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Sulfate-reducing bacteria (SRB) play pivotal roles in the biotransformation of mercury (Hg). However, unrevealed global responses of SRB to Hg have restricted our understanding of details of Hg biotransformation processes. The absence of protein-protein interaction (PPI) network under Hg stimuli has been a bottleneck of proteomic analysis for molecular mechanisms of Hg transformation. This study constructed the first comprehensive PPI network of SRB in response to Hg, encompassing 67 connected nodes, 26 independent nodes, and 121 edges, covering 93% of differentially expressed proteins from both previous studies and this study. The network suggested that proteomic changes of SRB in response to Hg occurred globally, including microbial metabolism in diverse environments, carbon metabolism, nucleic acid metabolism and translation, nucleic acid repair, transport systems, nitrogen metabolism, and methyltransferase activity, partial of which could cover the known knowledge. Antibiotic resistance was the original response revealed by this network, providing insights into of Hg biotransformation mechanisms. This study firstly provided the foundational network for a comprehensive understanding of SRB's responses to Hg, convenient for exploration of potential targets for Hg biotransformation. Furthermore, the network indicated that Hg enhances the metabolic activities and modification pathways of SRB to maintain cellular activities, shedding light on the influences of Hg on the carbon, nitrogen, and sulfur cycles at the cellular level., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Algae are an entry point for mercury (Hg) into the food web. Bioconcentration of Hg by algae is crucial for its biogeochemical cycling and environmental risk. Herein, considering the cell heterogeneity, we investigated the bioconcentration of coexisting isotope-labeled inorganic ( 199 IHg) and methyl Hg ( 201 MeHg) by six typical freshwater and marine algae using dual-mass single-cell inductively coupled plasma mass spectrometry (scICP-MS). First, a universal pretreatment procedure for the scICP-MS analysis of algae was developed. Using the proposed method, the intra- and interspecies heterogeneities and the kinetics of Hg bioconcentration by algae were revealed at the single-cell level. The heterogeneity in the cellular Hg contents is largely related to cell size. The bioconcentration process reached a dynamic equilibrium involving influx/adsorption and efflux/desorption within hours. Algal density is a key factor affecting the distribution of Hg between algae and ambient water. Cellular Hg contents were negatively correlated with algal density, whereas the volume concentration factors almost remained constant. Accordingly, we developed a model based on single-cell analysis that well describes the density-driven effects of Hg bioconcentration by algae. From a novel single-cell perspective, the findings improve our understanding of algal bioconcentration governed by various biological and environmental factors.

The Paris Agreement and the Minamata Convention on Mercury are two of the most important environmental conventions being implemented concurrently, with a focus on reducing carbon and mercury emissions, respectively. The relation between mercury and carbon influences the interactions and outcomes of these two conventions. This perspective investigates the link between mercury and CO 2 , assessing the consequences and exploring the policy implications of this link. We present scientific evidence showing that mercury and CO 2 levels are negatively correlated under natural conditions. As a result of this negative correlation, the CO 2 level under the current mercury reduction scenario is predicted to be 2.4-10.1 ppm higher than the no action scenario by 2050, equivalent to 1.0-4.8 years of CO 2 increase due to human activity. The underlying causations of this negative correlation are complex and need further research. Economic analysis indicates that there is a trade-off between the benefits and costs of mercury reduction actions. As reducing mercury emission may inadvertently undermine efforts to achieve climate goals, we advocate for devising a coordinated implementation strategy for carbon and mercury conventions to maximize synergies and reduce trade-offs.

Biodegradation of soil organic matter (SOM), which involves greenhouse gas (GHG) emissions, plays an essential role in the global carbon cycle. Over the past few decades, this has become an important research focus, particularly in natural ecosystems. SOM biodegradation significantly affects contaminants in the environment, such as mercury (Hg) methylation, producing highly toxic methylmercury (MeHg). However, the potential link between GHG production from SOM turnover in contaminated soils and biogeochemical processes involving contaminants remains unclear. In this study, we investigated the dynamics of GHG, MeHg production, and the relationship between biogeochemical processes in soils from two typical Hg mining sites. The two contaminated soils have different pathways, explaining the significant variations in GHG and MeHg production. The divergence of the microbial communities in these two biogeochemical processes is essential. In addition to the microbial role, abiotic factors such as Hg species can significantly affect MeHg production. On the other hand, we found an inverse relationship between CH 4 and MeHg, suggesting that carbon emission reduction policies and management could inadvertently increase the MeHg levels. This highlights the need for an eclectic approach to organic carbon sequestration and contaminant containment. These findings suggest that it is difficult to establish a general pattern to describe and explain the SOM degradation and MeHg production in contaminated soils within the specific scenarios. However, this study provides a case study and helpful insights for further understanding the links between environmental risks and carbon turnover in Hg mining areas., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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 Fe 3 O 4 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 (Fe 3 O 4 @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 Hg 2+ , 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 Hg 2+ , 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., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Guimin Zhang reports financial support was provided by Department of Science and Technology of Shandong Province. Ligang Hu reports financial support was provided by Jinan Science and Technology Bureau. Zhenhua Wang reports financial support was provided by National Natural Science Foundation of China. Bing Li reports financial support was provided by Department of science and technology of Inner Mongolia. Zhenhua Wang reports financial support was provided by Qilu University of Technology (Shandong Aceadmy of Sciences). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

To elucidate the potential risks of the toxic pollutant mercury (Hg) in polar waters, the study of accumulated Hg in fish is compelling for understanding the cycling and fate of Hg on a regional scale in Antarctica. Herein, the Hg isotopic compositions of Antarctic cod Notothenia coriiceps were assessed in skeletal muscle, liver, and heart tissues to distinguish the differences in Hg accumulation in isolated coastal environments of the eastern (Chinese Zhongshan Station, ZSS) and the antipode western Antarctica (Chinese Great Wall Station, GWS), which are separated by over 4000 km. Differences in odd mass-independent isotope fractionation (odd-MIF) and mass-dependent fractionation (MDF) across fish tissues were reflection of the specific accumulation of methylmercury (MeHg) and inorganic Hg (iHg) with different isotopic fingerprints. Internal metabolism including hepatic detoxification and processes related to heart may also contribute to MDF. Regional heterogeneity in iHg end-members further provided evidence that bioaccumulated Hg origins can be largely influenced by polar water circumstances and foraging behavior. Sea ice was hypothesized to play critical roles in both the release of Hg with negative odd-MIF derived from photoreduction of Hg 2+ on its surface and the impediment of photochemical transformation of Hg in water layers. Overall, the multitissue isotopic compositions in local fish species and prime drivers of the heterogeneous Hg cycling and bioaccumulation patterns presented here enable a comprehensive understanding of Hg biogeochemical cycling in polar coastal waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Microbial reduction plays a crucial role in Hg redox and the global cycle. Although intracellular Hg(II) reduction mediated by MerA protein is well documented, it is still unclear whether or how bacteria reduce Hg(II) extracellularly without its internalization. Herein, for the first time, we discovered the extracellular reduction of Hg(II) by a widely distributed aerobic marine bacterium Alteromonas sp. KD01 through a superoxide-dependent mechanism. The generation of superoxide by Alteromonas sp. KD01 was determined using 3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide and methyl cypridina luciferin analogue as probes via UV-vis and chemiluminescence detection, respectively. The results demonstrated that Hg(II) reduction was inhibited by superoxide scavengers (superoxide dismutase (SOD) and Cu(NO 3 ) 2 ) or inhibitors of reduced nicotinamide adenine dinucleotide (NADH) oxidoreductases. In contrast, the addition of NADH significantly improved superoxide generation and, in turn, Hg(II) reduction. Direct evidence of superoxide-mediated Hg(II) reduction was provided by the addition of superoxide using KO 2 in deionized water and seawater. Moreover, we observed that even superoxide at an environmental concentration of 9.6 ± 0.5 nM from Alteromonas sp. KD01 (5.4 × 10 6 cells mL -1 ) was capable of significantly reducing Hg(II). Our findings provide a greater understanding of Hg(II) reduction by superoxide from heterotrophic bacteria and eukaryotic phytoplankton in diverse aerobic environments, including surface water, sediment, and soil.

Particulate HgS play crucial roles in the mercury (Hg) cycle. Approximately 20-90% of dissolved Hg can be transformed into particulate HgS by algae. However, detailed knowledge regarding these particles, including sizes and distribution, remains unknown. The present study explored the formation, distribution, and excretion of mercury nanoparticles (HgNPs) in diatom Chaetoceros curvisetus . The results demonstrated that HgNPs (HgS nanoparticles, 29.6-66.2 nm) formed intracellularly upon exposure to 5.0-100.0 μg L -1 Hg(II), accounting for 12-27% of the total Hg. HgNP concentrations significantly increased with increasing intracellular Hg(II) concentrations, while their sizes remained unaffected. HgNPs formed intracellularly and partly accumulated inside the cells (7-11%). Subsequently, the sizes of intracellular HgNPs gradually decreased to facilitate expulsion, 21-50% of which were excreted. These suggested the vital roles of HgNPs in comprehending marine Hg fate. Their unique physicochemical properties and bioavailability would influence Hg biotransformation in the ocean. Additionally, both intracellular and extracellular HgNPs contributed to Hg settling with cells, ultimately leading to Hg burial in sediments. Overall, these findings further deepened our understanding of Hg biotransformation and posed challenges in accurately estimating marine Hg flux and Hg burial.

Liquid elemental mercury droplet (Hg(0) l ) is an important species in heavy Hg-contaminated environments. The oxidation processes of Hg(0) l and its related mechanisms are still poorly understood. Herein, for the first time, it was verified that mercurous species [Hg(I)] was an important species in natural water contaminated by Hg(0) l as well as in the simulated dark oxidation of Hg(0) l . The formation and further transformation of Hg(I) controlled the overall oxidation process of Hg(0) l and were affected by different environmental factors. Through kinetic modeling using ACUCHEM program, oxidation of Hg(0) to Hg(I) (Hg(0) → Hg(I)) was determined to be the rate-limiting step in Hg(0) l oxidation because its k value ((8.7 ± 0.21) × 10 -11 s -1 ) is seven orders of magnitude lower than that of Hg(I) oxidation (Hg(I) → Hg(II), (4.7 ± 0.15) × 10 -4 s -1 ). Ligands like OH - , Cl - , and natural organic matter enhanced the formation of Hg(I) via promoting the constants of comproportionation (up to (9.5 ± 0.78) × 10 -4 s -1 ). These findings highlight the importance of Hg(I) in Hg(0) l oxidation process by controlling the transformation kinetics of Hg species, facilitating an improved understanding of the environmental redox cycles of Hg., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Dissolved organic matter (DOM)-mediated divalent mercury (Hg(II)) aging kinetics play a crucial role in controlling Hg(II) transformation and bioavailability in natural aquatic environments. However, the differential environmental behaviors of new and aged Hg(II) in a same reaction system remains unknown. In this study, multi-isotope tracing was used to investigate the impacts of binding site and sulfidation during DOM-mediated Hg(II) aging processes on Hg(II) reduction and microbial methylation in the same reaction system. Stepwise reduction approach and liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS) demonstrate that DOM-mediated dark aging processes are mainly driven by the rearrangement of DOM binding sites with Hg(II), but not the formation of mercury sulfide nanoparticles (HgS NP ). The abundant but weaker RO/N (carboxyl and amino) Hg(II)-binding sites are replaced with stronger RSH (thiol) moieties towards Hg(II) binding with aging, resulting in a decrease in Hg(II) reduction. In contrast, besides reduction, DOM-mediated Hg(II) photoaging induces the formation of HgS NP , as revealed by LC-ICP-MS, which in turn decreases the microbial methylation potential of Hg(II). These findings help better understand and predict the kinetic characteristics of Hg(II) reactivity and its influence on Hg cycle within natural aquatic environments., Competing Interests: Declaration of Competing Interest The authors declare that they have no knowing competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Developing practical and cost-effective adsorbents with satisfactory mercury (Hg) remediation capability is indispensable for aquatic environment safety and public health. Herein, a recyclable hierarchical MoS 2 /Fe 3 O 4 nanocomposite (by in-situ growth of MoS 2 nanosheets on the surface of Fe 3 O 4 nanospheres) is presented for the selective removal of Hg(II) from aquatic samples. It exhibited high adsorption capacity (∼1923.5 mg g  -1 ), fast kinetics (k 2 ∼ 0.56 mg g  -1 min -1 ), broad working pH range (2-11), excellent selectivity (K d > 1.0 × 10 7  mL g  -1 ), and great reusability (removal efficiency > 90% after 20 cycles). In particular, removal efficiencies of up to ∼97% for different Hg(II) concentrations (10-1000 μg L  -1 ) in natural water and industrial effluents confirmed the practicability of MoS 2 /Fe 3 O 4 . The possible mechanism for effective Hg(II) removal was discussed by a series of characterization analyses, which was attributed to the alteration of the MoS 2 structure and the surface coordination of Hg-S. The accessibility of surface sulfur sites and the diffusion of Hg(II) in the solid-liquid system were enhanced due to the advantage of the expanded interlayer spacing (0.96 nm) and the hierarchical structure. This study suggests that MoS 2 /Fe 3 O 4 is a promising material for Hg(II) removal in actual scenarios and provides a feasible approach by rationally constructing hierarchical structures to promote the practical applications of MoS 2 in sustainable water treatments., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Understanding of how mercury species cause cellular impairments at the molecular level is critical for explaining the detrimental effects of mercury exposure on the human body. Previous studies have reported that inorganic and organic mercury compounds can induce apoptosis and necrosis in a variety of cell types, but more recent advances reveal that mercuric mercury (Hg2+) and methylmercury (CH3Hg+) may result in ferroptosis, a distinct form of programmed cell death. However, it is still unclear which protein targets are responsible for ferroptosis induced by Hg2+ and CH3Hg+. In this study, human embryonic kidney 293T cells were used to investigate how Hg2+ and CH3Hg+ trigger ferroptosis, given their nephrotoxicity. Our results demonstrate that glutathione peroxidase 4 (GPx4) plays a key role in lipid peroxidation and ferroptosis in renal cells induced by Hg2+ and CH3Hg+. The expression of GPx4, the only lipid repair enzyme in mammal cells, was downregulated in response to Hg2+ and CH3Hg+ stress. More importantly, the activity of GPx4 could be markedly inhibited by CH3Hg+, owing to the direct binding of the selenol group (-SeH) in GPx4 to CH3Hg+. Selenite supplementation was demonstrated to enhance the expression and activity of GPx4 in renal cells, and consequently relieve the cytotoxicity of CH3Hg+, suggesting that GPx4 is a crucial modulator implicated in the Hg-Se antagonism. These findings highlight the importance of GPx4 in mercury-induced ferroptosis, and provide an alternative explanation for how Hg2+ and CH3Hg+ induce cell death., (© The Author(s) 2023. Published by Oxford University Press.)

Mercury sulfide nanoparticles (HgS NP ), as natural metal-containing nanoparticles, are the dominant Hg species in anoxic zones. Although the microbial Hg methylation of HgS NP has been previously reported, the importance of this process in Hg methylation has yet to be clarified due to the lack of knowledge on the internalization and transformation of HgS NP . Here, we investigated the internalization and transformation of HgS NP in microbial methylator Geobacter sulfurreducens PCA through total Hg analysis and different Hg species quantification in medium and cytoplasm. We found that the microbial uptake of HgS NP , via a passive diffusion pathway, was significantly higher than that of the Hg 2+ -dissolved organic matter (Hg 2+ -DOM) complex. Internalized HgS NP were dissolved to Hg 2+ in cytoplasm with a maximal dissolution of 41%, suggesting a "Trojan horse" mechanism. The intracellular Hg 2+ from HgS NP exposure at the initial stage (8 h) was higher than that in Hg 2+ -DOM group, which led to higher methylation of HgS NP . Furthermore, no differences in methylmercury (MeHg) production from HgS NP were observed between the hgcAB gene knockout (Δ hgcAB ) and wild-type strains, suggesting that HgS NP methylation may occur through HgcAB-independent pathways. Considering the possibility of a broad range of hgcAB -lacking microbes serving as methylators for HgS NP and the ubiquity of HgS NP in anoxic environments, this study highlights the importance of HgS NP internalization and methylation in MeHg production and demonstrates the necessity of understanding the assimilation and transformation of nutrient and toxic metal nanoparticles in general.

Sediment is the primary hotspot for microbial production of toxic and bio-accumulative methylmercury (MeHg). Common remediation strategies such as sediment dredging and capping can be too expensive and cannot degrade MeHg efficiently. Here, we constructed an Escherichia coli strain overexpressing merB gene (DH5α J23106) and assessed the effectiveness of this recombinant strain in degradation of MeHg in culture medium and sediment. DH5α J23106 can efficiently degrade MeHg (with initial concentration from 0.01 to 50 ng/mL) to more than 81.6% in a culture medium under anoxic and oxic conditions. Enriched isotope addition ( 199 HgCl 2 ) revealed that this recombinant strain can degrade 78.6% of newly produced Me 199 Hg in actual sediment, however the biodegradation decreased to 36.3% for intrinsic MeHg. Degradation of spiked MeHg after aging in anoxic and oxic sediments further demonstrated DH5α J23106 can efficiently degrade newly produced MeHg and the degradation decreased with aging significantly, especially for oxic sediment. Eight sediments were further assessed for the biodegradation of aged MeHg by DH5α J23106 under oxic conditions, with degradation ratios ranging from 9.0% to 66.9%. When combined with (NH 4 ) 2 S 2 O 3 leaching, the degradation of MeHg increased by 15.8-38.8% in on-site and off-site modes through enhanced MeHg bioavailability in some of these sediments. Thus, this recombinant strain DH5α J23106 can degrade MeHg efficiently and have the potential for remediating bioavailable MeHg in contaminated sediments., Competing Interests: Declaration of Competing Interest The authors declare that they have no knowing competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Particle-bound mercury (Hg P ), ubiquitously present in aquatic environments, can be methylated into highly toxic methylmercury, but it remains challenging to assess its bioavailability. In this study, we developed an Escherichia coli -based whole-cell biosensor to probe the microbial uptake of inorganic Hg(II) and assess the bioavailability of Hg P sorbed on natural and model particles. This biosensor can quantitatively distinguish the contribution of dissolved Hg(II) and Hg P to intracellular Hg. Results showed that the microbial uptake of Hg P was ubiquitous in the environment, as evidenced by the bioavailability of sorbed-Hg(II) onto particulate matter and model particles (Fe 2 O 3 , Fe 3 O 4 , Al 2 O 3 , and SiO 2 ). In both oxic and anoxic environments, Hg P was an important Hg(II) source for microbial uptake, with enhanced bioavailability under anoxic conditions. The composition of particles significantly affected the microbial uptake of Hg P , with higher bioavailability being observed for Fe 2 O 3 and lower for Al 2 O 3 particles. The bioavailability of Hg P varied also with the size of particles. In addition, coating with humic substances and model organic compound (cysteine) on Fe 2 O 3 particles decreased the bioavailability of Hg P . Overall, our findings highlight the role of Hg P in Hg biogeochemical cycling and shed light on the enhanced Hg-methylation in settling particles and sediments in aquatic environments.

Natural mercury-containing nanoparticles (Hg-NPs) have been found in the environment, but the information for Hg-NPs in organisms was still limited. Clarifying the unique roles of Hg-NPs in organisms is crucial to fully understand the health risks of Hg. Herein, liver and muscle tissues of cetaceans were collected to identify the presence and characteristics of Hg-NPs. We found that methylmercury (MeHg) was the dominant species of Hg in muscles, while inorganic Hg (IHg) accounted for 84.4-99.0% (average 94.0%) of Hg in livers. By using transmission electron microscopy (TEM), size exclusion chromatography coupled with inductively coupled plasma mass spectrometry (SEC-ICPMS) and single particle ICPMS (sp-ICPMS), large amounts (9-161 μg/g) of Hg-NPs in livers and small amounts (0.1-0.4 μg/g) in muscles were observed, indicating that Hg-NPs was an important form of Hg in livers. Both small sized (5-40 nm) and large sized (>100 nm) Hg-NPs were identified, which were mainly complexed with selenium (Se) and sulfur (S) as well as a few cadmium (Cd), lead (Pb) and silver (Ag). This study provided direct evidence of Hg-NPs in marine mammals as well as their chemical form and size distribution, which are helpful for further understanding the biogeochemical cycle and health risk of Hg., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Deposition of atmospheric mercury (Hg) is the most important Hg source on the high-altitude Himalayas and Tibetan Plateau. Herein, total gaseous Hg (TGM) at an urban and a forest site on the Tibetan Plateau was collected respectively from May 2017 to October 2018, and isotopic compositions were measured to clarify the influences of landforms and monsoons on the transboundary transport of atmospheric Hg to the Tibetan Plateau. The transboundary transported anthropogenic emissions mainly originated over Indo-Gangetic Plain and carried over the Himalayas by convective storms and mid-tropospheric circulation, contributing over 50% to the TGM at the Lhasa urban site, based on the binary mixing model of isotopes. In contrast, during the transport of TGM from South Asia with low altitude, the uptake by evergreen forest in Yarlung Zangbo Grand Canyon largely decreased the TGM level and shifted isotopic compositions in TGM at the Nyingchi forest site, which are located at the high-altitude end of the canyon. Our results provided direct evidence from Hg isotopes to reveal the distinct patterns of transboundary transport to the Tibetan Plateau shaped by landforms and climates, which is critical to fully understand the biogeochemical cycling of Hg in the high-altitude regions.

Redox transformation of mercury (Hg) is critical for Hg exchange at the air-sea interface and it can also affect the methylation of Hg in marine environments. However, the contributions of microalgae and aerobic bacteria in oxic seawater to Hg 2+ reduction are largely unknown. Here, we studied the reduction of Hg 2+ mediated by microalgae and aerobic bacteria in surface marine water and microalgae cultures under dark and sunlight conditions. The comparable reduction rates of Hg 2+ with and without light suggest that dark reduction by biological processes is as important as photochemical reduction in the tested surface marine water and microalgae cultures. The contributions of microalgae, associated free-living aerobic bacteria, and extracellular substances to dark reduction were distinguished and quantified in 7 model microalgae cultures, demonstrating that the associated aerobic bacteria are directly involved in dark Hg 2+ reduction. The aerobic bacteria in the microalgae cultures were isolated and a rapid dark reduction of Hg 2+ followed by a decrease of Hg 0 was observed. The reduction of Hg 2+ and re-oxidation of Hg 0 were demonstrated in aerobic bacteria Alteromonas spp. using double isotope tracing ( 199 Hg 2+ and 201 Hg 0 ). These findings highlight the importance of algae-associated aerobic bacteria in Hg transformation in oxic marine water.

Blood mercury reflects the amount available from tissues, which is an indication of the exposure level. Here we confirm that Hg 2+ caused hemolytic effects at high concentrations; while at light concentrations, most of the ions were bound to human serum albumin (HSA). The binding mechanism of Hg 2+ to HSA has been investigated, which indicated that the presence of Hg 2+ significantly perturbed the structure of HSA and quenched the fluorescence of protein in a hybrid dynamic and static mode. Hg 2+ was preferably bound to cysteine and cystine, where the R‒S‒S‒R structure is responsible for maintaining the protein's structure by stabilizing the α-helical bundles. The metal-protein interaction mitigated the cellular toxicity as concealed by A498 cell lines. The fundamental and comprehensive data in this work is beneficial to elucidating and understanding the identification and binding mechanisms of heavy metals with proteins, as well as possible risks on human beings and the environment., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Clarifying the sources and fates of atmospheric mercury (Hg) in the Antarctic is crucial to understand the global Hg circulation and its impacts on the fragile ecosystem of the Antarctic. Herein, the annual variations in the isotopic compositions of total gaseous Hg (TGM), with 5-22 days of sampling duration for each sample, were presented for the first time to provide isotopic evidence of the sources and environmental processes of gaseous Hg around the Chinese Great Wall Station (GWS) in the western Antarctic. Different from the Arctic tundra and lower latitude areas in the northern hemisphere, positive δ 202 Hg (0.58 ± 0.21‰, mean ± 1SD) and negative Δ 199 Hg (-0.30 ± 0.10‰, mean ± 1SD) in TGM at the GWS indicated little impact from the vegetation-air exchange in the Antarctic. Correlations among TGM Δ 199 Hg, air temperature, and ozone concentrations suggested that enhanced katabatic wind that transported inland air masses to the continental margin elevated TGM Δ 199 Hg in the austral winter, while the surrounding marine surface emissions controlled by sea-ice dynamics lowered TGM Δ 199 Hg in the austral summer. The oxidation of Hg(0) might elevate Δ 199 Hg in TGM during atmospheric Hg depletion events but have little impact on the seasonal variations of atmospheric Hg isotopes. The presented atmospheric Hg isotopes were essential to identify the transport and transformation of atmospheric Hg and further understand Hg cycling in the Antarctic.

Fish consumption is one of the major ways through which humans receive exposure to mercury (Hg). The existing forms of Hg in food, particularly Hg bound to proteins, may affect the absorption of Hg by humans and subsequently its potentially toxic effects. However, the knowledge regarding Hg-binding proteins in edible fish muscle is scarce. In the present study, salmon and tuna fish muscles, collected from seven different regions and countries, were analyzed using metallomics- and proteomics-based techniques. The concentration of Hg in sashimi samples ranged from 4.4 to 317.4 ng/g. Size exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometer (ICP-MS) showed that beta-actin was a novel Hg-binding protein from the fish muscles, and this protein could also bind bismuth (Bi), silver (Ag), and copper (Cu). Hg bound to beta-actin accounted for approximately 30.2-37.6% of the total Hg in the tuna muscles and was significantly correlated to total Hg in the fish muscles (r = 0.98, p < 0.01) and in the fraction of soluble proteins (r = 0.94, p < 0.01). These findings suggest that proteins act as the main Hg accumulation sites in edible fish; thus, increasing human exposure to Hg following gastrointestinal digestion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

As a kind of unicellular eukaryotic protozoa, Tetrahymena is located at the bottom of the aquatic food webs and plays an essential role in the bioaccumulation of mercury (Hg). To track Hg in individual Tetrahymena , a capillary single-cell inductively coupled plasma mass spectrometry (ICPMS) online system was developed. The experimental and instrumental conditions were optimized to ensure the signal detected was the Hg uptake in individual Tetrahymena . Moreover, a quantitative method was established and validated by detecting Hg 2+ standard solutions. The limit of quantity was calculated to be approximately 3.8 × 10 -15 g Hg/cell, and the detection limit for Hg 2+ exposure of Tetrahymena was 0.05 μg/L. By using the proposed method, we found the peak became wider with increasing of exposure concentrations, indicating the accumulated Hg by different Tetrahymena varied greatly, and the difference was more significant at higher exposure concentration. This novel method has the advantages of high sensitivity and real-time detection in individual Tetrahymena , and it could be widely used for further tracking the accumulation of mercury and other metals at the single cell level.

To trace the circulation history of aquatic bioavailable Hg in the Antarctic, the species and isotopic compositions of Hg in sediment, Archaeogastropoda (Agas), Neogastropoda (Ngas), and fish collected from King George Island were studied in detail. Positive mass independent fractionation (MIF) was observed and positively correlated with the percentages of methylmercury (MeHg%) in Agas and Ngas, suggesting an effect of MeHg accumulation during trophic transfer on MIF signatures. However, both the ratios of Δ 199 Hg/δ 202 Hg and Δ 199 Hg/Δ 201 Hg indicated different circulation histories of Hg in Agas, Ngas, and fish. The microbial methylation in sediment was the primary source of MeHg in Agas and Ngas (Δ 199 Hg/δ 202 Hg ∼0, Δ 199 Hg/Δ 201 Hg ∼1.00). In contrast, the MeHg in fish (Δ 199 Hg/δ 202 Hg = 0.55 ± 0.06, Δ 199 Hg/Δ 201 Hg = 1.19 ± 0.17) came from the combined sources of residual MeHg which had sunk from the surface water and microbial-methylated MeHg in sediments, and the bioavailable Hg in the sediments contributed to approximately 44% of the total Hg in fish. Subsequently, the Δ 199 Hg values of bioavailable MeHg and IHg in sediments were quantitatively calculated, which provided key end-member information for future source apportionment in the Antarctic and other pelagic regions. It was also found that the Hg accumulated in Agas and Ngas had no history of MeHg photo-degradation, indicating that the methylated Hg in benthic zones suffered little photo-degradation and thus presented high bioavailability and environmental risk., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Mercury-binding protein profiles in rat plasma at different levels of mercury exposure in vitro and in vivo were systematically investigated using column gel electrophoresis coupled with inductively coupled plasma-mass spectrometry. The current finding provided various protein candidates that may play critical roles in mercury binding and transporting in plasma.

Metal-binding proteins play important roles in biological functions of metals. However, only very limited mercury-binding proteins with high abundance were characterized in cells or organisms. Characterization of mercury-binding proteins in proteome-wide is important for elucidating mechanisms of mercury toxicity comprehensively. In this study, a method based on immobilized mercury ion affinity chromatography was developed for identification of putative mercury-binding proteins. The method was then successfully applied to profile mercury-binding proteins in human neuroblastoma SK-N-SH cells. In total, 38 proteins were identified as mercury-binding proteins, in which most of them were uncharacterized to associate with mercury in cells. The identified mercury-binding proteins did not show obvious relevance to protein abundance and were mainly involved in protein processing in endoplasmic reticulum, protein folding, and cytoskeleton organization. The newly built metalloproteomic approach provided valuable information on the possible molecular mechanisms and protein candidates for mercury transport and toxicity., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The oceans, serving as some of the most extensive reservoirs of mercury (Hg) on Earth, play an essential role in the global Hg biogeochemical circulation, as a sink for atmospheric deposits and surface runoff while simultaneously emitting Hg to the atmosphere. Clarifying the mechanisms during cycling of Hg in marine ecosystems is a crucial segment in elucidating global Hg behavior and assessing its risks to wildlife and humans. The stable Hg isotope technique has emerged as a powerful tool for identifying potential sources and certain processes of Hg. Herein, the research advances in marine Hg biogeochemical cycling were reviewed from an isotopic tracing perspective, including sources of marine Hg, isotopic fingerprints across various marine media, and applications of Hg isotopes in pathways, transport, and transformation mechanisms associated with marine environments. The knowledge gaps and challenges were further discussed in the development of ultratrace level and species-specific isotopic analytical methods, the isotope fractionation mechanisms in reactions and processes, and the integration of multiple approaches and cross disciplines. These future studies would advance our understanding of Hg behavior in oceanic environments, its authentic function, and interactions with other ecosystems in the global Hg cycle, and evaluate its response to environmental changes. [ABSTRACT FROM AUTHOR]

Characterizing natural mercury (Hg) isotopic compositions in geological and environmental matrices provides a better understanding of the biogeochemical cycles of Hg. However, preconcentration is indispensable for the determination of samples with low Hg contents (e.g., ng L−1 levels), which is time-consuming and requires a lot of manpower and materials. Herein, a sensitive method for the online determination of Hg isotopic compositions by automated purge & trap (P&T) coupled with multicollector inductively coupled plasma-mass spectrometry (MC-ICPMS) was developed. Rapid Hg isotopic analysis was realized in 15 min (single sample-standard bracketing procedure) with a sample consumption of 25 mL per measurement. The optimization of the P&T module and MC-ICPMS was conducted to obtain a high sensitivity for Hg isotopic determination (202Hg max intensity over 10 V for 40 ng L−1 Hg solution). Strategic signal acquisition and data treatment using the linear regression slope without time-lag correction were applied. Accurate isotopic compositions in a referenced standard solution at 8 ng L−1 (NIST 3177, δ202Hg −0.55 ± 0.29‰, Δ199Hg −0.02 ± 0.23‰, Δ200Hg 0.01 ± 0.19‰, Δ201Hg −0.02 ± 0.16‰, 2SD, and N = 31) and certified reference materials (CRMs) at 40 ng L−1 were obtained (NRC DORM-4, δ202Hg 0.45 ± 0.14‰, Δ199Hg 1.73 ± 0.16‰, Δ200Hg 0.06 ± 0.08‰, Δ201Hg 1.42 ± 0.13‰, 2SD, N = 13; NIST 1632e, δ202Hg −2.22 ± 0.19‰, Δ199Hg −0.02 ± 0.07‰, Δ200Hg 0.00 ± 0.07‰, Δ201Hg −0.01 ± 0.09‰, 2SD, and N = 20). The measuring concentration of this proposed method has decreased from μg L−1 to ng L−1 levels compared to CV introduction. The sample size and analytical time are 2–3 orders of magnitude lower compared to offline preconcentration methods (several hours to process several to dozens of liters). This proposed method can be used for the analysis of Hg isotopic compositions in solution samples with low Hg concentrations including natural aquatic samples. [ABSTRACT FROM AUTHOR]

Dominant microorganisms and functional genes, including hgc A, hgc B, mer A, and mer B, have been identified to be responsible for mercury (Hg) methylation or methylmercury (MeHg) demethylation. However, their in situ correlation with MeHg levels and the processes of Hg methylation and MeHg demethylation in coastal areas remains poorly understood. In this study, four functional genes related to Hg methylation and MeHg demethylation (hgc A, hgc B, mer A, and mer B) were all detected in the sediments of the Eastern China Coastal Seas (ECCSs) (representative coastal seas highly affected by human activities) using metagenomic approaches. Hgc A was identified to be the key gene controlling the in situ net production of MeHg in the ECCSs. Based on metagenomic analysis and incubation experiments, sulfate-reducing bacteria were identified as the dominant microorganisms controlling Hg methylation in the ECCSs. In addition, hgc A gene was positively correlated with the MeHg content and Hg methylation rates, highlighting the potential roles of Hg methylation genes and microorganisms influenced by sediment physicochemical properties in MeHg cycling in the ECCSs. These findings highlighted the necessity of conducting similar studies in other natural systems for elucidating the molecular mechanisms underlying MeHg production in aquatic environments. [Display omitted] • Hgc A, hgc B, mer A, and mer B genes are prevalent in the Eastern China Coastal Seas (ECCSs). • Hgc A abundance was significantly correlated with the net production rate of methylmercury in the ECCSs sediments. • Sulfate-reducing bacteria significantly contributed to Hg methylation in ECCSs sediments. [ABSTRACT FROM AUTHOR]

Trace levels of organic and inorganic lead and mercury species in the environment, including divalent lead (Pb2+), trimethyllead (TML), divalent mercury (Hg2+), monomethylmercury (MeHg), and ethylmercury (EtHg), are highly toxic to humans and ecology. It is of great importance for speciation of lead and mercury to evaluate the toxicity of lead and mercury and their biogeochemistry in the environment. However, simultaneous multi-elemental enrichment and speciation at trace level remains a challenge. There are few reports of simultaneous magnetic solid-phase extraction (MSPE) of organic and inorganic lead and mercury species at trace level in the real water. In this work, a novel core-shell magnetic hydrazine-linked covalent organic frameworks (Fe 3 O 4 @COF-TCH) was prepared for the first time by grafting hydrazine-linked COFs on the Fe 3 O 4 nanoparticles. Fe 3 O 4 @COF-TCH with abundant thione and imino groups has strong adsorption for lead and mercury species. Based on it, a simple and practical magnetic solid-phase extraction high-performance liquid chromatography-inductively coupled plasma mass spectrometry (MSPE-HPLC-ICP-MS) method was developed for extraction and determination of trace lead and mercury species, including Hg2+, MeHg, EtHg, Pb2+ and TML. The limits of detection (3δ) of the developed method were 0.08, 0.81, 0.90, 0.56 and 0.88 ng L−1 with the enrichment factors (EFs) of 384, 376, 379, 389 and 360-fold for Pb2+, TML, Hg2+, MeHg and EtHg, respectively. The high accuracy and reproducibility have been proved by the spiked recoveries (94.4–103 %) in real samples. The proposed method with simple operation and high sensitivity has been successfully applied to simultaneous speciation of lead and mercury at trace levels in the water samples with complicated matrices, including underground water, surface water, sea water. Meanwhile, it has the advantages of cost-saving, labor-saving and time-saving and is suitable for the investigation and risk assessment in water. The development of MSPE-HPLC-ICP-MS method provides ideas and guidance for the simultaneous multi-elemental enrichment and speciation. [Display omitted] • A core-shell magnetic hydrazine-linked COFs was prepared for the first time. • A MSPE-HPLC-ICP-MS method was developed for simultaneous enrichment and speciation of organic and inorganic lead and mercury. • Figures of merit: LODs (0.08–0.90 ng L−1), Linearity ranges (0.26–1000 ng L−1), RSD (<4.5 %). • The proposed method has excellent anti-interference ability. • The proposed method can be applied in the samples with complex matrix, such as seawater, surface water. [ABSTRACT FROM AUTHOR]

Coal combustion is an important source of anthropogenic mercury (Hg) emissions. Air pollution control devices (APCDs) are widely used in coal-fired power plants (CFPPs) to reduce pollutant emissions including Hg. To gain insight into the Hg isotopic fractionation produced by APCDs, the Hg isotopic compositions of feed coal (FC) samples and combustion byproducts from 7 CFPP utility boilers in Hebei Province of China were studied. Significant mass-dependent fractionation (MDF) was observed in combustion byproducts when comparing with FC samples, while mass-independent fractionation (MIF) was not identified. Compared to FC samples, no significant difference in bottom ash (BA, δ202Hg BA-FC = 0.08 ± 0.16‰, 1SD, n = 3) samples while light isotopes were enriched in fly ash (FA, δ202Hg FA-FC = −0.38 ± 0.75‰, 1SD, n = 7) samples. Boilers lacking of a selective catalytic reducer (SCR) unit produced gypsum (GY) samples with negative MDF signatures compared to FC samples (δ202Hg GY-FC, no SCR = −0.22 ± 0.10‰, 1SD, n = 3). In contrast, boilers equipped with a SCR unit produced GY samples with higher MDF signatures (δ202Hg GY-FC, SCR = 0.54 ± 0.40‰, 1SD, n = 3), probably as a result of the oxidation of Hg0 in the SCR unit. Calculated isotopic signatures of gaseous Hg in the stack emission (SE, δ202Hg SE-FC = 0.03 ± 0.20‰, 1SD, n = 7) had no significant difference from that of FC samples. The results suggested distinct isotopic compositions should be fully considered during tracing Hg pollution via Hg isotopic signatures, especially when solid produced by CFPPs were involved. Unlabelled Image • Hg isotopic mass dependent fractionation was found in air pollution control devices. • Selective catalytic reducer shifted Hg isotopic compositions in gypsums. • Regional Hg isotopic fingerprints in solid wastes and flue gas were calculated. [ABSTRACT FROM AUTHOR]