Mercury (Hg) is a global environmental concern due to its microbial conversion to methylmercury (MeHg), a potent neurotoxin that bioaccumulates in food webs and poses risks to ecosystems and human health. Thiol functional groups (RSH) play an important role in controlling Hg(II) speciation and bio-uptake in methylating bacteria, yet the spatial distribution and density of these thiols within cells remain largely unknown. We isolated subcellular fractions of the Hg methylating bacterium Geobacter sulfurreducens in the exponential growth phase, and used Hg L III -edge EXAFS (Extended X-ray Absorption Fine Structure) to quantify thiols in the extracellular medium, inner and outer membranes, periplasm and cytoplasm. The whole-cell thiol content was determined to be 1.3 × 10-10 μmol cell-1. The inner membrane contributed 7.1 × 10-11 (53%), the outer membrane 1.2 × 10-11 (9%), the periplasm 3.6 × 10-11 (27%) and the cytoplasm 1.5 × 10-11 μmol cell-1 (11%). The extracellular fraction contributed an additional 5.7 × 10-11 μmol cell-1, corresponding to 30% of the thiols of the cell culture. Local thiol density (thiols normalized to TOC in individual compartment, RSH/TOC, μmol g-1 C) was 36, 450, 140, 600 and 29 μmol g-1 C in the cytoplasm, inner membrane, periplasm, outer membrane and extracellular fractions, respectively. EXAFS analyses demonstrate Hg-thiolate coordination across all compartments, with Hg-O/N bonding and elemental Hg0 formed at higher Hg loadings. In the periplasm, Hg-disulfide and traces of β-HgS were detected. The high thiol density at the membranes, relative to other compartments, may imply they have an important role in the retention and internalization of Hg(II). Periplasmic thiols may modulate Hg(II) transfer between membranes, and cytoplasmic thiols may regulate the intracellular availability of Hg(II) for methylation. This work provides the first compartment-resolved quantification of thiol abundances and densities in a model Hg-methylating bacterium at subcellular level, offering a mechanistic framework for understanding the speciation, bioavailability, and subcellular transformation of Hg(II) with relevance for other soft metals (e.g., Cd, Pb, Zn, Ag, and Cu).

Artisanal and Small-Scale Gold Mining (ASGM, known as garimpo in Brazilian Portuguese) remains a significant source of mercury (Hg) contamination worldwide, posing threats to both environmental integrity and One Health. Elevated Hg levels in affected regions typically arise from three interconnected pathways: (1) direct anthropogenic inputs of new mercury, such as elemental Hg released during gold amalgamation; (2) anthropogenic mobilization of existing Hg stocks through the mechanical disturbance of soils and sediments, including both legacy mining residues and naturally stored mercury; and (3) naturally occurring background mercury, derived from geogenic substrates and long-term atmospheric deposition into forested and aquatic ecosystems. This review synthesizes findings from peer-reviewed studies on garimpo-related Hg contamination in Brazil across multiple matrices, including human tissues, soils, sediments, water, air, and biota-and identifies the Amazon as a critical hotspot where high natural Hg backgrounds converge with historical and ongoing garimpos. Human exposure occurs primarily through occupational inhalation of elemental Hg vapor and dietary intake of methylmercury (MeHg) via fish consumption, particularly among riverine and Indigenous populations. Environmental compartments such as sediments, soils, and suspended particulate matter frequently exceed national prevention limits, underscoring mercury's persistence, mobility, and remobilization potential. Bioaccumulation is evident across trophic levels, with MeHg formation intensified under flooded, anoxic conditions typical of Amazonian wetlands and reservoirs. This complex interplay of geogenic, legacy, and active sources poses a sustained threat to ecological and human health. While Brazil's 2017 ratification of the Minamata Convention marks progress, reductions in fish MeHg may take decades, as stored Hg in floodplains continues to methylate. Effective mitigation will require mercury-free mining technologies, rigorous law enforcement, culturally appropriate health responses, and expanded monitoring tailored to geological and biogeochemical variability. Collectively, this integrated assessment highlights the multi-faceted nature of garimpo-related Hg contamination and provides insights to guide research priorities, policy frameworks, and stakeholder actions aimed at safeguarding human well-being and ecosystem health across Brazil.

Three-year dynamics of methylmercury production in Hg2+-spiked paddy soils: Mercury speciation, microbial communities, and rice contamination.

Blood metal(loid)s, haemoglobin and goitre in pregnant women from the mercury-exposed and non-exposed environment (Aidarken area vs Kara-Suu area; Kyrgyz Republic).

Abstract. This study investigates mercury (Hg) biogeochemical cycling and Hg uptake mechanisms in three common staple crops at a contaminated farm (Farm1) ≈ 500 m from an artisanal and small-scale gold mining (ASGM) processing site (PS) and a background farm (Farm2; ≈ 8 km upwind) in Nigeria. We examine air, soil, and various crop tissues using total Hg (THg), Hg stable isotope, Hg speciation, and methyl-Hg (MeHg) analyses. Results show elevated gaseous elemental Hg (GEM) levels in the air (mean concentrations: 1200 ± 400 ng m−3) and soil (mean THg concentration: 2470 ± 1640 µg kg−1) at the PS, significantly higher than those at Farm1 (GEM: 54 ± 19 ng m−3; THg: 76.6 ± 59.7 µg kg−1), which are in turn significantly higher than those at the background site, Farm2 (GEM: 1.7 ng m−3; THg: 11.3 ± 8 µg kg−1). These data confirm the ASGM-derived Hg contamination at the PS and the exposures of crops at Farm1 to elevated levels of Hg in both air and soil. Aligning with Hg concentrations in air and soil, Farm1 had significantly higher THg concentrations in all crop tissues compared to Farm2. At Farm1, foliage exhibits the highest THg concentrations in tissues, particularly for peanuts and cassava (up to 385 ± 20 µg kg−1 in peanuts). These data, along with highly negative δ202Hg values in foliage and other crop tissues (indicative of light Hg isotope enrichment imparted during stomatal assimilation of Hg) demonstrate atmospheric uptake of GEM as the primary uptake pathway for Hg in these crops. We observe air-to-foliage mass-dependent enrichment factors (ε202Hg) of −2.60 ± 0.35, −2.54 ± 0.35, and −1.28 ± 0.43 ‰ for cassava, peanuts, and maize, respectively. While our two-endmember mixing model shows that Hg in crop roots is influenced by both soil (59 %–74 %) and atmospheric (26 %–41 %) uptake pathways, we suggest soil Hg in roots is largely associated with the root epidermis/cortex (external root tissues) and that little soil-derived Hg is transferred to aboveground tissues (< 7 % across all crops). The lower THg concentrations in edible parts (with the exception of cassava leaves, commonly eaten in Nigeria) indicate that even translocation from foliage to other tissues is a relatively slow process. MeHg concentrations were < 1 % across all tissues, and probable daily intakes (PDIs) for both MeHg and THg based on typical diets in Nigeria were all below reference dose thresholds, indicating these crops are generally a lower health risk to the local population.

ABSTRACT Surface water pollution through uncontrolled industrial discharge is a global concern. In this study, 50 water samples from Dhaleshwari River (Bangladesh) were collected and analyzed for 27 water quality parameters (temperature, DO, BOD, pH, EC, TDS, alkalinity, hardness, Pb, Cd, Cr, As, Hg, Ag, Mn, Co, Fe, Ni, Zn, Cu, Mg, F−, Cl−, NO2 −, Br−, NO3 −, and SO4 2-) in wet and dry seasons. The aim of this study was to delineate seasonal river water quality, trace pollutants source, and evaluate public health risks through exposure, for environmental sustainability. Water physicochemical properties were measured using a Multimeter. Toxic metals were determined using an atomic absorption spectrophotometer while anions were estimated using the ion chromatography. Spatial and seasonal variation of the parameters were evaluated through GIS and statistically. Several indices were used for water quality and health risk evaluations. Investigation revealed Cr, Mn, Fe, Ni, and Hg were the most prevalent pollutants in this river in both wet and dry seasons, while temperature, DO, BOD, EC, TDS, Cl−, and NO3 − were the most concerning parameters in the dry season. One-way ANOVA indicates significant (p < 0.05) variations in concentration for most of the parameters over the studied region in both seasons. Water quality indices indicate severe heavy metal pollution in the river water. Discharged pollutants have changed the water physicochemical parameters significantly. Principal component analysis revealed significant anthropogenic elemental (Cr, Pb, Cd, As, Hg, Ag, Mn, Co, Ni, Zn, and Cu) contributions to the river water. Health risk assessment suggests that Mn, Cr, Co, Hg, and As in the river water could cause adverse effects on human health. Therefore, effective legislative and administrative measures should be implemented for the regulated discharge of industrial effluents in the area to ensure a safe and sustainable environment for aquatic organisms and human beings.

Mercury methylation in methanogenic archaea: A protocol for stabilized cultivation and accurate assessment.

Stenotrophomonas pavanii AS1 and blue light synergistically enhance kinetin riboside biosynthesis and mercury tolerance in Oryza sativa.

ABSTRACT Experiments and models are used to investigate the potential of H2 injection to encourage mercury oxidation to enhance removal from coal-fired power plant exhaust streams. A laboratory-scale quartz reactor creates a surrogate combustor exhaust stream within which mercury oxidation is measured. The experiments focus on the effects of multiple reactor temperatures and varying concentrations of O2, H2O, HCl, and H2. The modeling study first evaluated several chemical kinetic mechanisms for mercury oxidation and identified a set of reaction parameters that replicated experimental trends. The models then explore the chemical kinetic basis for increased mercury oxidation due to H2 injection. The models indicate that injected H2 increases the radical pool of H and OH, provided sufficient time is allowed at an elevated temperature. The radicals then react with HCl to produce a pool of Cl (and subsequently Cl2). The increased Cl2 concentration reacts with Hg and HgCl, improving mercury oxidation to HgCl2. Water-soluble HgCl2 is much more easily removed from combustion exhaust gases by standard air pollution control equipment than elemental Hg. Implications: In this study, the authors present experimental data and chemical kinetic models to investigate the opportunity of reducing mercury emissions from coal-fired power plants by injecting the exhaust with H2. The study concludes that injecting H2 at an elevated temperature in a temporary isothermal environment is a way to enhance mercury oxidation and, ultimately, mercury removal. The implications of this work could be a reduction in mercury emissions by leveraging a new technological solution.

Geochemical records from loess-paleosol deposits offer valuable insights into past paleoclimate and paleoecological changes. Here we explore the potential of mercury (Hg) stable isotopes to study the changes of paleoprecipitation and paleovegetation and their causal effect on terrestrial Hg accumulation on the Chinese Loess Plateau (CLP). We first document how variations of Hg concentrations, Δ199Hg and Δ200Hg isotope signatures in modern soils and loess are controlled by coupled precipitation-vegetation gradients on the CLP, and unaltered by postdepositional processes. Increased precipitation promotes vegetation growth and foliar gaseous elemental Hg uptake, lowering Δ199Hg and Δ200Hg in modern soils and loess. Similar to modern soils and loess, we attribute Hg accumulation and isotope signatures in loess-paleosol deposits to changes in vegetation Hg uptake in response to variation in paleoprecipitation. Both modern and paleo loess and soils suggest faster Δ199Hg changes and Hg accumulation to precipitation under high precipitation conditions (e.g., > 500 mm yr-1) than under arid conditions, reflecting their potential as proxies for pronounced wet and dry climate changes in the CLP. Our results evidence enhanced sequestration of atmospheric Hg emissions in loess soils during interglacial wetter periods. Warming and changes in precipitation patterns in response to global climate change may therefore lead to enhanced Hg burial in soils.

IntroductionRiver deltas play an important role in sequestering and storing mercury (Hg), restricting its release into downstream bodies of water. Delta landscapes encompass a patchwork of distinct wetland soils and vegetation, which accumulate Hg from both atmospheric and watersheds sources, and have varying capacities for long-term Hg retention.MethodsTo better understand Hg retention in the complex mosaic of delta soils, this study used soil age models based on fallout radionuclides (FRNs, 210Pb, 7Be, 241Am) to measure Hg flux to three distinct natural communities in the Missisquoi River Delta, Vermont.ResultsSoil profiles of radionuclide and Hg flux from a pitch pine bog, a silver maple floodplain forest, and a wild rice marsh all revealed long-term retention of Hg, despite varying susceptibilities to frequent hydrological disturbances. A mass balance approach was applied to apportion Hg fluxes to each region of the delta based on regional values of Hg wet deposition, measured FRN and Hg inventories, and measured or estimated foliar Hg inputs. Spaghnum peat soils of the pitch pine bog had the lowest Hg flux, consistent with uptake predominantly from wet deposition, while Hg accumulation doubled in bog soils developed under shrub or tree canopies, due to strong foliar and non-foliar uptake of gaseous elemental Hg (GEM). Soils in the silver maple floodplain received the highest Hg flux, driven by both GEM uptake and large riverine sedimentary inputs. Surprisingly, submerged soils in the wild rice marsh recorded substantially lower Hg flux than the adjacent silver maple forest, with low inputs of Hg from both GEM and watershed sources.ConclusionThis novel chronometry framework for elucidating pathways of Hg accumulation across distinct deltaic environments revealed the variable roles of vegetation type and flooding regime in controlling Hg inputs to delta soils.

Novel enhancement strategy for Hg adsorption in wastewater: Nonthermal plasma-mediated advanced modification of zero-valent iron-carbon galvanic cells with thiol functionalization.

Reduction and amalgamation of mercury in silver nanoparticle suspensions under dark conditions.

Mercury (Hg) contamination poses a persistent threat to the remote Arctic ecosystem, yet the mechanisms driving the pronounced summer rebound of atmospheric gaseous elemental Hg (Hg0) and its subsequent fate remain unclear due to limitations in large-scale seasonal studies. Here, we use an integrated atmosphere–land–sea-ice–ocean model to simulate Hg cycling in the Arctic comprehensively. Our results indicate that oceanic evasion is the dominant source (~80%) of the summer Hg0 rebound, particularly driven by seawater Hg0 release facilitated by seasonal ice melt (~42%), with further contributions from anthropogenic deposition and terrestrial re-emissions. Enhanced Hg0 dry deposition across the Arctic coastal regions, especially in the Arctic tundra, during the summer rebound highlights the potential transport of Hg from the pristine Arctic Ocean to Arctic terrestrial ecosystems. Arctic warming, with a transition from multi-year to first-year ice and tundra greening, is expected to amplify oceanic Hg evasion and intensify Hg0 uptake by the Arctic tundra due to increased vegetation growth, underlining the urgent need for continued research to evaluate Hg mitigation strategies effectively in the context of a changing Arctic.

In January 2022, gaseous elemental Hg (GEM) concentrations were continuously monitored at Syowa Station on East Ongul Island, located ∼4 km from the continent on the eastern coast of Lützow-Holm Bay in the Antarctic region.

Mercury (Hg) is a widespread pollutant that poses significant risks to both ecosystems and human health. While previous studies have evaluated Hg concentrations in soils, few have measured Hg emissions in areas with high Hg concentrations or related these measurements to estimates of exposure via air inhalation based on Hg flux values. This study addresses this gap by proposing the use of gaseous elemental Hg (GEM) flux measurements for exposure risk assessments, with a particular focus on the importance of inhalation exposure, which has implications for future risk management strategies. Sensitivity analysis of the site-specific exposure and risk estimation model revealed that the fraction of land area in surface water had a significant impact on the estimated exposure through air inhalation. Additionally, the analysis showed that the GEM flux measured in situ in a high-Hg concentration area of Itomuka was not directly proportional to the Hg concentration, although the risk estimation model treated it as a function of concentration. Furthermore, we found that the flux values are influenced by both the fraction of land area in surface water and Hg concentration, indicating that this new flux-based indicator should be integrated into exposure risk assessments.

In this study, we investigated the behavior and emission characteristics of Hg across diverse industrial combustion sources, such as coal-fired power plants, solid refuse fuel (SRF) power plants, medical waste incinerators, and industrial waste incinerators, as well as the development of emission factors, Among the facilities, the estimated Hg control efficiency was 86% for coal-fired power plants, 69% for SRF power plants, and over 95% for medical and industrial waste incinerators. The oxidation and regulation of elemental Hg (Hg0) are considered important factors in reducing Hg air emissions, with the flue gas HCl concentration being the primary factor affecting Hg oxidation. Particulate Hg was mainly controlled in the electrostatic precipitator (ESP) at the power plant, effectively capturing dust particles ranging from 10 to 100 μm. The emission factors estimated by measuring stack flue gas exhibited their highest values at SRF power plants, with an estimated average of 127±25 mg/ton, while the lowest values were observed for industrial waste incinerators, with an average of 2.5±0.3 mg/ton. This study is significant in that it provides a comparative analysis of various real industrial cases, and the Hg emission factors are expected to offer valuable data for estimating future national Hg air emissions.

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

Deactivation effect of elemental mercury oxidation over a V2O5-WO3/TiO2 catalyst by Pb in simulated coal-fired flue gas

Mercury (Hg), a potent neurotoxin posing risks to human health, is cycled through vegetation uptake, which is susceptible to climate change impacts. However, the extent and pattern of these impacts are largely unknown, obstructing predictions of Hg’s fate in terrestrial ecosystems. Here, we evaluate the effects of climate change on vegetation elemental Hg [Hg(0)] uptake using a state-of-the-art global terrestrial Hg model (CLM5-Hg) that incorporates plant physiology. In a business-as-usual scenario, the terrestrial Hg(0) sink is predicted to decrease by 1870 Mg yr−1 in 2100, that is ~60% lower than the present-day condition. We find a potential decoupling between the trends of CO2 assimilation and Hg(0) uptake process by vegetation in the 21st century, caused by the decreased stomatal conductance with increasing CO2. This implies a substantial influx of Hg into aquatic ecosystems, posing an elevated threat that warrants consideration during the evaluation of the effectiveness of the Minamata Convention.