New Ln-MOFs based on mixed organic ligands: synthesis, structure and efficient luminescence sensing of the Hg2+ ions in aqueous solutions

In view of Hg²⁺ ion sensing by luminescence, a series of new, phenanthroline-decorated 3D lanthanide metal organic frameworks (Ln-MOFs) valorising an original combination of four different lanthanides and two organic ligands, i.e. thiobis(4-methylene-benzoic acid) (H₂tmba) and 1,10-phenanthroline (phen), have been successfully synthesized, namely {[Ln₄(tmba)₆(phen)₄]·m(H₂O)(phen)}_n [Ln = Ce, m = 3 (1); Pr, m = 1 (2); Eu, m = 3 (3); and Tb, m = 3 (4)]. Compounds 1-4 were characterised by single-crystal X-ray diffraction, elemental and thermogravimetric analyses, and powder X-ray diffraction. The luminescence properties of complexes 3 and 4 were thoroughly investigated. It is herein proved that compound 3 sensitively and selectively acts as an excellent luminescent probe for the detection of Hg²⁺ ions in waters, with a detection limit of 1.00 μM. As additional assets, 3 displays superb stability over a wide pH range (3-12) of the aqueous media, as well as convenient recycling after completion of the detection experiments. The rationale for the observed luminescence quenching effect of mercury might be a strong interaction arising between Hg²⁺ ions and the carboxylate oxygen atoms of the tmba^2- ligand. The results open new perspectives for applications in environmental remediation.

A review of constraints and solutions for collecting raptor samples and contextual data for a European Raptor Biomonitoring Facility

The COST Action 'European Raptor Biomonitoring Facility' (ERBFacility) aims to develop pan-European raptor biomonitoring in support of better chemicals management in Europe, using raptors as sentinel species. This presents a significant challenge involving a range of constraints that must be identified and addressed. The aims of this study were to: (1) carry out a comprehensive review of the constraints that may limit the gathering in the field of raptor samples and contextual data, and assess their relative importance across Europe; and (2) identify and discuss possible solutions to the key constraints that were identified. We applied a participatory approach to identify constraints and to discuss feasible solutions. Thirty-one constraints were identified, which were divided into four categories: legal, methodological, spatial coverage, and skills constraints. To assess the importance of the constraints and their possible solutions, we collected information through scientific workshops and by distributing a questionnaire to stakeholders in all the countries involved in ERBFacility. We obtained 74 answers to the questionnaire, from 24 of the 39 COST participating countries. The most important constraints identified were related to the collection of complex contextual data about sources of contamination, and the low number of existing raptor population national/regional monitoring schemes and ecological studies that could provide raptor samples. Legal constraints, such as permits to allow the collection of invasive samples, and skills constraints, such as the lack of expertise to practice necropsies, were also highlighted. Here, we present solutions for all the constraints identified, thus suggesting the feasibility of establishing a long-term European Raptor Sampling Programme as a key element of the planned European Raptor Biomonitoring Facility.

The silver linings of mercury: Reconsideration of its impacts on living organisms from a multi-timescale perspective

Research on mercury (Hg), a naturally occurring element in Earth's lithosphere, has been extremely hot in the past few decades due to the outbreak of a series of disastrous poisoning incidents. However, such studies might provide us a biased view towards Hg if no thorough review about its long-term effects on living organisms from a multi-timescale perspective was performed. Hg might have played a mysterious role in critical intervals (e.g., mass extinction and oceanic anoxia events) in several geologic periods due to the elevated Hg levels induced by volcanism whereas it has long been used for various purposes in human history. Therefore, it is necessary to go through previous studies and historical records of different timescales (10⁰ to 10⁶ yr). In this work, we conducted a thorough review of Hg knowledge at three different timescales, i.e., geologic periods (10⁶ yr), human history (10³ yr), and contemporary history (10⁰ yr), summarizing recent advances and indicated potential research gaps. By doing so, we demonstrated that it is possible to achieve safe and sustainable Hg applications despite the current Hg crisis. However, such silver linings depend on a better understanding of ecosystem dynamics. Besides, considering the possible dire consequences of erupted Hg levels as suggested in geological periods, swift actions to mitigate the impacts of anthropogenic activities on the Hg cycle will be another key point. Overall, this review presented a unique perspective of Hg combining different timescales, shedding light on the importance of a better understanding of the global ecosystem as a whole and maintaining the sustainability of planet Earth in the future.

Mercury stable isotopes constrain atmospheric sources to the ocean

Human exposure to toxic mercury (Hg) is dominated by the consumption of seafood^1,2. Earth system models suggest that Hg in marine ecosystems is supplied by atmospheric wet and dry Hg(II) deposition, with a three times smaller contribution from gaseous Hg(0) uptake^3,4. Observations of marine Hg(II) deposition and Hg(0) gas exchange are sparse, however⁵, leaving the suggested importance of Hg(II) deposition⁶ ill-constrained. Here we present the first Hg stable isotope measurements of total Hg (tHg) in surface and deep Atlantic and Mediterranean seawater and use them to quantify atmospheric Hg deposition pathways. We observe overall similar tHg isotope compositions, with median Δ²⁰⁰Hg signatures of 0.02‰, lying in between atmospheric Hg(0) and Hg(II) deposition end-members. We use a Δ²⁰⁰Hg isotope mass balance to estimate that seawater tHg can be explained by the mixing of 42% (median; interquartile range, 24-50%) atmospheric Hg(II) gross deposition and 58% (50-76%) Hg(0) gross uptake. We measure and compile additional, global marine Hg isotope data including particulate Hg, sediments and biota and observe a latitudinal Δ²⁰⁰Hg gradient that indicates larger ocean Hg(0) uptake at high latitudes. Our findings suggest that global atmospheric Hg(0) uptake by the oceans is equal to Hg(II) deposition, which has implications for our understanding of atmospheric Hg dispersal and marine ecosystem recovery.

Mercury in European topsoils: Anthropogenic sources, stocks and fluxes

Mercury (Hg) is one of the most dangerous pollutants worldwide. In the European Union (EU), we recently estimated the Hg distribution in topsoil using 21,591 samples and a series of geo-physical inputs. In this manuscript, we investigate the impact of mining activities, chrol-alkali industries and other diffuse pollution sources as primary anthropogenic sources of Hg hotspots in the EU. Based on Hg measured soil samples, we modelled the Hg pool in EU topsoils, which totals about 44.8 Gg, with an average density of 103 g ha-1. As a following step, we coupled the estimated Hg stocks in topsoil with the pan-European assessment of soil loss due to water erosion and sediment distribution. In the European Union and UK, we estimated that about 43 Mg Hg yr-1 are displaced by water erosion and c. a. 6 Mg Hg yr-1 are transferred with sediments to river basins and eventually released to coastal Oceans. The Mediterranean Sea receives almost half (2.94 Mg yr-1) of the Hg fluxes to coastal oceans and it records the highest quantity of Hg sediments. This is the result of elevated soil Hg concentration and high erosion rates in the catchments draining into the Mediterranean Sea. This work contributes to new knowledge in support of the policy development in the EU on the Zero Pollution Action Plan and the Sustainable Development Goal (SDGs) 3.9 and 14.1, which both have as an objective to reduce soil pollution by 2030.

Mercury Levels in Feathers of Penguins from the Antarctic Peninsula Area: Geographical and Inter-Specific Differences

Polar regions, symbols of wilderness, have been identified as potential sinks of mercury coming from natural and anthropogenic sources at lower latitudes. Changes in ice coverage currently occurring in some areas such as the Antarctic Peninsula could enhance these phenomena and their impacts on local biota. As long-lived species at the top of food chains, seabirds are particularly sensitive to this highly toxic metal with the capacity to be biomagnified. Specifically, their feathers can be useful for Hg monitoring since they mainly accumulate its most toxic and persistent form, methyl-Hg. To that end, feathers of gentoo (Pygoscelis papua), chinstrap (P. antarcticus), and Adélie penguins (P. adeliae) (n = 108) were collected by passive sampling in seven different locations throughout the Antarctic Peninsula area and analyzed by ICP-MS after microwave-digestion. More than 93% of the samples showed detectable Hg levels (range: 6.3–12,529.8 ng g⁻¹ dry weight), and the highest ones were found in the feathers of chinstrap penguins from King George Island. Hg bioconcentration and biomagnification seem to be occurring in the Antarctic food web, giving rise to high but non-toxic Hg levels in penguins, similar to those previously found in Arctic seabirds.

Gaseous Elemental Mercury Exchange Fluxes over Air-Soil Interfaces in the Degraded Grasslands of Northeastern China

Mercury (Hg) is a global pollutant that may potentially have serious impacts on human health and ecologies. The gaseous elemental mercury (GEM) exchanges between terrestrial surfaces and the atmosphere play important roles in the global Hg cycle. This study investigated GEM exchange fluxes over two land cover types (including Artemisia anethifolia coverage and removal and bare soil) using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The daily mean ambient levels of GEM and the total mercury concentrations of the soil (TSM) were determined to be 12.4 ± 3.6 to 16.4 ± 5.6 ng·m-3 and 32.8 to 36.2 ng·g-1, respectively, for all the measurements from May to September. The GEM exchange fluxes (ng·m-2·h-1) during the five-month period for the three treatments included the net emissions from the soil to the atmosphere (mean 5.4 to 7.1; range of -27.0 to 47.3), which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months (p < 0.05). In addition, it was determined that the Hg fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air relative humidity and soil moisture under all the conditions (p < 0.05). Overall, the results obtained in this study demonstrated that the grassland soil served as both a source and a sink for atmospheric Hg, depending on the season and meteorological factors. Furthermore, the plants played an important inhibiting role in the Hg exchanges between the soil and the atmosphere.

Biotransport of mercury and human methylmercury exposure through crabs in China - A life cycle-based analysis

Exposure to methylmercury (MeHg) has various toxic effects on humans. The evaluation of human MeHg exposure has previously focused on fish consumption. However, in this study, we found that MeHg levels in domestic crabs in China were also relatively high (range: 50-1400 ng/g, dry weight). The high MeHg levels in crabs and their high consumption do not match the risk assessment of MeHg, indicating an underestimated exposure risk, especially in MeHg-sensitive groups such as pregnant women. The annual crab MeHg content output in China was estimated to be 30 ± 27 kg. A total of 6.8% of the country's land area contributes 71% of the MeHg output. However, 66% of the output is redistributed to non-crab-producing regions via interregional food trade, posing risks to the population on a national scale. The daily intake of MeHg from crabs could easily exceed the reference dose (0.1 µg/kg of body weight per day) suggested by the United States Environmental Protection Agency with consideration of coexposure from fish, rice, and other food sources. We suggest that future MeHg exposure analysis includes crab MeHg as a coexposure pathway to estimate the dietary MeHg limit accurately and emphasize the influence of interregional food trade on MeHg exposure.

Spherical-shaped CuS modified carbon nitride nanosheet for efficient capture of elemental mercury from flue gas at low temperature

Mercury (Hg⁰) pollution poses a huge threat to human health and the environment due to its high toxicity, long persistence and bioaccumulation in the environment. Most of the traditional Hg⁰ adsorbents have a low reaction rate, high operating cost, especially poor resistance to SO₂, which limited their practical application. In this work, nanosheet g-C₃N₄ was used as the support and modified by CuS to capture flue gas mercury. Take advantage of the large specific surface area of g-C₃N₄ to increase the BET of the composite and decrease the use of CuS. The effects of CuS loading, reaction temperature, and common components in the coal-fired flue gas on the mercury removal performance were studied respectively. The experimental outcomes showed that the 10CuS/g-C₃N₄ (10CuS/CN) reaches as high as almost 100% Hg⁰ removal efficiency under the temperature of 40-120 ℃. Meanwhile the common components like SO₂, NO, HCl and H₂O have no obvious inhibition effects on Hg⁰ removal efficiency of the 10CuS/CN adsorbent. S_x^2- and Cu²⁺ as the primary bonding sites shows a synergy effect on Hg⁰ removal. 10CuS/CN is a promising material for Hg⁰ removal under various flue gas conditions, which is expected to be a substitute for traditional adsorbents.

Real-time in vitro monitoring of the subcellular toxicity of inorganic Hg and methylmercury in zebrafish cells

Mercury (Hg) is a prominent environmental contaminant and can cause various subcellular effects. Elucidating the different subcellular toxicities of inorganic Hg (Hg²⁺) and methylmercury (MeHg) is critical for understanding their overall cytotoxicity. In this study, we employed aggregation-induced emission (AIE) probes to investigate the toxicity of Hg at the subcellular level using an aquatic embryonic zebrafish fibroblast cell line ZF4 as a model. The dynamic monitoring of lysosomal pH and the mapping of pH distribution during Hg²⁺ or MeHg exposure were successfully realized for the first time. We found that both Hg²⁺ and MeHg decreased the mean lysosomal pH, but with contrasting effects and mechanisms. Hg²⁺ had a greater impact on lysosomal pH than MeHg at a similar intracellular concentration. In addition, Hg²⁺ in comparison to MeHg exposure led to an increased number of lysosomes, probably because of their different effects on autophagy. We further showed that MeHg (200 nM) exposure had an inverse effect on mitochondrial respiratory function. A high dose (1000 nM) of Hg²⁺ increased the amount of intracellular lipid droplets by 13%, indicating that lipid droplets may potentially play a role in Hg²⁺detoxification. Our study suggested that, compared with other parameters, lysosome pH was most sensitive to Hg²⁺ and MeHg. Therefore, lysosomal pH can be used as a potential biomarker to assess the cellular toxicity of Hg in vitro.

Evolution and Driving Mechanism of Ecological Security Pattern: A Case Study of Yangtze River Urban Agglomeration

Urbanization adversely affects the ecological environment and reduces the quality of life in China. In view of the current situation, this study aims to determine the dynamics of the ecological security pattern of urban agglomerations using the Yangtze River urban agglomeration (YRUA) as a case study. We used the pressure-state-response (PSR) framework to establish an ecological security assessment system, combined with the technique for order of preference by similarity to an ideal solution (TOPSIS) method and gray correlation method, to estimate a comprehensive ecological security index, and we analyzed its evolution trends and driving mechanisms. The results indicated that the distribution of the regional ecological security level had a linked effect and that industrial pollutants posed the greatest threat to ecological security. Moreover, the main factors affecting the YRUA were urbanization, ecopathology, economic development, population pressure, land pressure, and water resource pressure. For the protection of ecological security, it is necessary to establish an ecological security governance mechanism. Moreover, the study stresses changing the traditional sewage discharge model and establishing an ecologically safe market system. Integr Environ Assess Manag 2021;17:573-583. © 2020 SETAC.

Effects of mercury stress on methylmercury production in rice rhizosphere, methylmercury uptake in rice and physiological changes of leaves

Methylmercury (MeHg) in rice is presumed to be derived from MeHg formed in the soil, although it is still controversial. Moderate soil mercury (Hg) concentration can affect the diversity of soil microorganisms and may also impact the physiological changes and MeHg absorption of rice. In this study, the pot experiment was conducted to explore the effects of Hg concentration gradients (0, 0.3, 3, and 30 mg kg^-1) stress on Hg transformation in the rhizosphere, Hg translocation in rice, and physiological changes in rice leaves during the whole rice growing season. Moderate soil Hg concentration (3 mg kg^-1) greatly increased the MeHg/THg (1.69%) of rhizosphere, while 30 mg kg^-1 soil Hg concentration sharply reduced the MeHg/THg (0.29%) of rhizosphere. Highest MeHg/THg of the four groups all appeared at the blooming or filling stage. There was a significant positive correlation between Fe²⁺ in rhizosphere and MeHg/THg, but no significant correlation between SO₄^2- and MeHg/THg was observed. Although the 3 mg kg^-1 soil Hg concentration significantly enhanced MeHg concentrations in seeds, it considerably reduced the bioaccumulation factors of MeHg in roots, stalks, old leaves and young leaves. Soil Hg concentration of 30 mg kg^-1, to a certain extent, curtailed MeHg concentrations in seeds, while MeHg concentrations in the husk were significantly increased. Consistent with the result that there was no significant difference for THg concentrations in old and young leaves among the four Hg treatment groups, the content of chlorophyll, H₂O₂, malondialdehyde and antioxidant substances, and the activities of antioxidant enzyme in old and young leaves varied indistinctly among groups. MAIN FINDING: Moderate soil mercury concentration (3 mg kg^-1) could extremely enhance MeHg production in the rhizosphere soil and its accumulation in rice; MeHg production in the rhizosphere soil increased greatly at the blooming or filling stage, whereas little effect on antioxidant systems in leaves was observed.

Global distribution and environmental drivers of methylmercury production in sediments

Neurotoxic methylmercury (MeHg) in environments poses substantial risks to human health. Saturated sediments are basic sources of MeHg in food chains; however, distribution patterns and environmental drivers of MeHg at a global scale remain largely unexplored. Here, we characterized global patterns of MeHg distribution and environmental drivers of MeHg production based on 495 sediment samples across five typical ecosystems from the literature (1995-2018) and our own field survey. Our results showed the MeHg concentration ranged from 0.009 to 55.7 μg kg^-1 across the different ecosystems, and the highest MeHg concentration and Hg methylation potential were from the sediments of paddy and marine environments, respectively. Further, using combined analysis of random forest and structural equation modeling, we identified temperature and precipitation as important regulators of MeHg production after accounting for the well-known drivers including Hg availability and sediment geochemistry. More importantly, we found increased MeHg production in sediments with elevated mean annual Hg precipitation, and warmer temperature could also accelerate MeHg production by facilitating activities of microbial methylators. Together, this work advances our understanding of global MeHg distribution in sediments and environmental drivers, which are fundamental to the prediction and management of MeHg production and its potential health risk globally.

Mercury consumption and human health: Linking pollution and social risk perception in the southeastern United States

The study of the relationships between freshwater organisms, pollution and public awareness has been little researched. The public's perception of risk from pollution is a fundamental component in determining consumer behavior and promoting healthy habits. For instance, understanding how consumers perceive the risks associated with pollution can help with adoption of safe behaviors to reduce the health hazard associated with pollutant exposure. This study focused on the southeastern United States, a region predicted to be exposed to high mercury stress by increasing mercury deposition and methylation. First, we placed our study region in the world map of regions more prone to suffer from increasing mercury stress in a climate change scenario. Second, mercury levels in fish tissues was quantified by direct mercury analyzer (DMA). Third, we explored human fish consumption habits and risk social perception, including willingness to adapt fish consumption based on two future hypothetical scenarios of mercury stress. From a global perspective, our analysis demonstrates that the southern US is one of five world areas of greatest conservation concern for mercury stress. In this region, the average mono-methyl mercury concentration in fish tissues exceeded the limits considered safe for human consumption. Even though many in the local population were aware of the health hazards associated with fish consumption, only women of reproductive age were willing to adopt safe consumption habits. Altogether, these results show how bringing together field data, social perceptions, and consumption habits can help in designing an adaptive strategy to confront mercury pollution. Although our results are for the United States, other world regions prone to suffer increasing mercury stress have been identified and should be the focus of future studies and prescriptions.

Charge-distribution modulation of copper ferrite spinel-type catalysts for highly efficient Hg0 oxidation

Hg⁰ catalytic oxidation is an attractive approach to reduce mercury emissions from industrial activities. However, the rational design of highly active catalysts remains a significant challenge. Herein, the charge distribution modulation strategy was proposed to design novel catalysts: copper ferrite spinel-type catalysts were developed by introducing Cu²⁺ cations into octahedral sites to form electron-transfer environment. The synthesized catalysts with spinel-type stoichiometry showed superior catalytic performance, and achieved > 90 % Hg⁰ oxidation efficiency in a wide operation temperature window of 150-300 °C. The superior catalytic performance was closely associated with the mobile-electron environment of copper ferrite. Hg⁰ oxidation by HCl over copper ferrite followed the Eley-Rideal mechanism, in which physically adsorbed Hg⁰ reacted with active chlorine species. Density functional theory calculations revealed that octahedral Cu atom is the most active site of Hg⁰ adsorption on copper ferrite surface. Both direct oxidation pathway (Hg* → HgCl₂*) and HgCl-mediated oxidation pathway (Hg* → HgCl* → HgCl₂*) played important role in Hg⁰ oxidation over copper ferrite. HgCl₂* formation was identified as the rate-limiting step of Hg⁰ oxidation. This work would provide a new perspective for the development of admirable catalysts with outstanding Hg⁰ oxidation performance.

Porous BMTTPA-CS-GO nanocomposite for the efficient removal of heavy metal ions from aqueous solutions

In this study, a stable, cost-effective and environmentally friendly porous 2,5-bis(methylthio)terephthalaldehyde-chitosan-grafted graphene oxide (BMTTPA-CS-GO) nanocomposite was synthesized by covalently grafting BMTTPA-CS onto the surfaces of graphene oxide and used for removing heavy metal ions from polluted water. According to well-established Hg2+-thioether coordination chemistry, the newly designed covalently linked stable porous BMTTPA-CS-GO nanocomposite with thioether units on the pore walls greatly increases the adsorption capacity of Hg2+ and does not cause secondary pollution to the environment. The results of sorption experiments and inductively coupled plasma mass spectrometry measurements demonstrate that the maximum adsorption capacity of Hg2+ on BMTTPA-CS-GO at pH 7 is 306.8 mg g-1, indicating that BMTTPA-CS-GO has excellent adsorption performance for Hg2+. The experimental results show that this stable, environmentally friendly, cost-effective and excellent adsorption performance of BMTTPA-CS-GO makes it a potential nanocomposite for removing Hg2+ and other heavy metal ions from polluted water, and even drinking water. This study suggests that covalently linked crucial groups on the surface of carbon-based materials are essential for improving the adsorption capacity of adsorbents for heavy metal ions.

Rapid Increase in Cement-Related Mercury Emissions and Deposition in China during 2005-2015

The cement industry has become the largest mercury (Hg) emission source in China. Better understanding Hg emission and deposition characteristics and drivers of Hg emission changes can increase the awareness of related risks and support effective policy making. The results show that due to the substantial increase in the use of new suspension preheater and precalciner (NSP) technology in China, an approximate two-fold increase from 80.0 to 144.0 Mg year^-1 was observed for the cement-related Hg emissions during 2005-2015, which has resulted in a considerable increase in atmospheric deposition over terrestrial China from 37.9 to 75.9 Mg year^-1. Compared to the great majority of emission sectors, the same increase in Hg emissions from cement production can cause more deposition due to the large share of highly water-soluble divalent Hg in the sector. Each 1% increase in the share of divalent Hg can result in an increase of 0.37 Mg year^-1 in deposition over terrestrial China. Technical improvement and diversification of cement products are two major driving forces offsetting the economy-induced growth in cement-related Hg emissions during 2005-2015. Measures aimed at reducing the Hg emission intensity against the further increase in the use of NSP technology and avoiding overcapacity against the stimulation of real estate and increasing cement demands are urgently needed for the cement industry in China.

Direct Measurement of Aqueous Mercury(II): Combining DNA-Based Sensing with Diffusive Gradients in Thin Films

A highly specific DNA-functionalized hydrogel sensing layer was integrated with the diffusive gradients in thin films (DGT) technique for the direct determination of aqueous mercury(II). The DNA-functionalized layer in the DGT unit exhibited both high affinity (complexation constant K_c = 10^19.8 at 25 °C) and high binding capacity (9.5 mg Hg disk^-1) toward Hg²⁺. The diffusion coefficient for Hg²⁺ complexed with common inorganic ligands was an order of magnitude higher than that for Hg²⁺ complexed with natural dissolved organic matter: 9.0 × 10^-6 versus 9.8 × 10^-7 cm² s^-1 at 25 °C. The performance of the DNA-DGT sensor was further assessed under variable pH (3-10) and temperature (5-40 °C) conditions, as well as across a range of hydrochemically diverse artificial and natural freshwaters. The observed effects of the environmental and solution compositional variables on Hg²⁺ binding to the DNA in the sensing layer were successfully accounted for by equilibrium speciation calculations and temperature-corrected, multicomponent diffusion coefficients for aqueous Hg(II). The results therefore support the use of the DNA-DGT sensor as an alternative to traditional sampling and analysis methods for measuring aqueous Hg(II) concentrations down to the nanomolar level in freshwater environments.

Formalin-preserved zooplankton are not reliable for historical reconstructions of methylmercury bioaccumulation

Time-series measurements of methylmercury (MeHg) concentrations in short-lived planktic animals, such as copepods, could allow for an evaluation of mercury (Hg) inputs and transferability to organisms in marine environments. If reliable, MeHg measurements in formalin-preserved marine animals could offer insights into past environmental MeHg levels. In the present study, we examined whether the amount of MeHg changed over time in formalin-preserved copepods for two species, Acartia tonsa, and Temora longicornis. Over a 51 (A. tonsa) and 7 (T. longicornis) week incubation, we found significant changes in MeHg content in both copepods, while the timing of these changes differed between species. Furthermore, we investigated the mechanism behind these temporal changes through a separate incubation experiment of formalin spiked with two levels of organic matter (OM), and stable-isotope-enriched Hg tracers. We found that the methylation of an inorganic ¹⁹⁹Hg tracer was significantly higher in OM-enriched solutions in comparison to a control seawater-formalin solution. Our results suggest that formalin-preserved copepods are not fit for studies of past trends due to ongoing and unpredictable abiotic transformations of Hg in chemically preserved animal tissue.

Mercury variation and export in trans-Himalayan rivers: Insights from field observations in the Koshi River

Strengthening the research of riverine mercury (Hg) export is of great significance for understanding the regional and global Hg cycle, especially for the data lacking trans-Himalayan rivers. In this study, three systematic sampling campaigns were conducted in the Koshi River Basin (KRB) during the post-monsoon, pre-monsoon and monsoon seasons. Hg speciation and distribution of river water were analyzed among the different seasons for a total of 88 water samples. The total Hg (THg) concentration of surface water in the KRB ranged from 0.64 to 32.96 ng·L^-1 with an average of 5.83 ± 6.19 ng·L^-1 and decreased in the order of post-monsoon (8.79 ± 7.32 ng·L^-1) > monsoon (6.68 ± 6.12 ng·L^-1) > pre-monsoon (2.18 ± 1.29 ng·L^-1). Particulate Hg (PHg) accounted for 63% of THg on average and had a positive correlation with THg among all the three sampling seasons, indicating that the differences in PHg concentration were likely one of the main factors leading to the seasonal and spatial variations in THg in the KRB surface water. The annual Hg exports and fluxes were estimated to be 339.04 kg and 3.88 μg·m^-2·yr^-1, respectively. Furthermore, Hg export from the KRB had significant seasonal variation and decreased in the order of monsoon (259.47 kg) > post-monsoon (61.18 kg) > winter (9.31 kg) > pre-monsoon (9.08 kg), and this pattern was mainly related to seasonal changes in river runoff. The annual Hg export is projected to increase in the future, especially in the post-monsoon season. Therefore, more attention should be paid to river runoff observations and riverine Hg research for water resources management in the Himalaya.

Mercury Uptake Affects the Development of Larus fuscus Chicks

Current emission and mobilization rates of mercury (Hg) in the environment pose extensive threats to both wildlife and human health. Assessing the exposure risk and effects of Hg contamination in model species such as seabirds is essential to understand Hg risks at the population and ecosystem levels. The lesser black-backed gull (Larus fuscus), a generalist seabird species, is an excellent model species because it forages in both marine and terrestrial habitats, which in turn differ in their Hg exposure risk. To identify possible deleterious effects of Hg exposure on developing L. fuscus chicks, a dietary experiment was carried out and chicks were provided a marine, terrestrial, or mixed diet. The effects of embryonic and dietary Hg exposure on chick body condition and physiological state were assessed at different developmental stages until fledging age (30 d). Overall physiological condition was lower in chicks fed a predominantly marine diet, which coincided with higher Hg loads in blood and primary feathers. However, no effect of dietary uptake of Hg was observed on body condition or in terms of genotoxic damage. Body condition and genotoxic damage correlated instead with Hg exposure during embryonic development, which seems to indicate that embryonic exposure to Hg may result in carry-over effects on later chick development. Environ Toxicol Chem 2020;39:2008-2017. © 2020 SETAC.

High mercury levels in Antarctic toothfish Dissostichus mawsoni from the Southwest Pacific sector of the Southern Ocean

Mercury is a bioaccumulating toxic pollutant which can reach humans through the consumption of contaminated food (e.g. marine fish). Although the Southern Ocean is often portrayed as a pristine ecosystem, its fishery products are not immune to mercury contamination. We analysed mercury concentration (organic and inorganic forms - T-Hg) in the muscle of Antarctic toothfish, Dissostichus mawsoni, a long-lived top predator which supports a highly profitable fishery. Our samples were collected in three fishing areas (one seamount and two on the continental slope) in the Southwest Pacific Sector of the Southern Ocean during the 2016/2017 fishing season. Mercury levels and the size range of fish varied between fishing areas, with the highest levels (0.68 ± 0.45 mg kg^-1 wwt) occurring on the Amundsen Sea seamount where catches were dominated by larger, older fish. The most parsimonious model of mercury concentration included both age and habitat (seamount vs continental slope) as explanatory variables. Mean mercury levels for each fishing area were higher than those in all previous studies of D. mawsoni, with mean values for the Amundsen Sea seamount exceeding the 0.5 mg kg^-1 food safety threshold for the first time. It might therefore be appropriate to add D. mawsoni to the list of taxa, such as swordfish and sharks, which are known to exceed this threshold. This apparent increase in mercury levels suggests a recent contamination event which affected the Southwest Pacific sector, including both the Amundsen and Dumont D'Urville seas.

Mercury exposure in relation to foraging ecology and its impact on the oxidative status of an endangered seabird

Mercury is a natural element extensively found in the Earth's crust, released to the atmosphere and waters by natural processes. Since the industrial revolution, atmospheric deposition of Hg showed a three-to-five-fold enrichment due to human activities. Marine top predators such as seabirds are recognized valuable bioindicators of ocean health and sensitive victims of Hg toxic effects. Hg negatively affects almost any aspect of avian physiology; thus, birds prove valuable to study the effect of Hg exposure in vertebrates. The Black-vented Shearwater is endemic to the North-Eastern Pacific Ocean, where it forages along the Baja California Peninsula during the breeding period. The area has no industrial settlement and is in the southern portion of the California Current System (CCS). After observing possible contamination effects in eggshells, we decided to quantify the exposure of breeding birds to Hg and test for possible effects on oxidative status of the species. The concentration of Hg in erythrocytes averaged 1.84 μg/g dw and varied from 1.41 to 2.40 μg/g dw. Males and females had similar Hg concentrations. The individual trophic level (reflected by δ¹⁵N) did not explain Hg exposure. In contrast, individuals foraging inshore had higher Hg concentrations than those foraging more offshore (reflected by δ¹³C). Shearwaters having higher concentrations of Hg had lower activity of the antioxidant enzyme glutathione peroxidase and showed lower non-enzymatic antioxidant capacity. Levels of plasma oxidative damage, superoxide dismutase and catalase were not associated with Hg. Our results indicate that (i) the foraging habitat is the factor explaining Hg exposure and (ii) there is some evidence for potential harmful effects of Hg exposure to this seabird species of conservation concern. CAPSULE: The foraging habitat is the factor explaining Hg exposure in seabirds and we observed potential harmful effects of Hg exposure in a seabird species of conservation concern.

Functionalized Electrospun Nanofibers as a Versatile Platform for Colorimetric Detection of Heavy Metal Ions in Water: A Review

The increasing heavy metal pollution in the aquatic ecosystem mainly driven by industrial activities has raised severe concerns over human and environmental health that apparently necessitate the design and development of ideal strategies for the effective monitoring of heavy metals. In this regard, colorimetric detection provides excellent opportunities for the easy monitoring of heavy metal ions, and especially, corresponding solid-state sensors enable potential opportunities for their applicability in real-world monitoring. As a result of the significant interest originating from their simplicity, exceptional characteristics, and applicability, the electrospun nanofiber-based colorimetric detection of heavy metal ions has undergone radical developments in the recent decade. This review illustrates the range of various approaches and functional molecules employed in the fabrication of electrospun nanofibers intended for the colorimetric detection of various metal ions in water. We highlight relevant investigations on the fabrication of functionalized electrospun nanofibers encompassing different approaches and functional molecules along with their sensing performance. Furthermore, we discuss upcoming prospectus and future opportunities in the exploration of designing electrospun nanofiber-based colorimetric sensors for real-world applications.

Permafrost Thaw Dominates Mercury Emission in Tibetan Thermokarst Ponds

Increasing evidence shows that warming is driving Hg release from the cryosphere. However, Hg cycling in thawing permafrost is less understood to date. Here we show that permafrost thaw dominantly supplied no-run thermokarst ponds by permafrost melt waters (PMWs) with high concentration of photoreducible Hg (PRHg) and subsequently controlled Hg(0) emissions in the Tibetan Plateau. This study was motivated by field survey suggesting that thermokarst ponds as recipient aquatic systems of PMWs could be an active converter of PRHg to Hg(0). Annual Hg mass balance in three seasonally ice-covered thermokarst ponds suggests that PMWs were the dominant input (81.2% to 91.2%) of PRHg in all three thermokarst ponds, and PRHg input would be a constraint of Hg(0) emission owing to the fast photoreduction of PRHg to Hg(0) in the water column. Annual Hg(0) emission in the thermokarst ponds of study region was conservatively estimated to increase by 15% over the past half century. Our findings highlight that climate-induced landscape disturbances and changes in hydrogeochemical processes in climate-sensitive permafrost will quickly and in situ drive Hg stored in permafrost for a very long time into the modern day Hg cycle, which potentially offsets the anthropogenic Hg mitigation policies.

Relationships between mercury burden, sex, and sexually selected feather ornaments in crested auklet (Aethia cristatella)

Individuals with higher contaminant burdens are expected to be in poorer physical health and be of lower individual body condition and energetic status, potentially resulting in reduced ornamentation or increased asymmetry in bilateral features. The degree and magnitude of this effect also would be expected to vary by sex, as female birds depurate contaminants into eggs. We tested for relationships among mercury in feathers, sex, and elaborate feather ornaments that relate to individual quality in crested auklets (Aethia cristatella), small planktivorous seabirds in the North Pacific Ocean. We found no relationships between mercury and the size of individuals' forehead crest or degree of measurement asymmetry in auricular plumes, both of which are favoured by intersexual selection. Females had significantly greater mercury concentrations than males (females. 1.02 ± 0.39 μg/g; males, 0.75 ± 0.32 μg/g); but concentrations were below that known to have physiological effects, as expected for a secondary consumer. Sex differences in overwintering area for this long-distance migrant species (more females in the Kuroshio Current Large Marine Ecosystem than males) could be the reason for this seemingly counterintuitive result between sexes. Further research relating mercury burden to overwintering ecology and diet contents would build on our results and further elucidate interrelationships between sex, sexually selected feather ornaments and contaminant burden.

Spatiotemporal Variations in Dissolved Elemental Mercury in the River-Dominated and Monsoon-Influenced East China Sea: Drivers, Budgets, and Implications

Distinct spatiotemporal distributions of sea surface dissolved elemental mercury (DEM) and its air-sea exchange flux were observed in the river-dominated and monsoon-influenced East China Sea (ECS). Spatially, DEM concentrations were higher in the nearshore Changjiang diluted water (90 ± 20 to 260 ± 40 fM) than in the offshore Kuroshio water (60 ± 10 to 160 ± 40 fM) and correlated with salinity and total Hg concentrations, suggesting that the total Hg discharged from the Changjiang river is a controlling factor. In summer, monsoon-driven coastal upwelling formed a transient nearshore water mass with very elevated DEM concentrations (290 ± 20 to 320 ± 70 fM). Seasonally, DEM concentrations in all water masses were the highest in summer (120 ± 30 to 320 ± 70 fM). Estimated rate coefficients for DEM production varied seasonally and strongly correlated with sea surface temperature (SST). Hg⁰ evasion fluxes also peaked in summer (670 ± 380 pmol m^-2 day^-1), while in winter, DEM was close to equilibrium with gaseous elemental mercury in the atmosphere. Based on the air-sea Hg fluxes for all four seasons from this study and regional atmospheric deposition fluxes from others, we conclude that the ECS is a net sink of Hg annually, but it is a source of Hg to the atmosphere in summer. Moreover, the contribution of the ECS to Hg evasion may increase as a result of flood-associated high Changjiang discharge and rising SST.

Food stress, but not experimental exposure to mercury, affects songbird preen oil composition

Mercury is a global pollutant and potent neurotoxic metal. Its most toxic and bioavailable form, methylmercury, can have both lethal and sublethal effects on wildlife. In birds, methylmercury exposure can disrupt behavior, hormones, the neuroendocrine system, and feather integrity. Lipid-rich tissues and secretions may be particularly susceptible to disruption by lipophilic contaminants such as methylmercury. One such substance is feather preen oil, a waxy secretion of the uropygial gland that serves multiple functions including feather maintenance, anti-parasitic defense, and chemical signaling. If methylmercury exposure alters preen oil composition, it could have cascading effects on feather quality, susceptibility to ectoparasites, and mate choice and other social behaviors. We investigated whether exposure to methylmercury, either alone or in association with other stressors, affects preen oil chemical composition. We used a two-factor design to expose adult song sparrows (Melospiza melodia) to an environmentally relevant dietary dose of methylmercury and/or to another stressor (unpredictable food supply) for eight weeks. The wax ester composition of preen oil changed significantly over the 8-week experimental period. This change was more pronounced in the unpredictable food treatment, regardless of dietary methylmercury. Contrary to our prediction, we found no main effect of methylmercury exposure on preen oil composition, nor did methylmercury interact with unpredictable food supply in predicting the magnitude of chemical shifts in preen oil. While it remains critical to study sublethal effects of methylmercury on wildlife, our findings suggest that the wax ester composition of preen oil is robust to environmentally relevant doses of this contaminant.

An updated review of atmospheric mercury

The atmosphere is a key component of the biogeochemical cycle of mercury, acting as a reservoir, transport mechanism, and facilitator of chemical reactions. The chemical and physical behavior of atmospheric mercury determines how, when, and where emitted mercury pollution impacts ecosystems. In this review, we provide current information about what is known and what remains uncertain regarding mercury in the atmosphere. We discuss new ambient, laboratory, and theoretical information about the chemistry of mercury in various atmospheric media. We review what is known about mercury in and on solid- and liquid-phase aerosols. We present recent findings related to wet and dry deposition and spatial and temporal trends in atmospheric mercury concentrations. We also review atmospheric measurement methods that are in wide use and those that are currently under development.

A DNA-based biosensor for aqueous Hg(II): Performance under variable pH, temperature and competing ligand composition

Mercury (Hg) is a toxic metal posing major health risks to human beings and wildlife. The characterization of Hg fate and transport in aquatic environments is hindered by a lack of sensitive, selective and easily field-deployable analytical techniques. Here we assess the reliability and performance of a Hg²⁺ sensor based on the selective binding of Hg²⁺ to a thymine-rich DNA under environmentally-relevant conditions. Experimental results indicate that the interactions between the DNA and SYBR Green I, which produce the detection fluorescence signal, are significantly impacted by pH, metal ligands and natural dissolved organic matter (NDOM). These interferences are largely eliminated by immobilizing the DNA in a polyacrylamide hydrogel, although high concentrations of NDOM, such as fulvic acids, still affect the sensor's performance due to competitive binding of Hg²⁺. The binding of Hg²⁺ to NDOM, however, can be accounted for via equilibrium speciation calculations, which also yield the complexation constant for Hg²⁺ binding to the DNA in the hydrogel. The equilibrium calculations reproduce the results for the entire set of experimental conditions, from simple electrolyte solutions to complex aqueous compositions mimicking natural lake waters, and across large ranges of pH (3-10) and temperature (5-50 °C).

Synthesis of Maternal Transfer of Mercury in Birds: Implications for Altered Toxicity Risk

Maternal transfer is a predominant route of methylmercury (MeHg) exposure to offspring. We reviewed and synthesized published and unpublished data on maternal transfer of MeHg in birds. Using paired samples of females' blood (n = 564) and their eggs (n = 1814) from 26 bird species in 6 taxonomic orders, we conducted a meta-analysis to evaluate whether maternal transfer of MeHg to eggs differed among species and caused differential toxicity risk to embryos. Total mercury (THg) concentrations in eggs increased with maternal blood THg concentrations; however, the proportion of THg transferred from females to their eggs differed among bird taxa and with maternal THg exposure. Specifically, a smaller proportion of maternal THg was transferred to eggs with increasing female THg concentrations. Additionally, the proportion of THg that was transferred to eggs at the same maternal blood THg concentration differed among taxonomic orders, with waterfowl (Anseriformes) transferring up to 382% more THg into their eggs than songbirds (Passeriformes). We provide equations to predict THg concentrations in eggs using female blood THg concentrations, and vice versa, which may help translate toxicity benchmarks across tissues and life stages. Our results indicate that toxicity risk of MeHg can vary among bird taxa due to differences in maternal transfer of MeHg to offspring.

Tracking mercury in the southwestern Atlantic Ocean: the use of tuna and tuna-like species as indicators of bioavailability

Mercury is a trace element that is potentially dangerous due its high toxicity and tendency to bioaccumulate in organisms. Currently, high mercury concentrations are seen in the environment especially due climate changes. Studies regarding mercury bioavailability in the southwestern Atlantic Ocean using tuna and tuna-like species are rare. The aim of the present study was to use tuna and tuna-like species (Thunnus atlanticus, Thunnus albacares, Katsuwonus pelamis, Euthynnus alletteratus, Coryphaena hippurus and Sarda sarda) as indicators of the availability of total mercury (THg) in oceanic food webs of the southwestern Atlantic Ocean. THg concentrations varied significantly among species for both muscle and liver (Kruskal-Wallis test; H_5,130 = 52.7; p < 0.05; H_5,130 = 50.1; p < 0.05, respectively). The lowest concentrations were found in C. hippurus (0.008 mg kg^-1 wet weight in the muscle and 0.003 mg kg^-1 wet weight in the liver), and the highest concentrations were reported in the muscle of T. atlanticus (1.3 mg kg^-1 wet weight) and in the liver of S. sarda (2.5 mg kg^-1 wet weight). The continued monitoring of tuna and tuna-like species is necessary to assist in their conservation since tuna can be sentinels of mercury pollution.

Interfacial oxygen nanobubbles reduce methylmercury production ability of sediments in eutrophic waters

Eutrophication can induce hypoxia/anoxia and rich organic matter at the sediment-water interface in surface waters. When eutrophic waters are impacted with mercury (Hg) pollution, methylmercury (MeHg) production ability (MPA) of surface sediment would increase and more MeHg might be produced. To tackle this risk, this study firstly collected samples of surface sediment and overlying water from a typical eutrophic lake-Taihu Lake. Then from a sediment-water simulation system, we demonstrated that eutrophic waters were able to methylate Hg spontaneously, and that sediment is the major Hg sink in the system. After the addition of HgCl₂ solution (approximately 1 mg L^-1 in the slurry), MeHg concentrations in the sediment increased by 11.7 times after 48 h. The subsequent column experiments proved that O₂ nanobubbles could significantly decrease the MPA of surface sediment, by up to 48%. Furthermore, we found that O₂ nanobubbles could remediate anoxia mainly by increasing dissolved oxygen (from 0 to 2.1 mg L^-1), oxidation-reduction potentials (by 37% on average), and sulfate (by 31% on average) in the overlying water. In addition, O₂ nanobubbles could also help decrease organic matter concentration, as was revealed by the decline of dissolved organic carbon in the overlying water (by up to 57%) and total organic carbon in surface sediment (by up to 37%). The remediation of anoxia and reduction of organic matter could contribute to the decrease of hgcA gene abundance (by up to 86%), and thus result in the reduction of MPA after the addition of O₂ nanobubbles. This study revealed the risk of MeHg production in case Hg pollution occurs in eutrophic waters and proposed a feasible solution for MeHg remediation.

Nitrogen-doped porous carbon from biomass with superior catalytic performance for acetylene hydrochlorination

Acetylene hydrochlorination is an important aspect of the industrial synthesis of polyvinyl chloride, but it requires a toxic mercury chloride catalyst. Here we report a green, highly efficient and low cost nitrogen-doped soybean meal carbon (SBMC) catalyst obtained from the simple carbonization of biomass soybean meal (SBM) in the presence of zinc chloride. This material exhibits excellent catalytic performance during acetylene hydrochlorination, with an initial acetylene conversion greater than 99% and 98% selectivity for vinyl chloride at 200 °C over 110 h. Analyses by X-ray photoelectron spectroscopy and temperature programmed desorption as well as catalytic activity evaluations show that pyridinic species are the active sites for hydrogen chloride, while pyrrolic N species are the main active sites for acetylene. An analysis of charge calculations based on model catalysts further indicates that the activity of pyrrolic N species essentially determines the performance of the SBMC catalyst. This investigation of the mechanism of acetylene hydrochlorination over SBMC confirms that such nitrogen-doped catalysts have two different active sites for the adsorption and activation of hydrogen chloride and acetylene molecules. This mechanism is different from that associated with metal chloride catalysts such as HgCl₂. This SBMC catalyst is a potential alternative to HgCl₂@AC catalysts for vinyl chloride synthesis and suggests a new means of designing carbon catalysts with basic surfaces for acetylene hydrochlorination.

A green, highly efficient and low-cost nitrogen-doped soybean metal carbon (SBMC) catalyst obtained from the simple carbonization of biomass soybean meal (SBM) in the presence of zinc chloride.

MnO2 flowery nanocomposites for efficient and fast removal of mercury(ii) from aqueous solution: a facile strategy and mechanistic interpretation

MnO2 flowery nanocomposites were explored as a novel and cost effective nanoadsorbent for the fast and efficient extraction of toxic inorganic contaminants from aqueous solution.

Quantification of Trace Mercury in Water: Solving the Problem of Adsorption, Sample Preservation, and Cross-Contamination

Adsorption, sample preservation, and cross-contamination are the major impediments to the accurate and sensitive analysis of low-level mercury samples. Common measures to deal with this issue are to use Teflon, quartz, or borosilicate glass bottles for sampling, standard solution and sample preservation with oxidative chemicals, to prepare standard solutions daily and to use dedicated glassware. This paper demonstrates that these measures are neither efficient nor effective. Two common laboratory sample containers (borosilicate volumetric glass flasks and polypropylene tubes) are investigated for the preparation and preservation of water samples and standard solutions of 0.2-1 µg L-1 with 2% HNO3. Mercury adsorption rates of 6-22% are observed within 30 min and after 48 days, the adsorption is greater than 98%. In stark contrast, no adsorption is found during a testing period of 560 days when the solutions are subject to potassium permanganate-persulfate digestion. New glass flasks and polypropylene bottles are free of mercury contamination but reused flasks are a major source of mercury cross-contamination. To minimize adsorption and cross-contamination, standard solutions are treated by potassium permanganate-persulfate or BrCl digestion, and each individual sample and standard solution should be stored and prepared in single-use polypropylene bottle, without transference.

Elemental sulfur amendment enhance methylmercury accumulation in rice (Oryza sativa L.) grown in Hg mining polluted soil

The influence of elemental sulfur (S(0)) amendment on methylmercury (MeHg) accumulation in rice and the chemical form of Hg in the rhizosphere were investigated under waterlogged conditions in Hg-contaminated soil (the majority of the Hg (˜70%) in forms similar to HgS). Different levels of S(0) addition increased the MeHg accumulation in rice. After a sequential extraction analysis of the chemical forms of Hg in the rhizosphere, the results showed that S(0) addition increased the organic bound Hg and decreased the residual Hg in the soils. An Hg L_III XANES further showed that S(0) addition increased the proportion of Hg in the form of RS-Hg-SR and decreased the proportion of Hg in the form of HgS, indicating that S(0) input may reactivate the non-bioavailable Hg in the rhizosphere and improve the net Hg methylation. These findings suggest that the application of S fertilizers to Hg-contaminated paddy soils may increase the MeHg concentration in the edible parts of crops, which may lead to more potential health problems in humans depending on the crop type. However, our study also suggests that S(0) addition could be an effective measure for mobilizing the insoluble Hg and accelerating the phytoremediation process in Hg-contaminated paddy soils.

Vanadium silicate (EVS)-supported silver nanoparticles: A novel catalytic sorbent for elemental mercury removal from flue gas

Vanadium silicate (EVS) is a vanadium-substituted form of titanosilicate that has a high potential for use as a sorbent for mercury removal. In the present study, EVS with supported silver nanoparticles (EVS-Ag100) as the catalytic sorbent was synthesized for elemental mercury (Hg°) capture. The physical and chemical properties of the sorbents were investigated. The raw EVS exhibited a poor Hg° capture capacity (7.7 μg g^-1), because most of the vanadium species in the structure of EVS were V⁴⁺. The loading of the silver could significantly enhance the Hg° capture capacity (63.4 μg g^-1). EVS-Ag100 exhibited a superior Hg° capture performance at temperatures of approximately 150 °C. Silver nanoparticles that formed on the EVS were the active sites. In addition, the vanadium species of EVS-Ag100 exhibited higher Hg° oxidation activity than those in the framework of raw EVS. The XPS results revealed the activation of the vanadium species by the silver nanoparticles. After the capture of Hg° in the presence of O₂, more V⁵⁺ was observed on the surface of EVS-Ag100. Exposure of EVS-Ag100 to a continuous simulated flue gas at 150 °C with a gas hourly space velocity of 220,000 h^-1 led to Hg° removal efficiency of >96% in a 1 h test.

In-Situ Capture of Mercury in Coal-Fired Power Plants Using High Surface Energy Fly Ash

Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a byproduct of these plants, as a sorbent to remove mercury has proven to be difficult. Here, we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. On the basis of this mechanism, our study provides a method to in situ capture mercury with high surface energy modified fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, which is the industry benchmark for the treatment of mercury emission in fossil power generation units. This is a breakthrough and indicates that modified fly ash can become an efficient and convenient industrial sorbent for the removal of mercury.

Au@gap@AuAg Nanorod Side-by-Side Assemblies for Ultrasensitive SERS Detection of Mercury and its Transformation

As one of the most toxic heavy metal elements, mercury ion (Hg²⁺ ) and its methylated product, methylmercury (MeHg) can pose a threat to human health and the environment. Herein, a novel Raman biosensor with cascade sensitivity is developed for Hg²⁺ detection through Au@gap@AuAg nanorod side-by-side assemblies. Due to the strong electromagnetic coupling from the assemblies and core-shell structure, the Raman sensor possesses high sensitivity with the limit of detection (LOD) of 0.001 ng mL^-1 , which is about one order lower than traditional atomic fluorescence spectrometer (AFS) methods. Moreover, the fabricated biosensor is used to measure residual mercury levels in tissues and eggs of hens fed high-mercury diets, and the results show total mercury in collected egg yolks is 20 times higher than whites. Furthermore, the form of mercury in the eggs is also analyzed by high-performance liquid chromatography coupled with AFS, and, unexpectedly, the methylated product MeHg tends to only be found in egg whites. These interesting differences may indicate a new research direction for the toxicity of mercury in living organisms, and the developed ultrasensitive Surface Enhanced Raman Scattering (SERS) method could pave a broad way for the application of biosensors in Hg detection.

Optimization of pretreatment procedure for MeHg determination in sediments and its applications

Methylmercury (MeHg) in sediment is difficult to be determined due to its low concentration and binding compounds like sulfide and organic matter. Moreover, wet sediment samples have been suggested to behave differently from certified reference materials in MeHg analysis. Optimal pretreatment procedure for MeHg determination in sediments has not been ascertained and whether the procedure could apply to sediment samples with complex matrix merits further research. This work firstly compared recovery results of five pretreatment procedures for MeHg determination using ERM-CC580. Using the optimal pretreatment procedure, recovery results were analyzed in different sediment samples after manipulation of moisture content, organic matter, and acid volatile sulfide. The procedure using CuSO₄/HNO₃ as leaching solutions and mechanical shaking as extraction method was proved to produce the most satisfactory recovery results (100.67 ± 6.75%, mean ± standard deviation). And when moisture content varied from 20 to 80%, average recovery results in sediment samples ranged from 100 to 125%. Furthermore, before and after the manipulation of organic matter or acid volatile sulfide, spiking recovery results varied little and were all within acceptable limit (85~105%). Therefore, the procedure of CuSO₄/HNO₃-mechanical is proposed as a universal pretreatment method for MeHg determination in sediment samples with various characteristics.

Adsorption of gaseous elemental mercury on soils: Influence of chemical and/or mineralogical characteristics

Gaseous elemental Hg is stable enough to be transported over long distances. Some of the most important sources of Hg in the atmosphere are artisanal gold mining activities and forest fires. Both of these sources are particularly prevalent in the Amazonia region. Information regarding the capacity of soils for retaining Hg transported by the atmosphere is very important for understanding the metal cycle in the environment. The aim of this work was to study gaseous elemental Hg adsorption in soils with different physical and chemical characteristics. For this purpose, soils from different regions in Brazil and Colombia influenced or possibly influenced by gold mining activities and forest fires were studied. Hg adsorption tests were conducted by exposing soil samples to a gaseous elemental Hg atmosphere for 144 h. The total Hg concentration (THg) and Hg oxidation states were monitored using a direct Hg analyzer. Sample characterization analyses were performed. THg values obtained before the adsorption tests were 43-413 and 144-590 µg kg^-1 for grain size fractions below 2 and 0.063 mm, respectively. The predominant species found was Hg²⁺, with abundance levels from 68% to 99%. The results show a wide range of enhanced Hg retention capacities among the samples, ranging from 13 to 2236 times the initial concentration, and the speciation results demonstrate a decrease in the oxidized species range, from 21% to 78%. The statistical analysis indicated the importance of Mn-bearing minerals for the processes of adsorption/oxidation of gaseous elemental Hg in soils. These results contribute to the elucidation of the processes that occur with Hg at the soil/atmosphere interface and may help to explain the high concentrations of Hg found in Amazonian soils where no gold mining activities are practiced.

Combined experimental and theoretical studies on adsorption mechanisms of gaseous mercury(II) by calcium-based sorbents: The effect of unsaturated oxygen sites

Accurate mercury speciation measurements are critical for developing methods for mercury removal from flue gas, but the lack of reliable adsorbents has made Hg²⁺ selective retention challenging. Calcium oxide (CaO) loaded on porous support is promising for HgCl₂ selective adsorption because of its porosity and alkaline nature. The main hypothesis investigated in this paper is if the capacity of CaO sorbent for HgCl₂ selective adsorption is attributed to its basic sites, then this will be drastically impacted by the calcium precursors. We synthesized a suite of CaO/SiO₂ sorbents from different precursors, including hydrated calcium oxide (CaO-HS), calcium nitrate tetrahydrate (CaO-NS), and calcium acetate monohydrate (CaO-AcS), to investigate their performance on HgCl₂ selective adsorption in a fixed-bed reactor. Compared with CaO-HS and CaO-NS, CaO-AcS was demonstrated to have the strongest affinity for HgCl₂ and almost complete breakthrough for Hg⁰. Advanced porosity and surface basicity of CaO-AcS were confirmed by characterization analysis. CaO (001) and CaO (011) facet as well as surface defects that have different unsaturated O sites were observed using the high resolution transmission electron microscope (HRTEM). Combined theoretical and experimental methods were used to study the interaction mechanisms between HgCl₂ and basic sites on CaO-AcS surfaces. Density functional theory (DFT) calculations indicated all CaO surfaces weakly interact with Hg⁰, while four robust bonding states of HgCl₂ were predicted on different basic sites with the intensity in increasing order: Monodentate < Tridendate < Bidentate < Bridging. This was consistent with HgCl₂-TPD experiments that demonstrated that the four HgCl₂ adsorption configurations on CaO-AcS were attributed to different unsaturated O sites. The findings in this work highlight the application potential of CaO-AcS for gaseous Hg²⁺ sampling and measurement from coal-fired flue gas.

High-resolution inventory of mercury emissions from biomass burning in tropical continents during 2001-2017

Mercury emissions from biomass burning contribute significantly to the atmospheric mercury budget and the interannual variation of mercury concentrations in the troposphere. This study developed a high-resolution (0.1° × 0.1°) monthly inventory of mercury emissions from biomass burning across five land types in the tropical continents (Central and South America, Africa, and South and Southeast Asia) during 2001-2017. The inventory estimates of mercury emissions from biomass burning are based on the newly released MCD64A1 Version 6 Burned Area data product, satellite and observational data of biomass density, and spatial and temporal variable combustion factors. Results from the inventory demonstrated that during 2001-2017, the average annual mercury emissions from biomass burning in tropical continents was 497 Mg and ranged from 289 Mg to 681 Mg. Forest fires were the largest contributor, accounting for 61% (300 Mg) of the total mercury emissions from biomass burning, followed by fires in woody savanna/shrubland (30%, 151 Mg), savanna/grassland (7%, 35 Mg), peatland (1%, 6 Mg), and cropland (1%, 5 Mg). However, these proportions varied between the continents; in the Americas and Asia, the largest biomass burning emissions came from forest fires, and in Africa the largest emissions were from fires woody savanna/shrubland. Between the three continents, Africa released 41% of the mercury emissions from biomass burning (202 Mg year^-1), Asia released 31% (154 Mg year^-1), and the Americas released 28% (141 Mg year^-1). The total mercury emissions from biomass burning in these tropical continents exhibited strong interannual variations from 2001 to 2017, with peak emissions in March and August to September, and forest fires were the primary land type controlling the interannual variations.

Application of hardwood biochar as a reactive capping mat to stabilize mercury derived from contaminated floodplain soil and riverbank sediments

Hardwood biochar (pyrolyzed at 700 °C), a potential candidate for Hg removal, has been proposed for use as reactive capping mats along groundwater discharge zones or riverbanks to control release of Hg from contaminated riverbank sediments. Frequent flooding and drainage in fluvial settings can influence the effectiveness of remediation systems in contaminated riverbank sediments and floodplain soils. This study evaluated the effectiveness of Hg removal using hardwood biochar under hydrogeochemical conditions representative of those present within a reactive capping mat installed in a fluvial setting. Two sets of treatment columns, containing 50% v.v biochar and quartz sand, were subjected to 100 weekly wetting/drying cycles that included dry air, water-saturated air, and drainage using leachate derived from two source columns as input solutions: 1. Passing simulated acid rain water through floodplain soil, 2. Passing river water through riverbank sediment. In both treatment columns, >80% of the Hg was retained on the biochar without promoting Hg methylation and the release of other unintended dissolved constituents (including N, P, DOC). Results from solidphase extraction analyses suggest that Hg accumulated near the air/biochar-sand interface (0-2 cm) in the treatment columns at low loadings but was present at greater depths at higher loadings. Results of micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) for the biochar collected at depths 0-2 cm in treatment columns suggest retention of Hg-bearing particles derived from riverbank sediment and floodplain soil within the pore structure of the biochar. Sulfur K-edge XANES analysis of the unused biochar and the biochar after treatment suggest formation of Hg complexes on the biochar surface. These results indicate that hardwood biochar is potentially an effective media for application in reactive mats for controlling Hg discharging from contaminated riverbank sediments.