skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Abiotic Reduction of Mercury(II) in the Presence of Sulfidic Mineral Suspensions
Monomethylmercury (CH 3 Hg) is a neurotoxic pollutant that biomagnifies in aquatic food webs. In sediments, the production of CH 3 Hg depends on the bacterial activity of mercury (Hg) methylating bacteria and the amount of bioavailable inorganic divalent mercury (Hg II ). Biotic and abiotic reduction of Hg II to elemental mercury (Hg 0 ) may limit the pool of Hg II available for methylation in sediments, and thus the amount of CH 3 Hg produced. Knowledge about the transformation of Hg II is therefore primordial to the understanding of the production of toxic and bioaccumulative CH 3 Hg. Here, we examined the reduction of Hg II by sulfidic minerals (FeS (s) and CdS (s) ) in the presence of dissolved iron and dissolved organic matter (DOM) using low, environmentally relevant concentrations of Hg and ratio of Hg II :FeS (s) . Our results show that the reduction of Hg II by Mackinawite (FeS (s) ) was lower (<15% of the Hg II was reduced after 24 h) than when Hg II was reacted with DOM or dissolved iron. We did not observe any formation of Hg 0 when Hg II was reacted with CdS (s) (experiments done under both acidic and basic conditions for up to four days). While reactions in solution were favorable under the experimental conditions, Hg was rapidly removed from solution by co-precipitation. Thermodynamic calculations suggest that in the presence of FeS (s) , reduction of the precipitated Hg II is surface catalyzed and likely involves S −II as the electron donor. The lack of reaction with CdS may be due to its stronger M-S bond relative to FeS, and the lower concentrations of sulfide in solution. We conclude that the reaction of Hg with FeS (s) proceeds via a different mechanism from that of Hg with DOM or dissolved iron, and that it is not a major environmental pathway for the formation of Hg 0 in anoxic environments.  more » « less
Award ID(s):
1607913
PAR ID:
10290534
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Frontiers in Environmental Chemistry
Volume:
2
ISSN:
2673-4486
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; (, Environmental Science: Processes & Impacts)
    The methylation of mercury is known to depend on the chemical forms of mercury (Hg) present in the environment and the methylating bacterial activity. In sulfidic sediments, under conditions of supersaturation with respect to metacinnabar, recent research has shown that mercury precipitates as β-HgS(s) nanoparticles (β-HgS(s) nano ). Few studies have examined the precipitation of β-HgS(s) nano in the presence of marine dissolved organic matter (DOM). In this work, we used dynamic light scattering (DLS) coupled with UV-Vis spectroscopy and transmission electron microscopy (TEM) to investigate the formation and fate of β-HgS(s) nano formed in association with marine DOM extracted from the east and west of Long Island Sound, and at the shelf break of the North Atlantic Ocean, as well as with low molecular weight thiols. We found that while the β-HgS(s) nano formed in the presence of oceanic DOM doubled in size after 5 weeks, those forming in solutions with coastal DOM did not grow over time. In addition, when the Hg II  : DOM ratio was varied, β-HgS(s) nano only rapidly aggregated at high ratios (>41 μmol Hg II per mg C) where the concentration of thiol groups was determined to be substantially low relative to Hg II . This suggests that functional groups other than thiols could be involved in the stabilization of β-HgS(s) nano . Furthermore, we showed that β-HgS(s) nano forming under anoxic conditions remained stable and could therefore persist in the environment sufficiently to impact the methylation potential. Exposure of β-HgS(s) nano to sunlit and oxic environments, however, caused rapid aggregation and sedimentation of the nanoparticles, suggesting that photo-induced changes or oxidation of organic matter adsorbed on the surface of β-HgS(s) nano affected their stability in surface waters. 
    more » « less
  2. ; ; ; ; ; (, Rapid Communications in Mass Spectrometry)
    ABSTRACT RationaleThe complexation with dissolved organic matter (DOM) is a pivotal factor influencing transformations, transport, and bioavailability of mercury (Hg) in aquatic environments. However, identifying these complexes poses a significant challenge because of their low concentrations and the presence of coexisting ions. MethodsIn this study, mercury–dissolved organic matter (Hg‐DOM) complexes were isolated through solid‐phase extraction (SPE) from Hg–humic acid suspensions, and complexes were putatively identified using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS). ResultsDissolved organic carbon (DOC) and total Hg analysis before and after SPE showed an increase in DOC:Hg ratio. The DOC:Hg ratio was lower in extracts from cartridges with silica structure bonded with hydrocarbon chains (C18) than priority pollutant (PPL) cartridges at circumneutral pH, indicating that C18 was more effective at extracting DOM complexed Hg. These results were confirmed with FTICR‐MS analysis, where two Hg‐DOM complexes were putatively identified from PPL extracts as opposed to eight from C18 (Winnow score > 75%). In addition, C8H13HgN2O2S, a molecular formula with am/zratio of 403.04, was identified across three separate extractions using a C18 cartridge, suggesting that the complexes were preserved during extraction and, presumably, electrospray ionization. ConclusionsThe results highlight the effectiveness of the methodology developed in this study—SPE coupled with FTICR‐MS for isolating and identifying Hg‐DOM complexes. This approach allows for the exploration of the elemental and structural composition of Hg‐DOM complexes, which affects Hg speciation, bioavailability, and transformations in aquatic ecosystems. SynopsisA methodology was developed to identify Hg‐DOM complexes at low concentrations to gain insight into mercury bioavailability, transformations, and transport in the environment. 
    more » « less
  3. ; (, Limnology and Oceanography)
    Abstract Elemental mercury (Hg0) formation from other mercury species in seawater results from photoreduction and microbial activity, leading to possible evasion from seawater to overlying air. Microbial conversion of monomethylmercury (MeHg) to Hg0in seawater remains unquantified. A rapid radioassay method was developed using gamma‐emitting203Hg as a tracer to evaluate Hg0production from Hg(II) and MeHg in the low pM range. Bacterioplankton assemblages in Atlantic surface seawater and Long Island Sound water were found to rapidly produce Hg0, with production rate constants being directly related to bacterial biomass and independent of dissolved Hg(II) and MeHg concentrations. About 32% of Hg(II) and 19% of MeHg were converted to Hg0in 4 d in Atlantic surface seawater containing low‐bacterial biomass, and in Long Island Sound water with higher bacterial biomass, 54% of Hg(II) and 8% of MeHg were transformed to Hg0. Decreasing temperatures from 24°C to 4°C reduced Hg0production rates cell−1from Hg(II) 3.3 times as much as from a MeHg source. Because Hg0production rates were linearly related to microbial biomass and temperature, and microbial mercuric reductase was detected in our field samples, we inferred that microbial metabolic activities and enzymatic reactions primarily govern Hg0formation in subsurface waters where light penetration is diminished. 
    more » « less
  4. ; ; ; ; ; ; (, ACS ES&T Water)
    null (Ed.)
    Atmospheric delivery of mercury (Hg) is important to the Upper Great Lakes, and understanding gaseous Hg exchange between surface water and air is critical to predicting the effects of declining mercury emissions. Speciated atmospheric Hg, dissolved gaseous Hg (DGM), and particulate and filter passing total Hg were measured on a cruise in Lake Michigan. Low mercury levels reflected pristine background conditions, especially in offshore regions. In the atmosphere, reactive and particle-associated fractions were low (1.0 ± 0.5%) compared to gaseous elemental Hg (1.34 ± 0.14 ng m–3) and were elevated in the urbanized southern basin. DGM was supersaturated, ranging from 17.5 ± 4.8 pg L–1 (330 ± 80%) in the main lake to 33.2 ± 2.4 pg L–1 (730 ± 70%) in Green Bay. Diel cycling of surface DGM showed strong Hg efflux during the day due to increased winds, and build-up at night from continued DGM production. Epilimnetic DGM is formed from photochemical reduction, while hypolimnetic DGM originates from biological Hg reduction. We found that DGM concentrations were greatest below the thermocline (30.8 ± 13.6 pg L–1), accounting for 68–92% of the total DGM in Lake Michigan, highlighting the importance of nonphotochemical reduction in deep stratified lakes. 
    more » « less
  5. ; ; ; ; ; (, Analytical and Bioanalytical Chemistry)
    Understanding the elemental and structural composition of mercury-dissolved organic matter (Hg-DOM) complexes is crucial for comprehending Hg speciation, bioavailability, and transformations in aquatic ecosystems. However, low concentrations of these organo-metal complexes in natural waters and extraction at acidic pH constrain their characterization. Here, we used solid phase extraction (SPE) methodology to extract Hg-DOM complexes at ambient pH and validated their preconcentration by preserving the composition for identification using ultra-high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). While the dissolved organic carbon (DOC) extraction efficiency was higher with cartridges containing styrene divinylbenzene copolymer (PPL) than silica structure bonded with hydrocarbon chains (C18), Hg in both extracts showed no significant difference. FT-ICR-MS analysis revealed that Hg-DOM complexes extracted by C18 cartridges were aliphatic with smaller carbon chains (16-18), whereas complexes extracted with PPL exhibited both aliphatic and aromatic characteristics with a wide distribution of carbon chains ranging from 17 to 25. The C18 cartridge appeared to be selective in extracting and preserving the nonpolar complexes, as evidenced by the identification of two molecular formulae, C16H31HgNO3 and C16H35HgNO2S, with m/z ratios of 487.2 and 507.21, across triplicate extractions. This study addresses the challenge of the spectroscopic limitation of Hg-DOM identification by extracting these complexes at circumneutral pH and presumably preserving them from dissociation during extraction. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email