Dithizone-functionalized C18 online solid-phase extraction-HPLC-ICP-MS for speciation of ultra-trace organic and inorganic mercury in cereals and environmental samples

Widespread mercurous [Hg(I)] species in mercury droplet impacted environments: Evidence from an abandoned Hg smelting plant in Xunyang, China

Mercury (Hg) emissions from Hg smelting (roasting HgS ores) and artisanal small-scale gold mining predominantly include elemental Hg, in either liquid [Hg(0)l] or gaseous [Hg(0)g] form. The oxidation of Hg(0) into Hg(I) is the first step during Hg(0) oxidation, which enables Hg to enter the food web. However, this oxidation process remains poorly understood, particularly in Hg(0)l/Hg(0)g-impacted environments. Herein, we show the widespread occurrence of Hg(I) in Hg(0)l/Hg(0)g-exposed environmental matrices near an abandoned Hg smelting plant in Xunyang, Shaanxi, China, including water, sediment, soil, plant, fish, and insect. This plant produced elemental Hg by roasting HgS ore, leaving Hg(0)l in the factory area after abandonment, which continuously released Hg(0)l/Hg(0)g into the surrounding environment. In Hg(0)-impacted water, Hg(I) was one of the primary Hg species, with an average concentration of 876 (not detected to 6109) ng L-1 and an average Hg(I) to total dissolved Hg ratio of 46% (0-92%), exhibiting a decrease with increasing distance from the plant. Elevated levels of Hg(I) were observed when the upstream sample was simultaneously exposed to Hg(0)l and Hg(0)g, arising from aqueous Hg(0)l oxidation and comproportionation between Hg(II) (mainly from Hg(0)l oxidation) and dissolved Hg(0) (i.e., Hg2+ + Hg0 → Hg22+). These findings highlight the impact of Hg(0) (as Hg(0)l and Hg(0)g) on the environment, emphasizing the comproportionation formation of Hg(I) in natural waters.

Rapid, easy and catalyst-free preparation of magnetic thiourea-based covalent organic frameworks at room temperature for enrichment and speciation of mercury with HPLC-ICP-MS

The complex and cumbersome preparation of magnetic covalent organic frameworks (COFs) nanocomposites on a small scale limits their application. Herein, a rapid and easy route was employed for the preparation of magnetic thiourea-based COFs nanocomposites. COFs were coated on Fe3O4 nanoparticles at room temperature without a catalyst within approximately 30 min. This method is suitable for the large-scale preparation of magnetic adsorbent. Using the as-prepared magnetic adsorbent (Fe3O4@COF-TpTU), we developed a simple, efficient, and sensitive magnetic solid-phase extraction-high performance liquid chromatography-inductively coupled plasma-mass spectrometry (MSPE-HPLC-ICP-MS) for the enrichment and determination of mercury species, including Hg2+, methylmercury (MeHg), and ethylmercury (EtHg). The effects of the experimental parameters on the extraction efficiency, including solution pH, adsorption and desorption time, composition and volume of the elution solvent, salinity, coexisting ions, and dissolved organic matter, were comprehensively investigated. Under optimised conditions, the limits of detection in the developed method were 0.56, 0.34, and 0.47 ng L-1 with enrichment factors of 190, 195, and 180-fold for Hg2+, MeHg, and EtHg, respectively. The satisfactory spiked recoveries (97.0-103%) in real water samples and high consistency between the certified and determined values in a certified reference material demonstrate the high accuracy and reproducibility of the developed method. The as-proposed method with simple operation, high sensitivity, and excellent anti-matrix interference performance was successfully applied to the enrichment and determination of trace levels of mercury species in the natural samples with complicated matrices, such as underground water, surface water, seawater and biological samples.

Portable smartphone-assisted highly sensitive detection of mercury ions based on gold nanoparticle-modified NH2-UiO-66 metal-organic framework

A novel portable smartphone-assisted colorimetric method was reported for the determination of Hg2+ with good analytical performance. A Zr(IV)-based metal-organic framework functionalized with amino groups (NH2-UiO-66) has been adopted as a supporting platform to anchor gold nanoparticles (AuNPs), avoiding the migration and aggregation of AuNPs. With the addition of Hg2+, the formation of gold amalgam proved possible to enhance peroxidase-like activity of the composite (AuNPs/NH2-UiO-66), accelerating the oxidization of zymolyte 3,3',5,5'-tetramethylbenzidine (TMB). In the meantime, the color of the reaction solution turned a vivid blue, and the red, green, and blue (RGB) values of the solution color changed accordingly. On account of this strategy, the quantitative detection of Hg2+ could be achieved. After the optimization of the experiment conditions, the average color intensity (Ic) resulting from RGB values was linear related to the concentration of Hg2+ from 10 to 100 nM, accompanied with a detection limit (LOD) down to 5.4 nM calculated by 3σ/S. The successful application of the designed method has been promoted to detect Hg2+ in some water samples, displaying a great potential in practical application. Furthermore, the use of a smartphone made our proposed method simple and accurate, and thus puts forward a possible way for in situ and real-time monitoring.

Fasten the analysis of metal-binding proteins with GE-ICP-MS via increasing the electrolyte concentration of the running buffer

The coupled system of column gel electrophoresis and inductively coupled plasma mass spectrometry (GE-ICP-MS) is a highly effective technique for detecting metal-binding proteins. However, it takes a long time for this method to test a single sample, which greatly limits its application. In this study, GE-ICP-MS system was optimized by adjusting the analytical conditions, including the concentration and pH of running buffer and the proportion of polyacrylamide gel. The results of the experiment showed that the migration speed of proteins in GE was enhanced by increasing the electrolyte concentration in the running buffer solution. Additionally, the ICP-MS response, which was dramatically decreased because of the change in running buffer solution, can be stabilized by adjusting pH of running buffer. Meanwhile, the optimization of polyacrylamide gel ratio allows GE-ICP-MS to maintain high resolution for proteins of similar molecular weight with increased detection speed. After increasing the concentration of running buffer by 10 times, four iodine labeled proteins were successfully separated at baseline by the GE-ICP-MS system at pH 8.0 in 40 min using a resolving gel (8%, 7 cm) and a stacking gel (4%, 1 cm), which was three times faster than the original one. Finally, the optimized method was proved by detecting a silver-binding protein in rat plasma samples. The above method provided an effective and rapid detection for metal-binding proteins in organism.

Mechanism and controlling factors on rapid methylmercury degradation by ligand-enhanced Fenton-like reaction at circumneutral pH

Methylmercury (MeHg), derived from industrial processes and microbial methylation, is still a worldwide environmental concern. A rapid and efficient strategy is necessary for MeHg degradation in waste and environmental waters. Here, we provide a new method with ligand-enhanced Fenton-like reaction to rapidly degrade MeHg under neutral pH. Three common chelating ligands were selected (nitriloacetic acid (NTA), citrate, and ethylenediaminetetraacetic disodium (EDTA)) to promote the Fenton-like reaction and degradation of MeHg. Results showed that MeHg can be rapidly degraded, with the following efficiency sequence: EDTA > NTA > citrate. Scavenger addition demonstrated that hydroxyl radical (^▪OH), superoxide radical (O₂^▪-), and ferryl (Fe^ⅣO²⁺) were involved in MeHg degradation, and their relative contributions highly depended on ligand type. Degradation product and total Hg analysis suggested that Hg(Ⅱ) and Hg⁰ were generated with the demethylation of MeHg. Further, environmental factors, including initial pH, organic complexation (natural organic matter and cysteine), and inorganic ions (chloride and bicarbonate) on MeHg degradation, were investigated in NTA-enhanced system. Finally, rapid MeHg degradation was validated for MeHg-spiked waste and environmental waters. This study provided a simple and efficient strategy for MeHg remediation in contaminated waters, which is also helpful for understanding its degradation in the natural environment.

The present and potential future of aqueous mercury preservation: a review

Mercury is considered to be one of the most toxic elements to humans. Due to pollution from industry and artisanal gold mining, mercury species are present globally in waters used for agriculture, aquaculture, and drinking water. This review summarises methods reported for preserving mercury species in water samples and highlights the associated hazards and issues with each. This includes the handling of acids in an uncontrolled environment, breakage of sample containers, and the collection and transport of sample volumes in excess of 1 L, all of which pose difficulties for both in situ collection and transportation. Literature related to aqueous mercury preservation from 2000-2021 was reviewed, as well as any commonly cited and relevant references. Amongst others, solid-phase extraction techniques were explored for preservation and preconcentration of total and speciated mercury in water samples. Additionally, the potential as a safe, in situ preservation and storage method for mercury species were summarised. The review highlighted that the stability of mercury is increased when adsorbed on a solid-phase and therefore the metal and its species can be preserved without the need for hazardous reagents or materials in the field. The mercury species can then be eluted upon return to a laboratory, where sensitive analytical detection and speciation methods can be better applied. Developments in solid phase extraction as a preservation method for unstable metals such as mercury will improve the quality of representative environmental data, and further improve toxicology and environmental monitoring studies.

Natural deep eutectic solvent-based microextraction for mercury speciation in water samples

A new natural deep eutectic solvent (NADES)-based analytical method for mercury speciation in water samples is presented. A NADES (i.e., decanoic acid:DL-menthol in a molar ratio of 1:2) is used as an environmentally friendly extractant for separation and preconcentration using dispersive liquid-liquid microextraction before LC-UV-Vis. Under optimal extraction conditions (i.e., NADES volume, 50 µL; sample pH, 12; volume of the complexing agent, 100 µL; extraction time, 3 min; centrifugation speed, 3000 rpm; and centrifugation time, 3 min), the limit of detection values were 0.9 µg L^-1 for the organomercurial species and 3 µg L^-1 for Hg²⁺, which had a slightly higher value. The relative standard deviation (RSD, n = 6) has been evaluated at two concentration levels (25 and 50 µg L^-1) obtaining values for all the mercury complexes within the range of 6-12% and 8-12%, respectively. The trueness of the methodology has been evaluated using five real water samples from four different sources (i.e., tap, river, lake, and wastewater). The recovery tests have been performed in triplicate obtaining relative recoveries between 75 and 118%, with RSD (n = 3) between 1 and 19%, for all the mercury complexes in surface water samples. However, wastewater sample showed a significant matrix effect (recoveries ranged between 45 and 110%), probably due to the high amount of organic matter. Finally, the greenness of the method has also been evaluated by the analytical greenness metric for sample preparation (i.e., AGREEprep).

Air quality prediction models based on meteorological factors and real-time data of industrial waste gas

With the rapid economic growth, air quality continues to decline. High-intensity pollution emissions and unfavorable weather conditions are the key factors for the formation and development of air heavy pollution processes. Given that research into air quality prediction generally ignore pollutant emission information, in this paper, the random forest supervised learning algorithm is used to construct an air quality prediction model for Zhangdian District with industrial waste gas daily emissions and meteorological factors as variables. The training data include the air quality index (AQI) values, meteorological factors and industrial waste gas daily emission of Zhangdian District from 1st January 2017 to 30th November 2019. The data from 1st to 31th December 2019 is used as the test set to assess the model. The performance of the model is analysed and compared with the backpropagation (BP) neural network, decision tree, and least squares support vector machine (LSSVM) function, which has better overall prediction performance with an RMSE of 22.91 and an MAE of 15.80. Based on meteorological forecasts and expected air quality, a daily emission limit for industrial waste gas can be obtained using model inversion. From 1st to 31th December 2019, if the industrial waste gas daily emission in this area were decreased from 6048.5 million cubic meters of waste gas to 5687.5 million cubic meters, and the daily air quality would be maintained at a good level. This paper deeply explores the dynamic relationship between waste gas daily emissions of industrial enterprises, meteorological factors, and air quality. The meteorological conditions are fully utilized to dynamically adjust the exhaust gas emissions of key polluting enterprises. It not only ensures that the regional air quality is in good condition, but also promotes the in-depth optimization of the procedures of regional industrial enterprises, and reduces the conflict between environmental protection and economic development.