Increasing chloride concentration causes retention of mercury in melted Arctic snow due to changes in photoreduction kinetics

Mann, Erin; Ziegler, Susan E.; Steffen, Alexandra; O’Driscoll, Nelson J.

doi:10.1016/j.jes.2018.01.006

Cited by 11 publications

(5 citation statements)

References 52 publications

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“…This rapid exchange rate is only possible for reactions involving one electron transfer, such as between Fe(II) and Fe(III), as multiple electron transfers during a single collision of molecules are deemed very slow, − especially at nanomolar concentrations. Recognizing the formation of Hg(I) intermediates or products in the environment may shed additional light on the fundamental reaction processes of Hg, − such as chemical-photochemical redox reactions and biological transformations in the environment. For example, the formation of Hg(I) intermediates is thought to control Hg stability and reaction kinetics in melted Arctic snow and ocean surface water, , in photocatalytic decomposition of phenylmercury in aqueous solutions, in volatilization loss of Hg(0) in dilute solutions of Hg(II), or in BrO – -initiated oxidation of gaseous Hg(0) .…”

Section: Resultsmentioning

confidence: 99%

“…Recognizing the formation of Hg(I) intermediates or products in the environment may shed additional light on the fundamental reaction processes of Hg, − such as chemical-photochemical redox reactions and biological transformations in the environment. For example, the formation of Hg(I) intermediates is thought to control Hg stability and reaction kinetics in melted Arctic snow and ocean surface water, , in photocatalytic decomposition of phenylmercury in aqueous solutions, in volatilization loss of Hg(0) in dilute solutions of Hg(II), or in BrO – -initiated oxidation of gaseous Hg(0) . A recent study reported widespread presence of Hg(I) species in environmental solid matrices, although evidence of Hg(I) existence and its roles in affecting Hg fate and transformations in natural aquatic systems remain scarce and warrant further investigation.…”

Section: Resultsmentioning

confidence: 99%

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Rates and Dynamics of Mercury Isotope Exchange between Dissolved Elemental Hg(0) and Hg(II) Bound to Organic and Inorganic Ligands

Wang

Zhang

Liang

et al. 2020

Environ. Sci. Technol.

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Mercury (Hg) isotope exchange is a common process in biogeochemical transformations of Hg in the environment, but it is unclear whether and at what rates dissolved elemental Hg(0) aq may exchange with divalent Hg(II) bound to various organic and inorganic ligands in water. Using enriched stable isotopes, we investigated the rates and dynamics of isotope exchange between 202 Hg(0) aq and 201 Hg(II) bound to organic and inorganic ligands with varying chemical structures and binding affinities. Timedependent exchange reactions were followed by isotope compositional changes using both inductively coupled plasma mass spectrometry and Zeeman cold vapor atomic absorption spectrometry. Rapid, spontaneous isotope exchange (<1 h) was observed between 202 Hg(0) aq and 201 Hg(II) bound to chloride (Cl − ), ethylenediaminetetraacetate (EDTA), and thiols, such as cysteine (CYS), glutathione (GSH), and 2,3-dimercaptopropanesulfonic acid (DMPS) at a thiol ligand-to-Hg(II) molar ratio of 1:1. Without external reductants or oxidants, the exchange resulted in transfer of two electrons and redistribution of Hg isotopes bound to the ligand but no net changes of chemical species in the system. However, an increase in the ligand-to-Hg(II) ratio decreased the exchange rates due to the formation of 2:1 or higher thiol:Hg(II) chelated complexes, but had no effects on exchange rates with 201 Hg(II) bound to EDTA or Cl − . The exchange between 202 Hg(0) aq and 201 Hg(II) bound to dissolved organic matter (DOM) showed an initially rapid followed by a slower exchange rate, likely resulting from Hg(II) complexation with both low-and high-affinity binding functional groups on DOM (e.g., carboxylates vs bidentate thiolates). These results demonstrate that Hg(0) aq readily exchanges with Hg(II) bound to various ligands and highlight the importance of considering exchange reactions in experimental enriched Hg isotope tracer studies or in natural abundance Hg isotope studies in environmental matrices.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Rates and Dynamics of Mercury Isotope Exchange between Dissolved Elemental Hg(0) and Hg(II) Bound to Organic and Inorganic Ligands

Wang

Zhang

Liang

et al. 2020

Environ. Sci. Technol.

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“…Oxidized Hg II species deposited during AMDEs can undergo photoreduction in snow where a large part (on average ~80%, observed at coastal sites 10 ) is re-emitted as Hg 0 to the atmosphere. The re-emitted Hg fraction is lower from snow on sea ice than from snow on coastal land 21 , due to the higher marine-derived concentrations of Cl - which inhibit Hg II photoreduction 22 . The integrated summertime rebound in Hg 0 at Alert represents 62% of the springtime drop in Hg 0 over the period 1995–2002 20 .…”

Section: Introductionmentioning

confidence: 99%

Mercury isotope evidence for Arctic summertime re-emission of mercury from the cryosphere

et al. 2022

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During Arctic springtime, halogen radicals oxidize atmospheric elemental mercury (Hg0), which deposits to the cryosphere. This is followed by a summertime atmospheric Hg0 peak that is thought to result mostly from terrestrial Hg inputs to the Arctic Ocean, followed by photoreduction and emission to air. The large terrestrial Hg contribution to the Arctic Ocean and global atmosphere has raised concern over the potential release of permafrost Hg, via rivers and coastal erosion, with Arctic warming. Here we investigate Hg isotope variability of Arctic atmospheric, marine, and terrestrial Hg. We observe highly characteristic Hg isotope signatures during the summertime peak that reflect re-emission of Hg deposited to the cryosphere during spring. Air mass back trajectories support a cryospheric Hg emission source but no major terrestrial source. This implies that terrestrial Hg inputs to the Arctic Ocean remain in the marine ecosystem, without substantial loss to the global atmosphere, but with possible effects on food webs.

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“…The possible formation of a Hg(I) chloride complex or precipitate (e.g., Hg 2 Cl 2 ) may control Hg(I) stability, its further reduction, and therefore the whole photoreduction kinetics and the reducible Hg pool. 48,49 Considering the wide occurrence of Hg(I) in various environmental and biological matrices as revealed in this study, further studies are warranted to examine its transport (e.g., evasion) and transformation (e.g., methylation) in the environment, as well as its bioavailability and toxicity to living organisms. It is worth noting that the determination of Hg(I) usually cannot account for multiple redox conversions occurring in sample storage, preparation, and analysis due to the involvement of active Hg(I) species but rather measures the net conversions at a point in time, as is the case in this study.…”

Section: ■ Results and Discussionmentioning

confidence: 92%

Occurrence of Mercurous [Hg(I)] Species in Environmental Solid Matrices as Probed by Mild 2-Mercaptoethanol Extraction and HPLC-ICP-MS Analysis

Wang

Liu

et al. 2020

Environ. Sci. Technol. Lett.

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Mercurous Hg [Hg(I)] is, from the perspective of chemistry, an inevitable intermediate in Hg(II)/Hg(0) redox, presumably playing a critical role in the environmental transformation of common toxic Hg species, such as Hg(II), Hg(0), and methylmercury. The occurrence of Hg(I) in the environment, however, has been scarcely documented, due to its instability, which greatly limits its isolation and identification. We probed the occurrence of Hg(I) in various environmental solid matrices by developing and employing a method based on mild 2mercaptoethanol extraction and HPLC-ICP-MS analysis. Various complexation agents and assisted extraction methods were investigated for their effects on Hg(I) stability. A variety of solid matrices were used to demonstrate extraction, separation, and detection of Hg(I) under optimized conditions. The occurrence of Hg(I) was widely evident in various solid matrices, including desulfurized gypsum, fly ash, phosphorus powder in used fluorescent lamps, PM 2.5 , soil, and plants, despite Hg(I) reduction possibly being catalyzed by a solid matrix during extraction that could underestimate Hg(I) in the samples. More importantly, Hg(I) was detected in Hg(II)-exposed microalgae, exemplifying the environmental relevance of Hg(II) to Hg(I) transformation. These findings highlight the environmental significance of Hg(I), which should be further studied to examine the role of Hg(I) in the transformation, bioavailability, and toxicity of Hg.

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Increasing chloride concentration causes retention of mercury in melted Arctic snow due to changes in photoreduction kinetics

Cited by 11 publications

References 52 publications

Rates and Dynamics of Mercury Isotope Exchange between Dissolved Elemental Hg(0) and Hg(II) Bound to Organic and Inorganic Ligands

Rates and Dynamics of Mercury Isotope Exchange between Dissolved Elemental Hg(0) and Hg(II) Bound to Organic and Inorganic Ligands

Mercury isotope evidence for Arctic summertime re-emission of mercury from the cryosphere

Occurrence of Mercurous [Hg(I)] Species in Environmental Solid Matrices as Probed by Mild 2-Mercaptoethanol Extraction and HPLC-ICP-MS Analysis

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