Mercury In Natural Waters Research Articles

Application of biochar prepared from wheat bran as the binding phase in diffusive gradient in thin films technique for determination of mercury in natural waters

A novel binding gel for the DGT technique, containing biochar produced through the pyrolysis of wheat bran, was developed. The results of this study indicate that wheat bran biochar (WBBC) is a porous material with a surface area of 25 m2/g. The primary functional group on the surface of WBBC was identified as a carbonyl group, although some hydroxyl and imino groups were also detected. Furthermore, the findings demonstrate that the accumulation of Hg on WBBC was significantly influenced by an increase in ionic strength, particularly in NaCl solution, owing to Hg’s high affinity for chloride ions. The performance of the DGT with WBBC binding gel was also affected by solution pH, with the optimal pH for WBBC application falling within the range of 3–7. The diffusion coefficient of Hg, depending on the matrix environment, varied between 5.44 and 6.99 × 10−6 cm2/s. When applying the newly designed DGT technique to spiked samples of river water, an R value of 0.68 was achieved. The results of this work proved that modified DGT technique allows for a cost-effective analysis of Hg in natural waters with lower salinity, while retaining the fundamental properties of the binding gel incorporating a particulate adsorbent with anchored functional groups.Graphical

Carbon-coated Fe3O4 derived from metal-organic frameworks on reduced graphene as electrochemical sensor platform for Hg(II) determination

Mercury, a well-known neurotoxicant, mainly occurs as Hg0, Hg2+ or Hg (CH3)2 in the environment. Therefore, there is an urgent need to develop new analytical methods to rapidly screen for mercury in natural water. In this work, rGO-MIL-101(Fe) was fabricated using reduced graphene oxide (rGO) and MIL-101 by one spot solvothermal method, and then was pyrolyzed at 500 °C to yield carbon-coated Fe3O4 dispersed on rGO (hereafter rGO-Fe@C). The rGO-Fe@C was characterized by SEM, TEM, TGA, XRD, XPS and Raman spectroscopic methods for its morphological features, particulate size & gradations, element redox states. An electrochemical sensing interface was constructed for Hg2+ determination using rGO-Fe@C modified glassy carbon electrode(rGO-Fe@C/GCE) by square wave anode stripping voltammetry (SWASV). The rGO-Fe@C/GCE exhibits high sensitivity for Hg2+ determination with a sensitivity of 34.47 μA/μM and a limit detection of 4.5 nM. The sensitive mechanism of Hg2+ in the electrochemical interface was investigated by XPS and DFT calculations. The presence of common cations as Cd2+, Cu2+ and Pb2+ in comparable molarities does not interfere with Hg2+ detection. Moreover, the electrode sensor possesses good stability and reproducibility for repetitive analysis of samples. The rGO-Fe@C/GCE sensor can be used in Hg2+ detection with minimal matrix interference by ions ubiquitous in natural water.

Multi-Emission Carbon Dots Combining Turn-On Sensing and Fluorescence Quenching Exhibit Ultrahigh Selectivity for Mercury in Real Water Samples.

Mercury is a ubiquitous heavy-metal pollutant and poses serious ecological and human-health risks. There is an ever-growing demand for rapid, sensitive, and selective detection of mercury in natural waters, particularly for regions lacking infrastructure specialized for mercury analysis. Here, we show that a sensor based on multi-emission carbon dots (M-CDs) exhibits ultrahigh sensing selectivity toward Hg(II) in complex environmental matrices, tested in the presence of a range of environmentally relevant metal/metalloid ions as well as natural and artificial ligands, using various real water samples. By incorporating structural features of calcein and folic acid that enable tunable emissions, the M-CDs couple an emission enhancement at 432 nm and a simultaneous reduction at 521 nm, with the intensity ratio linearly related to the Hg(II) concentration up to 1200 μg/L, independent of matrix compositions. The M-CDs have a detection limit of 5.6 μg/L, a response time of 1 min, and a spike recovery of 94 ± 3.7%. The intensified emission is attributed to proton transfer and aggregation-induced emission enhancement, whereas the quenching is due to proton and electron transfer. These findings also have important implications for mercury identification in other complex matrices for routine, screening-level food safety and health management practices.

Chemical Oxidation and Reduction Pathways of Mercury Relevant to Natural Waters: A Review

Mercury (Hg) pollution in the environment is a global issue and the toxicity of mercury depends on its speciation. Chemical redox reactions of mercury in an aquatic environment greatly impact on Hg evasion to the atmosphere and the methylation of mercury in natural waters. Identifying the abiotic redox pathways of mercury relevant to natural waters is important for predicting the transport and fate of Hg in the environment. The objective of this review is to summarize the current state of knowledge on specific redox reactions of mercury relevant to natural waters at a molecular level. The rate constants and factors affecting them, as well as the mechanistic information of these redox pathways, are discussed in detail. Increasing experimental evidence also implied that the structure of natural organic matter (NOM) play an important role in dark Hg(II) reduction, dark Hg(0) oxidation and Hg(II) photoreduction in the aquatic environment. Significant photooxidation pathways of Hg(0) identified are Hg(0) photooxidation by hydroxyl radical (OH•) and by carbonate radical (CO3−•). Future research needs on improving the understanding of Hg redox cycling in natural waters are also proposed.

Ivy extract-assisted photochemical vapor generation for sensitive determination of mercury by atomic fluorescence spectrometry

Making use of the natural plant extract as assistant matrix or photocatalyst provides an efficient strategy to break the limitation of traditional photochemical vapor generation atomic fluorescence spectrometry in efficiency, sensitivity, and biocompatibility. In this work, ivy extract-assisted photochemical vapor generation was proposed for the determination of trace mercury in natural water by atomic fluorescence spectrometry. The influencing factors such as irradiation time, irradiation wavelength and concentration of extract were systematically studied. Under the optimized experimental conditions, the limit of detection for total mercury was 0.03 ng mL−1 which is better than the ethanol- assisted photochemical vapor generation system. This method is green and sensitive, reduces the biological toxicity of photocatalytic materials and secondary pollution in the reduction process, and provides experimental basis for expanding the photochemical vapor generation system.

Preconcentration and spectrophotometric determination of mercury in water, food and hair samples through ionic-liquid induced micelle-mediated extraction

A new, eco-friendly, and rapid micelle-mediated preconcentration technique was described for trace mercury in water, food and hair samples perior to its spectrophotometric determination. The developed method depended on cloud point extraction supported with ionic liquid (IL-CPE) for extraction of mercury utilizing a nonionic surfactant (Triton X-114) and 1-hexadecyl-3-methylimidazolium chloride (C16MeImCl) ionic liquid, as an extracting phase in the presence of 5-benzyl-4-[4-methoxybenzylideneamino)-4H-1,2,4-triazole-3-thiol (BMBATT) as a new chelating agent at pH 7.0. The influence of varous analytical variables on improving the extraction performance was tested. In the range of 2.0-600 µg L−1, the calibration curve was linear with correlation coefficient of 0.9997. The detection limit and preconcentration factor were 0.4 µg L−1 and 100, respectively. The reliability and precision of the developed IL-CPE system as the relative standard deviation (RSD %) of 100 and 400 µg L−1 mercury were in the range 1.0 and 2.4%, respectively (n=10). The validity of the developed IL-CPE approach was confirmed by the analysis of certified reference materials (NIST-1641d mercury in natural water and NCS ZC81002B human hair). The applicability of proposed IL-CPE technique was demonstrated successfully by estimation of trace mercury in real water, food and hair samples.

Reduction of mercury(II) by electrons contained in carbon dots: An environmentally friendly cold vapor generation for mercury analysis

In this work, the reduction of mercury ions (Hg2+) to elemental mercury (Hg0) was easily achieved using highly reductive carbon dots (r-CDs), which synthesized from sucrose by a simple and cost-effective method. After a careful mechanistic study, the reduction was probably accomplished with the large numbers of electrons contained in r-CDs rather than the oxidation of its functional groups. Additionally, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay showed that the r-CDs were nontoxic to wildlife and human beings. Consequently, the r-CDs were used as an alternative to toxic reductants (SnCl2 or NaBH4) for the sensitive and in situ determination of mercury by cold vapor generation (CVG) coupled to a miniature point discharge optical emission spectrometer (μPD-OES). Limit of detection of 0.05 μg/L was obtained for Hg2+, with relative standard deviation (RSD) less than 5.4% at a concentration of 5 μg/L. The accuracy of r-CDs induced CVG-μPD-OES was validated by the determination of mercury in a certified reference material (DOLT-5, dogfish liver) and five natural water samples collected from different rivers and lakes in Chengdu City. Since r-CDs are nontoxic and prepared from abundant and inexpensive sucrose, the r-CDs induced CVG-μPD-OES retains the great potential for the inexpensive and environmentally friendly field analysis of mercury in natural water. The accuracy of the proposed method was validated by the analysis of a certified reference material and several water samples with satisfactory results.

Development of green vortex-assisted supramolecular solvent-based liquid–liquid microextraction for preconcentration of mercury in environmental and biological samples prior to spectrophotometric determination

A new and green vortex-assisted supramolecular solvent liquid–liquid microextraction (VA-SMS-LLME) method has been advanced to pre-concentrate and assess mecury in different environmental and biological samples. The proposed approach was dependent on utilisation of quinalizarin as a chelating agent to form mercury-quinalizarin complex at pH 7.0 which extracted into (1-decanol/THF) as supramolecular solvent (SMS). The extracted complex was centrifuged and determined spectrophotometrically at λmax = 570 nm. The final experimental conditions including pH, amount of quinalizarin, type and volume of supramolecular solvent, centrifugation and vortex conditions, sample volume and matrix effects were studied and optimized. The calibration graph was linear within 1.0–100 µg L−1 concentration range. The limit of detection, preconcentration factor and relative standard deviation were 0.30 µg L−1, 100 and 1.80%, respectively. The validation of the developed VA-Ss-LLµE procedure was acheived by the analysis of (NIST-1641d mercury in natural water and NCS ZC81002B human hair) certified reference materials. The proposed approach was applied to the determination of mercury in real water, food and hair samples successfully.

Addition of thiourea and hydrochloric acid: Accurate nanogram level analysis of mercury in humic-rich natural waters by inductively coupled plasma mass spectrometry

An analytical method was developed for the direct determination of total mercury in natural waters at low ng L−1 level by inductively coupled plasma mass spectrometry (ICP-MS). The presented method overcomes previously observed problems relating to poor spike recoveries by adding 0.12% thiourea in addition to 3% HCl to all samples and standards. The sample preparation is fast and easy to perform by the developed method since it requires only the addition of HCl and thiourea to the water samples. A very low instrument detection limit (0.4 ng L−1) was obtained without time-consuming preconcentration procedures. The accuracy and precision of the developed method were found excellent by the analysis of a certified groundwater reference material (ERM-CA615). The determined Hg concentration of 38.6 ± 0.5 ng L−1 was within the 95% confidence interval of the certified concentration of 37 ± 4 ng L−1. The analysis of natural water samples showed that total mercury levels ranged from concentrations lower than the method detection limit (2.0 ng L−1) to 10.9 ng L−1. Excellent recoveries of 96–108% for inorganic mercury (iHg) and 102–110% for methylmercury (MeHg) were obtained for spiked humic-rich natural water samples. To our knowledge, the developed method is the first ICP-MS method for the analysis of humic-rich natural water samples at ng L−1 concentrations without the need for hyphenated techniques or preconcentration procedures.

Modification of the EPA method 1631E for the quantification of total mercury in natural waters

To support the effectiveness of the Minamata Convention, the accurate determinations of mercury (Hg) in natural waters is an important but certainly challenging task due to the low concentrations expected in ambient samples. Mercury contamination may occur from many sources such as the unproperly-cleaning of storage bottles or the use of reagents for sample analysis with Hg traces, thus leading the analyst to easily run into errors. In our work, we propose some key modifications to the United States Environmental Protection Agency(EPA) method 1631E aimed at reducing the Hg contamination of reagents, storage containers, and minimizing the carryover effect in the instrumental line of sampling. The changes introduced have been tailored for the use of the method with cold vapor atomic fluorescence spectroscopy (CV-AFS) instrumentation and tested as part of a United Nations Environment Program (UNEP) ring test. Although the edited method was tested with natural water samples, the proposed method improvements can also apply to the Hg analysis in solid matrices that require the prior acid digestion of the samples.•A customized version of the EPA method 1631E is proposed for the analysis of aqueous samples.•New protocols for the reduction of contamination in the storage bottles and reagents used for the preparation of BrCl solution are provided.•A useful strategy for the control of the memory effect is included.

Reliable quantification of mercury in natural waters using surface modified magnetite nanoparticles

Reliable determination of mercury (Hg) in natural waters is a major analytical challenge due to its low concentration and to the risk of Hg losses or contamination during sampling, storage and pre-treatment of samples. The present work proposes a simple, efficient, sensitive and easy-handling methodology for extraction, pre-concentration and quantification of total dissolved mercury in natural waters, using iron oxide nanoparticles (NPs) coated with silica shells functionalized with dithiocarbamate groups (Fe3O4@SiO2SiDTC). Ten mg L−1 of these NPs were sufficient to remove 83–97% of 500 to 10 ng L−1 of Hg in ultra-pure water and artificial seawater, used as model Hg solutions, within 24 h. Mercury sorbed to the NPs was then measured directly by thermal decomposition atomic absorption spectrometry with gold amalgamation. The detection limit of approximately 1.8 ng L−1 is lower than the values reported in dispersive solid phase extraction for other magnetic sorbents. As a proof-of-concept, the proposed methodology was successfully tested in real samples of fresh and saline waters and more than 91% of Hg was recovered. With this methodology the extraction and pre-concentration steps may be carried out in situ decreasing the risk of Hg losses or contamination during sampling, storage and pre-treatment of water samples.

Sub-ppt determination of butyltins, methylmercury and inorganic mercury in natural waters by dynamic headspace in-tube extraction and GC-ICPMS detection

Sub-ppt determination of butyltins, methylmercury and inorganic mercury in natural waters by dynamic headspace in-tube extraction and GC-ICPMS detection.

Elemental Mercury in Natural Waters: Occurrence and Determination of Particulate Hg(0)

Elemental mercury, Hg(0), is ubiquitous in water and involved in key Hg biogeochemical processes. It is extensively studied as a purgeable dissolved species, termed dissolved gaseous mercury (DGM). Little information is available regarding nonpurgeable particulate Hg(0) in water, Hg(0) bound to suspended particulate matter (SPM), which is presumably present due to high affinity of Hg(0) adsorption on solids. By employing stable isotope tracer and isotope dilution (ID) techniques, we investigated the occurrence and quantification of particulate Hg(0) after Hg(0) being spiked into natural waters, aiming to provide firsthand information on particulate Hg(0) in water. A considerable fraction of (201)Hg(0) spiked in water (about 70% after 4 h equilibration) was bound to SPM and nonpurgeable, suggesting the occurrence of particulate Hg(0) in natural waters. A scheme, involving isotope dilution, purge and trap, and inductively coupled plasma mass spectrometry detection, was proposed to quantify particulate Hg(0) by the difference between DGM and total Hg(0), determined immediately and at equilibration after spiking ID Hg isotope, respectively. The application of this newly established method revealed the presence of particulate Hg(0) in Florida Everglades water, as the determined DGM levels (0.14 to 0.22 ng L(-1)) were remarkably lower than total Hg(0) (0.41 to 0.75 ng L(-1)).

Functionalized polymer sheet sorbent for selective preconcentration and determination of mercury in natural waters

Mercury is considered as a highly toxic and widespread heavy-metal pollutant. In the present work, two flat-sheet polymer sorbents have been synthesized for the selective preconcentration of mercury from natural waters. These are a silver nanoparticle (AgNP)-embedded poly(acrylamide)-grafted poly(propylene) sheet (Ag-PAM-PP) and a 1,8-octanedithiol-functionalized gold-coated poly(propylene) sheet (HS-octyl-S-Au-PP). The functional groups acrylamide and thiol provide the binding sites for Hg2+ ions; whereas silver nanoparticles reduce Hg2+ to Hg0 and it is held on the sheet by amalgam formation. Various factors that influence the preconcentration of Hg2+ from aqueous solution were investigated. Based on the comparison of the experimental results, it was observed that Ag-PAM-PP had superior performance for uptake of Hg2+ from natural water samples in terms of sorption capacity, sorption kinetics and working pH range. The uptake of Hg2+was found to be pH dependent with a maximum of 95% at pH 7.5. The preconcentration of Hg2+ from a large volume of aqueous solution was used to extend the lower limit of the concentration range that can be quantified by EDXRF and CV-AAS. The sorbed Hg(II) from aqueous samples was quantitatively detected within 1 min using EDXRF. The LOD (3σ) for CV-AAS (RSD = 2%) and EDXRF (RSD = 5%) were 6 and 30 μg L−1, respectively. The method was applied for the determination of Hg2+ in groundwater and seawater samples in the presence of a high concentration of interfering ions.

Pillar[5]arenes bearing phosphine oxide pendents as Hg2+ selective receptors

Pillar[5]arenes bearing ten phosphine oxide groups (1a–e), as analogs of their corresponding calix[4]arene-based phosphine oxide, have demonstrated intriguing recognition performance for some representative heavy metal cations including Co2+, Cu2+, Ni2+, Zn2+, Cd2+, Pb2+, Ag2+ and Hg2+ compared to their acyclic species (2a–e). Their extraction abilities toward these cations were evaluated by the solvent extraction method. The extraction results revealed that 1a–e were efficient and selective cation receptors for Hg2+ over other selected cations. In addition, the complexation behavior of 1a–e for Hg2+ was also investigated by using NMR and UV–vis techniques. The pillarareen receptors have been first used in the determination of inorganic mercury in natural water by inductively coupled plasma atomic emission spectrometry (ICP-AES), after back-extracting into aqueous phase with 3molL−1 HCl and 1% CS(NH2)2 solution.

An effective analytical system based on a pulsed direct current microplasma source for ultra-trace mercury determination using gold amalgamation cold vapor atomic emission spectrometry

A novel analysis system based on a low power atmospheric pressure pulsed direct current (Pdc) microplasma is described for the determination of ultra-trace mercury in natural water by cold vapor generation atomic emission spectrometry (CV-AES). The plasma was generated with a miniaturized home-built high-voltage Pdc power supply which decreased the volume and weight of the whole experiment setup. The CV-Pdc-AES system is based on the preconcentration of mercury vapor on a gold filament trapping micro-column prior to detection that provides fast, reproducible absorption and desorption of mercury. The micro-column is produced by winding 30μm diameter 100m long gold filament to a small ball and then insert it into a quartz tube of 6mm i.d, 8mm o.d. Under the optimized experimental conditions, the new system provides high sensitivity (detection limit: 0.08pgmL−1) and good reproducibility (RSD 3.0%, [Hg]=20pgmL−1, n=11). The calibration curve is linear at levels near the detection limit up to at least 200pgmL−1 and the accuracy is on the order of 1–4%. The proposed method was applied to 5 real water samples for mercury ultra-trace analysis. The advantages and features of the newly developed system include high sensitivity, simple structure, low cost, and compact volume with field portable potential.

Ultraviolet vapor generation atomic fluorescence spectrometric determination of mercury in natural water with enrichment by on-line solid phase extraction

A novel method, which coupled an on-line solid phase extraction (SPE) enrichment with ultraviolet vapor generation (UVG) atomic fluorescence spectrometry (AFS), was developed to improve the sensitivity of mercury determination and to remove the interference of some anion and organics to UVG of mercury. A high mercury retention efficiency and maximum exclusion of inorganic and organic matrix in water samples were achieved by using C18 SPE mini cartridge modified with sodium diethyldithiocarbamate (DDTC). Fast and efficient elution from the cartridge was found by using l-cysteine mixing solution. Furthermore, through the investigation of different UV reactor designs, the most important factor was the structure of the reactor (which corresponded roughly to the photon flux) wherein the tubing was sintered into the UV lamp to give the highest UV generation efficiency. The second factor was the materials of the tubing (which roughly corresponded to the working wavelength). Synthetic quartz, characterized by the highest transparency at 185nm, attained the highest UVG efficiency, suggesting that the most favorable wavelength for UVG was 185nm. Under optimum conditions, the achievable detection limit (3σ) with sample loadings of 10.0mL was 0.03ngL−1 and 0.08ngL−1 with different manifolds, respectively. The method was successfully applied to the determination of Hg in tap water, river water and lake water samples.

Stability and behaviour of low level spiked inorganic mercury in natural water samples

The stability and partitioning of inorganic mercury (Hg2+) in natural waters was tested under different storage conditions. The experiments were carried out by spiking labelled Hg2+ to natural concentrations (from 3 to 13 ng L−1) in marine, coastal lagoon, lake, river, and rain waters. Hg2+ was labelled with high specific activity 197Hg. The experiments tested the dissolved and particulate-bound fractions in 10 to 13 days time trends under different storage conditions, namely temperature, natural and preserved by acidification, and container materials (Teflon, borosilicate glass and polyethylene). The concentration of labelled Hg2+ in non-preserved waters decreased significantly depending on the type of water and the storage conditions. In the case of marine and lake waters it was stable over a period of 10 days, whereas in the case of river and lagoon waters 20% of labelled Hg was lost. The partitioning of labelled Hg2+ between the solid and dissolved fractions during the storage period varied with the type of water and the storage conditions. For short term storage periods (1 day after labelled Hg2+ spiking) a significant amount of Hg2+ was transferred to particulates, ranging from 40 to 70%, with refrigerated samples reaching equilibrium more slowly. The labelled Hg2+ in water samples preserved by 1% HCl addition was stable at room temperature (20 °C) and in a refrigerator (5 °C) when stored in Teflon and borosilicate glass, but significant losses were observed when stored in polyethylene.

Determination of methyl mercury and inorganic mercury in natural waters at the pgL−1level: Intercomparison between PT-GC-Pyr-AFS and GC-ICP-MS using Ethylation or Propylation derivatization

Mercury speciation analysis of both inorganic and methyl Hg in ultrapure and natural waters by purge-and-trap gas chromatography pyrolysis atomic florescence spectrometry (PT-GC-Pyr-AFS, MERX-M, Brooks Rand) was performed. This automated analytical setup was also compared with gas chromatography inductively coupled plasma mass spectrometry (GC-ICPMS, X Serie 2 ThermoFisher). In addition, a reagent cleaning step of the buffer solution and derivatizing reagents (NaBEt4 and NaBPr4) was evaluated to improve the detection limit of the method. PT-GC-Pyr-AFS experiments analyzing Milli-Q and Deionized water (Millipore) using cleaned reagents and quantifying by external calibration led to MeHg + and Hg 2+ concentration values significantly lower than those obtained using uncleaned reagents. The limit of detections (LODs) after cleaning was found significantly low using both NaBEt4 and NaBPr4. However, the lowest LODs were obtained when using cleaned NaBPr4 (range: 1-2 pgL -1 for MeHg + and 9-10 pgL -1 for Hg 2+ ).

Speciation analysis of mercury in natural water and fish samples by using capillary electrophoresis–inductively coupled plasma mass spectrometry

A environment-friendly microwave-assisted extraction used to extract trace mercury compounds from fish samples, and a ultra-sensitive method for the analysis of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by using capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) were described in this study. The extraction method is environment-friendly, simple, effective, and can be used to extract trace mercury compounds in fish samples with a satisfied recovery within several minutes. The CE–ICP–MS analytical method has a detection limit as lower as 0.021–0.032ng Hg/mL for MeHg, EtHg and Hg(II), and can be used to determined ultratrace MeHg, EtHg and Hg(II) in natural water and fish samples directly without any preconcentration. With the help of the above methods, we have successfully determined MeHg, EtHg and Hg(II) in dried fish (Tapertail anchovy) muscle and natural water within 25min with a RSD (relative standard deviation, n=6) <5% and a recovery of 94–103%. Our results showed that dried muscle of T. anchovy contained only one species of mercury, MeHg, indicating that MeHg is easier to be accumulated by aquatic organisms.