Determination Of Methylmercury Research Articles

Optimized mercury speciation analysis using LC-ICP-MS and microwave assisted extraction for precise determination of methylmercury in fish, rice and soil

Mercury (Hg) is a toxic element that exists in various forms, each with its characteristics and impacts on the environment. Methylmercury (MeHg) bioaccumulates in the food chain and identifying mercury species is crucial to assessing risks to ecology and health. Therefore, accurate, sensitive, and broad-range analytical methods are essential for the determination of methylmercury. This study optimized and validated a procedure for Hg speciation analysis in rice, fish, and soil using different extractants, followed by liquid chromatography inductively-coupled plasma mass spectrometry (LC ICP-MS) using certified references. Microwave-assisted extraction (MAE) parameters were optimized using 25 % KOH, resulting in improved sensitivity, accuracy and processing time. The validated method achieved a limit of quantitation (LOQ) of 12 µg kg−1 and showed acceptable percentage recoveries (75.3–98.1 %) in all matrices, enabling precise determination of MeHg (%RSDr; 3.76–5.78, %RSDR; 2.34–6.75) and Hg in a large number of samples within a short time frame. The validated method is particularly well-suited for rice, followed by fish and then soil. Therefore, the method utilizing microwave-assisted extraction and LC ICP-MS ensures precise methylmercury determination in rice, fish, and soil, crucial for evaluating environmental and health risks associated with mercury bioaccumulation.

Integrating catalytic role of gold nanoparticles with in-situ confinement effect of zirconium-based metal-organic frameworks for electrochemical determination of methylmercury

Catalytic redox reactions and size matching effect between the target molecule and sensing material are reliable methods for highly efficient determination of heavy metal ions. In this work, the electrochemical determination of methylmercury (CH3Hg+) was carried out gold nanoparticles (AuNPs) incorporated into four zirconium-based metal organic frameworks (MOF) with different pore diameters, namely MOF-801, (University of Oslo) UiO-66, UiO-67, UiO-68. The work relates the role of dicarboxylic ligands of different lengths to the AuNPs load capacity and the adsorption and reduction of CH3Hg+. The voltammetric properties of CH3Hg+ at different modified electrodes were studied by differential pulse anodic stripping voltammetry (DPASV). It was found that the CH3Hg+ electrochemical behavior was greatly influenced by the pore confinement effect of MOFs. Under the optimal conditions, the pore sizes of Au/UiO-67 are matched to CH3Hg+ molecule and they showed the highest response current. The possible reduction process of CH3Hg+ at the sensitive interface was explored by X-ray photoelectron spectroscopy (XPS) and chronoamperometry (CA). These four Au/MOFs modified GCE can also be used in detection of CH3Hg+ spiked in river water, confirming their potential application in the rapid detection of methylmercury in environmental samples.

One-Pot Pretreatment Coupled to Microplasma Optical Emission Spectrometry for Field and Sensitive Determination of Inorganic Mercury and Methylmercury in Fish.

Field and sensitive analysis of mercury species in seafood is helpful to assess the risk of human exposure to mercury, but the cumbersome pretreatment process is time-consuming and laborious. Herein, a simple one-pot pretreatment system is designed for extraction, separation, and enrichment of inorganic mercury (Hg(II)) and methylmercury (MeHg) in fish, and coupled to dielectric barrier discharge (DBD) microplasma optical emission spectrometry (OES). Both Hg(II) and MeHg species in fish can be effectively extracted by tetramethylammonium hydroxide under ultrasound, then separated from the fish matrix by vapor generation and photochemical vapor generation, and finally enriched on the activated carbon electrode tips. Mercury trapped on the activated carbon electrode tips can be rapidly released to produce OES under the DBD microplasma excitation for quantitative analysis. The pretreatment and analysis of a batch of 12 samples are completed within 50 min, and the extraction efficiency of total mercury is up to 90% for 100 mg of freeze-dried fish or 86% for 1 g of fresh fish. Under the optimized conditions, the detection limits are 2 μg kg-1 for Hg(II) and 1.2 μg kg-1 for MeHg in freeze-dried fish, and precisions are 3.2% for Hg(II) and 3.9% for MeHg. The present method is applied to the analysis of the certified reference material and real marine fishes, giving rise to spiked recoveries of 95-103%. The present system hardly leads to MeHg and Hg(II) transforming into each other during extraction, providing a simple, convenient, and low-cost analytical tool to evaluate the risk of mercury species in fish.

Determination of methylmercury and inorganic mercury in human hair samples of individuals from Colombian gold mining regions by double spiking isotope dilution and GC-ICP-MS

With the aim to distinguish between routes of exposition to mercury (Hg) in artisanal and small-scale gold mining (ASGM) communities and to distinguish between Hg contamination sources, Hg species composition should be performed in human biomarkers. In this work, Hg species-specific determination were determined in human hair samples (N = 96), mostly non-directly occupied in ASGM tasks, from the six most relevant gold mining Colombian regions. Therefore, MeHg, Hg(II) and THg concentrations were simultaneously determined by double spiking species-specific isotope dilution mass spectrometry (IDMS) and GC-ICP-MS. Only 16.67% of participants were involved at some point in AGSM works and fish consumption ranged from 3 to 7 times/week, which is between medium and high intake levels. The median concentration of THg obtained from all samples is higher than the reference dose weekly acceptable of MeHg intake established by the EPA (1 ppm), whereas a 25% were more than 4 times higher than the WHO level (2.2 μg Hg g−1). Median THg value of individuals consuming fish 5–7 times per week was significantly higher (p < 0.05) than those of the other consuming groups (12.5 μg Hg g−1). Most of the samples presented a % of MeHg relative to THg higher than 80%. The average % of Hg(II)/THg was 11% and only 10 individuals presented a Hg(II) content over 30%. No significant differences (p > 0.05) were found when the amount of Hg(II) was compared between people involved in AGSM task and people not involved. Interestingly, significant differences among the evaluated groups where found when the percentage of the Hg(II)/THg ratio of these groups were compared. In fact, people involved in AGSM tasks showed 1.7 times higher Hg(II)/THg vs. inhabitants uninvolved. This suggest that Hg(II) determination by IDMS-GC-ICP-MS could be a good proxy for evaluating Hg(II) adsorption by direct exposure to mercury vapors onto hair.

Determination of methylmercury in urine by direct mercury analyzer

Objective: To develop asolvent extraction-direct mercury analyzer method for determination of methylmercury in urine. Methods: After the urinehydrolyzesd by hydrobromic acid, methylmercury was extracted by tolueneand reverse-extracted from L-cysteine solution, it was then detectedbydirect mercuryanalyzer. Results: The linear range was 0.2-50.0 μg/L, and the related coefficient was 0.9999. The relative standard deviations (RSD) within the group were 5.04%-6.64%, and the RSD between the group were 5.65%-8.11 %. The average recovery efficiencies were 85.4%-95.5%. The detection limitation was 0.0482 μg/L and the quantification concentrations was 0.1607 μg/L. Conclusion: The method, which has low detection limit, high sensitivity, easy to operate, is stability for the determination of methylmercury in urine.

Determination of Hg(II) and Methylmercury by Electrothermal Atomic Absorption Spectrometry after Dispersive Solid-Phase Microextraction with a Graphene Oxide Magnetic Material.

The toxicity of all species of mercury makes it necessary to implement analytical procedures capable of quantifying the different forms this element presents in the environment, even at very low concentrations. In addition, due to the assorted environmental and health consequences caused by each mercury species, it is desirable that the procedures are able to distinguish these forms. In nature, mercury is mainly found as Hg0, Hg2+ and methylmercury (MeHg), with the latter being rapidly assimilated by living organisms in the aquatic environment and biomagnified through the food chain. In this work, a dispersive solid-phase microextraction of Hg2+ and MeHg is proposed using as the adsorbent a magnetic hybrid material formed by graphene oxide and ferrite (Fe3O4@GO), along with a subsequent determination by electrothermal atomic absorption spectrometry (ETAAS). On the one hand, when dithizone at a pH = 5 is used as an auxiliary agent, both Hg(II) and MeHg are retained on the adsorbent. Next, for the determination of both species, the solid collected by the means of a magnet is suspended in a mixture of 50 µL of HNO3 (8% v/v) and 50 µL of H2O2 at 30% v/v by heating for 10 min in an ultrasound thermostatic bath at 80 °C. On the other hand, when the sample is set at a pH = 9, Hg(II) and MeHg are also retained, but if the solid collected is washed with N-acetyl-L-cysteine only, then the Hg(II) remains on the adsorbent, and can be determined as indicated above. The proposed procedure exhibits an enrichment factor of 49 and the determination presents a linear range between 0.1 and 10 µg L-1 of mercury. The procedure has been applied to the determination of mercury in water samples from different sources.

Determination and speciation of methyl mercury and total mercury in fish tissue samples by gold-coated W-coil atom trap cold vapor atomic absorption spectrometry

A sensitive analytical technique was developed where gaseous mercury formed by sodium tetrahydroborate reduction is transported to and trapped on a resistively heated gold-coated Tungsten-coil atom trap for in situ preconcentration. This technique was applied successfully for determination and speciation of methyl mercury and total mercury in some fish tissue samples (liver, muscle and gill) obtained from Muğla province. The analytical parameters were optimized both for trap and no-trap studies. Under the optimized conditions, a limit of detection (LOD) of 6.0 ng/L was obtained. The precision was evaluated by relative standard deviation (RSD%) corresponding to 4.1% (n = 11). Accuracy of the proposed method was evaluated by analyzing “DOLT:5 Dogfish Liver”, “NIST SRM 1640a Trace elements in natural water” and “NIST 1946 Lake Superior fish tissues”. The measurements of the certified reference materials were in good agreement with the certified values at the 95% confidence level.

On-Site Determination of Methylmercury by Coupling Solid-Phase Extraction and Voltammetry.

A measurement and speciation procedure for the determination of total mercury (HgTOT), inorganic mercury (HgIN), and methylmercury (CH3Hg) was developed and the applicability for on-site determination was demonstrated. A simple, portable sample pretreatment procedure was optimized to extract the analytes. Home-made columns, packed with a new sorbent material called CYXAD (CYPHOS 101 modified Amberlite XAD), were used to separate the two forms of the analyte. HgTOT and CH3Hg were determined by anodic stripping voltammetry (ASV), using a solid gold electrode (SGE). Two certified reference materials (BCR-463 Tuna Fish and Tuna Fish ERM-CE 464) and eight fresh fishes were analyzed. Then, the results that were obtained following the optimized portable procedure were compared with the concentrations obtained, using a direct mercury analyzer (DMA). This quantification, using the two techniques, demonstrated the good performance of the proposed method.

Preconcentration and speciation analysis of mercury: 3D printed metal scavenger-based solid-phase extraction followed by analysis with inductively coupled plasma mass spectrometry.

A selective method for preconcentration and determination of methylmercury (MeHg) and inorganic mercury (iHg) in natural water samples at the ng L-1 level has been developed. The method involves adsorption of Hg species into a 3D printed metal scavenger and sequential elution with acidic thiourea solutions before ICP-MS determination. Experimental parameters affecting the preconcentration of MeHg and iHg such as the sample matrix, effect of the flow rate on adsorption, eluent composition, and elution mode have been studied in detail. The obtained method detection limits, considering the preconcentration factors of 42 and 93, were found to be 0.05ngL-1 and 0.08ngL-1 for MeHg and iHg, respectively. The accuracy of the method was assessed with a certified groundwater reference material ERM-CA615 (certified total iHg concentration 37±4ngL-1). The determined MeHg concentration was below MDL while iHg concentration was determined to be 41.2±0.5ngL-1. Both MeHg and iHg were also spiked to natural water samples at 5ngL-1 concentration and favorable spiking recoveries of 88-97% were obtained. The speciation procedure was successfully applied to two lake water samples where MeHg and iHg concentrations ranged from 0.18 to 0.24ngL-1 and 0.50-0.62ngL-1, respectively. The results obtained demonstrate that the developed 3D printed metal scavenger-based method for preconcentration and speciation of Hg is simple and sensitive for the determination of Hg species at an ultra-trace level in water samples.

Use of selective quenching of a photoluminescent probe based on a Eu(III) β-diketonate complex for determination of methylmercury in produced water after liquid-liquid extraction

An Eu(III) β-diketonate complex was produced and employed as a photoluminescent probe to determine methylmercury (CH3Hg+). To establish its molecular structure, the Eu(III) complex was characterized by elemental (CHNS) and thermogravimetric analyses and infrared spectroscopy. After establishing robust conditions to use the Eu(III) complex as an analytical probe, it was employed for the analysis of produced water (PW) samples with the analytical response based on the luminescence suppression proportional to the concentration of CH3Hg+ (a linear model after normalization of the response within the concentration range from 0.2 μg L−1 up to 2.0 μg L−1). Selectivity was guaranteed by a simple liquid-liquid extraction of the analyte in dichloromethane, which also allowed a 50 times pre-concentration factor. The instrumental limit of quantification of 0.2 μg L−1 is equal to the limit established in Brazilian resolution for total mercury content in waters, but pre-concentration (50 times factor) improved the overall method limit of quantification down to 4 ng L−1. Recovery results agreed with the ones achieved using cold vapor atomic absorption spectrometry.

Recent Trends and Future Perspectives of Emergent Analytical Techniques for Mercury Sensing in Aquatic Environments.

Environmental emissions of mercury from industrial waste and natural sources, even in trace amounts, are toxic to organisms and ecosystems. However, industrial-scale mercury detection is limited by the high cost, low sensitivity/specificity, and poor selectivity of the available analytical tools. This review summarizes the key sensors for mercury detection in aqueous environments: colorimetric-, electrochemical-, fluorescence-, and surface-enhanced Raman spectroscopy-based sensors reported between 2014-2021. It then compares the performances of these sensors in the determination of inorganic mercury (Hg2+ ) and methyl mercury (CH3 Hg+ ) species in aqueous samples. Mercury sensors for aquatic applications still face serious challenges in terms of difficult deployment in remote areas and low robustness, reliability, and selectivity in harsh environments. We provide future perspectives on the selective detection of organomercury species, which are especially toxic and reactive in aquatic environments. This review is intended as a valuable resource for scientists in the field of mercury sensing.

Selective organomercury determination by ICP-MS made easy

A fast and cost-effective procedure based on Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) for the selective determination of methylmercury (MeHg) is proposed and validated for fish tissue analysis. Selectivity for MeHg is achieved by simply inserting a strong anion exchange resin to block inorganic mercury as negatively charged chloride species, leaving MeHg unretained. The procedure features a 15 min extraction time followed by a 100 s analysis time achieving a limit of detection of 1.6 μg kg−1 on solid samples. The effect of the solution composition and inorganic mercury concentration were extensively studied to fully assess the selectivity of the procedure: Hg(II):MeHg ratios up to 50 are tolerated and cause systematic errors lower than 15%. The entire procedure was successfully validated by standard reference material from the marine food web, namely fish muscle and liver plus zooplankton. The method was finally applied to the detection of MeHg in the marine trophic web of Djibouti (Gulf of Aden): a trophic magnification factor of 13.5 proved the high risk associated with the biomagnification of methylmercury.

Determination of Mercury, Methylmercury and Selenium Concentrations in Elasmobranch Meat: Fish Consumption Safety.

This study measures total mercury (THg), methylmercury (MeHg) and selenium (Se) concentrations in elasmobranch fish from an Italian market with the aim of evaluating the risk-benefit associated with their consumption, using estimated weekly intake (EWI), permissible safety level (MeHgPSL), selenium health benefit value (HBVSe) and monthly consumption rate limit (CRmm) for each species. THg and Se were analysed by atomic absorption spectrometry, while MeHg was determined by HrGc/Ms. THg and MeHg concentrations ranged from 0.61 to 1.25 μg g−1 w.w. and from 0.57 to 0.97 μg g−1 w.w., respectively, whereas Se levels were 0.49–0.65 μg g−1 w.w. In most samples European Community limits for THg were surpassed, while for MeHg none of the fish had levels above the limit adopted by FAO/WHO. EWIs for THg and MeHg in many cases were above the provisional tolerable weekly intakes (PTWIs). MeHgPSL estimate showed that fish should contain approximately 50% of the concentration measured to avoid exceeding the PTWI. Nevertheless, the HBVSe index indicated that solely skates were safe for human consumption (HBVSe = 3.57–6.22). Our results highlight the importance of a constant monitoring of THg and MeHg level in fish, especially in apex predators, to avoid the risk of overexposure for consumers.

Determination of Methylmercury and Inorganic Mercury in Human Hair Samples of Individuals from Colombian Gold Mining Regions by Double Spiking Isotope Dilution and Gc-Icp-Ms

Determination of Methylmercury and Inorganic Mercury in Human Hair Samples of Individuals from Colombian Gold Mining Regions by Double Spiking Isotope Dilution and Gc-Icp-Ms

Simple and sensitive method for the determination of methylmercury in hair using thin-layer chromatography with thermal decomposition gold amalgamation atomic absorption spectrophotometry.

An improved method is described for the determination of methylmercury (MeHg) in human hair that is based on thin-layer chromatography and thermal decomposition gold amalgamation atomic absorption spectrophotometry. The dithizone extraction and application procedure of this technique were optimized, thus improving its sensitivity and robustness and enabling the use of less toxic solvents than other approaches. The limit of detection was 0.18ngMeHg (as Hg), corresponding to 0.018mg MeHg kg-1 of hair relative to a 10mg sample. This method is appropriate for detecting MeHg in hair at the approximate reference dose level established by the United States Environmental Protection Agency.

Dielectric barrier discharge-assisted determination of methylmercury in particulate matter by atomic absorption spectrometry.

Particulate matter (PM) impregnated with methlymercury (MeHg+) was analyzed using atomic absorption spectrometry coupled to a customized dielectric barrier discharge (DBD) device. Chemical vapor generation (CVG) was applied to generate methylmercury hydride and the DBD device promoted bond cleavage with subsequent release of free Hg atoms to the gas phase. Hydride generation was carried out using a lab-made syringe-based device in batch mode using argon as a carrier gas. Optimized conditions included the use of 1.0 mL of a 0.05% m/v NaBH4 solution and 1.0 mL of a 10% v/v HCl solution. This system was coupled to the DBD device, designed to operate in "plasma jet" configuration. Assessment of the designed device for methylmercury detection was established based on an on-off switch, which promptly demonstrated that Hg signals could only be detected upon activation of the plasma discharge. In parallel, adsorption of MeHg+ to PM-loaded glass fiber filters was investigated. Direct analysis of methylmercury-impregnated PM resulted in significant signal suppression compared to the same mass of analyte from an aqueous standard, which suggests that methylmercury is efficiently adsorbed on PM. This was later confirmed by repeating the same experiment with "blank" (PM-free) glass fiber filters. Hence, extraction of methylmercury to a liquid phase was required for quantification. In order to demonstrate the feasibility of the proposed setup to carry out methylmercury detection in the presence oh Hg2+, recovery tests were conducted by mixing MeHg+ with Hg2+ at three distinct concentration levels (100 : 1, 10 : 1 and 1 : 1 MeHg+ : Hg2+). Recoveries better than 91% were obtained for MeHg+ under these conditions, which demonstrates that the device is efficient for MeHg+ determination by simply modulating the plasma (switching on-off). Limits of detection and quantification were established as 6 ng and 19 ng, respectively.

Comparison of GC-ICP-MS, GC-EI-MS and GC-EI-MS/MS for the determination of methylmercury, ethylmercury and inorganic mercury in biological samples by triple spike species-specific isotope dilution mass spectrometry

We present here the comparison of three mass spectrometric techniques coupled to gas chromatography for the speciation of Hg in complex matrices in order to evaluate the limiting factors for providing accurate and precise quantification results.

Magnetic solid-phase extraction based on sulfur-functionalized magnetic metal-organic frameworks for the determination of methylmercury and inorganic mercury in water and fish samples

A novel magnetic metal-organic frameworks (Fe3O4@UiO-66-SH) was successfully prepared by coating Fe3O4 nanospheres with sulfur-functionalized UiO-66. The Fe3O4@UiO-66-SH possesses both the magnetic properties of Fe3O4 and the diverse properties of metal-organic framework (MOF) in one material, which has the superiority of high surface area, easy-operation and strong adsorb ability with mercury, is used for the magnetic solid-phase extraction of methylmercury (MeHg+) and inorganic mercury (Hg2+) in water and fish samples. The analyzes were conducted by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The different pretreatment conditions influencing the extraction recoveries of Hg2+ and MeHg+, including adsorbent amount, pH, extraction time, elution solvent, elution volume, desorption time, co-existing ions and dissolved organic materials were investigated. Under the optimized conditions, the limits of detection (LODs) of Hg2+ and MeHg+ for water samples were 1.4 and 2.6 ng L−1, and the limits of quantification (LOQs) of Hg2+ and MeHg+ for water samples were 4.7 and 8.7 ng L−1. The enrichment factors (EFs) were 45.7 and 47.6 fold for Hg2+ and MeHg+, respectively. The accuracy of the proposed method was demonstrated by analyzing the certified reference material of fish tissue (GBW10029) and by determining the analyte content in spiked water and fish samples. The determined values were in good agreement with the certified values and the recoveries for the spiked samples were in the range of 84.5–96.8%.

Determination of methylmercury by differential pulse voltammetry with gold microelectrode

Methylmercury is a kind of fatal neurotoxin. It is of great importantance to establish a sensitive and rapid method to detect its content for the daily environmental monitoring. We propose a new method for direct determination of methylmercury by the differential pulse voltammetry with gold microelectrode and analyze the electrochemical behavior of methylmercury by this method. Meanwhile, we conduct comparative experiments by the differential pulse voltammetry with glassy carbon electrode. The results show that under the same experimental conditions, the gold microelectrode is more sensitive to methylmercury, and its minimum detection concentration reaches 0.10 μg/L. Under the optimal experimental parameters (pH=5.0, deposition potential of -0.80 V and deposition time of 800 s) , the linear range of methylmercury concentration detection by the gold microelectrode method is 0.05-0.50 μg/L, the sensitivity is 0.354 nA/(μg·L), and the minimum limit of detection is 0.012 μg/L, which is far lower than the standard detection value given by the World Health Organization (1.0 μg/L). In addition, the electrochemical sensor based on gold microelectrode shows good selectivity for methylmercury with the advantages of simple operation, low detection limit, high stability and good anti-interference performance. The gold microelectrode method provides a new platform for the trace detection of methyl mercury.

Ultrasound-assisted dual-cloud point extraction with high-performance liquid chromatography-hydride generation atomic fluorescence spectrometry for mercury speciation analysis in environmental water and soil samples.

A method for simultaneous preconcentration and determination of mercury species in water and soil samples was established using high-performance liquid chromatography with hydride generation atomic fluorescence spectrometry after ultrasound-assisted dual-cloud point extraction. The extraction process was divided into two steps. In the first cloud point extraction, inorganic mercury and methylmercury formed chelates with sodium diethyldithiocarbamate and were extracted into Triton X-114 micelles. In the second stage, a displacement reaction between sodium diethyldithiocarbamate-inorganic mercury/methylmercury and l-cysteine occurred, and the analytes entered the l-cysteine aqueous solution under ultrasonication. This aqueous solution was directly introduced to the high-performance liquid chromatography with hydride generation atomic fluorescence spectrometry and the detection was completed within 6min. Under the optimum experimental conditions, the linear range was 0.10-5.0 μg/L (r ≥0.9993) for inorganic mercury and methylmercury, and the enhancement factors were 15.7 for inorganic mercury and 6.35 for methylmercury. The limits of detection for inorganic mercury and methylmercury were 0.004 and 0.016 μg/L, respectively. The approach was successfully applied to the determination of trace inorganic mercury and methylmercury in water and soil samples with good recoveries (85.3-110%). This method solved the problem of peak fusion of the two analytes and was successfully applied to the speciation analysis of mercury.