Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Hg”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Synergistic Effects of a Chalkophore, Methanobactin, on Microbial Methylation of Mercury

Microbial production of the neurotoxin methylmercury (MeHg) is a significant health and environmental concern, as it can bioaccumulate and biomagnify in the food web. A chalkophore or a copper-binding compound, termed methanobactin (MB), has been shown to form strong complexes with mercury [as Hg(II)] and also enables some methanotrophs to degrade MeHg. It is unknown, however, if Hg(II) binding with MB can also impede Hg(II) methylation by other microbes. Contrary to expectations, MB produced by the methanotroph Methylosinus trichosporium OB3b (OB3b-MB) enhanced the rate and efficiency of Hg(II) methylation more than that observed with thiol compounds (such as cysteine) by the mercury-methylating bacteria Desulfovibrio desulfuricans ND132 and Geobacter sulfurreducens PCA. Compared to no-MB controls, OB3b-MB decreased the rates of Hg(II) sorption and internalization, but increased methylation by 5- to 7-fold, suggesting that Hg(II) complexation with OB3b-MB facilitated exchange and internal transfer of Hg(II) to the HgcAB proteins required for methylation. Conversely, addition of excess amounts of OB3b-MB or a different form of MB from Methylocystis strain SB2 (SB2-MB) inhibited Hg(II) methylation, likely due to greater binding of Hg(II). Collectively, our results underscore the complex roles of microbial exogenous metal-scavenging compounds in controlling net production and bioaccumulation of MeHg in the environment. Some anaerobic microorganisms convert inorganic mercury (Hg) into the neurotoxin methylmercury, which can bioaccumulate and biomagnify in the food web. While the genetic basis of microbial mercury methylation is known, factors that control net methylmercury production in the environment are still poorly understood. Here, it is shown that mercury methylation can be substantially enhanced by one form of an exogenous copper-binding compound (methanobactin) produced by some methanotrophs, but not by another. This novel finding illustrates that complex interactions exist between microbes and that these interactions can potentially affect the net production of methylmercury in situ .

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Mercury Remediation Technology Development for Lower East Fork Poplar Creek (FY2020 Update)

Mercury (Hg) remediation is a high priority for the US Department of Energy (DOE) Oak Ridge Office of Environmental Management. Mercury contamination in the environment can be found at all three DOE facilities in Oak Ridge, but probably the greatest environmental risk concern relative to Hg on the Oak Ridge Reservation is associated with historical Hg losses at and near the Y-12 National Security Complex (Y-12). Water and fish from East Fork Poplar Creek (EFPC) downstream of Y-12 exceed regulatory thresholds. Because of the complexities of Hg transport and fate in the aquatic environment, conventional remedial options for EFPC are highly uncertain. DOE is using a phased adaptive management approach to Hg remediation at Y-12 with a focus in the next few years on construction of the Mercury Treatment Facility (MTF) to treat the most contaminated Y-12 outfall entering EFPC (DOE 2017a; DOE 2017b). Once operational, the MTF will provide additional protection against inadvertent releases of Hg into the stream from decontamination and decommissioning of Y-12 Hg-use buildings. Although the MTF is anticipated to substantially decrease Hg water concentrations and flux in the upper part of EFPC, research and technology development are needed to develop appropriate and long-term remedial solutions for the downstream environment. Since late 2014, the Oak Ridge Office of Environmental Management and URS | CH2M Oak Ridge LLC/Restoration Services, Inc. have supported DOE’s Oak Ridge National Laboratory (ORNL) Environmental Sciences Division staff in conducting field and laboratory studies to develop Hg remedial technology solutions for lower EFPC (LEFPC). A technology development strategy for LEFPC was developed in 2014 that was consistent with the adaptive management paradigm and DOE’s technology readiness level (TRL) guidelines (Peterson et al. 2015). Initially, a thorough review of the literature was conducted and site-specific information was collected to develop a broad number of potential technologies that might be applied in LEFPC. An adaptive management approach was then used to focus on technologies that might have the most promise and potential remediation benefit. Field and laboratory studies conducted from 2014 to 2020 have identified the major drivers of Hg flux and bioaccumulation in EFPC and narrowed the list of high-merit technologies that might be of use in remediating the downstream environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Analysis of Solids Obtained from 201O, 201P, 202A, and 202B Contactors in the Salt Waste Processing Facility

In December 2022, Savannah River Mission Completion personnel recovered solids samples from four contractors (EXT-001, EXT-007, EXT-031, and EXT-040) employed at the Salt Waste Processing Facility (SWPF). These solids were submitted to Savannah River National Laboratory for analysis and characterization. This Technical Report outlines the analytical findings and observations associated with these samples and explores the potential source of solid generation within the SWPF. The following conclusions are offered as a result of this work: the light color solids recovered from EXT-007 are consistent with crystallized, soluble salt components (such as sodium nitrate, sodium hydroxide, and sodium carbonate), all of which can be easily re-dissolved in process water and do not represent a threat to SWPF CSSX processing. While the light solids from the top of EXT-040 were not analyzed, it is believed that they share similar characteristics to those recovered from EXT-007; The dark color solids recovered from EXT-001, EXT-031, and the inside of EXT-040 appear to be complex, consisting of several different types of solids: High concentrations of mercury (Hg, 40-75% by mass) partially present as elemental Hg are consistent with the precipitation of Hg 0 /Hg 2+ from disproportionation of Hg + species in pH swing conditions; Moderate concentrations of titanium (Ti) (2-7%, by mass) are also present, often co-located with Hg. This is consistent with co-precipitation, entrainment, and/or amalgamation of Ti and Hg; Moderate concentrations of iron (Fe) (1-3%, by mass) are observed in SWPF solids and are likely attributable to erosion of stainless-steel components within the CSSX process; Small concentrations of tungsten (W) and cobalt (Co) (<1%, by mass) are observed in SWPF solids. The presence of these solids is consistent with the erosion of components coated with W and Co (e.g., Stellite); Small concentrations of aluminum (Al) (<1%, by mass) are observed in the form of gibbsite and potentially sodium aluminosilicate. The presence of these compounds is likely attributable to the pH swing observed between the scrub and extraction cycles within the CSSX process. The following recommendations are made as a result of this work: Testing should be performed to determine the chemical drivers, process, and mechanism of Hg precipitation in CSSX processing. Special care should be taken to include titanium in tests to evaluate the potential for co-precipitation, entrainment, and amalgamation; Hg-mitigation options that would minimize or eliminate risks of Hg precipitation and solids accumulation (e.g., Hg-absorption techniques, ion exchange/adsorbents, flowsheet changes, etc.) should be assessed.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

Arabidopsis GALACTURONOSYLTRANSFERASE (GAUT) 1 synthesizes a homogalacturonan tightly bound to the cell wall and required for cell expansion

Arabidopsis GALACTURONOSYLTRANSFERASE1 (GAUT1) synthesizes homogalacturonan (HG), the most abundant pectin in growing plant cells. GAUT1 has the greatest in vitro enzyme activity of the six confirmed Arabidopsis HG biosynthetic GAUTs, but its biological activity remains elusive. Here we show that Arabidopsis GAUT1 homozygous mutants have a severe dwarfed seedling phenotype, survive several weeks as 2 to 3 mm seedlings, and have severely reduced shoot and root growth and hypocotyl epidermal, cortex and endodermal cell size. gaut1-1 pollen tubes are shorter than WT with increased bursting. Complementation of homozygous gaut1-1 with GAUT1 coding sequence driven by the GAUT1 promoter restored WT-like growth. The extreme dwarf phenotype of homozygous gaut1-1 seedlings precluded their use for detailed cell wall analysis, thus suspensions cultures were produced from callus generated from mutant and WT seedlings. Homozygous gaut1-1 suspension cells were smaller than WT with ∼30% reduced wall GalA content compared to WT. Sequential extraction of the walls with increasingly harsh solvents and sugar composition analysis revealed reduced GalA content in only the 4M KOH post-chlorite fraction, indicating that GAUT1-synthesized HG was held tightly in the wall by direct or indirect hydrogen bonding and/or oxidation-sensitive linkages. Treatment of wall fractions with endopolygalacturonase to hydrolyze HG and gel electrophoretic separation of hydrolysates exposed an HG-associated doublet band markedly downregulated in the homozygous gaut1-1 4M KOH post-chlorite fraction and to a lesser extent in 4M KOH and sodium chlorite fractions. NMR analysis identified the band as rhamnogalacturonan (RG)-II. Super resolution microscopy using anti-HG antibodies showed that, compared to WT, the homozygous gaut1-1 hypocotyl epidermal and callus cells had reduced content and length of HG nanofilaments, HG fibers associated with cell expansion in Arabidopsis. The results demonstrate that GAUT1-synthesized HG resides in a tightly-cell-wall-bound, RG-II-containing polymer required for HG nanofilament formation and seedling cell expansion.

Atmodjo↗
DOE OSTI2022

Stannous chloride as a tool for mercury stripping in contaminated streams: Experimental assessment of toxicity in an invertebrate model species

In this work, the chronic toxicity of an innovative Hg water treatment system using tin (Sn) (II) chloride (SnCl 2 ) followed by air stripping was assessed through measurements of survival, growth, and reproduction rate in the freshwater cladoceran Ceriodaphnia dubia, a model species for toxicity testing. We first calculated the concentrations of Hg causing 25% reduction in survival and reproduction (Lethal or Inhibition Concentrations, or LC 25 and IC 25 , for survival and reproduction, respectively) through exposure to aqueous Hg at concentrations ranging from 0 to 25,000 ng L -1 . Then, we treated media (DMW and natural stream water) contaminated with Hg at LC 25 and IC 25 concentrations with SnCl 2 at a Sn:Hg stoichiometric ratio of 8:1 and air stripping and exposed C. dubia to this Sn-amended media. Our results showed that Hg significantly affected survival, reproduction rates and impaired growth. SnCl 2 -treatment removed 100% of the Hg from the media at all concentrations tested with no deleterious effects on survival, growth and reproduction. Our results confirmed the efficacy of SnCl 2 in removing aqueous Hg from stream water and showed that the added Sn did not impact C. dubia at the concentrations tested, supporting the suitability of SnCl 2 -based treatments in appropriate Hg-contaminated environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The efficacy and ecological impact of mercury sorbents on the physiology and reproductive fitness of Daphnia magna

Environmental mercury (Hg) contamination threatens ecosystems due to its bioaccumulation and toxicity. Effective and sustainable remediation strategies are essential, with carbon-based sorbents like biochar (BC) and activated carbon (AC) gaining attention for their high adsorption capacity and cost-effectiveness. However, their ecological impacts remain poorly understood. This study evaluates the Hg removal efficacy and ecological effects of three sorbents—BC, granular AC (GAC), and AC fiber (ACF)—in a flow-through column system with and without Hg additions. We tested Hg removal at two concentrations (1 and 4 µg/L Hg) and assessed chronic exposure effects on a sentinel and sensitive freshwater organism, Daphnia magna, over 30 days of exposure to the columns’ effluent. GAC removed 100 % of Hg, while BC and ACF achieved 99 % removal. The ACF + 4 µg/L Hg effluent induced 70 % lethality in D. magna after nearly three weeks of exposure, while the GAC effluent significantly reduced fecundity, even in the absence of Hg exposure. In contrast, the BC effluent enhanced reproductive output, likely due to inputs of carbon and nitrogen in the effluent. These findings highlight the need to balance Hg removal efficacy with ecological safety, emphasizing the importance of considering both remediation effectiveness and potential environmental impacts.

Activated carbon↗
DOE OSTI2020

Materials Data on Ca5Hg3 by Materials Project

Ca5Hg3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Ca sites. In the first Ca site, Ca is bonded in a distorted square co-planar geometry to six Hg atoms. There are four shorter (3.21 Å) and two longer (3.71 Å) Ca–Hg bond lengths. In the second Ca site, Ca is bonded to five Hg atoms to form a mixture of distorted edge, corner, and face-sharing CaHg5 trigonal bipyramids. There are a spread of Ca–Hg bond distances ranging from 3.21–3.44 Å. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a 10-coordinate geometry to ten Ca atoms. In the second Hg site, Hg is bonded in a 8-coordinate geometry to eight Ca atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg3SeO6 by Materials Project

Hg3SeO6 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are nine inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Hg–O bond distances ranging from 2.07–2.87 Å. In the second Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Hg–O bond distances ranging from 2.25–2.69 Å. In the third Hg2+ site, Hg2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Hg–O bond distances ranging from 2.14–2.62 Å. In the fourth Hg2+ site, Hg2+ is bonded in a 2-coordinate geometry to five O2- atoms. There are a spread of Hg–O bond distances ranging from 2.15–2.89 Å. In the fifth Hg2+ site, Hg2+ is bonded in a distorted octahedral geometry to six O2- atoms. There are a spread of Hg–O bond distances ranging from 2.30–2.60 Å. In the sixth Hg2+ site, Hg2+ is bonded in a 4-coordinate geometry to four O2- atoms. There are a spread of Hg–O bond distances ranging from 2.18–2.63 Å. In the seventh Hg2+ site, Hg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Hg–O bond distances ranging from 2.19–2.87 Å. In the eighth Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Hg–O bond distances ranging from 2.29–2.43 Å. In the ninth Hg2+ site, Hg2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Hg–O bond distances ranging from 2.21–2.92 Å. There are three inequivalent Se6+ sites. In the first Se6+ site, Se6+ is bonded in a trigonal non-coplanar geometry to three O2- atoms. There are a spread of Se–O bond distances ranging from 1.69–1.88 Å. In the second Se6+ site, Se6+ is bonded in a tetrahedral geometry to four O2- atoms. There are a spread of Se–O bond distances ranging from 1.66–1.69 Å. In the third Se6+ site, Se6+ is bonded in a distorted trigonal non-coplanar geometry to three O2- atoms. There is two shorter (1.70 Å) and one longer (1.91 Å) Se–O bond length. There are eighteen inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Hg2+ and one Se6+ atom. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Hg2+ atoms. In the third O2- site, O2- is bonded in a 1-coordinate geometry to three Hg2+ and one Se6+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the fifth O2- site, O2- is bonded to four Hg2+ atoms to form a mixture of corner and edge-sharing OHg4 tetrahedra. In the sixth O2- site, O2- is bonded in a 1-coordinate geometry to two Hg2+ and one Se6+ atom. In the seventh O2- site, O2- is bonded in a distorted single-bond geometry to two Hg2+ and one Se6+ atom. In the eighth O2- site, O2- is bonded to four Hg2+ atoms to form distorted corner-sharing OHg4 tetrahedra. In the ninth O2- site, O2- is bonded in a 1-coordinate geometry to two Hg2+ and one Se6+ atom. In the tenth O2- site, O2- is bonded in a 2-coordinate geometry to three Hg2+ and one Se6+ atom. In the eleventh O2- site, O2- is bonded in a distorted water-like geometry to two Se6+ atoms. In the twelfth O2- site, O2- is bonded to four Hg2+ atoms to form corner-sharing OHg4 trigonal pyramids. In the thirteenth O2- site, O2- is bonded to four Hg2+ atoms to form a mixture of corner and edge-sharing OHg4 tetrahedra. In the fourteenth O2- site, O2- is bonded in a 1-coordinate geometry to three Hg2+ and one Se6+ atom. In the fifteenth O2- site, O2- is bonded in a distorted T-shaped geometry to two Hg2+ and one O2- atom. The O–O bond length is 1.36 Å. In the sixteenth O2- site, O2- is bonded in a distorted L-shaped geometry to one Hg2+ and one O2- atom. The O–O bond length is 1.42 Å. In the seventeenth O2- site, O2- is bonded in a 3-coordinate geometry to one Hg2+ and two O2- atoms. In the eighteenth O2- site, O2- is bonded in a 1-coordinate geometry to two Hg2+ and one Se6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg5Hg by Materials Project

Mg5Hg crystallizes in the orthorhombic Amm2 space group. The structure is three-dimensional. there are five inequivalent Mg sites. In the first Mg site, Mg is bonded to twelve Mg atoms to form a mixture of corner and face-sharing MgMg12 cuboctahedra. There are a spread of Mg–Mg bond distances ranging from 3.13–3.26 Å. In the second Mg site, Mg is bonded to two equivalent Mg and four equivalent Hg atoms to form distorted MgMg2Hg4 cuboctahedra that share corners with eight MgMg12 cuboctahedra, edges with six MgMg2Hg4 cuboctahedra, and faces with four MgMg2Hg4 cuboctahedra. All Mg–Hg bond lengths are 3.12 Å. In the third Mg site, Mg is bonded in a distorted water-like geometry to two equivalent Mg and two equivalent Hg atoms. Both Mg–Hg bond lengths are 3.12 Å. In the fourth Mg site, Mg is bonded to four equivalent Mg and two equivalent Hg atoms to form distorted MgMg4Hg2 cuboctahedra that share corners with twelve MgMg12 cuboctahedra, edges with six MgMg2Hg4 cuboctahedra, and faces with four MgMg2Hg4 cuboctahedra. Both Mg–Hg bond lengths are 3.13 Å. In the fifth Mg site, Mg is bonded in a 12-coordinate geometry to two equivalent Mg and two equivalent Hg atoms. Both Mg–Hg bond lengths are 3.08 Å. Hg is bonded in a 12-coordinate geometry to ten Mg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgAs2Xe5F22 by Materials Project

Xe5HgAs2F22 crystallizes in the orthorhombic Pna2_1 space group. The structure is zero-dimensional and consists of four Xe5HgAs2F22 clusters. there are five inequivalent Xe sites. In the first Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.07 Å) and one longer (2.11 Å) Xe–F bond lengths. In the second Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.15 Å) Xe–F bond lengths. In the third Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.13 Å) Xe–F bond lengths. In the fourth Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.14 Å) Xe–F bond lengths. In the fifth Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.13 Å) Xe–F bond lengths. Hg is bonded in a 7-coordinate geometry to seven F atoms. There are a spread of Hg–F bond distances ranging from 2.31–2.64 Å. There are two inequivalent As sites. In the first As site, As is bonded in an octahedral geometry to six F atoms. There are a spread of As–F bond distances ranging from 1.76–1.81 Å. In the second As site, As is bonded in an octahedral geometry to six F atoms. There is five shorter (1.77 Å) and one longer (1.82 Å) As–F bond length. There are twenty-two inequivalent F sites. In the first F site, F is bonded in a distorted bent 150 degrees geometry to one Xe and one Hg atom. In the second F site, F is bonded in a single-bond geometry to one Xe atom. In the third F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the fourth F site, F is bonded in a single-bond geometry to one Xe atom. In the fifth F site, F is bonded in a single-bond geometry to one As atom. In the sixth F site, F is bonded in a single-bond geometry to one Xe atom. In the seventh F site, F is bonded in a single-bond geometry to one As atom. In the eighth F site, F is bonded in a single-bond geometry to one As atom. In the ninth F site, F is bonded in a single-bond geometry to one As atom. In the tenth F site, F is bonded in a single-bond geometry to one As atom. In the eleventh F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the twelfth F site, F is bonded in a single-bond geometry to one Hg and one As atom. In the thirteenth F site, F is bonded in a single-bond geometry to one As atom. In the fourteenth F site, F is bonded in a single-bond geometry to one As atom. In the fifteenth F site, F is bonded in a single-bond geometry to one Xe atom. In the sixteenth F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the seventeenth F site, F is bonded in a single-bond geometry to one Xe atom. In the eighteenth F site, F is bonded in a bent 120 degrees geometry to one Xe and one Hg atom. In the nineteenth F site, F is bonded in a single-bond geometry to one As atom. In the twentieth F site, F is bonded in a single-bond geometry to one Hg and one As atom. In the twenty-first F site, F is bonded in a single-bond geometry to one As atom. In the twenty-second F site, F is bonded in a single-bond geometry to one As atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgSb2F13 by Materials Project

HgSb2F13 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Hg is bonded in a 7-coordinate geometry to seven F atoms. There are a spread of Hg–F bond distances ranging from 2.40–2.50 Å. There are two inequivalent Sb sites. In the first Sb site, Sb is bonded in an octahedral geometry to six F atoms. There are a spread of Sb–F bond distances ranging from 1.89–1.96 Å. In the second Sb site, Sb is bonded in an octahedral geometry to six F atoms. There are a spread of Sb–F bond distances ranging from 1.88–1.96 Å. There are thirteen inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Sb atom. In the second F site, F is bonded in a single-bond geometry to one Sb atom. In the third F site, F is bonded in a bent 150 degrees geometry to one Hg and one Sb atom. In the fourth F site, F is bonded in a single-bond geometry to one Hg atom. In the fifth F site, F is bonded in a bent 120 degrees geometry to one Hg and one Sb atom. In the sixth F site, F is bonded in a bent 150 degrees geometry to one Hg and one Sb atom. In the seventh F site, F is bonded in a distorted bent 120 degrees geometry to one Hg and one Sb atom. In the eighth F site, F is bonded in a single-bond geometry to one Sb atom. In the ninth F site, F is bonded in a bent 150 degrees geometry to one Hg and one Sb atom. In the tenth F site, F is bonded in a single-bond geometry to one Sb atom. In the eleventh F site, F is bonded in a single-bond geometry to one Sb atom. In the twelfth F site, F is bonded in a single-bond geometry to one Sb atom. In the thirteenth F site, F is bonded in a bent 150 degrees geometry to one Hg and one Sb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mn4Hg3Au by Materials Project

Mn4AuHg3 is Heusler-like structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Mn sites. In the first Mn site, Mn is bonded in a distorted body-centered cubic geometry to four equivalent Au and four equivalent Hg atoms. All Mn–Au bond lengths are 2.80 Å. All Mn–Hg bond lengths are 2.91 Å. In the second Mn site, Mn is bonded in a body-centered cubic geometry to eight Hg atoms. There are four shorter (2.86 Å) and four longer (2.87 Å) Mn–Hg bond lengths. Au is bonded in a body-centered cubic geometry to eight equivalent Mn atoms. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a distorted body-centered cubic geometry to eight Mn atoms. In the second Hg site, Hg is bonded in a body-centered cubic geometry to eight equivalent Mn atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgSb2Xe5F22 by Materials Project

Xe5HgSb2F22 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four Xe5HgSb2F22 clusters. there are five inequivalent Xe sites. In the first Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.13 Å) Xe–F bond lengths. In the second Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.04 Å) and one longer (2.15 Å) Xe–F bond lengths. In the third Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.05 Å) and one longer (2.13 Å) Xe–F bond lengths. In the fourth Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.03 Å) and one longer (2.13 Å) Xe–F bond lengths. In the fifth Xe site, Xe is bonded in a linear geometry to two F atoms. There are one shorter (2.06 Å) and one longer (2.11 Å) Xe–F bond lengths. Hg is bonded in a 7-coordinate geometry to seven F atoms. There are a spread of Hg–F bond distances ranging from 2.30–2.60 Å. There are two inequivalent Sb sites. In the first Sb site, Sb is bonded in an octahedral geometry to six F atoms. There are a spread of Sb–F bond distances ranging from 1.91–1.96 Å. In the second Sb site, Sb is bonded in an octahedral geometry to six F atoms. There are a spread of Sb–F bond distances ranging from 1.91–1.95 Å. There are twenty-two inequivalent F sites. In the first F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the second F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the third F site, F is bonded in a bent 150 degrees geometry to one Xe and one Hg atom. In the fourth F site, F is bonded in a single-bond geometry to one Xe atom. In the fifth F site, F is bonded in a single-bond geometry to one Xe atom. In the sixth F site, F is bonded in a single-bond geometry to one Hg and one Sb atom. In the seventh F site, F is bonded in a single-bond geometry to one Sb atom. In the eighth F site, F is bonded in a single-bond geometry to one Xe atom. In the ninth F site, F is bonded in a single-bond geometry to one Sb atom. In the tenth F site, F is bonded in a single-bond geometry to one Xe atom. In the eleventh F site, F is bonded in a bent 120 degrees geometry to one Xe and one Hg atom. In the twelfth F site, F is bonded in a single-bond geometry to one Sb atom. In the thirteenth F site, F is bonded in a single-bond geometry to one Sb atom. In the fourteenth F site, F is bonded in a distorted bent 120 degrees geometry to one Xe and one Hg atom. In the fifteenth F site, F is bonded in a single-bond geometry to one Xe atom. In the sixteenth F site, F is bonded in a distorted single-bond geometry to one Hg and one Sb atom. In the seventeenth F site, F is bonded in a single-bond geometry to one Sb atom. In the eighteenth F site, F is bonded in a single-bond geometry to one Sb atom. In the nineteenth F site, F is bonded in a single-bond geometry to one Sb atom. In the twentieth F site, F is bonded in a single-bond geometry to one Sb atom. In the twenty-first F site, F is bonded in a single-bond geometry to one Sb atom. In the twenty-second F site, F is bonded in a single-bond geometry to one Sb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Integrating Mercury Concentrations in American Alligators ( Alligator mississippiensis ) with Hunter Consumption Surveys to Estimate Exposure Risk

Mercury is a naturally occurring element but is also considered a widespread contaminant due to global anthropogenic activity. Even in moderate amounts, mercury (Hg) is an established neurotoxin and is associated with a range of adverse outcomes both in humans and wildlife. Humans in the United States are most commonly exposed to Hg through contaminated food or drinking water, and the consumption of game species, particularly those occupying higher trophic levels, has the potential to expose hunters to high concentrations of Hg. In the present study, we determined Hg concentrations in tail muscle and blood from American alligators (Alligator mississippiensis) inhabiting a region (Savannah River Site, SC, USA) with known Hg contamination. We then integrated these data with alligator harvest records and previously published surveys of alligator meat consumption patterns to estimate potential exposure risk. We found that the average Hg concentrations in tail muscle (1.34 mg/kg, wet wt) from sampled alligators exceeded the recommended threshold for Hg exposure based on the World Health Organization's guidelines (0.5mg/kg, wet wt). In addition, based on regional consumption patterns reported for both adults and children, we estimated Hg exposures (x¯ Adult = 0.419 μg/kg/day, x¯ Child = 2.24 μg/kg/day) occurring well above the US Environmental Protection Agency methylmercury reference dose of 0.1 μg/kg/day. Although the two reservoirs sampled in the present study are not currently open to alligator hunting, they are connected to waters that are publicly accessible, and the extent of alligator mobility across these sites is not known. Together, the findings reported in the present study further demonstrate the need for active monitoring of Hg concentrations in game species, which can convey substantial exposure risks to the public.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Non-mercury methylating microbial taxa are integral to understanding links between mercury methylation and elemental cycles in marine and freshwater sediments

The goal of this study was to explore the role of non-mercury (Hg) methylating taxa in mercury methylation and to identify potential links between elemental cycles and Hg methylation. Statistical approaches were utilized to investigate the microbial community and biochemical functions in relation to methylmercury (MeHg) concentrations in marine and freshwater sediments. Sediments were collected from the methylation zone (top 15 cm) in four Hg-contaminated sites. Both abiotic (e.g., sulfate, sulfide, iron, salinity, total organic matter, etc.) and biotic factors (e.g., hgcA, abundances of methylating and non-methylating taxa) were quantified. Random forest and stepwise regression were performed to assess whether non-methylating taxa were significantly associated with MeHg concentration. Co-occurrence and functional network analyses were constructed to explore associations between taxa by examining microbial community structure, composition, and biochemical functions across sites. Regression analysis showed that approximately 80% of the variability in sediment MeHg concentration was predicted by total mercury concentration, the abundances of Hg methylating taxa, and the abundances of the non-Hg methylating taxa. The co-occurrence networks identified Paludibacteraceae and Syntrophorhabdaceae as keystone non Hg methylating taxa in multiple sites, indicating the potential for syntrophic interactions with Hg methylators. Strong associations were also observed between methanogens and sulfate-reducing bacteria, which were likely symbiotic associations. The functional network results suggested that non-Hg methylating taxa play important roles in sulfur respiration, nitrogen respiration, and the carbon metabolism-related functions methylotrophy, methanotrophy, and chemoheterotrophy. Interestingly, keystone functions varied by site and did not involve carbon- and sulfur-related functions only. In conclusion, our findings highlight associations between methylating and non-methylating taxa and sulfur, carbon, and nitrogen cycles in sediment methylation zones, with implications for predicting and understanding the impact of climate and land/sea use changes on Hg methylation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Mercury linked to Deccan Traps volcanism, climate change and the end-Cretaceous mass extinction

Mercury (Hg) anomalies linked to Large Igneous Provinces (LIP) volcanism have been identified in sediments across all five major mass extinctions in Earth's history. This study tests whether Hg in marine sediments is a reliable proxy linking Deccan Traps volcanic eruptions to late Maastrichtian global climate warming and the mass extinction at the Cretaceous-Paleogene boundary (KPB). Our primary test site is the Elles section in Tunisia, the auxiliary Global Stratotype Section and Point (GSSP) to El Kef. Elles has the most complete marine sedimentary record and a high average sedimentation rate of ~4.7 cm/ky. Here, we chose the Hor Hahar section in Israel to corroborate the geographic distribution of Hg fallout from Deccan volcanism. Reliability of the Hg proxy over the last 550 ky of the Maastrichtian to early Danian was evaluated based on high-resolution age control (orbital cyclostratigraphy), stable isotope climate record, Hg concentrations, biotic turnover and mass extinction. These results were correlated with the pulsed Deccan eruptive history constrained previously by U-Pb zircon geochronology. Our results support Hg as robust proxy for Deccan volcanism with large Hg spikes marking “extreme event” (EE) pulsed eruptions correlative with climate warming peaks separated by steady, less intense eruptions. Long-term global climate warming began near ~350 ky pre-KPB, reached maximum warming (3–4 °C) between 285 and 200 ky pre-KPB, followed by gradual cooling and rapid temperature drop between 45 and 25 ky pre-KPB. During the last 25 ky before the KPB, multiple Hg EE eruptions correlate with hyperthermal warming that culminated in the rapid mass extinction at Elles during ≤1000 years of the Cretaceous. These latest Cretaceous Hg peaks may correlate with massive, distal, Deccan-sourced lava flows (>1000 km long) that traversed the Indian subcontinent and flowed into the Bay of Bengal, bracketing the mass extinction. These results support Deccan volcanism as a primary driver of the end-Cretaceous mass extinction.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Computational Chemistry-Based Evaluation of Metal Salts and Metal Oxides for Application in Mercury-Capture Technologies

Anthropogenic mercury emission to the atmosphere adversely affects the environment, wildlife, and human health. Accordingly, the design and implementation of improved mercury-capture technologies have received increased attention. We present a computational chemistry-based screening study to guide the development of mercury-capture materials. We use density functional theory (DFT) to probe the efficacy of metal salts and metal oxides (NaCl, NaBr, KCl, KBr, CaCl 2 , CaBr 2 , NaNO 3 , and MgO) toward mercury capture and their ability to be regenerated for continued use. We focus on three primary sources of mercury emission as elemental gaseous mercury (Hg(0)) or oxidized gaseous mercury species (Hg(II); HgCl 2 or HgBr 2 ): (i) Hg(0) emission from artisanal Au production; (ii) Hg(II)/Hg(0) emission from inlet/outlet streams for flue-gas desulfurization (FGD) operation; and (iii) Hg(0) and Hg(II) emission from cement production. Our results suggest that CaCl 2 and CaBr 2 are good candidates for capturing Hg(0) in artisanal Au production. For FGD operation, KBr, MgO, CaCl 2 , and CaBr 2 are good candidates for capturing HgCl 2 and HgBr 2 , while CaBr 2 is the only studied material that can capture Hg(0) from the outlet FGD stream. For cement production, CaBr 2 is the only material of those studied that can capture Hg(0), HgCl 2 , and HgBr 2 . Furthermore, our DFT results can accelerate the development of cheap and regenerable mercury-capture materials, as well as better prevent the release of mercury to the environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Mechanistic Investigation of Dimethylmercury Formation Mediated by a Sulfide Mineral Surface

Mercury (Hg) pollution is a global environmental problem, but many key transformations among 29 various Hg species are not well understood. Although anaerobic microorganisms are the primary 30 producers of monomethylmercury (MMeHg), the abiotic formation of dimethylmercury (DMeHg) 31 from MMeHg have been suggested to account for a large portion of DMeHg in the ocean. It has 32 been shown that abiotic formation of DMeHg from MMeHg can be facilitated by reduced sulfur 33 groups on mineral surfaces. However, a detailed mechanistic understanding of this reaction is 34 lacking. Here we perform density functional theory (DFT) calculations to explore mechanisms of 35 DMeHg formation on the 110 surface of a CdS(s) (hawleyite) nanoparticle. We show that 36 coordination of MMeHg substituents to adjacent reduced sulfur groups protruding from the surface 37 facilitate DMeHg formation and that the reaction proceeds through direct transmethylation from 38 one MMeHg substituent to another. Solvation effects were found to play an important role in the 39 surface reconstruction of the nanoparticle and in decreasing the energetic barrier for DMeHg 40 formation. We also investigate DMeHg formation from MMeHg mediated by organic dithiols and 41 compare the results to those mediated by the mineral surface. In contrast to the surface reaction, 42 the calculations suggest that dithiol-mediated formation of DMeHg instead proceeds through a 43 mechanism in which Hg–Hg interactions activate a methyl group from one MMeHg substituent 44 for intramolecular transfer to the adjacent MMeHg substituent. These findings refine previously 45 proposed mechanisms of abiotic DMeHg formation and fill gaps in our understanding of global 46 Hg cycling in the environment.

Lian, Peng↗