Chunlong (Carl) Zhang
Permanent URI for this collectionhttps://hdl.handle.net/10657.1/2212
Dr. Zhang is a Professor of Environmental Science and Environmental Chemistry at the University of Houston-Clear Lake where he is also the Program Chair of the Environmental Science Program. Dr. Zhang's General Research Interests include Environmental sampling and analysis; Environmental chemistry; Environmental remediation; Fate, transport, and remediation of organic chemicals and heavy metals in soil, groundwater, and sediment. Some past and on-going research projects include: Sustainable remediation; Analysis of emerging contaminants (endocrine disrupting chemicals; bromate); Biodegradation of surfactants, explosives chemicals, pharmaceutical and endocrine disrupting compounds; Sorption of polycyclic aromatic hydrocarbons, explosives and endocrine disrupting compounds in soil and sediment; Effects of surfactants on air-water partition of chlorinated solvents; Zero-valent iron for the remediation of chromium contaminated soil and sediment.
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Item Aerobic Biodegradation Kinetics of Four Anionic and Nonionic Surfactants at Sub and Supra Critical Micelle Concentrations(Water Resarch, 1999) Zhang, CarlAerobic biodegradation of four representative commercial surfactants under a range of concentrations (i.e., sub- and supra-critical micelle concentrations, CMCs) beyond those ordinarily used in biodegradation studies was investigated. Of the four surfactants tested, sodium dodecylbenzene sulfonate (SDBS) showed no biodegradation and foam degradation. At a sub-CMC (500 mg/l), primary biodegradation, as measured by methylene blue active substances (MBAS) for an anionic surfactant sodium dodecyl sulphate (SDS) and by cobalt thiocyanate active substances (CTAS) for a nonionic surfactant Witconol, followed Monod kinetics, substrate depletion being a function of both microbial growth and substrate concentrations. However, primary biodegradation at supra-CMCs (500 for Tergitol and 2500 mg/l for SDS and Witconol) and ultimate biodegradation (mineralization) at both sub- and supra-CMCs were best described by first-order kinetics, the degradation rate being a sole function of substrate concentrations. Parameters for the kinetic models (Ks, Y, μmax, and k) were estimated using non-linear least squares methods. Increasing surfactant concentrations from sub- to supra-CMCs significantly decreased primary biodegradation, ultimate biodegradation, and foam degradation. This decrease may be attributed to the limited bioavailability of surfactants in the micellar phase as compared to the monomeric surfactants. The results are of significance for surfactant-based remediation, since the concentrations of surfactants employed in remediation are typically much higher than CMCs, while surfactant concentrations of primary interest in biodegradation work are in the neighborhood of and below 10 mg/l, which is usually 10–100 times lower than CMCs.Item Anaerobic Biotransformation of 2,4-Dinitrotoluene and 2,6-Dinitotoluene by Clostridium acetobutylicum: A Pathway through Dihydroxylamino-Intermediates(Environmental Science and Technology, 1999) Zhang, CarlExperiments were conducted to isolate and identify the intermediates and products of 2,4-dinitrotoluene and 2,6-dinitrotoluene metabolism by Clostridium acetobutylicum. Transformation of both dinitrotoluenes initially resulted in the formation of hydroxylaminonitrotoluenes. Subsequent transformation favored the formation of dihydroxylaminotoluenes, with a limited reduction to aminonitrotoluene isomers. In cell cultures, metabolism beyond the level of dihyroxylaminotoluene was not observed. In cell extracts, where activity could be maintained for periods in excess of those in cell cultures, further transformation yielded aminohydroxylaminotoluenes and eventually diaminotoluenes. These findings further demonstrate the potential for hydroxylamines to be significant intermediates of nitroaromatic transformation under anaerobic fermentative conditions. Interestingly, the rearrangement of dihydroxylaminotoluenes was not observed, as was the case in previous studies of 2,4-dihydroxylamino-6-nitrotoluene metabolism (e.g., the dihydroxylamino metabolite of 2,4,6-trinitrotoluene transformation by C. acetobutylicum). Dihydroxylaminotoluenes were found to be quite unstable, decomposing rapidly upon exposure to oxygen, complicating the assessment of their fate in remediation processes.Item Analysis of Inorganic Nitrogen and Related Anions in High Salinity Water Using Ion Chromatography with Tandem UV and Conductivity Detectors(Journal of Chromatographic Science, 2011) Zhang, CarlOver 97% of the Earth's water is high salinity water in the form of gulfs, oceans, and salt lakes. There is an increasing concern for the quality of water in bays, gulfs, oceans, and other natural waters. These waters are affected by many different sources of contamination. The sources are, but not limited to, groundwater run-off of nitrogen containing fertilizer, pesticides, cleaning agents, solid wastes, industrial waters, and many more. The final destinations of these contaminants are rivers, lakes, and bayous that eventually will lead to bays, gulfs, and oceans. Many industries depend on the quality of these waters, such as the fishing industry. In addition to wild marine life, there are large aquariums and fish and shrimp farms that are required to know the quality of the water. However, the ability of these industries to monitor their processes is limited. Most analytical methods do not apply to the analysis of high salinity waters. They are dependent on wet chemistry techniques, spectrophotometers, and flow analyzers. These methods do not have the accuracy, precision, and sensitivity when compared to ion chromatography (IC). Since the inception of IC, it has become a standard practice for determining the content of many different water samples. Many IC methods are limited in the range of analytes that can be detected, as well as the numerous sample sources of which the methods are applicable. The main focus of current IC methods does not include high salinity waters. This research demonstrates an ion chromatographic method that has the ability to determine low level concentrations of inorganic nitrogen and related anions (nitrite-N, nitrate-N, phosphorous-P, sulfate, bromide, chloride, sulfide, fluoride, ammonia, calcium, and magnesium) in a single run using a combination of UV and conductivity detectors. This method is applicable to various waters, and uses both freshwater and high salinity water samples.Item Assessing the Underlying Breast Cancer risk of Chinese Females contributed by dietary intake of residual DDT from Agricultural Soils(Environment International, 2014) Zhang, CarlThe greatest concern over DDT exposure in China arose since the early 1990s for the rising breast cancer incidence, and the cause still remains to be elucidated. An extensive survey of DDT background in agricultural soils, covered the entire region of China, was conducted. DDT at concentrations greater than 100 ng/g (the China's Farmland Environmental Quality Evaluation Standards for Edible Agricultural Products) was found to impact 42.3 million Chinese population. Considering the geographical differences with diverse DDT contributions and different diet products and habits, the average daily dietary intake was modeled and estimated to be 0.34 μg/kg p,p'-DDE (the main bioactive constituent in DDT). Population attributable fraction derived from a case-control study from 78 women with breast cancer and 72 controls was used to assess the DDT exposure risk to breast cancer. Based on the estimated population attributable fraction with a median value of 0.6% (IQR 0.23-2.11%), the excess annual breast cancer incidence rate attributable to p,p'-DDE exposure averaged 0.06×10(-5) with significant spatial variations varying from 0.00021×10(-5) to 11.05×10(-5) in Chinese females. Exposure to DDT is a contributor to breast cancer, but the overall limited relative risk and population attributable fraction imply confounding factors for breast cancer in Chinese females. Exposure risk in a regional scale helps understand the cause and prevention of breast cancer. Our mapping and modeling method could be used to assess other environmental carcinogens and related cancer diseasesItem Atomic Insights into Distinct Hormonal Activities of Bisphenol A Analogues toward PPARy and ERa Receptors(2014) Zhang, CarlBisphenol A analogues (BPAs) belong to a wide variety of large volume chemicals with diverse applications yet emerging environmental concerns. Limited experimental data have demonstrated that BPAs with different halogenation patterns distinctly affect the agonistic activities toward proliferator-activated receptor (PPAR)γ and estrogen receptors (ER)α. Understanding the modes of action of BPAs toward different receptors is essential, however, the underlying molecular mechanism is still poorly understood. Here we probed the molecular recognition process of halogenated BPAs including TBBPA, TCBPA, BPAF, BPC, triBBPA, diBBPA, and monoBBPA toward PPARγ and ERα by molecular modeling, especially the impact of different halogen patterns. Increasing bromination at phenolic rings of BPAs was found highly correlated with electrostatic interactions (R2 = 0.978 and 0.865 toward PPARγ and ERα, respectively) and van der Waals interactions (R2 = 0.995 and 0.994 toward PPARγ and ERα, respectively). More halogenated phenolic rings at 3,5-positions of BPAs increase the shielding of the hormonally active phenolic OH and markedly decrease electrostatic interactions favorable for agonistic activities toward PPARγ, but unfavorable for agonistic activities toward ERα. The halogenation at the phenolic rings of BPAs exerts more impact on molecular electrostatic potential distribution than halogenation at the bridging alkyl moiety. Different halogenations further alter hydrogen bond interactions of BPAs and induce conformational changes of PPARγ ligand binding domain (LBD) and ERα LBD, specifically affecting the stabilization of helix H12 attributable to the different agonistic activities. Our results indicate that structural variations in halogenation patterns result in different interactions of BPAs with PPARγ LBD and ERα LBD, potentially causing distinct agonistic/antagonistic toxic effects. The various halogenation patterns should be fully considered for the design of future environmentally benign chemicals with reduced toxicities and desired properties.Item Bacterial Energetic, Stoichometry and Kinetic Modeling of 2,4-Dinitrotoluene Biodegradation in a Batch Respirometer(Environmental Toxicology and Chemistry, 2004) Zhang, CarlA stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, mumax, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium.Item Bacterial Energetics, Stoichiometry and Kinetic Modeling of 2,4-Dinitrotoluene Biodegradation in a Batch Respirometer(Environmental Toxicology and Chemistry, 2004) Zhang, CarlA stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, mumax, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium.Item Benzotriazole UV 328 and UV-P Showed Distict Antidandogenic Activity upon Human CYP3A4-mediated Biotransformation(2017) Zhang, CarlBenzotriazole ultraviolet stabilizers (BUVSs) are prominent chemicals widely used in industrial and consumer products to protect against ultraviolet radiation. They are becoming contaminants of emerging concern since their residues are frequently detected in multiple environmental matrices and their toxicological implications are increasingly reported. We herein investigated the antiandrogenic activities of eight BUVSs prior to and after human CYP3A4-mediated metabolic activation/deactivation by the two-hybrid recombinant human androgen receptor yeast bioassay and the in vitro metabolism assay. More potent antiandrogenic activity was observed for the metabolized UV-328 in comparison with UV-328 at 0.25 μM ((40.73 ± 4.90)% vs. (17.12 ± 3.00)%), showing a significant metabolic activation. In contrast, the metabolized UV-P at 0.25 μM resulted in a decreased antiandrogenic activity rate from (16.08 ± 0.95)% to (6.91 ± 2.64)%, indicating a metabolic deactivation. Three mono-hydroxylated (OH) and three di-OH metabolites of UV-328 were identified by ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-Q-TOF-MS/MS), which were not reported previously. We further surmised that the hydroxylation of UV-328 occurs mainly at the alicyclic hydrocarbon atoms based on the in silico prediction of the lowest activation energies of hydrogen abstraction from C-H bond. Our results for the first time relate antiandrogenic activity to human CYP3A4 enzyme-mediated hydroxylated metabolites of BUVSs. The biotransformation through hydroxylation should be fully considered during the health risk assessment of structurally similar analogs of BUVSs and other emerging contaminants.Item Biodegradation of Xenobiotics by Anaerobic Bacteria(Applied Microbiology and Biotechnology, 2005) Zhang, CarlXenobiotic biodegradation under anaerobic conditions such as in groundwater, sediment, landfill, sludge digesters and bioreactors has gained increasing attention over the last two decades. This review gives a broad overview of our current understanding of and recent advances in anaerobic biodegradation of five selected groups of xenobiotic compounds (petroleum hydrocarbons and fuel additives, nitroaromatic compounds and explosives, chlorinated aliphatic and aromatic compounds, pesticides, and surfactants). Significant advances have been made toward the isolation of bacterial cultures, elucidation of biochemical mechanisms, and laboratory and field scale applications for xenobiotic removal. For certain highly chlorinated hydrocarbons (e.g., tetrachlorethylene), anaerobic processes cannot be easily substituted with current aerobic processes. For petroleum hydrocarbons, although aerobic processes are generally used, anaerobic biodegradation is significant under certain circumstances (e.g., O2-depleted aquifers, oil spilled in marshes). For persistent compounds including polychlorinated biphenyls, dioxins, and DDT, anaerobic processes are slow for remedial application, but can be a significant long-term avenue for natural attenuation. In some cases, a sequential anaerobic-aerobic strategy is needed for total destruction of xenobiotic compounds. Several points for future research are also presented in this reviewItem Biodegradation Pathways of Hexahydro-1,3,5-Trinitro-1,3,5-Triazine (RDX) by Clostridium acetobutylicum Cell-free Extract,(Chemosphere, 2003) Zhang, CarlHexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a military high explosive, is becoming an increasingly important pollutant in the US. The cleanup of RDX-contaminated soil and groundwater has been a serious challenge due to its recalcitrance in the environment. This study was conducted to determine the biodegradation kinetics of RDX by crude cell extract of Clostridium acetobutylicum (ATCC 824), and to examine whether this bacterium will carry out reductive transformation pathways similar to the transformation of 2,4,6-trinitrotoluene (TNT), 2,4- and 2,6-dinitrotoluenes (DNTs) we have reported previously. Batch studies on the anaerobic transformation of RDX were conducted in serum bottles with U-ring-14C-RDX. RDX and its transformation products were quantified by HPLC and qualified by LC/ MS interfaced to two soft ionization techniques--an atmospheric pressure ionization and an electron spray ionization (API-ES). Results demonstrated that C. acetobutylicum is capable of transforming RDX with H2 as the electron donor. The transformation followed a zero-order kinetics and the rates increased with increasing H2. RDX was transformed into several polar intermediates that could not be separated by reverse-phase HPLC and its molecular ions were unstable under the condition of commonly used electron impact detector. Using a polar and water immiscible solvent (ethyl acetate) and the softer MS ionization techniques, mass spectroscopy detected the presence of several RDX derivatives including mononitroso-, monohydroxylamino-, mononitrosomonohydroxylamino-, monoamino-, diamino-, and triamino-compounds. The presence of hydroxylamino compounds is analogous to the transformation of TNT and DNTs we elucidated previously.Item Biosorption and Toxicity Response to Arsenite (As(III) in Scenedesmus quadricauda(CHempsphere, 2013) Zhang, CarlToxicity and biosorption responses to arsenite (As[III]) were examined in a 96-h exposure study using Scenedesmus quadricauda, one of the most popular green algae distributed in freshwaters in China. Results indicated that the pH-dependent distribution of two arsenite species (H2AsO3(-) and H3AsO3) played an important role in biosorption and toxicity. The undissociated H3AsO3 was more toxic than its monoanionic H2AsO3(-) through comparison of algal cell numbers, chlorophyll-a contents, and algal ultrastructural changes observed with transmission electron microscopy. An effective biosorption of 89.0mgg(-1) at 100mgL(-1) As[III] was found in the treatments with an initial pH of 9.3 and 25.2μgg(-1) at 0.03mgL(-1) As[III] at an initial pH of 8.2 as a result of the predominant species of H2AsO3(-) under the ambient pH and Eh conditions. Our results imply that S. quadricauda may provide a new means for the removal of toxic arsenite species present in contaminated surface water.Item Current Techniques for Detecting and Monitoring Algal Toxins and Causative Harmful Algal Blooms(Journal of Environmental Analytical Chemistry, 2015) Zhang, CarlThe detection and monitoring techniques for algal toxins and the causative harmful algal blooms (HABs) are essential for the protection of aquatic lives, shellfish safety, drinking water quality, and public health. Toward the development of fast, easy, and reliable techniques, much progress has been made during the last decade for the qualitative and quantitative analysis of algal toxins. This review highlights the recent progress and new trends of these analytical and monitoring tools, ranging from in-situ quick screening protocols for the monitoring of algal blooms to mass spectrometric analysis of trace levels of various algal toxins and structural elucidation. Solid-phase adsorption toxin tracking (SPATT) deployed in the field for the passive sampling of algal toxins has been recently validated, and improved ELISA-based methods with lower detection limits for more toxins have become commercially available for both screening and routine monitoring purposes. Liquid chromatography-mass spectrometry with several recent mass spectrometric innovations has expanded our understanding of traditional toxins, their metabolites along with newly discovered toxins of ecological importance. Several established in vivo and in vitro bioassays will continue to be used as benchmark toxicological testing of algal toxins; however, newly emerged molecular probing techniques such as real-time quantitative polymerase chain reaction (qPCR) have extended our ability to trace algal toxins from causative organisms at the molecular level. New chemical and biological sensors, lab-on-chip and remote sensing of blooms being developed will hold promise for early warning and routine monitoring to better manage and protect our freshwater, coastal and marine resources from adverse impact by harmful algal bloomsItem Determination of Trace Level Bromate and Bromide in Drinking Water by Suppressed Conductivity and Mass Spectrometry(LC-MS North America, 2006) Zhang, CarlThe article discusses the use of suppressed conductivity and mass spectrometry procedures in determining the presence of trace level bromate and bromide in drinking water. According to researches, bromate in drinking water is commonly formed during ozonization of bromide containing waters for disinfection purposes.Item Direct Injection, Simple and Robust Analysis of Trace-level Bromate and Bromide in Drinking Water by IC with Suppressed Conductivity Detection(Journal of Chromatographic Science, 2010) Zhang, CarlBromide is ubiquitously found in drinking water. It is introduced into source water primarily by contact with bromide-containing soils or seawater having high bromide content. Bromide is converted into carcinogenic bromate during ozonation processes employed in some drinking water and wastewater treatment plants. Therefore, monitoring of bromate in drinking water and its precursor bromide in source water is required. The purpose of this study was to survey bromide and bromate concentrations in randomly selected bottle waters of various brands and several tap water samples in the coastal Houston area using a direct-injection ion chromatography (IC) and a suppressed conductivity system. The method employs a simple isocratic IC with loop injection with calculated detection limit of 0.009 µg/L for bromate and 0.028 µg/L for bromide (250-µL sample volume). Allowing the detection of both species at the µg/L level in drinking water, this method does not require specialized instrumentation such as two-dimensional IC, expensive sample preparation, or post-column reactions. The results show that, whereas bromate remains undetected in all five tap water samples, there are significant high concentrations of bromide in the coastal Houston area (294.79 ± 56.97 µg/L). Its link to potential seawater intrusion need to be further investigated. For bottle water samples randomly collected, 18.2% (2 out of 11) showed detectable amount of both bromide and bromate. The detection of bromate coincides with those bottle water samples that underwent ozonation treatment. Further sample campaign with exclusively ozonated bottle water samples (n = 19) showed 100% detection rate for both bromide and bromate. The 99% confidence intervals were 14.45–37.97 µg/L and 0.32–2.58 µg/L for bromide and bromate, respectively. The highest level of bromate among all ozonated bottle water samples was 7.57 µg/L, a concentration close to the U.S. EPA prescribed limit for drinking water standard. Regression analysis indicated that although a positive correlation exists between bromide and bromate concentrations, such a correlation is not statistically significant. This finding is not unexpected since a variety of other parameters in the ozonation process (such as water quality, ozone dose, and time in addition to bromide concentration) affect the formation of bromate. Our results strongly suggest that cautions should be exercised to examine the potential formation of bromate when source water from coastal zone undergoes ozonation treatment. Another strong proof of our findings is that all the tap waters collected were treated in jurisdictions that do not use ozonation for disinfection. The fact that none of these tap water samples contained bromate (despite an abundance in bromide) proves our hypothesis even further.Item Distinct Mechanisms of Endocrine Disruption of DDT-related Pesticides toward ER a and ERR y(Environmental Toxicology and Chemistry, 2012) Zhang, CarlDichlorodiphenyltrichloroethane (DDT) is ubiquitous in the environment, and the exposure to DDT and its related pesticides has long been linked to endocrine disruption. The mechanism of endocrine disruption toward targeted receptors, however, remains unclear. Probing the molecular recognition of DDT analogs by targeted receptors at the atomic level is critical for deciphering this mechanism. Molecular dynamics (MD) simulations were applied to probe the molecular recognition process of DDT and its five analogs, including dichlordiphenyldichloroethylene (DDE), dichlorodiphenyldichloroethane (DDD), methoxychlor (MXC), p,p′‐hydroxy‐DDT (HPTE), and dicofol by human estrogen receptor (ER) α and human ER‐related receptor (ERR) γ. Van der Waals interactions mainly drive the interactions of DDT analogs with ERα ligand‐binding domain (LBD) and ERRγ LBD. Minor structural changes of DDT analogs in the number and position of chlorine and phenolic hydroxyl moiety cause differences in binding modes through aromatic stacking and hydrogen bonding and thus affect differently conformational changes of ERα LBD and ERRγ LBD. The binding of DDT analogs affects the helix 12 orientation of ERα LBD but causes no rearrangement of helix 12 of ERRγ LBD. These results extend our understanding of how DDT analogs exert their estrogen‐disrupting effects toward different receptors via multiple mechanisms.Item Distribution, historical trends and inventories of polychlorinated biphenyls in sediment from Yangtze River Estuary and adjacent East China Sea(Environmental Pollution, 2012) Zhang, CarlA large portion of polychlorinated biphenyls (PCBs) from e-waste released into the coastal areas may be the potential source of PCBs to the global oceans. The paper presents data of PCBs concentrations in fifty surface sediment samples and a dated sediment core in Yangtze River Delta (YRE) and adjacent East China Sea (ECS). The total PCBs levels varied from 5.08 to 19.64 ng/g dry weight, with the highest concentrations situate within the river-sea boundary zone which is so-called “marginal filter”. Concurrent with the operation of e-waste recycling over the last two decades, PCB fluxes started to rise again after 1980s and reached a maximum in this century. The full data set was used to estimate the burden of PCBs in YRE and adjacent ECS. A total sediment burdens were 192.8 tons, with the spatial density of 364 ng/cm2 which accounts for 1.9% of all the PCBs in China.Item THe Effect of Agitation on Volatilization of Naphthalene from Solution Containing Surfactant(Journal of Hazardous Materials, 2009) Zhang, CarlThe effects of agitation on naphthalene volatilization from solutions with surfactant concentration exceeding critical micelle concentration were studied. Micellar partition coefficient (K(m)) and liquid-vapor mass transfer coefficient (K(L)) in the presence of three surfactants, i.e., anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTMAB), and nonionic Tween 20 were determined at different agitation speeds. Both K(m) and K(L) increased in the agitated solutions, indicating enhanced naphthalene micellization and water-vapor mass transfer due to agitation. The enhancement factor of K(L) in surfactant-laden solution was determined to be in the range of 1.3-6.3 (SDS), 0.7-7.9 (CTMAB), and 1.5-7.3 (Tween 20). However, agitation exhibited a greater enhancement on K(L), resulting in a net increased volatilization rate. A conceptual model was developed to describe the dependence of the bulk aqueous phase naphthalene concentration (C(L)) on Henry's constant (H), K(L), K(m), and surfactant concentration (S). This study is the first in reporting the combined effects of agitation and surfactant on the volatilization of semi-volatile naphthalene in air-water-micelle system. Results provided insight into the volatile emission as frequently encountered in certain waste streams.Item Effect of Chromium no Growth, Physiology, Nodulation and Nitrogen Fixation of Soybean(Acta Agriculture Universitat Zhejiangensis, 1988) Zhang, CarlItem Effect of Trivalent and Hexavalent Forms of Chromium on Soybean Growth(Agro-Environmental Protection, 1988) Zhang, CarlItem Effects of Mixed Surfactants on the Volatilization of Naphtalene from Aqueous Solutions(Journal of Hazardous Materials, 2007) Zhang, CarlThe effects of mixed anionic–nonionic surfactants, Tween40–SDS (sodium dodecyl sulfate), Tween40–SDBS (sodium dodecylbenzene sulfonate), Tween20–SDS and Tween20–SDBS, on the solubility and volatilization of naphthalene from static aqueous solutions were investigated. The experiment results indicated that mixed anionic–nonionic surfactants can solubilize naphthalene synergistically, which was resulted from the reduction in critical micelle concentration (CMC) of the mixed surfactant and the increase in micellar partition coefficient ( K mc) of naphthalene between micelles and aqueous phase. The synergistic effects of mixed surfactants resulted in further reduction in volatilization of naphthalene than that induced by single surfactant. A positive linear correlation was found between the synergistic solubilization ratio (Δ S) and the synergistic inhibitory capacity on naphthalene volatilization (Δ C) in the presence of mixed surfactants.
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