Chunlong (Carl) Zhang

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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.


Recent Submissions

Now showing 1 - 20 of 55
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    Side Chains of Parabens Modulate Antiandrogenic Activity: In Vitro and Molecular Docking Studies, Environmental Science and Technology
    (Environmental Science & Technology, 2017) Zhang, Carl
    Parabens have been widely used in packaged foods, pharmaceuticals, and personal-care products. Considering their potential hydrolysis, we herein investigated structural features leading to the disruption of human androgen receptor (AR) and whether hydrolysis could alleviate such effects using the recombinant yeast two-hybrid assay. Parabens with an aryloxy side chain such as benzyl paraben and phenyl paraben have the strongest antiandrogenic activity. The antiandrogenic activity of parabens with alkyloxyl side chains decreases as the side chain length increases from 1 to 4, and no antiandrogenic effect occurred for heptyl, octyl, and dodecyl parabens with the number of alkoxyl carbon atoms longer than 7. The antiandrogenic activity of parabens correlates significantly with their binding energies (R2 = 0.84, p = 0.01) and were completely diminished after the hydrolysis, particularly for parabens with aryloxy side chains. The Km for the hydrolysis of parabens with aromatic moiety side chain is 1 order of magnitude higher than that of the parabens with alkyl side chains. Both in vitro and in silico data, for the first time, suggest parabens with aromatic side chains are less prone to hydrolysis. Our results provide an insight into risk of various paraben and considerations for design of new paraben-related substitutes.
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    Spatial Distributions and Enantiomeric Signatures of DDT and its Metabolites in Tree Bark from Agricultural Regions across China
    (Environmental Pollution, 2017) Zhang, Carl
    Tree bark is considered as an effective passive sampler for estimating the atmospheric status of pollutants. In this study, we conducted a national scale tree bark sampling campaign across China. Concentration profiles revealed that Eastern China, especially the Jing-Jin-Ji region (including Hebei Province, Beijing and Tianjin) was a hot spot of bark DDT pollution. The enantioselective accumulation of o,p'-DDT was observed in most of the samples and 68% of them showed a preferential depletion of (+)-o,p'-DDT. These results suggest that DDTs in rural bark are likely from combined sources including historical technical DDTs and fresh dicofol usage. The tree bulk DDT levels were found to correlate with soil DDT concentrations, socioeconomy and PM2.5 of the sampling sites. It thus becomes evident that the reemission from soils and subsequent atmospheric deposition were the major pathways leading to the accumulation of DDTs in bark. Based on a previously established bark-air partitioning model, the concentrations of DDTs in the air were estimated from measured concentrations in tree bark, and the results were comparable to those obtained by the use of passive sampling with polyurethane foam (PUF) disks. Our results demonstrate the feasibility of delineating the spatial variations in atmospheric concentration and tracing sources of DDTs by integrating the use of tree bark with enantiomeric analysis
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    In Vitro an in Silico Investigations of the Binary-mixture Toxicity of Phthalate Esters and Cadmium (II) to Vibrio Qinghaiensis sp.-Q67
    (2017) Zhang, Carl
    Phthalate esters (PAEs) are widely used as plasticizers and have become one of the emerging contaminants with an increasing public concern. The residues of PAEs frequently co-exist with heavy metals such as cadmium (Cd) in waters; however, their joint ecotoxicity remains largely unknown. We herein investigated the single and joint toxicity of commonly used PAEs and Cd using freshwater luminescent bacteria Vibrio qinghaiensis sp.-Q67. The median effective concentration (EC50) of benzyl butyl phthalate (BBP), dibutyl phthalate (DBP), diethyl phthalate (DEP), dimethyl phthalate (DMP), diisooctyl phthalate (DIOP) and di-n-octyl phthalate (DOP) were determined to be in the range from 134.4mg/L to as high as 1000mg/L, indicating very weak toxicity to Vibrio qinghaiensis sp.-Q67. The toxicity of single PAEs showed a significant linear relationship with Log Kow, indicating the dependence of the elevated toxicity on the increasing hydrophilicity. The toxicity of binary mixture of PAEs was further evaluated in silico using the independent action (IA) model and concentration addition (CA) model. DMP-DEP, DEP-DBP or DMP-DBP exhibited antagonistic effects with the toxic unit value higher than 1.2. The CA and IA models poorly predicted the joint toxicity of DMP-DEP, DEP-DBP or DMP-DBP. The joint toxicity of the binary mixtures of DMP, DEP or DBP with Cd was simple additive as predicted by the CA and IA models. Our results indicated the potentially higher risk of PAEs in the presence of Cd, emphasizing the importance of determining the impact of their joint effects on aquatic organisms. The integrated in vitro and in silico methods employed in this study will be beneficial to study the joint toxicity and better assess the aquatic ecological risk of PAEs.
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    Benzotriazole UV 328 and UV-P Showed Distict Antidandogenic Activity upon Human CYP3A4-mediated Biotransformation
    (2017) Zhang, Carl
    Benzotriazole 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.
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    Estimating Nitrogen Oxides Emissions at City Scale in China with a Nighlight Remote Sensing Model
    (Science of the Total Environment, 2016) Zhang, Carl
    Increasing nitrogen oxides (NOx) emissions over the fast developing regions have been of great concern due to their critical associations with the aggravated haze and climate change. However, little geographically specific data exists for estimating spatio-temporal trends of NOx emissions. In order to quantify the spatial and temporal variations of NOx emissions, a spatially explicit approach based on the continuous satellite observations of artificial nighttime stable lights (NSLs) from the Defense Meteorological Satellite Program/Operational Linescan System (DMSP/OLS) was developed to estimate NOx emissions from the largest emission source of fossil fuel combustion. The NSL based model was established with three types of data including satellite data of nighttime stable lights, geographical data of administrative boundaries, and provincial energy consumptions in China, where a significant growth of NOx emission has experienced during three policy stages corresponding to the 9th-11th)Five-Year Plan (FYP, 1995-2010). The estimated national NOx emissions increased by 8.2% per year during the study period, and the total annual NOx emissions in China estimated by the NSL-based model were approximately 4.1%-13.8% higher than the previous estimates. The spatio-temporal variations of NOx emissions at city scale were then evaluated by the Moran's I indices. The global Moran's I indices for measuring spatial agglomerations of China's NOx emission increased by 50.7% during 1995-2010. Although the inland cities have shown larger contribution to the emission growth than the more developed coastal cities since 2005, the High-High clusters of NOx emission located in Beijing-Tianjin-Hebei regions, the Yangtze River Delta, and the Pearl River Delta should still be the major focus of NOx mitigation. Our results indicate that the readily available DMSP/OLS nighttime stable lights based model could be an easily accessible and effective tool for achieving strategic decision making toward NOx reduction.
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    A New Speciation Scheme of Soil PAHs toward Risk Assessment
    (Journal of Soil and Sediment, 2015) Zhang, Carl
    PURPOSE: The speciation of soil organic pollutants is of great importance for risk assessment and contaminant remediation, however, only few studies have attempted to develop a speciation scheme for a facilitated risk assessment. This paper postulates a pragmatic speciation scheme for the fractionation of soil polycyclic aromatic hydrocarbons (PAHs) that could correlate with their bioavailabilities, and the aim was to develop a reliable sequential ultrasonic extraction scheme that could differentiate PAHs into four fractions with different environmental relevance. We also investigated the key factors to the fraction distribution of PAHs, as well as the relationship between bioavailability of PAHs and their fractions. MATERIALS AND METHODS: Four representative PAHs were spiked into two soils and the distribution of PAH fractions was measured over a period of 90 to 210 days. The reliability of the sequential ultrasonic extraction method was cross-examined by an isotope experiment. The key factors to the fraction distribution, including aging time and properties of soil and PAH, were tested using ultrasonic extraction. The correlation between four fractionated PAHs and their bioavailabilities was assessed with a semipermeable membrane device (SPMD)-assisted desorption assay that mimics the bioconcentration of PAHs. RESULTS AND DISCUSSION: Soil PAHs were speciated into water-soluble-, organic acid-soluble-, organically bound-, and residual fractions via sequential ultrasonic extraction. The water-soluble- and organic acid-soluble fractions, which approximated the total PAHs estimated by SPMD, corresponded to the most bioavailable portions. The latter ones decreased significantly during aging. In contrast, the residual fraction, which limits the effectiveness of remediation, increased during aging following methanolic saponification. The concentrations of water-soluble-, organic acid-soluble-, and organically bound fractions are negatively correlated with the soil organic matter content and the partition coefficient between octanol and water (Kₒw) of pollutants CONCLUSIONS: The bioavailability of soil PAHs can be mimicked by a sequential chemical extraction protocol developed in this study. This speciation scheme can be readily used for studying the environmental fate and risk of PAHs, providing us with better rationales in selecting remediation strategies of soil contaminated with PAHs based bioavailability.
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    Enhanced Adsorption of Trivalent Arsenic from Water by Functionalized Diatom Silica Shells
    (PLoS ONE, 2015) Zhang, Carl
    The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.
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    Current Techniques for Detecting and Monitoring Algal Toxins and Causative Harmful Algal Blooms
    (Journal of Environmental Analytical Chemistry, 2015) Zhang, Carl
    The 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 blooms
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    Assessing the Underlying Breast Cancer risk of Chinese Females contributed by dietary intake of residual DDT from Agricultural Soils
    (Environment International, 2014) Zhang, Carl
    The 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 diseases
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    Atomic Insights into Distinct Hormonal Activities of Bisphenol A Analogues toward PPARy and ERa Receptors
    (2014) Zhang, Carl
    Bisphenol 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.
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    Hexachlorocyclohexanes in Tree Bark across Chinese Agricultural Region: Spatial Distribution and Enantiomeric Signatures
    (Environmental Science and Technology, 2014) Zhang, Carl
    The environmental issue caused by atmospheric hexachlorocyclohexanes (HCHs) has been a worldwide concern due to their long-range transport potential. Tree bark is an excellent passive sampler for monitoring atmospheric pollutants. In this study, bark samples from agricultural regions across China were collected and analyzed to elucidate the contamination status of atmospheric HCHs and the enantiomeric composition of chiral α-HCH. Average contents of α-HCH, β-HCH, γ-HCH, δ-HCH, and ∑HCHs in bark were 1.16, 2.51, 1.67, 0.368, and 5.71 ng/g (dry basis), respectively. Jing-Jin-Tang region was identified as the “hot-spot” of bark HCHs in China. Their residues were likely from the combined sources of historical applications of technical HCHs and lindane through long-distance transport. HCH contents were found inversely correlated with annual precipitation and temperature, but positively correlated with PM10 or PM2.5 due to the bioaccumulation of both vapor- and particle-phase HCHs by tree bark. Most bark samples preferentially accumulated (+)-α-HCH, and the enantiomeric fractions (EFs) of α-HCH were positively correlated with α-HCH concentrations and the elevations of sampling locations. Compared to atmospheric analysis, tree bark analysis and enantiomeric signatures provide valuable time-integrated information on the spatial distribution and transport pathways of atmospheric HCHs on the national scale in China.
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    Incorporation of Green Remediation into Soil and Groundwater Cleanups
    (International Journal of Sustainable Human Development, 2013) Zhang, Carl
    The remediation of contaminated soil and groundwater is essential toward the development of a sustainable society. However, remediation activities at various stages will also inherently add a significant burden of environmental footprints. Green remediation is thus increasingly recognized in the recent years by various regulatory agencies, responsible parties, remediation engineers, and various other stakeholders. This paper critically analyzes the evolution of green remediation and its context relating to various driving forces and potential impediments, the primary practices and opportunities to an increased sustainability in site cleanups, and quantitative sustainability evaluation tools employed to measure the greenness of soil and groundwater remediation technologies. Although the principles of green remediation are supported by the goals of several regulatory provisions in the U.S. and EU countries, there are not sufficient regulatory driving force and economic incentives to fully implement green practice in the remediation industries. Even though the incorporation of green remediation into contaminant cleanup can provide a better image for the responsible party, the negative side from the public may also exist because of the perception of selection preference to the less invasive cleanup technology (e.g., natural attenuation over pump-and-treat). The problems associated with the currently employed tools using life cycle assessment (LCA) also prevent the accurate comparison among various remedial options essential for the decision-makers. Lessons learned from several recent case studies on LCA are summarized in regard to its methodological flaws, such as subjective selection of functional units and impact categories, and inconsistent spatial and temporal boundaries. Current LCA methodology well quantified remediation options in the regional and global scale such as eutrophication, ozone depletion and global warming; however, with inherent issues of quantification and weighting, sitespecific primary impacts of contaminated sites are often underestimated, which are often the driving force for site cleanups. A remediation sustainability index is proposed in the context of six core elements of green remediation. Finally, the opportunities, challenges and some future perspective for the incorporation of sustainable principles into the practice of cleaning up contaminated sites are discussed in the paper.
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    Biosorption and Toxicity Response to Arsenite (As(III) in Scenedesmus quadricauda
    (CHempsphere, 2013) Zhang, Carl
    Toxicity 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.
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    The Role of Humic Acid in the Toxicity of Arsenite to the Diatom Navicula sp.
    (Environmental Science Pollution Research, 2013) Zhang, Carl
    Dissolved organic matter (DOM) affects arsenite [As(III)] toxicity by altering its sorption equilibrium at the cell wall interface. A better understanding of such mechanism is of great importance to assess As(III) ecotoxicity in aquatic systems. Batch experiments were conducted to study the effects of DOM on the regulation of As(III) sorption and toxicity in the diatom Navicula sp. The influence of humic acid (HA) on As(III) toxicity was assessed by measuring algal growth, chlorophyll a, and reactive oxygen species (ROS), whereas As(III) mobility across the cell wall was estimated by determining the concentration of intracellular, cell-wall-bound, and free As(III) ions in cell media. Results showed that the effects of HA on arsenite toxicity varied depending on various combinations of As(III)-HA concentrations. EC50 had an approximate threefold increase from 8.32 (HA-free control) to 22.39 μM (at 20 mg L(-1) HA) when Navicula sp. was exposed to 1.0-100.0 μM of As(III), compared to an overall low complexation ratio of HA-As(III) in a range of 0.91-6.00 %. The cell wall-bound and intracellular arsenic content decreased by 19.8 and 20.3 %, respectively, despite the lower arsenite complexation (2.10 ± 0.16 % of the total As). Meanwhile, intracellular ROS was decreased by 12.6 % in response to 10.0 μM As(III) and 10 mg L(-1) HA vs. the HA-free control. The significant contrast indicated that complexation alone could not explain the HA-induced reduction in arsenite toxicity and other factors including HA-cell surface interactions may come into play. Isotherms describing adsorption of HA to the Navicula sp. cells combined with morphological data by scanning electron microscopy revealed a protective HA floccule coating on the cell walls. Additional Fourier transform infrared spectroscopic data suggested the involvement of carboxylic groups during the adsorption of both HA and As(III) on the Navicula sp. cell surface. Collective data from this study suggest that cell wall-bound HA can moderate As(III) toxicity through the formation of a protective floccule coating occupying As(III) sorption sites and decreased effective functional groups capable of binding As(III). Our findings imply that As(III) toxicity can be alleviated due to the increased hindrance to cellular internalization of As(III) in the presence of naturally abundant DOM in water.
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    Optimal sample preservation and analysis of CR(VI) in drinking water smaplers by high resolution ion chromatography followed by post column ractioni and UV/Vis detection
    (2012) Zhang, Carl
    A recent study by the Environmental Working Group reported the detection of hexavalent chromium (Cr(VI)) in tap water at 31 out of 35 states investigated in the United States. Even though Cr(III) is an essential element for human diet, Cr(VI) is a potential carcinogen. Previous work has clearly identified a linear trend of increasing risk of lung cancer mortality with increasing cumulative exposure to water soluble Cr(VI). Regardless, Cr(VI) is still not regulated or monitored in drinking water in the US. There is an existing method (EPA 218.6) for the analysis of Cr(VI), however, this analytical method does not addresses detailed sample preservation techniques and optimization process to achieve lowest detection limit possible. In this study, five buffer solutions with pH of 9 and above were compared to determine the most suitable buffer to preserve Cr(VI) in drinking water samples for an extended period of time. Results showed that the five buffers responded very differently to Cr(VI)-fortified drinking water. The best preserving reagent was found to be Ammonium Hydroxide + Ammonium Sulfate (pH 9.2) and Sodium Carbonate + Sodium Bicarbonate+ Ammonium Sulfate (pH 9.7), whereas a buffer solution with Sodium Hydroxide + Sodium Carbonate (pH 11.5+) resulted in a poor chromatographic resolution. A controlled study with a fortified Cr(III) at 1 ppb was also conducted to ensure no false positive detection of Cr(VI) due to the potential oxidation of Cr(III) during sample storage. The optimal preserving reagent identified from this study was compatible with the existing EPA method 218.6 using ion chromatography followed by post column reaction, with a method quantitation limit of 0.020 ppb and matrix spike recovery of ± 10%.
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    Distribution, historical trends and inventories of polychlorinated biphenyls in sediment from Yangtze River Estuary and adjacent East China Sea
    (Environmental Pollution, 2012) Zhang, Carl
    A 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.
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    Enantioselective Cytotoxicity Profile of o,p'-DDT in PC 12 Cells
    (PLoS ONE, 2012) Zhang, Carl
    Background The continued uses of dichlordiphenyltrichloroethane (DDT) for indoor vector control in some developing countries have recently fueled intensive debates toward the global ban of this persistent legacy contaminant. Current approaches for ecological and health risk assessment has ignored the chiral nature of DDT. In this study by employing an array of cytotoxicity related endpoints, we investigated the enantioselective cytotoxicity of o,p’-DDT. Principal Findings we demonstrated for the first time that R-(−)-o,p’-DDT caused more neuron cell death by inducing more severe oxidative stress, which selectively imbalanced the transcription of stress-related genes (SOD1, SOD2, HSP70) and enzyme (superoxide dismutase and lactate dehydrogenase) activities, and greater cellular apoptosis compared to its enantiomer S-(+)-o,p’-DDT at the level comparable to malaria area exposure (parts per million). We further elucidated enantioselective modes of action using microarray combined with enzyme-linked immunosorbent assay. The enantioselective apoptosis might involve three signaling pathways via caspase 3, tumor protein 53 (p53) and NFkB. Conclusions Based on DDT stereochemistry and results reported for other chiral pesticides, our results pointed to the same directional enantioselectivity of chiral DDT toward mammalian cells. We proposed that risk assessment on DDT should consider the enantiomer ratio and enantioselectivities.
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    Distinct Mechanisms of Endocrine Disruption of DDT-related Pesticides toward ER a and ERR y
    (Environmental Toxicology and Chemistry, 2012) Zhang, Carl
    Dichlorodiphenyltrichloroethane (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.
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    Environmental Analytical Chemistry
    (Eolss Publishers, 2012) Zhang, Carl
    Environmental analytical chemistry has evolved from the traditional analytical chemistry to a well-established discipline and a profession attractive to a diverse group of environmental scientists / engineers, chemists, and educators. Environmental analysis and monitoring is a very challenging and dynamic field in a sense that it involves the most uncertain and error-prone stage of acquiring representative samples, laborious sample preparation from complex matrices, costly instrumental qualification and quantification of contaminants at the parts per million to parts per quadrillion levels, and the ever changing requirements for regulatory compliance in monitoring drinking water, UNESCO – EOLSS SAMPLE CHAPTERS ENVIRONMENTAL MONITORING – Environmental Analytical Chemistry – Chunlong Zhang ©Encyclopedia of Life Support Systems (EOLSS) wastewater, ambient / emission air, and solid / hazardous wastes. The discussions of this chapter start with the historical perspectives, unique features, and scopes of this discipline. The importance of representative sampling, the approaches to select costeffective sampling design schemes, as well as classical grab / active sampling vs. passive diffusion-based sampling techniques are delineated, followed by the discussions of environmental sample preparation goals, various digestion procedures for inorganic metals, and various extraction and partition based methods for volatile and semi-volatile compounds. Traditional chemical instrumental methods and their corresponding environmental applications are briefly described with respect to spectroscopic, chromatographic, mass spectrometric, electrochemical, thermal, and radiological methods. Complementary bioanalytical methods currently used in environmental analysis such as immunoassays and those with promise in future development such as biosensors are introduced. This chapter concludes with the remarks on the future perspectives and challenges of environmental analytical chemistry. There is an urgent need for advancing sampling methodology for practical applications, instrumental innovations for faster, more sensitive and affordable bench instruments, and miniatur
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    Use of fugacity model to analyze temperture-dependent removal of micro-contaminants in sewage treatment plants
    (Cheosphere, 2011) Zhang, Carl
    Effluents from sewage treatment plants (STPs) are known to contain residual micro-contaminants including endocrine disrupting chemicals (EDCs) despite the utilization of various removal processes. Temperature alters the efficacy of removal processes; however, experimental measurements of EDC removal at various temperatures are limited. Extrapolation of EDC behavior over a wide temperature range is possible using available physicochemical property data followed by the correction of temperature dependency. A level II fugacity-based STP model was employed by inputting parameters obtained from the literature and estimated by the US EPA’s Estimations Programs Interface (EPI) including EPI’s BIOWIN for temperature-dependent biodegradation half-lives. EDC removals in a three-stage activated sludge system were modeled under various temperatures and hydraulic retention times (HRTs) for representative compounds of various properties. Sensitivity analysis indicates that temperature plays a significant role in the model outcomes. Increasing temperature considerably enhances the removal of β-estradiol, ethinyestradiol, bisphenol, phenol, and tetrachloroethylene, but not testosterone with the highest biodegradation rate. The shortcomings of BIOWIN were mitigated by the correction of highly temperature-dependent biodegradation rates using the Arrhenius equation. The model predicts well the effects of operating temperature and HRTs on the removal via volatilization, adsorption, and biodegradation. The model also reveals that an impractically long HRT is needed to achieve a high EDC removal. The STP model along with temperature corrections is able to provide some useful insight into the different patterns of STP performance, and useful operational considerations relevant to EDC removal at winter low temperatures.