Probing mercury species-DNA interactions by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection

The interactions of inorganic mercury Hg(II), methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and phenylmercury (PhHg(I)) with DNA have been probed by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection (CE-ETAAS) in combination with circular dichroism and Fourier transform infrared spectroscopy. The CE-ETAAS assay allows sensitive probing of the level of DNA damage by mercury species, extraction of thermodynamic and kinetic information on the interactions of mercury species with DNA, and provides direct evidence for the formation of mercury species-DNA adducts. The binding affinity of mercury species to DNA increases in order of Hg(II) < EtHg(I) approximately PhHg(I) approximately MeHg(I). The interactions of mercury species with DNA follow a first-order kinetics for mercury species and zero-order kinetics for DNA. Mercury highly covalently coordinates to endocyclic and exocyclic N sites of DNA bases. However, the interactions of DNA with mercuric species cause no transition of the DNA original conformation. The results reveal that organomercuric species exhibit stronger affinity and faster binding to DNA and show more potential damage to DNA than Hg(II) in view of the kinetic and thermodynamic evaluations. Moreover, MeHg(I) exhibits the fastest binding to DNA, suggesting that MeHg(I) enjoys superiority over the other mercuric species for rapid formation of a stable complex with DNA, whereas Hg(II) shows the slowest binding to DNA. The present study provides new evidence and understanding of the binding modality of mercuric species to DNA.     

Au@gap@AuAg Nanorod Side‐by‐Side Assemblies for Ultrasensitive SERS Detection of Mercury and its Transformation

As one of the most toxic heavy metal elements, mercury ion (Hg²⁺) and its methylated product, methylmercury (MeHg) can pose a threat to human health and the environment. Herein, a novel Raman biosensor with cascade sensitivity is developed for Hg²⁺ detection through Au@gap@AuAg nanorod side‐by‐side assemblies. Due to the strong electromagnetic coupling from the assemblies and core–shell structure, the Raman sensor possesses high sensitivity with the limit of detection (LOD) of 0.001 ng mL^‐1, which is about one order lower than traditional atomic fluorescence spectrometer (AFS) methods. Moreover, the fabricated biosensor is used to measure residual mercury levels in tissues and eggs of hens fed high‐mercury diets, and the results show total mercury in collected egg yolks is 20 times higher than whites. Furthermore, the form of mercury in the eggs is also analyzed by high‐performance liquid chromatography coupled with AFS, and, unexpectedly, the methylated product MeHg tends to only be found in egg whites. These interesting differences may indicate a new research direction for the toxicity of mercury in living organisms, and the developed ultrasensitive Surface Enhanced Raman Scattering (SERS) method could pave a broad way for the application of biosensors in Hg detection.     

Validation of methylmercury determinations in aquatic systems by alkyl derivatization methods for GC analysis using ICP-IDMS

Isotope dilution mass spectrometry (IDMS), using an inductively coupled plasma quadrupole mass spectrometer (ICPMS) and a species-specific methylmercury spike was applied to validate the commonly used GC method for methylmercury (MeHg+) determination, which is based on the formation of volatile methylethylmercury by derivatizationwith NaBEt4. The spike compound, Me201Hg+, was synthesized by reaction of 201Hg-enriched mercury chloride with methylcobalamin. By analyzing different environmental aquatic samples, it was found that in most cases, transformation of MeHg+ into elemental mercury (Hg0) took place. From investigations of synthetic solutions, it could be followed that halide ions are responsible for this transformation process. Chloride and bromide converted MeHg+ into Hg0, whereas iodide caused transformation into Hg2+ and Hg0. It could also be shown that transformation of MeHg+ took place only during the derivatization step. In contrast to ethylation, propylation by NaBPr4 did not cause any transformation; however, accurate results of MeHg+ determinations could be obtained by propylation as well as by ethylation when GC/ ICP-IDMS was applied. This work demonstrates the great power of isotopically labeled element compounds for the validation of element speciation methods and for species-specific IDMS analyses.     

Preconcentration, speciation and determination of ultra trace amounts of mercury by modified octadecyl silica membrane disk/electron beam irradiation and cold vapor atomic absorption spectrometry

Mercury (II) and methyl mercury cations at the Sub-ppb level were adsorbed quantitatively from aqueous solution onto an octadecyl-bonded silica membrane disk modified by 2-[(2-mercaptophyenylimino)methyl] phenol (MPMP). The trapped mercury was then eluted with 3ml ethanol and Hg2+ ion was directly measured by cold vapor atomic absorption spectrometry, utilizing tin (II) chloride. Total mercury (Hgt) was determined after conversion of MeHg+ into Hg2+ ion by electron beam irradiation. A sample volume of 1500ml resulted in a preconcentration factor of 500 and the precision for a sampling volume of 500ml at a concentration of 2.5microgl(-1) (n=7) was 3.1%. The limit of detection of the proposed method is 3.8ngl(-1). The method was successfully applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Evaluation of small-scale constructed wetland for water quality and Hg transformation

Elevated concentrations of nutrients and mercury (Hg) make Steamboat Creek (SBC) the most polluted tributary of the Truckee River. Since wetlands are considered cost-effective, reliable, and potential sites for methylmercury (MeHg) production, a small-scale wetland system was constructed and monitored for several years in order to quantify both nutrient removal and transformation of mercury. Results indicated seasonal variations in nutrient removal with 40-75% of total nitrogen and 30-60% of total phosphorus being removed with highest removals during summer and lowest removals during winter. The wetland system behaved as a sink for MeHg during the winter months and as a source for MeHg during summer months.     

Detection of mercury ion by infrared fluorescent protein and its hydrogel-based paper assay

Mercury is a highly hazardous and widespread pollutant with bioaccumulative properties. Novel approaches that meet the criteria of desired selectivity, high sensitivity, good biocompatibility, and low background interference in natural settings are continuously being explored. We herein describe a new strategy utilizing the combination of infrared fluorescent protein (IFP) and its chromophore as an infrared fluorescence probe for mercury ion (Hg(II)) detection. Hg(II) has been validated to have specific binding affinity to a cysteine residue (C24) of IFP, thereby inhibiting the conjugation of IFP chromophore biliverdin (BV) to C24 and "turning off" the infrared emission of IFP. The IFP/BV sensor has high selectivity toward Hg(II) among other metal ions over a broad pH range. The in vitro detection limit was determined to be less than 50 nM. As a genetically encoded probe, we demonstrate the IFP/BV sensor can serve as a tool to detect Hg(II) in living organisms or tissues. Moreover, we have exploited a protein-agarose hydrogel-based paper assay to immobilize IFP for detection of Hg(II) in a portable and robust fashion.     

Development of a Spectrophotometric Optode for the Determination of Hg(II)

A new simple and inexpensive optical chemical sensor for mercury(II) ions is presented. The mercury sensing system has prepared by incorporating of l-[2-pyridylazo]-2-naphthol as a suitable ligand for Hg(II) on triacetyl cellulose. The proportionality in intensity of the membrane color on the optodes loaded with varying amounts of Hg(II) suggests its potential applications for screening of Hg(II) in aqueous samples by visual colorimetry. The optode has a dynamic range 1.0 to 1000.0 muM with a limit of detection of 0.8 muM Hg(II). Different experimental parameters such as variable affecting on sensor preparation and pH of the sample solution plus response time were studied. The optodes developed in the present work were found to be stable, cost effective, easy to prepare, and efficient for direct determination of Hg(II) in a variety of aqueous samples using spectrophotometric method.     

Detection of mercury(II) by quantum dot/DNA/gold nanoparticle ensemble based nanosensor via nanometal surface energy transfer

An ultrasensitive fluorescent sensor based on the quantum dot/DNA/gold nanoparticle ensemble has been developed for detection of mercury(II). DNA hybridization occurs when Hg(II) ions are present in the aqueous solution containing the DNA-conjugated quantum dots (QDs) and Au nanoparticles. As a result, the QDs and the Au nanoparticles are brought into the close proximity, which enables the nanometal surface energy transfer (NSET) from the QDs to the Au nanoparticles, quenching the fluorescence emission of the QDs. This nanosensor exhibits a limit of detection of 0.4 and 1.2 ppb toward Hg(II) in the buffer solution and in the river water, respectively. The sensor also shows high selectivity toward the Hg(II) ions.     

Speciation of mercury by hydrostatically modified electroosmotic flow capillary electrophoresis coupled with volatile species generation atomic fluorescence spectrometry

A novel method for speciation analysis of mercury was developed by on-line hyphenating capillary electrophoresis (CE) with atomic fluorescence spectrometry (AFS). The four mercury species of inorganic mercury Hg(II), methymercury MeHg(I), ethylmercury EtHg(I), and phenylmercury PhHg(I) were separated as mercury-cysteine complexes by CE in a 50-cm x 100-microm-i.d. fused-silica capillary at 15 kV and using a mixture of 100 mmol L(-1) of boric acid and 12% v/v methanol (pH 9.1) as electrolyte. A novel technique, hydrostatically modified electroosmotic flow (HSMEOF) in which the electroosmotic flow (EOF) was modified by applying hydrostatical pressure opposite to the direction of EOF was used to improve resolution. A volatile species generation technique was used to convert the mercury species into their respective volatile species. A newly developed CE-AFS interface was employed to provide an electrical connection for stable electrophoretic separations and to allow on-line volatile species formation. The generated volatile species were on-line detected with AFS. The precisions (RSD, n = 5) were in the range of 1.9-2.5% for migration time, 1.8-6.3% for peak area response, and 2.3-6.1% for peak height response for the four mercury species. The detection limits ranged from 6.8 to 16.5 microg L(-1) (as Hg). The recoveries of the four mercury species in the water samples were in the range of 86.6-111%. The developed technique was successfully applied to speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).     

Protein‐Directed Synthesis of NIR‐Emitting,Tunable HgS Quantum Dots and their Applications in Metal‐Ion Sensing

The development of luminescent mercury sulfide quantum dots (HgS QDs) through the bio‐mineralization process has remained unexplored. Herein, a simple, two‐step route for the synthesis of HgS quantum dots in bovine serum albumin (BSA) is reported. The QDs are characterized by UV–vis spectroscopy, Fourier transform infrared (FT‐IR) spectroscopy, luminescence, Raman spectroscopy, transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), circular dichroism (CD), energy dispersive X‐ray analysis (EDX), and picosecond‐resolved optical spectroscopy. Formation of various sizes of QDs is observed by modifying the conditions suitably. The QDs also show tunable luminescence over the 680–800 nm spectral regions, with a quantum yield of 4–5%. The as‐prepared QDs can serve as selective sensor materials for Hg(II) and Cu(II), based on selective luminescence quenching. The quenching mechanism is found to be based on Dexter energy transfer and photoinduced electron transfer for Hg(II) and Cu(II), respectively. The simple synthesis route of protein‐capped HgS QDs would provide additional impetus to explore applications for these materials.     

Removal of mercury(II) from wastewater using camel bone charcoal

Camel bone charcoal is used as an adsorbent for the removal of Hg(II) from wastewater effluents. The equilibrium data are fitted to Langmiur isotherm rather than linear and Freundlich isotherms. The adsorption capacity Qo is 28.24 mg of Hg(II)/g of the adsorbent. The optimum removal conditions are pH 2, contact time 30 min and temperature 25 degrees C. A comparison of the adsorption capacity (Qo) of camel bone charcoal with different adsorbents previously used for Hg(II) removal from wastewater effluents reveals its remarkable efficiency over many other treated and untreated natural and synthetic adsorbents. X-ray fluorescence and infrared spectrometry of camel bone charcoal after contact with mercury solutions confirm surface adsorption of Hg(II) ions. Electron microscopy reveals the formation of a spongy like structure on the adsorbent surface due to Hg(II) adsorption. Quantitative removal of mercury from hazardous effluents is demonstrated.     

Selective measurement of ultratrace methylmercury in fish by flow injection on-line microcolumn displacement sorption preconcentration and separation coupled with electrothermal atomic absorption spectrometry

A novel nonchromatographic speciation technique for ultratrace methylmercury in biological materials was developed by flow injection microcolumn displacement sorption preconcentration and separation coupled on-line with electrothermal atomic absorption spectrometry (ETAAS). In the developed technique, Cu(II) was first on-line complexed with diethyldithiocarbamate (DDTC), and the resultant Cu-DDTC was presorbed onto a microcolumn packed with the sorbent from a cigarette filter. Selective preconcentration of methylmercury (MeHg) in the presence of Hg(II), ethylmercury (EtHg), and phenylmercury (PhHg) was achieved at pH 6.8 through loading the sample solution onto the microcolumn due to a displacement reaction between MeHg and the presorbed Cu-DDTC. The retained MeHg was subsequently eluted with 50 microL of ethanol and on-line determined by ETAAS. Interferences from coexisting heavy metal ions with lower stability of their DDTC complexes relative to Cu-DDTC were minimized without the need of any masking reagents. No interferences from 5.5 mg L(-1) Cu(II), 4.5 mg L(-1) Cd(II), 2.5 mg L(-1) Cr(III), 3 mg L(-1) Fe(III), 10 mg L(-1) Ni(II), 10 mg L(-1) Pb(II), and at least 25 mg L(-1) Zn(II) were observed for the determination of MeHg at the 50 ng L(-1) level (as Hg). With the consumption of only 3.4 mL of sample solution, an enhancement factor of 75, a detection limit of 6.8 ng L(-1) (as Hg) in the digest (corresponding to 3.4 ng g(-1) in original solid sample for a final 50 mL of digest of 0.1 g of solid material), and a precision (RSD, n = 13) of 2.3% for the determination of methylmercury at the 50 ng L(-1) (as Hg) level were achieved at a sample throughput of 30 samples h(-1). The recoveries of methylmercury spike in real fish samples ranged from 97 to 108%. The developed technique was validated by determination of methylmercury in a certified reference material (DORM-2, dogfish muscle), and was shown to be useful for the determination of methylmercury in real fish samples.     

Diffusion tests of mercury through concrete, bentonite-enhanced sand and sand

The transport by diffusion of Hg(II) and Hg(0) through a barrier of concrete or bentonite-enhanced sand was examined under aerobic conditions. Sand was used as a reference system parallel to the two systems. Speciation of mercury was performed with a purge and trap method, where dissolved Hg(0) was purged with nitrogen gas from the sample, through a trap for volatile oxidized mercury species and finally trapped in an oxidative solution. The apparent diffusion coefficient (from Fick's second law of diffusion) for oxidized mercury was 1 x 10(-14)m(2)/s in Standard Portland concrete and 4 x 10(-13)m(2)/s in quartz sand. The diffusion of Hg(0) seemed to be faster than for Hg(II), Hg(0) was however oxidized to Hg(II) under aerobic conditions, and after 45 months only 1-10% of the total mercury concentration was Hg(0).     

Aqueous and vapor phase mercury sorption by inorganic oxide materials functionalized with thiols and poly-thiols

The objective of the study is the development of sorbents where the sorption sites are highly accessible for the capture of mercury from aqueous and vapor streams. Only a small fraction of the equilibrium capacity is utilized for a sorbent in applications involving short residence times (e.g., vapor phase capture of mercury from coal-fired power plant flue gases). So, dynamic capacity rather than equilibrium capacity is more relevant for these kinds of situations. Rapid sorption rates and higher dynamic capacity can be achieved by increasing the accessibility of active sites and decreasing the diffusional resistance to mass transport for the adsorbing species. This requires the use of open structured sorbent materials and attachment of functional groups on the external surface area of supports. The strong interaction of sulfur containing ligands (e.g., thiol) with mercury makes them suitable candidates for immobilization on these types of materials. In this study, inorganic oxide supports like alumina and silica are functionalized with thiol moieties like mercapto silane, cysteine and poly-cysteine for capturing mercury from aqueous and vapor phase. Aqueous phase Hg (II) sorption studies with cysteine/poly-cysteine functionalized silica showed that high dynamic capacity can be achieved by attaching active sites (thiol) on the external area of supports. Vapor phase Hg capture studies with thiol-functionalized mesoporous silica (Hg⁰ concentration = 3.37 mg/m³ with N₂ as the carrier, gas temperature = 70 ^°C) yielded a capacity of 143 g Hg/g for the sorbent. Although the sulfur content for the sorbent was low (0.80 wt. %) the molar ratio of Hg captured to sulfur was comparatively high (2.86×10^–3) pointing to the high accessibility of sulfur sites.     

Biosorption of mercury from aqueous solutions by powdered leaves of castor tree (Ricinus communis L.)

A new biosorbent produced from castor leaves powder [Ricinus communis L.] was used to remove mercury(II) from aqueous solutions. The initial mercury concentrations, contact time and initial pH were evaluated. The ability of castor leaves to remove mercury at various pH (2-8) was studied. The maximum capacity (Qmax) of biomass was found to be 37.2mg Hg(II)/g at pH 5.5. Biosorption equilibrium was established in approximately 1h. The equilibrium data were described well by Langmuir and Freundlich models. The adsorbed mercury on biomass was desorbed using 10 ml of 4M HCl solution. The biomass could be reused for other biosorption assays. The ability of biomass to adsorb mercury(II) in a column was investigated. These studies consider the possibility of using leaves of castor tree as an inexpensive adsorbent for the removal of Hg(II) from contaminated chemical and mining industry wastewaters. It is also suggested that the dried biomass might be simply kept and used in a very low cost metal ion removal system.     

Photo-induced transformations of mercury(II) species in the presence of algae, Chlorella vulgaris

The effects of algae (i.e., Chlorella vulgaris), Fe(III), humic substances, and pH on the photoreduction of Hg(II) under the irradiation of metal halide lamps (lambda>or=365 nm, 250 W) were investigated in this paper. The photoreduction rate of Hg(II) was found to increase with the increasing concentration of algae, Fe(III), and humic substances. The cooperation action of Fe(III) and humic substances accelerated the photoreduction of Hg(II). When the initial concentration of Hg(II) was in the range of 0.0-200.0 microg L(-1) with initial algae concentrations 7.0 x 10(9)cells L(-1) at pH 7.0, the initial photoreduction rate of Hg(II) could be expressed by the equation: -dC(Hg(II))/dt=0.65 x [C(Hg(II))](0.39) with a correlation coefficient of R=0.9912. The study on the photochemical process in terms of total mercury mass balance revealed that more than 40.86% of Hg(II) from the algal suspension was reduced to volatile metallic mercury. This paper discussed the photoreduction mechanism of Hg(II) in the presence of algae. This research will provide information for predicting the photoreduction of Hg(II) in the real environment. It will be helpful for understanding the photochemical transformation of Hg(II) and the formation of DGM in natural water in the presence of algae complexes. It will also be helpful for providing new methods to deal with heavy metal pollution.     

Functionalized diatom silica microparticles for removal of mercury ions

Abstract

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (–SH or –NH₂) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g^?1 for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.     

Functionalized diatom silica microparticles for removal of mercury ions

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (–SH or –NH₂) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g⁻¹ for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.     

Removal and recovery of mercury(II) from hazardous wastes using 1-(2-thiazolylazo)-2-naphthol functionalized activated carbon as solid phase extractant

As a part of removal of toxic heavy metals from hazardous wastes, solid phase extraction (SPE) of mercury(II) at trace and ultra trace levels was studied using 1-(2-thiazolylazo)-2-naphthol (TAN) functionalized activated carbon (AC). The SPE material removes traces of mercury(II) quantitatively in the pH range 6.0 +/- 0.2. Other parameters that influence quantitative recovery of mercury(II), viz. percent concentration of TAN in AC, amount of TAN-AC, preconcentration time and volume of aqueous phase were varied and optimized. The possible means of removal of Hg(II) from other metal ions that are likely to be present in the wastes of the chloroalkali industry is discussed. The potential of TAN-functionalized AC SPE material for decontaminating mercury from the brine sludge and cell house effluent of a chloralkali plant has been evaluated.     

Spectrophotometric determination of mercury in water samples after cloud point extraction using nonionic surfactant Triton X-114

A cloud point extraction process using the nonionic surfactant Triton X-114 for extracting mercury from aqueous solutions was investigated. The method is based on the complexation reaction of Hg(II) with Thio-Michler's Ketone (TMK) and micelle-mediated extraction of the complex. The optimal extraction and reaction conditions (e.g., pH, reagent concentration, effect of time) were studied, and the analytical characteristics of the method (e.g., limit of detection, linear range) were obtained. Linearity was obeyed in the range of 5.0-80.0 ng mL(-1) of Hg(II) ion. The detection limit of the method was 0.83 ng mL(-1) of Hg(II) ion. The interference effect of some anions and cations was also tested. The method was applied to the determination of mercury in water samples.