation. BPA caused chemical damage to developing cells by causing pericardial edema. The antagonistic effect of the AA/BPA mixtures combinational toxicity to embryos was found and explained by the accumulation of AA on the out surface of membrane inhibiting the transfer of BPA to the cytoplasm.

Quantification of parameters influencing methane generation due to biodegradation of municipal solid waste in landfills and laboratory experiments

The energy conversion potential of municipal solid waste (MSW) disposed of in landfills remains largely untapped because of the slow and variable rate of biogas generation, delayed and inefficient biogas collection, leakage of biogas, and landfill practices and infrastructure that are not geared toward energy recovery. A database consisting of methane (CH4) generation data, the major constituent of biogas, from 49 laboratory experiments and field monitoring data from 57 landfills was developed. Three CH4 generation parameters, i.e., waste decay rate (k), CH4 generation potential (L0), and time until maximum CH4 generation rate (tmax), were calculated for each dataset using U.S. EPAs Landfill Gas Emission Model (LandGEM). Factors influencing the derived parameters in laboratory experiments and landfills were investigated using multi-linear regression analysis. Total weight of waste (W) was correlated with biodegradation conditions through a ranked classification scheme. k increased with increasing percentage of readily biodegradable waste (Br0 (%)) and waste temperature, and reduced with increasing W, an indicator of less favorable biodegradation conditions. The values of k obtained in the laboratory were commonly significantly higher than those in landfills and those recommended by LandGEM. The mean value of L0 was 98 and 88L CH4/kg waste for laboratory and field studies, respectively, but was significantly affected by waste composition with ranges from 10 to 300L CH4/kg. tmax increased with increasing percentage of biodegradable waste (B0) and W. The values of tmax in landfills were higher than those in laboratory experiments or those based on LandGEMs recommended parameters. Enhancing biodegradation conditions in landfill cells has a greater impact on improving k and tmax than increasing B0. Optimizing the B0 and Br0 values of landfilled waste increases L0 and reduces tmax.

Factors Influencing Long-Term Settlement of Municipal Solid Waste in Laboratory Bioreactor Landfill Simulators

AbstractLong-term settlement of municipal solid waste (MSW) in bioreactor and conventional landfills is caused by a number of mechanisms. Laboratory tests in bioreactor landfill simulators allow for a careful assessment of each mechanism and of the factors that affect it. A systematic review and synthesis of 98 tests from 29 mesoscale simulator studies available in the literature are presented. Long-term settlement is divided into three phases: the transitional phase, the active biodegradation phase, and the residual phase. Duration, strain, and long-term compression ratio (equal to the ratio of strain to duration) are calculated for each phase. Statistical analysis of the data is conducted. The majority of the long-term settlement occurs during the active biodegradation phase (9.5% strain on average), and the mean compression ratio is 0.168. The other two phases contribute significantly less to the total long-term settlement. The effects of the initial and operational conditions of simulators on the magn...

Archaeal community structure in leachate and solid waste is correlated to methane generation and volume reduction during biodegradation of municipal solid waste

Duplicate carefully-characterized municipal solid waste (MSW) specimens were reconstituted with waste constituents obtained from a MSW landfill and biodegraded in large-scale landfill simulators for about a year. Repeatability and relationships between changes in physical, chemical, and microbial characteristics taking place during the biodegradation process were evaluated. Parameters such as rate of change of soluble chemical oxygen demand in the leachate (rsCOD), rate of methane generation (rCH4), rate of specimen volume reduction (rVt), DNA concentration in the leachate, and archaeal community structures in the leachate and solid waste were monitored during operation. The DNA concentration in the leachate was correlated to rCH4 and rVt. The rCH4 was related to rsCOD and rVt when waste biodegradation was intensive. The structures of archaeal communities in the leachate and solid waste of both simulators were very similar and Methanobacteriaceae were the dominant archaeal family throughout the testing period. Monitoring the chemical and microbial characteristics of the leachate was informative of the biodegradation process and volume reduction in the simulators, suggesting that leachate monitoring could be informative of the extent of biodegradation in a full-scale landfill.

An experimental setup for simultaneous physical, geotechnical, and biochemical characterization of municipal solid waste undergoing biodegradation in the laboratory

Municipal solid waste (MSW) is biodegradable in landfills under anaerobic conditions. The biodegradation of MSW consists of physical and biochemical processes that affect the geotechnical characteristics of the waste. Laboratory landfill simulators that enable simultaneous characterization of these processes are presented. The simulator configuration, testing procedure, sampling methods, and measurement methods are described. The temporal phases of MSW biodegradation were studied using the experimental setup. Good repeatability of the measurements was demonstrated between duplicate simulators. In addition to data on biogas and leachate samples, a solid waste core sampling technique for retrieving disturbed solid waste samples for chemical and microbial analyses is presented. It was demonstrated that core sampling did not significantly affect simulator operation and measurements. The simulators and sampling methods presented in this study can be used to generate data that will be useful in the development and calibration of comprehensive models for MSW biodegradation in landfills.

Response of Municipal Solid Waste to Mechanical Compression

The compressibility of municipal solid waste (MSW) is of engineering interest as it affects the short-term and long-term performance of landfills, as well as their expansion, closure, and postclosure development. An assessment of the field settlement behavior of MSW can be reliably executed only when the various mechanisms contributing to the settlement are properly taken into account. A comprehensive large-size experimental testing program that involved a total of 143 one-dimensional compression tests from five landfills, in Arizona, California, Michigan, and Texas of the United States as well as Greece was executed to systematically assess the compressibility characteristics of MSW subjected to a compressive load. Emphasis is given to the influence of waste structure, waste composition, unit weight, and confining stress on the compressibility parameters that are used in engineering practice, such as the constrained modulus and compression ratio, as well as long-term compression ratio due to mechanical creep only. The effect of waste composition and unit weight on the compressibility parameters is quantified. It is also found that the type of waste constituent (i.e., paper, plastic, or wood), as well as the waste’s anisotropic structure can have an effect on the compressibility characteristics of soil-waste mixtures. The proposed relationships can be used to estimate compressibility parameters of MSW at any degradation state as long as the waste composition and unit weight are known.

Cyclic Simple Shear Testing of Degraded Municipal Solid Waste from California Under Constant Volume and Constant Load Conditions

For municipal solid waste (MSW) landfills that are situated in seismically active regions, the response of MSW under dynamic loading is critical to landfill design. In this study, a large-size simple shear device is utilized to perform cyclic testing on MSW under constant load (CL) and constant volume (CV) conditions which are considered equivalent to drained and undrained conditions respectively. The MSW sample was excavated from a California landfill located in a seismically active zone and was fully degraded in the laboratory in controlled conditions. Degraded MSW specimens were compacted and consolidated, and then sheared cyclically using cyclic stress ratios (CSR) of 0.1, 0.2, 0.3 and 0.4 sequentially. For a given number of cycles, higher CSR and higher vertical stress result in higher vertical strain and shear strain under CL conditions, and higher excess pore pressure ratio and shear strain under CV conditions. When subjected to cyclic loading, MSW is found to experience significant vertical strain under CL conditions (i.e., compression), or generate potentially significant pore pressures under CV conditions.

Preliminary Observations from Robot-Enabled Surface Methane Concentration Monitoring at a MSW Landfill

The use of robots for surface methane concentration (SMC) monitoring at municipal solid waste (MSW) landfills has the potential to improve quality of data acquisition for fugitive methane measurement over current practices. Methane concentrations vary significantly, both spatially and temporally, across a MSW landfill. However, current monitoring methods do not necessarily account for these significant spatial variations. A land-based robot coupled with commerciallyavailable, relatively low-cost methane detection technology for SMC monitoring was field tested at an active MSW landfill. To more effectively monitor fugitive methane emissions at MSW landfills, an automatic, low-cost, field-deployable technique is needed to actively monitor methane concentrations. Three test areas within a landfill were selected; SMC surveys were performed both manually and by land-robot using the Landtec TDL-500, a tunable diode laser methane detector. The preliminary field observations indicate that a robotic platform can significantly improve quality in data acquisition for surface methane concentrations at MSW landfills; this paper also discusses the limitations of land-based robots for site-wide methane emission monitoring.