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The deposition of different atmospheric mercury (Hg) species into oceans determines the atmospheric Hg lifetime and the production of neurotoxin methylmercury. Yet, the relative contribution of atmospheric Hg(II) and Hg(0) is largely unconstrained. Here, we report the concentrations of total Hg and methylmercury, as well as Hg isotope composition in living corals collected from the tropical South China Sea (SCS). The results show that the Hg in corals is mainly present as inorganic Hg, exhibiting slightly negative δ202Hg and small yet significant Δ199Hg and Δ200Hg. These isotope features closely resemble those of pelagic waters, suggesting that shallow‐water corals that are widely distributed in oligotrophic waters could be used to trace atmospheric Hg deposition pathways. A mixture model based on coral Δ200Hg indicates that approximately 49% of the seawater Hg in the tropical SCS, a region characterized by high rainfall, originates from atmospheric gaseous Hg(0), much larger than previous estimates. Plain Language Summary: Mercury (Hg) is a toxic heavy metal pollutant that has significant impacts on the environment. The ocean plays a crucial role in the global Hg cycle, with atmospheric Hg deposition being a major source of Hg in seawater. By elucidating the sources, transport, and transformations of Hg in the marine environment, we can develop effective strategies for its mitigation and environmental management. However, our current understanding of how atmospheric mercury enters the open sea is limited, due to challenges in directly measuring trace amounts of mercury in seawater. The widely distributed shallow‐water coral could be an important supplement. Here we present the first‐ever examination of mercury isotope compositions in coral polyps and their symbiotic zooxanthellae from the tropical South China Sea to investigate atmospheric Hg sources into the open ocean. The result shows that the ratio of atmospheric divalent Hg(II) to elemental Hg(0) deposition derived from coral isotopes is only about one quarter of the estimate based on current observations. Our study presents a novel approach to constrain atmospheric Hg deposition pathways into the ocean and challenges the prevailing viewpoint that Hg in tropical oceans mainly originates from precipitation. Key Points: First study of Hg isotope compositions in coral polyps and their symbiotic zooxanthellaeShallow‐water coral tissue can serve as an archive for Hg isotopic compositions of the surface seawaterCoral Δ200Hg reveals that ∼49% of seawater Hg in the tropical South China Sea is derived from atmospheric gaseous elemental Hg [ABSTRACT FROM AUTHOR]

Abstract Mercury (Hg) stable isotopes are useful to understand Hg biogeochemical cycling because physical, chemical and biological processes cause characteristic Hg isotope mass-dependent (MDF) and mass-independent (MIF) fractionation. Here, source Hg isotope signatures and process-based isotope fractionation factors are integrated into a fully coupled, global atmospheric-terrestrial-oceanic box model of MDF (δ202Hg), odd-MIF (Δ199Hg) and even-MIF (Δ200Hg). Using this bottom-up approach, we find that the simulated Hg isotope compositions are inconsistent with the observations. We then fit the Hg isotope enrichment factors for MDF, odd-MIF and even-MIF to observational Hg isotope constraints. The MDF model suggests that atmospheric Hg0 photo-oxidation should enrich heavy Hg isotopes in the reactant Hg0, in contrast to the experimental observations of Hg0 photo-oxidation by Br. The fitted enrichment factor of terrestrial Hg0 emission in the odd-MIF model (5‰) is likely biased high, suggesting that the terrestrial Hg0 emission flux (160 Mg yr−1) used in our standard model is underestimated. In the even-MIF model, we find that a small positive atmospheric Hg0 photo-oxidation enrichment factor (0.22‰) along with enhanced atmospheric HgII photo-reduction and atmospheric Hg0 dry deposition (foliar uptake) fluxes to the terrestrial reservoir are needed to match Δ200Hg observations. Marine Hg isotope measurements are needed to further expand the use of Hg isotopes in understanding global Hg cycling. [ABSTRACT FROM AUTHOR]

Mercury (Hg) is commonly present at trace levels in coal deposits. Geological processes, particularly magmatic intrusion and hydrothermal cycling in coal-bearing strata can significantly increase Hg levels in coals. However, the effects of thermal stress, magmatic components, magmatic-hydrothermal fluids, low-temperature hydrothermal fluids on Hg enrichment are confounded in a magmatic-affected coal basin. Here, we demonstrate the use of stable Hg isotopes to understand the controlling factors on Hg enrichment in two well-known Chinese coal deposits affected by magmatic activities: Wulantuga low-temperature hydrothermal-altered coal deposit and Wolonghu magmatic-intruded coal deposit. The Wulantuga No. 6 coal seam is extremely enriched in Hg, varying from 0.37 μg/g in middle coal benches to 40–90 μg/g in the upper most and lowest coal benches. Approximately 2.5‰ variation in mass dependent fractionation (MDF, − 3.07‰ to − 0.58‰ in δ 202 Hg) is observed. δ 202 Hg vs. 1/[Hg] diagram suggests a mixture of three Hg end-members: original hydrothermal fluids, fractionated hydrothermal fluids and native coal-forming materials. In addition, Wulantuga coals all show positive mass independent fractionation (MIF) of odd isotopes, up to 0.87‰ in Δ 199 Hg and 0.66‰ in Δ 201 Hg. The Δ 199 Hg/Δ 201 Hg ratios range from 1.3 to 3.3, suggesting that a large fraction of photodegraded methylmercury was likely incorporated into the coal deposit. The magmatic-intruded Wolonghu No. 8 coal seam is only slightly to intermediately enriched in Hg, varying from 0.10 μg/g to 0.40 μg/g. The coals near the contact sill (≤ 5 cm, − 1.81‰ to − 1.52‰) have similar δ 202 Hg as the magmatic sill rocks (− 2.05‰ to − 1.80‰), both with insignificant MIF values. Coals far from the contact sill (≥ 15 cm) have δ 202 Hg values varying from − 3.40‰ to − 1.61‰ and Δ 199 Hg varying from 0.26‰ to 0.58‰, which are significantly enriched in light and odd Hg isotopes compared to coals near the contact sill. Δ 199 Hg and Δ 201 Hg in Wolonghu coals far from the contact sill resemble those of meteoritic waters and seawater in both magnitude and Δ 199 Hg/Δ 201 Hg ratio. Our two case studies show significant MDF and MIF of Hg isotopes, which inform on Hg migration and sequestration in the magmatic rocks and coal deposits, and on the roles of meteoric water and hydrothermal fluid circulation. [ABSTRACT FROM AUTHOR]

Coal deposits were important natural Hg sinks in the Late Paleozoic and Middle-Late Mesozoic. Coal combustion since the industrial revolution has emitted more than 35,000 t of Hg into the atmosphere. Environmental geochemistry research on Hg in coal is essential to understand the natural Hg cycle throughout Earth history and the present-day Hg cycle under human perturbation. In this review, we summarize the methods of Hg isotope measurement in coals, and compile recently published Hg isotope data of > 200 world coal samples according to their locations, formation periods (Carboniferous, Permian, Jurassic, Cretaceous, Early-Middle Cenozoic) and ranks (anthracite, bituminous coal, subbituminous coal, lignite), and illustrate the controls of sources and biogeochemical processes on Hg isotope compositions in coal deposits. Up to 4.7‰ variation (− 3.90 to 0.77‰) in mass dependent fractionation (MDF, represented by δ 202 Hg) and 1.0‰ variation (− 0.63 to 0.34‰) in mass independent fractionation (MIF, represented by Δ 199 Hg) are observed in world coal deposit, with an average value of − 1.16 ± 0.79‰ (1SD) and − 0.11 ± 0.18‰ (1SD) for δ 202 Hg and Δ 199 Hg, respectively. We find that coal δ 202 Hg and Δ 199 Hg are broadly controlled by two source materials: terrestrial plants (biogenic Hg) and crustal rocks (geogenic Hg), accounting for 37–46% and 54–63% of Hg in coals. No clear trends are seen in neither δ 202 Hg vs. coal-forming periods nor δ 202 Hg vs. coal ranks, which we attribute to important overlapping of δ 202 Hg in the source materials of different coal-forming periods and the multidirectional Hg MDF during coalification. Interestingly, a step-wise increase in total Hg and a disappearance of Δ 199 Hg are observed along with increasing coal rank, suggesting the addition of hydrothermal Hg into high-rank coals. The hydrothermal fluids not only upgraded the coal ranks, but also increased the Hg concentrations and Δ 199 Hg of coals. In addition, the addition of hydrothermal Hg into coal deposits was also partly responsible for the comparatively higher total Hg and Δ 199 Hg in the Late Paleozoic coals relative to the Mesozoic and Cenozoic coals. The co-variation of atmospheric oxygen levels and Δ 199 Hg of coals at different coal-forming time widows suggests that the removal of biogenic Hg in response to widespread swamp fires may have increased the Δ 199 Hg in Late Paleozoic coals as well. Our study indicates that coal Hg isotopes provide new insights into the biogeochemical cycle of Hg in coal deposits, and that Δ 199 Hg is a robust indicator to trace Hg addition/removal in coal deposits and biogeochemical processes (magmatic intrusion, hydrothermal fluids penetration, burning of coal swamp) occurring during coal deposition. [ABSTRACT FROM AUTHOR]

Mercury (Hg) stable isotope variations provide a potential tool to better understand the provenance and geochemical processes that control Hg occurrences in coal deposits. In this study, we explore the variations in Hg isotope compositions in coal benches of a single coal seam (No. 3-1 coal seam, Daizhuang Coal Mine, Jining Coalfield, Shandong Province), and in successive coals seams of a coal-bearing sequence (No. 1 to No. 11-2 coal seams, Zhuji Coal Mine, Huainan Coalfield, Anhui Province) to assess Hg isotopes as a Hg biogeochemical tracer in coal deposits. Large variations in mass dependent Hg isotope fractionation (MDF) were observed in both Daizhuang and Zhuji coal deposits, with δ 202 Hg values ranging from − 2.34 to − 0.25 ± 0.12‰ (2 SD, n = 8), and from − 1.62 to 0.44 ± 0.12‰ (2 SD, n = 18), respectively. Daizhuang coals showed insignificant mass independent Hg isotope fractionation (MIF) in most samples (− 0.04 to 0.12 ± 0.08‰ for Δ 199 Hg, 2 SD, n = 8), whereas MIF in the younger Nos. 7-11 coal seams of Zhuji coals (0.06 to 0.22 ± 0.08‰ for Δ 199 Hg, 2 SD, n = 7) were positive and significant. Increased trends in both Hg concentrations and δ 202 Hg values going from older to younger Zhuji coal seams were observed, and were possibly related to variations in coal-forming environment of different coal seams. The significant negative correlations of δ 202 Hg vs. 1/Hg in the Zhuji coals, and of δ 202 Hg vs. Δ 199 Hg in the Daizhuang coals suggest that Hg isotopes can potentially be used to trace organic and inorganic Hg end-members in coal deposits. Natural coke, a metamorphosed form of coal, is on average two-fold enriched in Hg compared to coal, indicating that hydrothermal fluids derived from magmatic intrusions bring Hg into coal deposits. In addition, coke has either distinctly higher (0.70 to 0.91 ± 0.12‰, 2 SD, n = 2) or lower δ 202 Hg (− 4.00 to − 3.47 ± 0.12‰, 2 SD, n = 3) than corresponding coals, demonstrating that significant Hg MDF occurred when coals were thermally contacted by intruded magmas. [ABSTRACT FROM AUTHOR]

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1-20 ng/g) by wet chemistry is challenging. Combustion-trapping techniques have been shown to be an appropriate alternative []. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into HO, CO, SO, etc. The O carrier gas, including combustion products and elemental Hg, is then purged into a 40 % ( v/ v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO/1HCl ( v/ v), 25 mL/min O flow rate, and a dynamic temperature ramp rate (15 °C/min for 25-150 and 600-900 °C; 2.5 °C/min for 150-600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81-102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80-120 %. This protocol has the advantages of a short sample processing time (∼3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis. [ABSTRACT FROM AUTHOR]

Abstract: Coal-fired utility boiler (CFUB) emissions of mercury (Hg) represent the largest anthropogenic Hg source to the atmosphere. Hg stable isotope signatures in coal have been shown to vary among coal deposits and coal basins. There is therefore a substantial interest in tracing CFUB Hg emissions at local, regional and global scales. However, CFUB operating conditions, Hg capture technologies and post-emission Hg transformations may potentially alter the original feed coal Hg isotope signatures. Here we investigate Hg isotopic fractionation between feed coal and coal combustion products in six utility boilers of two large power plants in Huainan City, Anhui Province, China. We observe identical trends in all six boilers: relative to feed coal with δ202Hg ranging from −0.67 to −0.18‰, oxidized Hg species in bottom ash and fly ash are enriched in the lighter isotopes with δ202Hg from −1.96 to −0.82‰. Flue gas desulphurization by-product gypsum shows δ202Hg from −0.99 to −0.47‰. No mass independent fractionation was observed during the transport and transformation of Hg inside the boilers. An isotope mass balance suggests that gaseous stack Hg emissions are enriched by up to 0.3‰ in the heavier Hg isotopes relative to feed coal and that the enrichment depends on the Hg capture technology. The observation that oxidized Hg species are enriched in the lighter isotopes suggests that oxidized and reduced forms of Hg in stack emission carry different isotope signatures. This has implications for near-field and far-field Hg emission tracing. [Copyright &y& Elsevier]

Mercury (Hg) stable isotopes have a great potential to track coal combustion Hg emissions, but mass-dependent fractionation (MDF) during Hg adsorption onto fly ash particles could significantly alter isotope signatures of emitted Hg species. The detailed processes causing this MDF, however, are not well understood. Here, we simulated how isotopes fractionate during gaseous Hg0 adsorption onto fly ash at different times and temperatures. Kinetic MDF that preferably transfers light Hg isotopes to fly ash dominated Hg0 adsorption processes. The magnitude of MDF during Hg0 adsorption was invariable in the time-series experiment but increased significantly with increasing temperature in the temperature-series experiment. The external mass transfer and chemisorption are suggested to be the controlling processes for isotopic fractionation. Relative to diffusion-driven Hg0 adsorption, chemisorption is suggested to be a more important Hg0 adsorption step causing MDF, especially at high temperatures. The chemisorption involves Hg redox change from Hg0 to HgII and is likely enhanced with increasing temperature (50–180 °C). The proposed kinetic MDF model reveals that MDF in modern coal-fired power plants is likely driven by temperature-induced redox processes during Hg0 adsorption, and has great implications for developing MDF models in coal-fired boilers and tracing coal combustion Hg emissions. ga1 • The adsorption of Hg onto coal ash mainly induced the kinetic MDF of Hg isotopes. • The external mass transfer and the chemisorption are the controlling process for Hg isotopes fractionation. • Chemisorption is suggested to be a more important Hg0 adsorption step causing MDF, especially at high temperatures. • MDF in coal-fired power plants is likely driven by temperature-induced redox processes during Hg0 adsorption. [ABSTRACT FROM AUTHOR]

The article presents a study of mercury (Hg) isotopes to trace the potential sources of Hg in thermally-intruded coals from the Huaibei coalfield in China. The Hg isotope composition of non-contacted coals deviates largely from the normal coals from Huainan coalfield which was less influenced by igneous intrusion. In addition, igneous intrusion causes important Hg isotope fractionation at the contact zone of igneous rock-coal.

We present a 3-year time series of lead (Pb) and mercury (Hg) concentrations and isotope signatures in total suspended particulate (TSP) matter and as total gaseous Hg (TGM) in Xi'an, Northwestern China. Mean concentrations of TSP (299 ± 120 µg m-3), PbTSP (0.33 ± 0.15 µg m-3) and HgTSP (0.64 ± 0.54 ng m-3), and TGM (5.7 ± 2.7 ng m-3) were elevated. We find that atmospheric Pb levels in winter in Xi'an have decreased by 4.6% per year since 2003, yet remain elevated relative to air quality guidelines and therefore a major health concern. δ202HgTSP and Δ199HgTSP averaged -0.80 ± 0.30‰ (1σ) and -0.02 ± 0.10‰ (1σ) and δ202HgTGM and Δ199HgTGM averaged -0.08 ± 0.41‰ (1σ) and 0.00 ± 0.04‰ (1σ). Relative to raw coal from Shaanxi and surrounding provinces, δ202HgTSP is enriched in the light Hg isotopes, whereas δ202HgTGM is enriched in the heavy isotopes. TSP and TGM Δ199Hg signatures are indistinguishable from raw coal, indicating little photochemical mass independent fractionation of atmospheric Hg in the near-field urban-industrial environment. δ202HgTGM correlates significantly with TGM levels (r2 = 0.3, p < 0.01) and likely reflects binary mixing of local industrial TGM emissions with global background TGM. [ABSTRACT FROM AUTHOR]

The Wuda coalfield, Inner Mongolia, China, has been suffering from serious coal fire disaster for more than half a century. In the past decade, the central and local governments have carried out many fire-fighting projects to put out the coal fires, but coal fires still sporadically occur in the coalfield. Previous studies showed that coal fires could release large amounts of mercury (Hg) into the environment. Meanwhile, the rapid industrial development in recent years in Wuda area has also discharged a certain amount of Hg. Identification and quantification of the Hg emitted from coal fires and industrial sources is critical to formulate appropriate environmental policies. This study determined Hg isotope compositions in different types of coals from Wuda coal fire area and surface soils with different distances to the coal fire area, with an aim of anchoring the potential Hg sources in soils. The results showed that the coals had moderately negative δ202Hg (−2.02∼-1.21‰) and slightly negative Δ199Hg (−0.14–0.00‰), while the soils generally had more positive δ202Hg (−1.97∼-0.26‰) and Δ199Hg (−0.07–0.04‰) with distinct isotope ranges among different sampling sites. According to characteristic Hg isotope compositions of different sources, we concluded that the Hg in Wuda soils mainly sourced from cement plants and coal fires, and coal fires were still an important Hg contamination source in Wuda area. Image 1 • Wuda coals have moderately negative δ202Hg and slightly negative Δ199Hg. • Wuda soils have distinct mercury isotope ranges among sites. • Mercury in Wuda soils mainly sourced from cement plants and coal fires. • Coal fires are still an important mercury contamination source in Wuda area. [ABSTRACT FROM AUTHOR]

The end-Permian mass extinction (EPME) is sudden, but prior to which, the ecological resilience has diminished. The Late Permian is an important geologic period for coal formation associated with extensive volcanic activities in South China and adjacent regions. Here we present a systematic analysis of organic carbon and mercury isotopes as well as elemental geochemistry and mineralogy of a coal-bearing section from the Lianying Coalfield in Yunnan Province, South China. The data show that organic carbon δ13C values are negatively shifted by −25.22‰ to −25.99‰ in pyroclastic tonstein partings, which are near-synchronous with the negative Eu anomaly (0.48–0.52), significant Hg enrichment (130–352 ppb) and near-zero Δ199Hg (−0.08–0.07‰). These C and Hg isotope anomalies and associated geochemical signatures, which are manifested by characteristic Al 2 O 3 /TiO 2 , Zr/TiO 2 , and Nb/Yb ratios, are likely caused by subduction or collision-related volcanism. Our study provides evidence for the occurrences of volcanism before the advent of EPME, which played a significant role in stressing the environment and consequently diminishing the ecological resilience in the latest Permian. [ABSTRACT FROM AUTHOR]