Mercury Physicochemical and Biogeochemical Transformation in the Atmosphere and at Atmospheric Interfaces: A Review and Future Directions

Biomass-derived carbon dots with pharmacological activity for biomedicine: Recent advances and future perspectives

Carbon dots (CDs), a type of nanoparticle with excellent optical properties, good biocompatibility, and small size, are finding increasing application across the fields of biology and biomedicine. In recent years, biomass-derived CDs with pharmacological activity (BP-CDs) derived from herbal medicines (HMs), HMs extracts and other natural products with demonstrated pharmaceutical activity have attracted particular attention. Herein, we review recent advances in the development of BP-CDs, covering the selection of biomass precursors, different methods used for the synthesis of BP-CDs from natural sources, and the purification of BP-CDs. Additionally, we summarize the many remarkable properties of BP-CDs including optical properties, biocompatibility and pharmaceutical efficacy. Moreover, the antibacterial, antiviral, anticancer, biosensing, bioimaging, and other applications of BP-CDs are reviewed. Thereafter, we discuss the advantages and disadvantages of BP-CDs and Western drug-derived CDs, highlighting the excellent performance of BP-CDs. Finally, based on the current state of research on BP-CDs, we suggest several aspects of BP-CDs that urgently need to be addressed and identify directions that should be pursued in the future. This comprehensive review on BP-CDs is expected to guide the precise design, preparation, and future development of BP-CDs, thereby advancing the application of BP-CDs in biomedicine.

Thermal desorption technique to speciate mercury in carbonate, silicate, and organic-rich soils

Thermal desorption is a well-assessed technique to speciate mercury (Hg) in soils and sediments. However, the effects related to the different matrices are still not properly assessed. In this study, thermal desorption was applied to Hg-free calcite mixed with Hg standard and soils rich in carbonate and silicate minerals, as well as organic matter. Hg0, HgCl2, HgO, α-HgS, β-HgS and organo-mercuric compounds were recognized, pointing out that the soil matrix operates notable differences in terms of breakdown temperatures of the Hg-compounds and suggesting that the mineralogical composition of soil has to be investigated before applying the thermal desorption technique. Furthermore, the presence of Hg0 was carefully evaluated since, as already observed, it forms Hg2+, which increases mercury mobility in the pedological cover with important consequences for those soils contaminated and located close to decommissioned or active mining areas and/or industrial sites (e.g. chloro-alkali industries). Experimental runs were thus carried out by using carbonate-, silicate- and organic-rich soils doped with liquid Hg. It was observed that Hg0 tends to be oxidized to form Hg+ and then Hg2+ as a function of soil matrix and reaction time. Surprisingly, the oxidation rate is rather fast, since after 42 days the initial content of Hg0 is halved, thus following an exponential decay. This implies that in Hg0-polluted areas, the fate of the resulting Hg2+ can be that to: i) be adsorbed by organic matter and/or Fe-Mn-Al oxides and/or ii) feed shallow aquifers. This study is a further step ahead to understand the behavior of Hg in contaminated soils from industrial and mining areas where liquid Hg is occurring in different soil matrices and may provide useful indications for remediation operations.

Effects of legacy mining on mercury concentrations in conifer needles and mushrooms in northern Palatinate, Germany

Due to integrated pollution prevention and control measures and the reduced burning of coal, air concentrations of mercury (Hg0) are currently levelling off. In the future, however, evasion from land surfaces will probably reverse this trend. Reasons are the rising temperatures and the loss of forest cover caused by calamities, droughts, storms and wildfires. Plant leaves constitute an important matrix for the accumulation of gaseous mercury and uptake and re-volatilisation by plants depends on the species, the vitality and the age and morphology of leaf organs. It has been shown that older conifer needles show higher concentrations than young needles and Hg accumulation is increasing throughout the season. In present study, we collected branches from Norway Spruce (Picea abies) in a former cinnabar mining region in Northern Palatinate, where artisanal and small-scale mining left innumerable waste dumps. While mining, smelting and processing of the ores were terminated during WWII, high total mercury concentrations remained in the top soils locally, with presumably only small fractions being plant available. In the lab, up to seven needle age classes were analysed. 1000 needle weights increased with age and as expected, also the Hg concentrations were elevated in the older needles. Needle concentrations were higher than those reported from other national biomonitoring programs confirming the regional imprint from legacy mercury. To complement our biomonitoring study, we collected edible mushrooms in former mining areas. Hg concentrations in most samples exceeded the EU maximum residue levels (MRL), while only a few broke the existing cadmium and lead limits. Tolerable weekly intake (TWI) for inorganic mercury would be surpassed with the consumption of a small portion of mushrooms. Further studies should be performed on the outgassing of Hg from mine wastes and the incorporation of Hg in the local food web, including its methylation and biomagnification.

Hg-Hg bonding and its influence on the stability of (HgS)n clusters

Pulsed laser ablation of a HgS(s) precursor shows the formation of small cluster ions, (HgS)n=2-4+, together with HgSn=1-8± and [(HgS)n + Sm]±. The computed structure, atomization energy, and HOMO-LUMO gap energy values of the lowest energy ring singlet show stable (HgS)n=2-8. However, the computed bond conductance of the Hg-Hg bond in (HgS)n shows a high value for (HgS)n=2-4 (ξ = 1.072-0.122), whereas it is low for (HgS)n=5-8 (ξ = 0.039-0.006) and decreases significantly as the ring expands, indicating that (HgS)n≥5 is unstable. It evidences that the weak chemical bonding between Hg2+-Hg2+ closed shell (5d10-5d10) electrons plays a significant role in the stability of ring (HgS)n=2-4. Thus, it validates the experimental observation of stable cluster ions up to (HgS)4+. In contrast, the low energy chain triplet (HgS)n=2-8 shows a progressive increase in stability and bond conductance with chain length, indicating sustained mercurophilic interactions in long chain clusters like its crystal structure. Furthermore, the lowest/low energy isomers of HgSn=1-8 have been computed for their energetics, HOMO-LUMO gaps, and electron affinity using DFT-B3LYP/PBE0 methods.

Atmospheric Mercury Concentrations and Isotopic Compositions Impacted by Typical Anthropogenic Mercury Emissions Sources

Coal-fired power plants (CFPPs) and cement plants (CPs) are important anthropogenic mercury (Hg) emission sources. Mercury speciation profiles in flue gas are different among these sources, leading to significant variations in local atmospheric Hg deposition. To quantify the impacts of Hg emissions from CFPPs and CPs on local-scale atmospheric Hg deposition, this study determined concentrations and isotopes of ambient gaseous elemental mercury (GEM), particulate-bound mercury (PBM), and precipitation total Hg (THg) at multiple locations with different distances away from a CFPP and a CP. Higher concentrations of GEM and precipitation THg in the CFPP area in summer were caused by higher Hg emission from the CFPP, resulting from higher electricity demand. Higher concentrations of GEM, PBM, and precipitation THg in the CP area in winter compared to those in summer were related to the higher output of cement. Atmospheric Hg concentration peaked near the CFPP and CP and decreased with distance from the plants. Elevated GEM concentration in the CFPP area was due to flue gas Hg0 emissions, and high PBM and precipitation Hg concentrations in the CP area were attributed to divalent Hg emissions. It was estimated that Hg emissions from the CFPP contributed 58.3 ± 20.9 and 52.3 ± 25.9% to local GEM and PBM, respectively, and those from the CP contributed 47.0 ± 16.7 and 60.0 ± 25.9% to local GEM and PBM, respectively. This study demonstrates that speciated Hg from anthropogenic emissions posed distinct impacts on the local atmospheric Hg cycle, indicating that Hg speciation profiles from these sources should be considered for evaluating the effectiveness of emission reduction policies. This study also highlights the Hg isotope as a useful tool for monitoring environmental Hg emissions.

Modelling the anthropogenic Hg pollution fingerprint on the marine fishery production worldwide: A preliminary exposure assessment for people living in countries having different income levels

Mercury is a toxic pollutant that poses risks for the human population, mainly by eating contaminated fish. Mercury is released into the atmosphere from a variety of anthropogenic activities, with levels of emissions and under policy controls that largely vary across the world, leading thus to different relative contributions to the environmental matrices. Establishing the exact sources of this contaminant in the environment is crucial to optimising the policies aimed at mitigating the exposure risks for specific populations or ecosystems. In this study, we modelled, for the first time, the fingerprint of mercury anthropogenic emissions, jointly released by source-sectors (11) and source-regions (13), on the deposition over (19) FAO fishery zones, and on the FAO official fishery productions worldwide over the 2012-2021 decade. Using mercury anthropogenic emissions for 2012 from EDGAR, East Asia and "Artisanal and Small scale Gold Mining" result the source-region and the source-sector, respectively, that contribute the most to the mercury deposition over all the FAO fishery zones. The only exception applies for the FAO fishery zone 37, the Mediterranean Sea, where the "Industrial Combustion" from the closest Europe is the pair region-sector whose joint contribution is the greatest. When normalised to the overall fishery production worldwide, representing the global fish consumption, the anthropogenic mercury fingerprint showed a similar general pattern, however with notable differences, amplifying the relative contributions of all source-sectors from East Asia and attenuating the relative contributions of the regions in the Southern Hemisphere. This fingerprint further changes when the fish consumption in countries, classified by the World Bank as having different incomes, is considered. These results demonstrate that the same anthropogenic mercury deposited on any fishery zone actually affects in a different way the different population segments worldwide. This study aims to urge the science community as well as the policy makers to use a measure that better represents the mercury hazard for human health. Further, we hope that this study, using nomenclatures that are largely used on final shelf-product, could increase the people's awareness regarding the products they consume.

Assessment of total mercury in urban particulate matter by filter fiber assisted matrix solid-phase dispersion coupling with microplasma assisted-cold vapor generation

BACKGROUND

The evaluation of particle-bound mercury (PBM) exposure is a crucial aspect of assessing the global cycle of mercury (Hg) and its adverse effects on human health and ecosystems. Nevertheless, the precise and reliable measurement of PBM remains a formidable task because of the costly and cumbersome equipment required, as well as the inadequate sensitivities exhibited by current analytical techniques. In this study, we provided a unique and straightforward approach utilising filter fiber-assisted matrix solid-phase dispersion (FF-MSPD) in conjunction with single-drop solution electrode discharge-induced cold vapor generation atomic fluorescence spectrometry (SD-SEGD-CVG-AFS) for the precise quantification of PBM. The PBM contained in a small filter was efficiently extracted with 200 μL of eluent (0.2 % L-cysteine and 4 % HCOOH) by FF-MSPD and subsequently converted to Hg0 using SD-SEGD-CVG, before being subjected to examination using AFS.

RESULTS

The resulted limit of detection (LOD, 3σ) was 0.17 pg m-3, obtained with a sample volume of 12 m3, which was much higher than that of the techniques published in the literatures. The aforementioned technique was effectively utilised for the detection of mercury in 19 samples of PM2.5 and PM10 which were collected over a span of several months.

SIGNIFFCANCE

Contrast to conventional methods, the proposed method offers a range of distinct advantages, including simplified operation, absence of memory effects, enhanced sensitivity, substantial reduction in reagent usage, and decreased secondary pollution. These advantages are particularly valuable for advancing research on the fate, transport, and exposure routes of environmental mercury.

Characteristics of Gaseous Elemental Mercury in a Suburban Area of Shanghai, China

To clarify gaseous elemental mercury (GEM) in suburban megacities in the Yangtze River Delta region, China, we observed GEM concentrations from December 2019 to November 2020 in Wujing town, a suburban area of Shanghai. The annual mean GEM concentration was 1.44 ± 0.88 ng m-3. Compared with the historical monitoring data of GEM in Shanghai over the past 10 years, the concentration of GEM showed a decreasing trend. The monthly mean concentrations of GEM showed clear seasonal variation, with higher values in the spring and winter. In spring and winter, typical Hg pollution events were observed, which could be mostly associated with increased local anthropogenic activity and temperature inversion. The results of the correlation analysis of the daily mean GEM concentrations with the AQI and backward trajectory calculations indicate that mercury pollution at monitoring sites can be affected by local, regional and interregional influences.

Particles-involved photochemical processes: A review for the case of mercury reduction in relation to aquatic mercury cycling

Mercury (Hg) is one of the toxic metals of global and environmental concern, with aquatic Hg cycling being central in determining the production of highly toxic methylmercury and the air-water Hg exchange influencing the long-range intercontinental atmospheric Hg transport. Both inorganic and organic forms of Hg can be bound by suspended particles, including inorganic minerals (in particular metal oxides/sulfides) and particulate organic matter. Photochemical transformation is a critical process in surface water, and the role of suspended particles in Hg redox photoreactions has increasingly emerged, albeit in limited studies in comparison to extensive studies on aqueous (homogeneous) photoreactions of Hg. The lack of understanding of what roles suspended particles play might result in inaccurate estimation of how Hg species transform and/or cycle in the environment. In view of this gap, this paper critically reviews and synthesizes information on the studies conducted on different natural surface waters with respect to the potential roles of suspended particles on Hg photo-redox reactions. It robustly discusses the various possible pathways and/or mechanisms of particle-mediated Hg (II) reduction, in enhancing or lowering the production of dissolved gaseous mercury. These processes include photo hole-electron pair formation and reactive oxygen species generation from particle excitation and their involvement in Hg photoreduction, in addition to the light attenuation effect of particles. This paper highlights the necessity of future studies exploiting these particles-mediated Hg photoreactions pathways and the implications of including these heterogeneous photoreactions (together with particulate elemental Hg species) on the air-water Hg exchange estimation.

Traceable Calibration of Atmospheric Oxidized Mercury Measurements

Most previous measurements of oxidized mercury were collected using a method now known to be biased low. In this study, a dual-channel system with an oxidized mercury detection limit of 6-12 pg m-3 was deployed alongside a permeation tube-based automated calibrator at a mountain top site in Steamboat Springs Colorado, USA, in 2021 and 2022. Permeation tubes containing elemental mercury and mercury halides were characterized via an International System of Units (SI)-traceable gravimetric method and gas chromatography/mass spectrometry before deployment in the calibrator. The dual-channel system recovered 97 ± 4 and 100 ± 8% (±standard deviation) of injected elemental mercury and HgBr2, respectively. Total Hg permeation rates and Hg speciation from the gravimetric method, the chromatography system, the dual-channel system, and an independent SI-traceable measurement method performed at the Jožef Stefan Institute laboratory were all comparable within the respective uncertainties of each method. These are the first measurements of oxidized mercury at low environmental concentrations that have been verified against an SI-traceable calibration system in field conditions while sampling ambient air, and they show that accurate, routinely calibrated oxidized mercury measurements are achievable.

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.

Anthropogenic short-lived halogens increase human exposure to mercury contamination due to enhanced mercury oxidation over continents

Mercury (Hg) is a contaminant of global concern, and an accurate understanding of its atmospheric fate is needed to assess its risks to humans and ecosystem health. Atmospheric oxidation of Hg is key to the deposition of this toxic metal to the Earth's surface. Short-lived halogens (SLHs) can provide halogen radicals to directly oxidize Hg and perturb the budget of other Hg oxidants (e.g., OH and O3). In addition to known ocean emissions of halogens, recent observational evidence has revealed abundant anthropogenic emissions of SLHs over continental areas. However, the impacts of anthropogenic SLHs emissions on the atmospheric fate of Hg and human exposure to Hg contamination remain unknown. Here, we show that the inclusion of anthropogenic SLHs substantially increased local Hg oxidation and, consequently, deposition in/near Hg continental source regions by up to 20%, thereby decreasing Hg export from source regions to clean environments. Our modeling results indicated that the inclusion of anthropogenic SLHs can lead to higher Hg exposure in/near Hg source regions than estimated in previous assessments, e.g., with increases of 8.7% and 7.5% in China and India, respectively, consequently leading to higher Hg-related human health risks. These results highlight the urgent need for policymakers to reduce local Hg and SLHs emissions. We conclude that the substantial impacts of anthropogenic SLHs emissions should be included in model assessments of the Hg budget and associated health risks at local and global scales.

Multimedia fate simulation of mercury in a coastal urban area based on the fugacity/aquivalence method

Due to intensive industrial production and living activities, urban areas are the main anthropogenic mercury (Hg) emission sources. After entering the environment through exhaust gases, wastewater or waste residues, Hg can migrate and transform among different environmental compartments in various species, such as elemental mercury (Hg0), divalent mercury (Hg2+) and methylmercury (MeHg). Studies have yet to report on the multimedia behaviors of Hg in urban areas due to the complexity of the processes involved. In this study, the atmospheric Hg emission in Dalian, a coastal city in Northeast China, was estimated by an anthropogenic emission inventory, and a Level III multimedia model was constructed based on the fugacity/aquivalence method to simulate the fate of Hg in air, water, soil, sediment, vegetation and film. The total annual atmospheric emission was 9.91 t, of which coal combustion and non-coal sources accounted for 70.1 % and 29.9 %, respectively. Atmospheric emission and advection were dominated by Hg0, and aquatic emission and advection were dominated by Hg2+. The migration of air-vegetation, vegetation-soil and soil-air were three important pathways of Hg in urban areas. The model was validated by collecting local soil and vegetation samples and regional air, seawater and sediment monitoring data. The scenario simulation indicated that the local load would decrease to different extents with a 21.0 % reduction in atmospheric Hg emission by implementing the "coal-to-gas" measures. Our developed model can characterize the fate of Hg in coastal urban areas and provide a reference for control strategies.

Mercury species induce metabolic reprogramming in freshwater diatom Cyclotella meneghiniana

Mercury is a hazardous pollutant of global concern. While advances have been made in identifying the detrimental effects caused by Hg species in phytoplankton, knowledge gaps remain regarding the metabolomic perturbations induced by inorganic mercury (Hg(II)) and monomethylmercury (MeHg) in these organisms. Diatoms represent a major phytoplankton group essential in various global biogeochemical cycles. The current study combined targeted metabolomics, bioaccumulation, and physiological response assays to investigate metabolic perturbations in diatom Cyclotella meneghiniana exposed for 2 h to nanomolar concentrations of Hg(II) and MeHg. Our findings highlight that such exposures induce reprogramming of the metabolism of amino acids, nucleotides, fatty acids, carboxylic acids and antioxidants. These alterations were primarily mercury-species dependent. MeHg exposure induced more pronounced reprogramming of the metabolism of diatoms than Hg(II), which led to less pronounced effects on ROS generation, membrane permeability and chlorophyll concentrations. Hg(II) treatments presented distinct physiological responses, with more robust metabolic perturbations at higher exposures. The present study provides first-time insights into the main metabolic alterations in diatom C. meneghiniana during short-term exposure to Hg species, deepening our understanding of the molecular basis of these perturbations.

A rapid and specific fluorescent probe based on aggregation-induced emission enhancement for mercury ion detection in living systems

Mercury is a harmful heavy metal that seriously threatens the environment and organisms. In this study, we combined the aggregation-induced emission mechanism and the advantages of peptides to design a novel tetraphenylene (TPE)-based peptide fluorescent probe, TPE-Cys-Pro-Gly-His (TPE-CPGH), in which the sulfhydryl group of Cys in the peptide chain and the imidazolium nitrogen provided by His were used to mimic the Hg2+ binding site of metalloproteins. The β-fold formed by Pro-Gly was used to promote the spatial coordination of the probe with Hg2+ and the formation of the coordination complex aggregates, these changes led to the "turn on" response to Hg2+. The detection of Hg2+ by TPE-CPGH not only showed high specificity and sensitivity (LOD=46.2 nM), but also had the advantages of fast response and applicability for detection over a wide pH range. Additionally, TPE-CPGH effectively detected Hg2+ in environmental samples, living cells and organisms due to its low cytotoxicity, high water solubility and cell membrane permeability. More interestingly, TPE-CPGH was also mitigated Hg2+ exposure-induced oxidative stress toxicity in vitro and in vivo.

Formation of Chlorine in the Atmosphere by Reaction of Hypochlorous Acid with Seawater

The highly reactive dihalogens play a significant role in the oxidative chemistry of the troposphere. One of the main reservoirs of these halogens is hypohalous acids, HOX, which produce dihalogens in the presence of halides (Y-), where X, Y = Cl, Br, I. These reactions occur in and on aerosol particles and seawater surfaces and have been studied experimentally and by field observations. However, the mechanisms of these atmospheric reactions are still unknown. Here, we establish the atomistic mechanism of HOCl + Cl- → Cl2 + OH- at the surface of the water slab by performing ab initio molecular dynamics (AIMD) simulations. Main findings are (1) This reaction proceeds by halogen-bonded complexes of (HOCl)···(Cl-)aq surrounded with the neighboring water molecules. (2) The halogen bonded (HOCl)···(Cl-)aq complexes undergo charge transfer from Cl- to OH- to form transient Cl2 at neutral pH. (3) The addition of a proton to one proximal water greatly facilitates the Cl2 formation, which explains the enhanced rate at low pH.

Seasonal variation of mercury in cloud water at a mountaintop in subtropical Hong Kong: Influences of transboundary transport and sea-salt aerosol

Understanding the distribution and controlling factors of mercury (Hg) speciation in cloud water is crucial for predicting the fate of atmospheric Hg and assessing the environmental impacts of Hg in cloud water. In this study, we collected 85 cloud water samples during autumn and spring at a mountaintop (957 m a.s.l.) in Hong Kong, China. The concentrations of total Hg (THg) in cloud water varied from 3.6 to 225.3 ng L-1, with volume-weighted mean values of 32.1 ng L-1 in autumn and 24.4 ng L-1 in spring. Due to the strong acidic condition of the cloud water, dissolved Hg (DHg) contributed to two-thirds of THg, with Hg complexes by dissolved organic matter (DOM) and chloride being the predominant species of DHg according to chemical equilibrium modeling simulations. Moreover, the levels of Hg-DOM were significantly higher in autumn cloud water compared to spring, and the latter contained more Hg(II)-halide complexes. These differences could be attributed to the different air mass pathways and their emission sources. By combining backward trajectories and Positive Matrix Factorization (PMF) models, we found that air masses originating from the inland Pearl River Delta region, which were only present in autumn cloud water and strongly influenced by stationary coal combustion, were responsible for the highest concentrations of THg, DHg, particulate Hg (PHg) and Hg-DOM. Additionally, air masses originating from regions in China-Indochina Peninsula were only found in spring samples and were significantly influenced by stationary coal combustion, industrial and biogenic sources, contributing to elevated proportions of methylmercury (MeHg) and PHg. In contrast, marine air masses mainly from the western Pacific Ocean contributed to high levels of Hg(II)-halide complexes, especially in spring cloud water. The dissolution and conversion of Hg from sea salt aerosols played a significant role in the enhanced DHg levels observed during cloud processing.

Long-Range Atmospheric Mercury Transport from Across East Asia to a Suburban Coastal Area in Southern Vietnam

Exports of atmospheric mercury (Hg) from continental East Asia, a major Hg emitter in the globe, have been reported by several studies in neighboring countries such as Japan and Korea. Nonetheless, studies concerning this topic in Southeast Asia (SEA) countries are still limited. Accordingly, gaseous elemental mercury (GEM) has been measured from Can Thanh High School (CTHS), a suburban coastal site in southern Vietnam to study its characterization and discover the evidence of Hg trans-boundary transport from regional sources (e.g., East Asia). Data collected in July, August, and October 2022 were used in this study, and the overall GEM concentration was 1.61 ± 0.32 ng m-3. The GEM levels were higher in October than in July and August, potentially due to the discrepancy in air mass transport patterns induced by tropical monsoon and source origins of Hg. MERRA-2, backward trajectories, and CALIPSO images revealed the trans-boundary air pollution from continental East Asia to southern Vietnam, evidenced by significantly elevated (> 30%) atmospheric Hg concentrations as well as other air pollutants when the plume arrived at CTHS. Furthermore, our results also imply that atmospheric Hg exported from East Asia could influence large areas in SEA, suggesting the need for more studies in various SEA countries in the upcoming future. This study illustrated the influence of regional Hg emissions on local atmospheric Hg pollution and provided data to improve knowledge of the Hg biogeochemical cycle in SEA.

Synchrotron X-ray methods in the study of mercury neurotoxicology

In situ methods are valuable in all fields of research. In toxicology, the importance of dose is well known, elevating the need for in situ techniques to measure levels of toxicants and their byproducts in precise anatomically identifiable locations. More recently, additional emphasis has been placed on the value of techniques which can detect chemical form or speciation, which is equally important in the toxicology of a chemical compound. Many important but conventional methods risk losing valuable information due to extractions, digestions, or the general reliance on mobile phases. Few analytical tools possess the power and diversity of X-ray methods as in-situ methods. Here we present an overview, intended for toxicologists and pathologists, of a variety of synchrotron X-ray methods for determining in situ chemical form and distribution of heavier elements. The versatility and range of these synchrotron techniques, which are both established and emerging, is demonstrated in the context of the study of neurotoxicology of mercury, a global pollutant with the ability to harm both human health and the environment.

Gaseous mercury exchange between air and highly dynamic tidal flats: A laboratory incubation experiment

Gaseous mercury (mainly elemental mercury, Hg(0)) exchange between air and Earth's surfaces is one of the most critical fluxes governing global Hg cycle. As an important and unique part of intertidal ecosystem, tidal flat is characterized by periodic inundation and exposure due to tidal cycle, generating varying hydrological, photochemical and biogeochemical processes. However, quantitative and mechanistic understanding of Hg(0) dynamics between air and exceptionally dynamic tide flats has remained limited to date. In this study, we select five representative tidal flat sediments from typical coastal habits of Chinese coastlines to perform laboratory incubation experiments for deciphering the effect of the interaction of tidal cycle and solar radiation on Hg(0) dynamics over tidal flats with different sediment compositions. We show that sediment Hg concentration, tidal cycle and solar radiation collectively modulate the air-surface Hg(0) exchange over tidal flats and highlight that the photochemistry dominates the Hg(0) production and emission over tidal flats. We find that the daytime inundation presents highest Hg(0) emission fluxes for Hg-poor sediment, but the daytime exposure is the hot moment of Hg(0) emission from Hg-rich sediments and substantially contributes to daily Hg(0) emission fluxes. In the treatment to mimic semidiurnal tide, the daily Hg(0) fluxes are positively correlated to sediment Hg concentrations. Combining our mechanistic insights on air-surface Hg(0) exchange over tidal flats and related data and knowledge reported by other studies, we discuss the implications of our study for field measurement and model development of Hg(0) dynamics over highly dynamic tidal flats. We conclude that the air-surface Hg(0) dynamics over tidal flats are extremely complex and highly variable, and a greater understanding the interactions between natural processes, human impacts and climate forcings will better constrain current and future Hg biogeochemical cycle in global tidal flats.

Mercury (Hg) in the "Skin" of the Ocean: Dissolved Gaseous Hg, Total Hg, and Hg Redox Chemistry in Sea Surface Microlayer and Implication for Air-Sea Hg Exchange

The sea surface microlayer (SML) is the uppermost ∼1000 μm of the surface of the ocean. With distinct physicochemical properties and position relative to the adjacent subsurface waters (SSWs), the ubiquitous distribution and high dynamics of the SML greatly regulate the global air-sea gas exchange and biogeochemistry. Mercury (Hg) redox chemistry in surface seawaters and air-sea exchange of gaseous Hg (mainly Hg(0)) fundamentally control the global oceanic Hg cycle. However, the occurrence and transformation of Hg in the SML have been poorly quantified. Here we optimize the traditional SML sampling system to make it more suitable for dissolved gaseous Hg (DGM, mainly Hg(0)) sampling. We then assess the temporal and spatial variability of DGM, total Hg, dissolved organic carbon (DOC), and Hg redox chemistry in the SML and SSWs of diverse marine environments. Our data suggest a general DGM, total Hg, and DOC enrichment in the SML relative to the SSWs but with complex variability in time and space. The incubation experiments further reveal the complex characteristics of Hg redox chemistry between the SML and SSWs. We discuss important implications of the SML Hg cycle on air-sea Hg exchange and suggest wider investigations of the SML Hg cycle in the global hydrosphere.

Intellectualized Visualization of Single-Particle Raman Spectra for Sensitive Detection and Simultaneous Multianalysis of Heavy Metal Ions

Easy-to-use, reliable, and real-time methods for detecting heavy metal ion contamination are urgently required, which is a primary concern for water pollution control and human health. However, present methods for this aim are still unable to achieve simultaneous multianalysis for complex real sample detection. Herein, an intellectualized vision-based single-nanoparticle Raman imaging strategy combined with ion-responsive functional nucleic acids (FNAs) was proposed to address these issues. We reported a correspondence between the concentration of the analytes and the density of particles (DOP) of specifically captured nanoparticles to achieve sensitive detection and simultaneous multianalysis of heavy metal ions. The specific detection of Pb2+ (Hg2+) was obtained with a detection linear range from 100 pM to 100 nM (from 500 fM to 100 nM) and limit of detections low to 1 pM (100 fM), with the advantages of good specificity, excellent homogeneity, and reproducibility. Furthermore, the differentiation of different heavy metal ions (Pb2+/Hg2+) was achieved, i.e., the simultaneous multianalysis, based on Raman imaging of the single particle and intelligent machine vision method. Finally, the Raman imaging assay was utilized for real sample analysis, and it provided a powerful and reliable tool for detecting trace Pb2+/Hg2+ in real water samples and facilitated the portable on-site monitoring of heavy metal ions.

Changed mercury speciation in clouds driven by changing cloud water chemistry and impacts on photoreduction: Field evidence at Mt. Tai in eastern China

Chemical speciation of mercury (Hg) in clouds largely determines the photochemistry of Hg in the atmosphere and consequently influences Hg deposition on the surface through precipitation. Cloud water chemistry has notably changed over the last decade in response to global changes, however, the effects on Hg speciation remain poorly understood. During summer 2021, we collected sixty cloud water samples at Mt. Tai in eastern China and compared the cloud chemistry and Hg speciation with our previous findings during summer 2015. The results showed that although there were no statistically significant differences in the concentrations of total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg), there was a distinct shift in DHg species from the predominated Hg-DOM (78.6% in 2015 campaign) to the more homogeneously distributed Hg(OH)2 (28.4% in 2021 campaign), HgBr2 (26.5%), Hg-DOM (17.3%) and HgBrOH (17.0%). Changes in cloud water chemistry, particularly the significant increase in pH values to 6.49 ± 0.27 and unexpectedly high levels of bromide ions (Br-, 0.19 ± 0.22 mg L-1), were found to drive the changing of Hg speciation by enhancing Hg(II) hydrolysis and binding by Br-. Elevated Br- originating primarily from the continent likely caused noticeable differences in the dominating DHg species between cloud water sourced from marine and continental regions. The changes in chemical speciation of DHg were estimated to result in a 2.6-fold decrease in Hg(II) photoreduction rate between 2015 and 2021 campaigns (0.178 ± 0.054 h-1 vs. 0.067 ± 0.027 h-1), implying a shortened lifetime of atmospheric Hg and increased ecological risks associated with Hg wet deposition.

Atmospheric mercury in a developed region of eastern China: Interannual variation and gas-particle partitioning

Atmospheric mercury plays a crucial role in the biogeochemical cycle of mercury. This study conducted an intensive measurement of atmospheric mercury from 2015 to 2018 at a regional site in eastern China. During this period, the concentration of particle-bound mercury (PBM) decreased by 13%, which was much lower than those of gaseous elemenral mercury (GEM, 30%) and reactive gaseous mercury (GOM, 62%). The gradual decrease in the correlation between PBM and CO, K, and Pb indicates that the influence of primary emissions on PBM concentration was weakening. Moreover, the value of the partitioning coefficient (Kp) increased gradually from 0.05 ± 0.076 m3/μg in 2015 to 0.16 ± 0.37 m3/μg in 2018, indicating that GOM was increasingly inclined to adsorb onto particulate matter. Excluding the influence of meteorological conditions and the primary emissions, the change in aerosol composition is designated as the main trigger factor for the increasing gas-particle partitioning of reactive mercury (RM). The increasing ratio of Cl-, NO3-, and organics (Org) in the chemical composition of particle matters (PM2.5), as well as the decrease in the proportion of SO42-, NH4+, and K+, are conducive to the adsorption of GOM onto particles, forming PBM, which led to an increase of Kp and a lag of PBM reduction compared to GEM and GOM under the continuous control measures of anthropogenic mercury emissions. The evolution of aerosol compositions in recent years affects the migration and transformation of atmospheric mercury, which in turn can affect the biogeochemical cycle of mercury.

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas

Gaseous elemental mercury (Hg0) extraction from industrial flue gases is undergoing intense research due to its unique properties. Selective adsorption that renders Hg0 to HgO or HgS over metal oxide- or sulfide-based sorbents is a promising method, yet the sorbents are easily poisoned by sulfur dioxide (SO2) and H2O vapor. The Se-Cl intermediate derived from SeO2 and HCl driven by SO2 has been demonstrated to stabilize Hg0. Thus, a surface-induced method was put forward when using γ-Al2O3 supported selenite-chloride (xSeO32--yCl-, named xSe-yCl) for mercury deposition. Results confirmed that under 3000 ppm SO2 and 4% H2O, Se-2Cl exhibited the highest induced adsorption performance at 160 °C and higher humidity can accelerate the induction process. Driven by SO2 under the wet interface, the in situ generated active Se0 has high affinity toward Hg0, and the introduction of Cl- enabled the fast-trapping and stabilization of Hg0 due to its intercalation in the HgSe product. Additionally, the long-time scale-up experiment showed a gradient color change of the Se-2Cl-induced surface, which maintained almost 100% Hg0 removal efficiency over 180 h with a normalized adsorption capacity of 157.26 mg/g. This surface-induced method has the potential for practical application and offers a guideline for reversing the negative effect of SO2 on gaseous pollutant removal.

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.

Real-time 4D tracking of airborne virus-laden droplets and aerosols

There is currently no real-time airborne virus tracking method, hindering the understanding of rapid virus changes and associated health impacts. Nano-digital in-line holographic microscopy (Nano-DIHM) is a lensless technology that can directly obtain the interference patterns of objects by recording the scattered light information originating from the objects. Here, we provide evidence for real-time physicochemical tracking of virus-laden droplets and aerosols in the air using desktop label-free Nano-DIHM. The virus interference patterns, as single and ensemble particles, were imaged by the Nano-DIHM with 32.5 ms resolution. The next-generation Stingray and Octopus software was used to automate object detection, characterization and classification from the recorded holograms. The detection system was demonstrated to detect active MS2 bacteriophages, inactivated SARS-CoV-2 and RNA fragments, and an MS2 mixture with metallic and organic compounds. This work demonstrates the feasibility of using Nano-DIHM to provide rapid virus detection to improve transmission management in real time.

Devendra Pal and coworkers report an imaging system using Nano-Digital in-line Holographic Microscopy (NanoDIHM) to detect airborne viruses in droplets and aerosols in real time. This system is able to detect various viruses in air, water and heterogeneous matrices within one minute, enabling real-time tracking of pollutant particles for efficient epidemic management.

Dissolved gaseous mercury production and sea-air gaseous exchange in impacted coastal environments of the northern Adriatic Sea

The northern Adriatic Sea is well known for mercury (Hg) contamination mainly due to historical Hg mining which took place in Idrija (Slovenia). The formation of dissolved gaseous mercury (DGM) and its subsequent volatilisation can reduce the amount of Hg available in the water column. In this work, the diurnal patterns of both DGM production and gaseous Hg fluxes at the water-air interface were seasonally evaluated in two selected environments within this area, a highly Hg-impacted, confined fish farm (VN: Val Noghera, Italy) and an open coastal zone less impacted by Hg inputs (PR: Bay of Piran, Slovenia). A floating flux chamber coupled with real-time Hg⁰ analyser was used for flux estimation in parallel with DGM concentrations determination through in-field incubations. Substantial DGM production was observed at VN (range = 126.0-711.3 pg L^-1) driven by both strong photoreduction and possibly dark biotic reduction, resulting in higher values in spring and summer and comparable concentrations throughout both day and night. Significantly lower DGM was observed at PR (range = 21.8-183.4 pg L^-1). Surprisingly, comparable Hg⁰ fluxes were found at the two sites (range VN = 7.43-41.17 ng m^-2 h^-1, PR = 0-81.49 ng m^-2 h^-1), likely due to enhanced gaseous exchanges at PR thanks to high water turbulence and to the strong limitation of evasion at VN by water stagnation and expected high DGM oxidation in saltwater. Slight differences between the temporal variation of DGM and fluxes indicate that Hg evasion is more controlled by factors such as water temperature and mixing conditions than DGM concentrations alone. The relative low Hg losses through volatilisation at VN (2.4-4.6% of total Hg) further confirm that static conditions in saltwater environments negatively affect the ability of this process in reducing the amount of Hg retained in the water column, therefore potentially leading to a greater availability for methylation and trophic transfer.

Paper-based bipolar electrode electrochemiluminescence sensors for point-of-care testing

In the past few years, point-of-care testing (POCT) technology has crossed the boundaries of laboratory determination and entered the stage of practical applications. Herein, the latest advances and principal issues in the design and fabrication of paper-based bipolar electrode electrochemiluminescence (BPE-ECL) sensors, which are widely used in the POCT field, are highlighted. After introducing the attractive physical and chemical properties of cellulose paper, various approaches aimed at enhancing the functions of the paper, and their underlying principles are described. The materials typically employed for fabricating paper-based BPE are also discussed in detail. Subsequently, the universal method of enhancing BPE-ECL signal and improving detection accuracy is put forward, and the ECL detector widely used is introduced. Furthermore, the application of paper-based BPE-ECL sensors in biomedical, food, environmental and other fields are displayed. Finally, future opportunities and the remaining challenges are analyzed. It is expected that more design concepts and working principles for paper-based BPE-ECL sensors will be developed in the near future, paving the way for the development and application of paper-based BPE-ECL sensors in the POCT field and providing certain guarantee for the development of human health.

Atmospheric Mercury Isotope Shifts in Response to Mercury Emissions from Underground Coal Fires

Pollutant emissions from coal fires have caused serious concerns in major coal-producing countries. Great efforts have been devoted to suppressing them in China, notably at the notorious Wuda Coalfield in Inner Mongolia. Recent surveys revealed that while fires in this coalfield have been nearly extinguished near the surface, they persist underground. However, the impacts of Hg volatilized from underground coal fires remain unclear. Here, we measured concentrations and isotope compositions of atmospheric Hg in both gaseous and particulate phases at an urban site near the Wuda Coalfield. The atmospheric Hg displayed strong seasonality in terms of both Hg concentrations (5-7-fold higher in fall than in winter) and isotope compositions. Combining characteristic isotope compositions of potential Hg sources and air mass trajectories, we conclude that underground coal fires were still emitting large amounts of Hg into the atmosphere that have been transported to the adjacent urban area in the prevailing downwind direction. The other local anthropogenic Hg emissions were only evident in the urban atmosphere when the arriving air masses did not pass directly through the coalfield. Our study demonstrates that atmospheric Hg isotope measurement is a useful tool for detecting concealed underground coal fires.

Predominant contributions through lichen and fine litter to litterfall mercury deposition in a subalpine forest

Litterfall, typically referring to needles/leaves, may stand for >50% of the total mercury (Hg) deposition in forest ecosystems. By detailed categorisation, we reveal for the first time that the contributions through lichens and fine litter, together 9.98 μg Hg m^-2 yr^-1, could be as high as that in needle litter (9.96 μg m^-2 yr^-1) to the annual total Hg deposition (44.6 μg m^-2 yr^-1) in a subalpine forest in Switzerland. Noticeably, needle litter had the highest contribution (53%) to total Hg in the autumn litterfall but lichens and fine litter together predominated in other seasons (47-59%). Such a seasonal pattern is caused by the high ability of lichens and fine litter to accumulate Hg and the high needle litterfall in autumn, which is related to a good rainfall in summer followed by a dry period in autumn. The constantly higher Hg levels in lichens and fine litter than in needle litter together with similar seasonal patterns of litterfall during 2009-2019 and rainfall during 1980-2019 suggest that our finding can be generally valid. Here, we highlight not only the considerable role of non-needle litterfall in Hg deposition but also the association with weather for seasonal Hg dynamics in different litterfall components.

Elevated methylmercury in Antarctic surface seawater: The role of phytoplankton mass and sea ice

Methylmercury is a neurotoxin that is biomagnified in marine food webs. Its distribution and biogeochemical cycle in Antarctic seas are still poorly understood due to scarce studies. Here, we report the total methylmercury profiles (up to 4000 m) in unfiltered seawater (MeHg_T) from the Ross Sea to the Amundsen Sea. We found high MeHg_T levels in oxic unfiltered surface seawater (upper 50 m depth) in these regions. It was characterized by an obviously higher maximum concentration level of MeHg_T (up to 0.44 pmol/L, at a depth of 3.35 m), which is higher than other open seas (including the Arctic Ocean, the North Pacific Ocean and the equatorial Pacific), and a high MeHg_T average concentration in the summer surface water (SSW, 0.16 ± 0.12 pmol/ L). Further analyses suggest that the high phytoplankton mass and sea-ice fraction are important drivers of the high MeHg_T level that we observed in the surface water. For the influence of phytoplankton, the model simulation showed that the uptake of MeHg by phytoplankton would not fully explain the high levels of MeHg_T, and we speculated that high phytoplankton mass may emit more particulate organic matter as microenvironments that can sustain Hg in-situ methylation by microorganisms. The presence of sea-ice may not only harbor a microbial source of MeHg to surface water but also trigger increased phytoplankton mass, facilitating elevation of MeHg in surface seawater. This study provides insight into the mechanisms that impact the content and distribution of MeHg_T in the Southern Ocean.

Effects of natural particles on photo-reduction of divalent mercury in everglades waters

Photo-reduction of divalent mercury (Hg(II)) in waters plays an important role in the air-water exchange of Hg and biogeochemical cycle of Hg in general. As previous studies on photo-reduction of Hg(II) have mainly focused on dissolved Hg species, the effects of natural particles on photo-reduction of Hg(II) remain largely unknown, except the presumed light attenuating effect through light absorption and scattering. Considering the prevalence of particulate Hg due to adsorption of divalent and elemental Hg species on aquatic particles that are often photochemically active, natural particles may play a more direct role in Hg photo-reduction. By using incubation experiments with Everglades waters and additions of isotopically labelled Hg(II), we studied the effects of particles on photo-reduction of Hg(II) in natural waters. The effect of natural particles on Hg(II) photo-reduction was not observed between filtered or unfiltered Everglades waters, probably because of the low particle concentrations (<3 mg/L). When suspended particles isolated from original water was used to amend its concentration to 6.9 times the ambient Everglades waters, photo-reduction of Hg(II) was significantly enhanced. Given that the particles in Everglades waters are often semiconducting in nature, particulate Hg(II) may undergo heterogenous photo-reduction and lead to higher Hg(II) photo-reduction. However, in Everglades waters with both suspended and settling particles, high concentrations (∼100 mg/L) of particles did not result in enhanced Hg(II) photo-reduction. In this case, the enhancing effects of particles on Hg(II) photo-reduction were likely offset by inhibiting effects due to the higher irradiation attenuation and lower Hg(II) partition coefficients of the settling particles with larger sizes. This study highlights the direct involvements of particles in photoreaction of Hg species in natural waters and calls for more mechanistic research on heterogenous photo-reduction of Hg species on particles' surfaces.

Isotopic Fractionation Characteristics of Speciated Mercury from Local Biomass Combustion in the Tibetan Plateau

As the Third Pole of the world, the Tibetan Plateau (TP) is sensitive to anthropogenic influences. Biomass combustion is one of the most important anthropogenic sources of mercury (Hg) emissions in the TP. However, due to the lack of knowledge about Hg emission characteristics and activity levels in the plateau, atmospheric Hg emissions from biomass combustion in the TP are under large uncertainties. Here, based on pilot-scale experiments, we found that particle-bound mercury (PBM; mean of 83.1-87.7 ng/m³) occupied 17.93-49.31% of the total emitted Hg and the PBM δ²⁰²Hg values (average -1.65‰ to -0.77‰) were significantly higher than those of the corresponding feeding biomass. The Δ²⁰⁰Hg values of total gaseous mercury and PBM were more negative (-0.08‰ to -0.05‰) than other anthropogenic emissions, providing unique isotopic fingerprints for this sector. Together with the investigated local activity levels, Hg emissions from biomass combustion reached 402 ± 74 kg/a, which were dozens of times higher than previous estimates. The emissions were characterized by conspicuous spatial heterogeneity, concentrated in the northern and central TP. Specialized Hg emissions and the Hg isotope fingerprint of local biomass combustion can aid in evaluating the influence of this sector on the fragile ecosystems of the TP.

Quantum Chemical Investigation of Snow-Mercury Interactions and Their Implication of Mercury Deposition in the Arctic

Elemental gaseous Hg is emitted into the atmosphere through various anthropogenic and natural processes. Mercury's different species and respective transport ranges, atmospheric physical and chemical transformations, and interaction with the earth's surfaces all contribute to the global cycling of toxic mercury. Under sunlight, halogens, ozone, and nitro species oxidize the emitted elemental Hg to gaseous Hg (II) molecules, which deposit onto the snow and ice surfaces in the Arctic. To investigate the fate of deposited mercury, a quantum chemical investigation was conducted using first-principles density functional theory (DFT) to analyze the interaction between various mercury molecules and snow clusters of differing sizes. Results show that all oxidized mercury molecules: XHgY, BrHgOX, BrHgXO XHgOH, XHgO₂H, and XHgNO₂, with X, Y = Cl, Br, and I atoms have thermodynamically stable interactions with snow clusters. Further, the adsorption energy of all mercury molecules increases with increasing size of snow clusters. Additionally, the orientations of deposited mercury molecules on the cluster surface also influence the mercury-snow interactions.

Tracing the transboundary transport of atmospheric Particulate Bound Mercury driven by the East Asian monsoon

Taking Beijing-Tianjin-Hebei (BTH) with severe atmospheric mercury (Hg) and PM_2.5 pollution as a typical region, this study clarified the characteristics and transboundary transport of atmospheric Particulate Bound Mercury (PBM_2.5) affected by the East Asian monsoon. Five sampling sites were conducted in rural, suburban, urban, industrial, and coastal areas of BTH from northwest to southeast along the East Asian monsoon direction. PBM_2.5 showed increasing concentrations from northwest to southeast and negative δ²⁰²Hg values, indicating significant contributions from anthropogenic sources. However, the mean Δ¹⁹⁹Hg values of PBM_2.5 at the five sites were significantly positive, probably triggered by the photoreduction of Hg(II) during long-range transport driven by the East Asian monsoon. Apart from local anthropogenic emissions as the primary sources, the transboundary transport of PBM_2.5, driven by west and northwest air masses originating in Central Asia and Russia, contributed significantly to the PBM_2.5 pollution of BTH. Moreover, these air masses reaching BTH would carry elevated PBM_2.5 concentrations further transported to the ocean by the East Asian monsoon. In contrast, the southeast air masses transported from the ocean by the East Asian monsoon in summer diluted inland PBM_2.5 pollution. This study provides insight into the atmospheric Hg circulation affected by the East Asian monsoon.

Hybrid films composed of ethyl(hydroxyethyl)cellulose and silica xerogel functionalized with a fluorogenic chemosensor for the detection of mercury in water

Ethyl(hydroxyethyl)cellulose (EHEC) and a silica-based xerogel (SBX) were functionalized with a (18-crown-6)-styrylpyridine precursor (1) to obtain the modified polymers EHEC-1 and SBX-1, respectively. Films were obtained and the resulting materials were used as fluorogenic devices for the detection of Hg²⁺ in water. The films produced from EHEC-1 showed high water retention, making it difficult to apply as a reusable optical chemosensor. Since SBXs are recognized in the literature for their hydrophobicity, a hybrid film composed of EHEC and SBX-1 which did not show water retention was produced and characterized. This system showed rapid response time, outstanding selectivity compared to several other studied metal ions, and sensitivity for the detection of Hg²⁺ in water. The detection limit for this material using fluorescence technique was 2 ppb (∼10^-8 mol L^-1). The reversibility of the complex formed between EHEC-SBX-1 film and Hg²⁺ was demonstrated by the addition of cysteine to the medium. The result obtained also allowed the assembly of INHIBIT and IMPLICATION molecular logic gates, using Hg²⁺ and cysteine as inputs. The results described in this article have important significance in the development of novel reversible fluorogenic chemosensors and adsorbent materials for the effective removal of Hg²⁺ ions.

Field Evidence for Asian Outflow and Fast Depletion of Total Gaseous Mercury in the Polluted Coastal Atmosphere

Atmospheric mercury (Hg) cycling in polluted coastal atmosphere is complicated and not fully understood. Here, we present measurements of total gaseous mercury (TGM) monitored at a coastal mountaintop in Hong Kong downwind of mainland China. Sharp TGM peaks during cold front passages were frequently observed due to Asian pollution outflow with typical TGM/CO slopes of 6.8 ± 2.2 pg m^-3 ppbv^-1. Contrary to the daytime maximums of other air pollutants, TGM exhibited a distinct diurnal variation with a midday minimum. Moreover, we observed four cases of extremely fast TGM depletion after sunrise, during which TGM concentrations rapidly dipped to 0.3-0.6 ng m^-3 accompanied by other pollutants on the rise. Simulated meteorological fields revealed that morning upslope flow transporting anthropogenically polluted but TGM-depleted air masses from the mixed layer caused morning TGM depletion at the mountaintop location. The TGM-depleted air masses were hypothesized to result mainly from fast photooxidation of Hg after sunrise with minor contributions from dry deposition (5.0%) and nocturnal oxidation (0.6%). A bromine-induced two-step oxidation mechanism involving abundant pollutants (NO₂, O₃, etc.) was estimated to play a dominant role, contributing 55%-60% of depleted TGM and requiring 0.20-0.26 pptv Br, an amount potentially available through sea salt aerosol debromination. Our findings suggest significant effects of the interaction between anthropogenic pollution and marine halogen chemistry on atmospheric Hg cycling in the coastal areas.

Sonochemical oxidation and stabilization of liquid elemental mercury in water and soil

Over 3000 mercury (Hg)-contaminated sites worldwide contain liquid metallic Hg [Hg(0)_l] representing a continuous source of elemental Hg(0) in the environment through volatilization and solubilization in water. Currently, there are few effective treatment technologies available to remove or sequester Hg(0)_l in situ. We investigated sonochemical treatments coupled with complexing agents, polysulfide and sulfide, in oxidizing Hg(0)_l and stabilizing Hg in water, soil and quartz sand. Results indicate that sonication is highly effective in breaking up and oxidizing liquid Hg(0)_l beads via acoustic cavitation, particularly in the presence of polysulfide. Without complexing agents, sonication caused only minor oxidation of Hg(0)_l but increased headspace gaseous Hg(0)_g and dissolved Hg(0)_aq in water. However, the presence of polysulfide essentially stopped Hg(0) volatilization and solubilization. As a charged polymer, polysulfide was more effective than sulfide in oxidizing Hg(0)_l and subsequently stabilizing the precipitated metacinnabar (β-HgS) nanocrystals. Sonochemical treatments with sulfide yielded incomplete oxidation of Hg(0)_l, likely resulting from the formation of HgS coatings on the dispersed µm-size Hg(0)_l bead surfaces. Sonication with polysulfide also resulted in rapid oxidation of Hg(0)_l and precipitation of HgS in quartz sand and in the Hg(0)_l-contaminated soil. This research indicates that sonochemical treatment with polysulfide could be an effective means in rapidly converting Hg(0)_l to insoluble HgS precipitates in water and sediments, thereby preventing its further emission and release to the environment. We suggest that future studies are performed to confirm its technical feasibility and treatment efficacy for remediation applications.

Monitoring Hg2+ and MeHg+ poisoning in living body with an activatable near-infrared II fluorescence probe

Noninvasively imaging mercury poisoning in living organisms is critical to understanding its toxicity and treatments. Especially, simultaneous fluorescence imaging of Hg²⁺ and MeHg⁺in vivo is helpful to disclose the mysteries of mercury poisoning. The key limitation for mercury imaging in vivo is the low imaging signal-to-background ratio (SBR) and limited imaging depth, which may result in unreliable detection results. Here, we designed and prepared a near-infrared II (NIR II) emissive probe, NIR-Rh-MS, leveraging the "spirolactam ring-open" tactic of xanthene dyes for in situ visualization of mercury toxicity in mice. The probe produces a marked fluorescence signal at 1015 nm and displays good linear responses to Hg²⁺ and MeHg⁺ with excellent sensitivity, respectively. The penetration experiments elucidate that the activated NIR-II fluorescence signal of the probe penetrates to a depth of up to 7 mm in simulated tissues. Impressively, the probe can monitor the toxicity of Hg²⁺ in mouse livers and the accumulation of MeHg⁺ in mouse brains via intravital NIR-II imaging for the first time. Thus, we believe that detecting Hg²⁺ and MeHg⁺ in different organs with a single NIR-II fluorescence probe in mice would assuredly advance the toxicologic study of mercury poisoning in vivo.

Optimization and application of passive air sampling method for gaseous elemental mercury in Ulsan, South Korea

We compared uptake rates and concentrations of gaseous elemental mercury (GEM) by passive sampling conditions and investigated the spatial distribution of GEM in Ulsan, the largest industrial city in South Korea. For the optimization of sampling conditions, two outer sampling containers (cylindrical polyethylene terephthalate and two stainless steel bowls), two different sulfur contents of the sorbent (16.3% and 26.3%), and three sampling periods (1, 2, and 3 months) were considered. The uptake rates of GEM were not statistically different by the sampling container, but they were increased with the sulfur contents of activated carbon. A sampling condition using two stainless bowls and lower sulfur contents of activated carbon for 2-3 months was preferred with the highest precision of GEM concentrations. With the same method, passive air samples were collected for 3 months in duplicate from 10 sites in Ulsan. The concentrations of GEM ranged from 3.13 to 11.2 ng/m³ (mean 4.65 ng/m³), and the highest concentration was measured at a non-ferrous industrial complex. A zinc smelter in the non-ferrous industrial complex was identified as a major mercury source in Ulsan. This study is the first passive air sampling study investigating the spatial distributions of GEM in different types of industrial areas as well as residential areas of Ulsan.

Elemental mercury accumulation in Eichhornia crassipes (Mart.) Solms-Laubach

The aquatic macrophyte Eichhornia crassipes has great potential for the control of Hg pollution in the environment. The aim of this study was to investigate the capability of E. crassipes to accumulate elemental mercury (Hg⁰). The plants were exposed for 30 days to 5, 10, 20, 40, and 80 mg of Hg⁰ in a 1-L Hoagland medium with the Hg⁰ settled at the bottom of the flask. The roots of the plants did not touch the mercury during the treatment. After exposure, the total Hg (T-Hg) concentrations in the roots, leaves, and stems were measured using a direct mercury (Hg) analyzer. The highest concentrations were found at 80 mg Hg⁰ treatment in the roots, leaves, and stems, in that order. The translocation factor indicated a poor capability of Hg to translocate from the roots to the shoots. The relative growth and the root-length inhibition measurements showed that the differences between Hg⁰ treatments were not significant. In addition, the treatments negatively affected the chlorophyll concentration. The carotenoid content was found to be significantly different at 20 and 40 mg of Hg⁰ in 1 L. Regarding the carbonyl index in root proteins, significant differences compared to control were found at the highest Hg treatment. Based on these results, it was shown that E. crassipes is able to take up elemental Hg from Hoagland medium. However, the Hg⁰ treatments did not show a strong stress-response activation mechanism in the evaluated plant tissues.

Fractionation of mercury stable isotopes in lichens

Bio-monitoring of mercury (Hg) in air using transplanted and in-situ lichens was conducted at three locations in Slovenia: (I) the town of Idrija in the area of the former Hg mine, where Hg contamination is well known; (II) Anhovo, a settlement with a cement production plant, which is a source of Hg contamination, and (III) Pokljuka, a part of a national park. Lichens from Pokljuka were transplanted to different sites and sampled four times-once per season, from January 2020 to February 2021. Lichens were set on tree branches, fences, and under cover, allowing them to be exposed to different environmental conditions (e.g., light and rain). The in-situ lichens were sampled at the beginning and the end of the sampling period. The highest concentrations were in the Idrija area, which was consistent with previous research. Significant mass-dependent fractionation has been observed in transplanted lichens during summer period. The δ²⁰²Hg changed from -3.0‰ in winter to -1.0‰ in summer and dropped again to the same value in winter the following year. This trend was observed in all samples, except those from the most polluted Idrija sampling site, which was in the vicinity of the former Hg ore-smelting plant. This was likely due to large amounts of Hg originating from polluted soil close to the former smelting plant with a distinct isotopic fingerprint in this local area. The Δ¹⁹⁹Hg in transplanted lichens ranged from -0.5‰ to -0.1‰ and showed no seasonal trends. These findings imply that seasonality, particularly in summer months, may affect the isotopic fractionation of Hg and should be considered in the sampling design and data interpretation. This trend was thus described in lichens for the first time. The mechanism behind such change is not yet fully understood.

Atmospheric particulate-bound mercury (PBM10) in a Southeast Asia megacity: Sources and health risk assessment

Particulate-bound mercury (PBM) is a global environmental concern owing to its large dry deposition velocities and scavenging coefficients, both of which drive Hg into terrestrial and marine ecosystems. PBM observation studies have been widely conducted over East Asia, but comparable studies in Peninsular Southeast Asia (PSEA) remain scarce. This is the first study reporting PBM concentrations for Ho Chi Minh City (HCMC), the biggest metropolitan area in Vietnam. A total of 222 samples were collected in 2018 and contained an average PBM₁₀ (particulate matter - PM with diameter ≤10 μm) concentration and Hg mass fraction (i.e. PBM/PM) of 67.3 ± 45.9 pg m^-3 and 1.18 ± 1.12 μg g^-1, respectively. Although PBM concentration was lower than those reported in Chinese megacities, the Hg mass fraction was similar to those in China, suggesting strong enrichment from anthropogenic Hg emissions in HCMC. Traffic-induced particulate emission and deposition processes were major factors governing PBM temporal variation at our site. In addition, the prevailing southwest monsoon winds brought air masses that passed through industrial areas and were associated with a higher Hg mass fraction. Statistically significant positive correlations (R² = 0.11-0.52, p < 0.01) were observed for PBM with PM and the Hg mass fraction, indicating similar PM and Hg sources or oxidized Hg adsorption onto PM via gas-particle partitioning. Moreover, PCA results revealed a higher contribution of primary sources than secondary sources to PBM concentration variability in HCMC. A health risk assessment indicated that the PBM concentrations at HCMC posed minimal non-carcinogenic risks (HI < 1) for children and adults, but dermal contact may act as an important exposure route since lightweight clothing is common among residents. This PBM dataset over PSEA, a region with high atmospheric Hg emissions, provides a valuable resource for the Hg scientific community to improve our understanding of Hg biogeochemical cycle.

Sustained high atmospheric Hg level in Beijing during wet seasons suggests that anthropogenic pollution is continuing: Identification of potential sources

Gaseous elemental Hg (GEM), particulate bound Hg (PBM), and gaseous oxidized Hg (GOM) were monitored at an urban site in Beijing, China during wet seasons (July-November) of 2021. The mean (± standard deviation) GEM, PBM, and GOM concentrations were 3.45 ± 1.27 ng m^-3, 48.2 ± 88.6 pg m^-3, and 13.7 ± 55.0 pg m^-3, respectively. GEM level was stable (generally 3.0-4.0 ng m^-3) and the average concentration was about twice that of the background level in Beijing, while the occasionally very high PBM and GOM concentrations (>1000 pg m^-3) suggest pollution events. Moreover, GEM, CO, and NO₂ exhibit a conspicuous similar diurnal trend with lower values during daytime compared to nighttime under the combined influence of anthropogenic emissions and meteorological factors, and the significantly positive relationship between them indicates that they had similar or common sources. However, the diurnal pattern of reactive Hg (i.e., RM = PBM + GOM) was not pronounced. Both cluster and potential source contribution function analyses show that southern Beijing, Tianjin, as well as central and east Hebei provinces were the dominant source regions for elevated GEM at this monitoring site. The dominant reason for the elevated GEM level (generally >3.5 ng m^-3) during pollution event is that majority of air masses originated from the southern polluted regions of this sampling site and traveled at low heights, while the long-range transport of upper clean air masses and continuous high traveling heights were attributed to the low GEM level (<2.0 ng m^-3) during clean event. Positive matrix factorization results reveal that regional transport of coal fired air pollutants and local vehicle emissions were the dominant contributors to elevated GEM level, while RM mainly originated from local sources.

Dispersion of airborne mercury species emitted from the cement plant

The cement industry is the second largest source of anthropogenic mercury (Hg) emissions in Europe, accounting for 11% of global anthropogenic Hg emissions. The main objective of this study was to examine the influence of Hg emissions from the Salonit Anhovo cement plant on Hg levels measured in the ambient air at Vodarna, 1 km downwind from the flue gas chimney. The findings reveal that the plant raw mill operational status plays an important role in Hg concentrations in the flue gas emitted from the plant. Emitted total gaseous mercury was, on average, higher (49.4 μg/m³) when raw mills were in the direct mode (both raw mills-off) and lower (23.4 μg/m³) in the combined mode (both raw mills-on). The average Hg concentrations in Vodarna were 3.14 ng/m³ for gaseous elemental mercury, 53.7 pg/m³ for gaseous oxidised mercury, and 41.9 pg/m³ for particulate bound mercury for the whole measurement period. Atmospheric Hg speciation in Vodarna, coupled with plant emissions and wind data, has revealed that the total gaseous mercury emitted from the cement plant is clearly related to all Hg species measured in Vodarna. Wind blowing from the northeastern quadrant (mostly NE, ENE) is responsible for the elevated Hg levels in Vodarna, where gaseous oxidised mercury levels are highly linked to the cement plant emissions. However, elevated levels of Hg species in the absence of northeastern winds indicate potential inputs from other unknown local sources as well as inputs from regional and global transport mechanisms.