This study evaluates the utility of sedimentary mercury (Hg) contents as a proxy for fingerprinting ancient massive volcanism, which is often associated with biogeochemical perturbations. Herein we ...present new Hg geochemical data from anoxic marine basins across the Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma) as a test of the complex Hg cycle. The T-OAE was likely initiated by the main eruptive phase of the Karoo–Ferrar large igneous province, which caused a subsequent cascade of environmental perturbations and resulting mass extinction. At present the leading interpretation of sedimentary Hg anomalies has been volcanogenic outgassing as the primary source. Our study and compilation results suggest, however, that Hg/TOC anomalies were restricted to shallow-water, and/or proximal environments, while deep-water, more distal depositional settings document no significant Hg-related anomalies. Furthermore, asynchronous stratigraphic deviations in Hg enrichments favor terrestrially sourced materials and local redox variability, rather than direct volcanogenic emissions, as a primary control mechanism. Additionally, Hg isotope signatures from our only study site documenting an Hg anomaly are also consistent with a terrestrial Hg origin during the T-OAE. Therefore, our results suggest that Hg anomalies in the geological record need to be re-evaluated as a “smoking gun” proxy that only infers volcanogenic inputs.
•Mercury concentration and isotopes from anoxic basins across the Toarcian OAE.•Compilation shows mercury anomalies are observed near landmasses.•Compilation suggests that Hg is dominantly delivered via terrestrial sources.•Mercury isotopes from one section agree with terrestrial source delivering Hg.•Sedimentary Hg anomalies are not a direct proxy for past volcanism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A mercury resistant bacterial strain, SA2, was isolated from soil contaminated with mercury. The 16S rRNA gene sequence of this isolate showed 99% sequence similarity to the genera Sphingobium and ...Sphingomonas of α-proteobacteria group. However, the isolate formed a distinct phyletic line with the genus Sphingobium suggesting the strain belongs to Sphingobium sp. Toxicity studies indicated resistance to high levels of mercury with estimated EC50 values 4.5 mg L−1 and 44.15 mg L−1 and MIC values 5.1 mg L−1 and 48.48 mg L−1 in minimal and rich media, respectively. The strain SA2 was able to volatilize mercury by producing mercuric reductase enzyme which makes it potential candidate for remediating mercury. ICP-QQQ-MS analysis of Hg supplemented culture solutions confirmed that almost 79% mercury in the culture suspension was volatilized in 6 h. A very small amount of mercury was observed to accumulate in cell pellets which was also evident according to ESEM-EDX analysis. The mercuric reductase gene merA was amplified and sequenced. The deduced amino acid sequence demonstrated sequence homology with α-proteobacteria and Ascomycota group.
•First report on Sphingobium with high mercury true tolerance and volatilization.•80% of mercury is volatilized in six hours which has bioremediation potential.•The merA gene from SA2 shows homology with α-proteobacteria and Ascomycota fungi.•The mercury reductase enzyme, MerA could be employed in bioremediation process.•Bacteria grown in complex media does not reflect true tolerance to mercury.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Mercury (Hg) methylation, methylmercury (MeHg) demethylation, and inorganic redox transformations of Hg are microbe-mediating processes that determine the fate and cycling of Hg and MeHg in many ...environments, and by doing so influence the health of humans and wild life. The discovery of the Hg methylation genes, hgcAB, in the last decade together with advances in high throughput and genome sequencing methods, have resulted in an expanded appreciation of the diversity of Hg methylating microbes. This review aims to describe experimentally confirmed and recently discovered hgcAB gene-carrying Hg methylating microbes; phylogenetic and taxonomic analyses are presented. In addition, the current knowledge on transformation mechanisms, the organisms that carry them out, and the impact of environmental parameters on Hg methylation, MeHg demethylation, and inorganic Hg reduction and oxidation is summarized. This knowledge provides a foundation for future action toward mitigating the impact of environmental Hg pollution.
Mercury (Hg) is naturally released by volcanoes and geothermal systems, but the global flux from these natural sources is highly uncertain due to a lack of direct measurements and uncertainties with ...upscaling Hg/SO2 mass ratios to estimate Hg fluxes. The 2021 and 2022 eruptions of Fagradalsfjall volcano, southwest Iceland, provided an opportunity to measure Hg concentrations and fluxes from a hotspot/rift system using modern analytical techniques. We measured gaseous Hg and SO2 concentrations in the volcanic plume by near-source drone-based sampling and simultaneous downwind ground-based sampling. Mean Hg/SO2 was an order of magnitude higher at the downwind locations relative to near-source data. This was attributed to the elevated local background Hg at ground level (4.0 ng m−3) likely due to emissions from outgassing lava fields. The background-corrected plume Hg/SO2 mass ratio (5.6 × 10−8) therefore appeared conservative from the near-source to several hundred meters distant, which has important implications for the upscaling of volcanic Hg fluxes based on SO2 measurements. Using this ratio and the total SO2 flux from both eruptions, we estimate the total mass of gaseous Hg released from the 2021 and 2022 Fagradalsfjall eruptions was 46 ± 33 kg, equivalent to a flux of 0.23 ± 0.17 kg d−1. This is the lowest Hg flux estimate in the literature for active open-conduit volcanoes, which range from 0.6 to 12 kg d−1 for other hotspot/rift volcanoes, and 0.5–110 kg d−1 for arc volcanoes. Our results suggest that Icelandic volcanic systems are fed from an especially Hg-poor mantle. Furthermore, we demonstrate that the aerial near-source plume Hg measurement is feasible with a drone-based active sampling configuration that captures all gaseous and particulate Hg species, and recommend this as the preferred method for quantifying volcanic Hg emissions going forward.
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•Lowest mercury concentrations and fluxes reported for any active volcano on Earth•Iceland volcanic systems appear to be sourced from a particularly Hg-poor mantle.•Simultaneous near-vent and downwind data suggest Hg/SO2 is conserved over distance.•First drone-based measurements of plume gaseous mercury above an erupting volcano•Drone-based volcanic mercury sampling now feasible and should be the preferred method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mercury (Hg) is a potentially harmful trace element in the environment and one of the World Health Organization's foremost chemicals of concern. The threat posed by Hg contaminated soils to humans is ...pervasive, with an estimated 86 Gg of anthropogenic Hg pollution accumulated in surface soils worldwide. This review critically examines both recent advances and remaining knowledge gaps with respect to cycling of mercury in the soil environment, to aid the assessment and management of risks caused by Hg contamination. Included in this review are factors affecting Hg release from soil to the atmosphere, including how rainfall events drive gaseous elemental mercury (GEM) flux from soils of low Hg content, and how ambient conditions such as atmospheric O3 concentration play a significant role. Mercury contaminated soils constitute complex systems where many interdependent factors, including the amount and composition of soil organic matter and clays, oxidized minerals (e.g. Fe oxides), reduced elements (e.g. S2−), as well as soil pH and redox conditions affect Hg forms and transformation. Speciation influences the extent and rate of Hg subsurface transportation, which has often been assumed insignificant. Nano-sized Hg particles as well as soluble Hg complexes play important roles in soil Hg mobility, availability, and methylation. Finally, implications for human health and suggested research directions are put forward, where there is significant potential to improve remedial actions by accounting for Hg speciation and transportation factors.
•Mercury contaminated soils constitute complex systems with many interdependent factors.•Speciation, complexation and particle size play important roles in subsurface transport.•Rainfall events and atmospheric ozone levels influence Hg flux to the atmosphere.•Implications for human health and suggested research directions are put forward.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Small-molecule based fluorescent probes for Hg2+, Pb2+ and Cd2+ since 2003 concluded in this review.
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•Probes to detect toxic metal ions focused on Hg2+, Pb2+ and Cd2+ ...ions.•Fluorescent probes are subdivided according to sensing mechanism.•Reaction-based probes are listed separately.•Typical examples in cells are emphasized with colorful image.
Heavy-metal pollution, especially Hg2+, Pb2+ and Cd2+, have become a serious issue worldwide. Exposure to even very low concentrations of these metals will threaten human health and cause various illness. More seriously, these metals could not be biodegraded, and would gradually accumulate in environment as well as livingorganism. The development of rapid, accurate and economic methods to detect them is significant important to reduce or avoid exposure to these metals. Consequently, much effort has been dedicated to design and synthesize fluorescent probes that can selectively detect Hg2+, Pb2+ and Cd2+. Herein, we summarized recent small molecular fluorescent probes for these metals. To be helpful for rational design, these probes are divided into three types according to response modes (turn-off, turn-on, ratiometric probes) and are further subdivided according to sensing mechanism (PET, ICT, AIE and others). Especially, reaction-based probes are listed separately because of its good selectivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Corn cultivation potentially plays a vital role in the global mercury (Hg) biogeochemical cycle. Nevertheless, there have been limited studies quantifying the Hg mass flow during corn cultivation. ...This study focuses on Hg uptake by corn plants in China, integrating data from both sample collection and prior studies, resulting in 400 datasets. The findings reveal that the Hg in corn plants is mainly incorporated in leaves (45.5 %–47.5 %) and husks (14.5 %–15.7 %). Despite a decrease in total gaseous Hg (TGM) concentrations in the atmosphere over time, annual Hg uptake by corn cultivation in China has risen from 72.0 (ranging from 47.6 to 96.3) tons (2009–2014) to 84.3 (ranging from 51.9 to 109.6) tons (2015–2020) due to the increasing in corn kernel production. Spatial analysis demonstrates regional disparities in Hg uptake, primarily influenced by corn kernel production, TGM levels, and soil Hg content. Furthermore, temporal analysis reveals a shift in the fate of Hg in corn plants, which can be attributed to variations in corn straw treatment policy or methods. From 2009 to 2014, a substantial amount of absorbed Hg by corn plants was re-released into the atmosphere (48.9 %) due to corn residues burning, whereas, between 2015 and 2020, a greater proportion of Hg ended up accumulating in the soil (51.1 %) after the imposition of the straw burning ban in China. Prior to the ban (2009–2014), corn cultivation contributed approximately 7.7 tons of Hg input to soil annually, with a range from 1.7 to 13.5. However, following the ban (2015–2020), Hg input into the soil increased by approximately 4.5 times, reaching 34.5 (ranging from 17.5 to 52.6) tons per year. These findings emphasize the significant risks associated with soil Hg pollution caused by corn cultivation due to the straw burning ban.
The mass follow of Hg in corn plants in China. Display omitted
•Corn plants incorporated the highest proportion of Hg in leaves (45.5 %–47.5 %) and husks (14.5 %–15.7 %).•Annual Hg uptake in corn plants increased from 72.0 tons (2009–2014) to 84.3 tons (2015–2020) in China.•The Hg emission from corn residues burning counted about 1.9 % to 8.9 % of global biomass burning.•Straw burning ban amplified soil Hg input by 4.5 times and reduced emissions by 17.6 tons/year.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mercury (Hg) methylation genes (hgcAB) mediate the formation of the toxic methylmercury and have been identified from diverse environments, including freshwater and marine ecosystems, Arctic ...permafrost, forest and paddy soils, coal‐ash amended sediments, chlor‐alkali plants discharges and geothermal springs. Here we present the first attempt at a standardized protocol for the detection, identification and quantification of hgc genes from metagenomes. Our Hg‐cycling microorganisms in aquatic and terrestrial ecosystems (Hg‐MATE) database, a catalogue of hgc genes, provides the most accurate information to date on the taxonomic identity and functional/metabolic attributes of microorganisms responsible for Hg methylation in the environment. Furthermore, we introduce “marky‐coco”, a ready‐to‐use bioinformatic pipeline based on de novo single‐metagenome assembly, for easy and accurate characterization of hgc genes from environmental samples. We compared the recovery of hgc genes from environmental metagenomes using the marky‐coco pipeline with an approach based on coassembly of multiple metagenomes. Our data show similar efficiency in both approaches for most environments except those with high diversity (i.e., paddy soils) for which a coassembly approach was preferred. Finally, we discuss the definition of true hgc genes and methods to normalize hgc gene counts from metagenomes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The formation of neurotoxic methylmercury (MeHg) in paddy fields and its accumulation by rice plants is of high environmental concern. The contribution of different geochemical mercury (Hg) pools in ...paddy soils to MeHg production and its accumulation by rice seedlings is not well-studied up to now. Therefore, we investigated the impact of different inorganic Hg forms, including HgCl2, nano-particulated HgS (nano-HgS), Hg bound with dissolved organic matter (Hg-DOM), β-HgS, and α-HgS, at levels of 5 mg Hg/kg soil and 50 mg Hg/kg soil, on the production of MeHg in the soil during rice growing season. Further, we studied the uptake of MeHg by the roots, stalks, leaves, and grains of rice in the tillering, panicle formation, and ripening growth stages, and compared these treatments to a non-polluted soil (control). MeHg contents in HgCl2 polluted soil were the highest, and were 13.5 times and 36.1 times higher than control in 5 and 50 mg/kg Hg treatments, respectively. MeHg contents in α-HgS, β-HgS, nano-HgS, and Hg-DOM polluted soil were 3.9, 2.6, 2.4, and 1.7 times, and 4.4, 15.1, 6.7, and 10.9 times higher than control in 5 and 50 mg/kg Hg treatments, respectively, suggesting the mobilization and methylation of these Hg complexes. The ratio of MeHg to total Hg in the pore water (indication of methylation potential) in HgCl2 and β-HgS treatments were higher than in Hg-DOM, α-HgS, and nano-HgS treatments. HgCl2 treatment resulted in significantly higher MeHg contents in the root, stalk, leaf, and brown rice than nano-HgS, Hg-DOM, β-HgS, and α-HgS treatments both in 5 and 50 mg/kg Hg polluted soils. Rice grain in HgCl2 treatment showed a potential hazard to human health, as indicated by high health risk index (HRI > 1) of MeHg. Current results improve our understanding of MeHg production in soil polluted with different Hg forms, and the assessment of human health risks from consumption of MeHg-laden rice grain at Hg polluted sites with different Hg forms in soils.
•The methylation of Hg(II), nano-HgS, Hg-DOM, β-HgS, and α-HgS in soil was studied.•The Hg(II) treatment resulted in the highest MeHg content in soil, pore water, rice.•The nano HgS, Hg-DOM, β-HgS, and α-HgS were more mobilized relative to control.•Hg-DOM and nano HgS polluted soils showed the highest THg in pore water.•Hg(II) polluted soils showed a hazard to human health.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The sustainable development of the world civilization requires a proper waste handling and management. Mercury is one of the most hazardous water pollutants. Additionally, hydrogen sulfide is a ...life-threatening natural gas contaminant. In this work, a one-pot process for the concurrent removal of mercury (Hg(II)) from mercury-polluted wastewaters and hydrogen sulfide (H2S) scavenging from sour natural gas has been developed. In this process, the sour natural gas is fed into a bubble column reactor filled with synthetic wastewater containing different levels of Hg(II). The contact of H2S in the inlet gas with the dissolved Hg(II) in the wastewater samples promotes the reaction of H2S with Hg(II), forming a water-insoluble HgS precipitant. This leads to the purification of both, the water sample and the gas stream without the need for adding any external material. Almost a complete Hg(II) removal (≥97.6%) from the synthetic wastewater samples is attainable irrespective of the initial Hg(II) concentration. Additionally, each kilogram of Hg(II) could scavenge up to 147.3 and 169.3 g H2S from the entering sour natural gas at the breakthrough and the saturation time, respectively. These findings reveal the efficacy of the proposed process for the simultaneous removal of Hg(II) from mercury-contaminated waters and H2S from sour gases using a single unit operation. Thus, the proposed process herein is novel and very appealing from economic, operational, environmental, and safety/occupational health perspectives.
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•A bubble column reactor has been used to concurrently remove Hg(II) and H2S.•≥ 97.6% Hg(II) removal from wastewater can be obtained.•About 170 g/kg H2S scavenging capacity might be obtained.•Hg(II) removal and H2S scavenging capacity are independent of Hg(II) initial concentration.•The proposed process has multiple economic, environmental, and societal benefits.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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