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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
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↗
NASA NTRS2016

Seasonal Variation of Total Mercury Burden in the American Alligator (Alligator Mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), Florida

Seasonal variation of mercury (Hg) is not well studied in free-ranging wildlife. Atmospheric deposition patterns of Hg have been studied in detail and have been modeled for both global and specific locations with great accuracy and correlates to environment impact. However, monitoring these trends in wildlife is complicated due to local environmental parameters (e.g., rainfall, humidity, pH, bacterial composition) that can affect the transformation of atmospheric Hg to the biologically available forms. Here, we utilized an abundant and healthy population of American alligators (Alligator mississippiensis) at Merritt Island National Wildlife Refuge (MINWR), FL, and assessed Hg burden in whole blood samples over a span of 7 years (2007 2014; n 174) in an effort to assess seasonal variation of total [Hg]. While the majority of this population is assumed healthy, 18 individuals with low body mass indices (BMI, defined in this study) were captured throughout the 7 year sampling period. These individual alligators exhibited [Hg] that were not consistent with the observed overall seasonal [Hg] variation, and were statistically different from the healthy population of alligators. The alligators with low BMI had elevated concentrations of Hg compared to their age/sex/season matched counterparts with normal BMI. Statistically significant differences were found between the winter and spring seasons for animals with normal BMI. The data in this report supports the conclusion that organismal total [Hg] do fluctuate directly with seasonal deposition rates as well as other seasonal environmental parameters, such as average rainfall and prevailing wind direction. This study highlights the unique environment of MINWR to permit annual assessment of apex predators, such as the American alligator, to determine detailed environmental impact of contaminants of concern.

Hg↗
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↗
DOE OSTI2023

Competition between Dissolved Organic Matter and Freshwater Plankton Control Methylmercury Isotope Fractionation during Uptake and Photochemical Demethylation

Isotope fractionation related to photochemical reactions and planktonic uptake at the base of the food web is a major uncertainty in the biological application of mercury (Hg) stable isotopes. In freshwater systems, it is unclear how competitive interactions among methylmercury (MeHg), dissolved organic matter (DOM), and phytoplankton govern the magnitude of mass-dependent and mass-independent fractionation. This study investigated how DOM alters rates of planktonic MeHg uptake and photodegradation and corresponding Hg isotope fractionation in the presence of freshwater phytoplankton species, Raphidocelis subcapitata. Outdoor sunlight exposure experiments utilizing R. subcapitata were performed in the presence of different DOM samples using environmentally relevant ratios of MeHg-DOM thiol groups. The extent of Δ199Hg in phytoplankton incubations (2.99‰ St. Louis River HPOA, 1.88‰ Lake Erie HPOA) was lower compared to paired abiotic control experiments (4.29 and 2.86‰, respectively) after ~30 h of irradiation, resulting from cell shading or other limiting factors reducing the extent of photodemethylation. Although the Δ 199 Hg/Δ 201 Hg ratio was uniform across experiments (~1.4), Δ 199 Hg/δ 202 Hg slopes varied dramatically (from -0.96 to 15.4) across incubations with R. subcapitata and DOM. In addition, no evidence of Hg isotope fractionation was observed within R. subcapitata cells. This study provides a refined examination of Hg isotope fractionation markers for key processes occurring in the lower food web prior to bioaccumulation, critical for accurately accounting for the photochemical processing of Hg isotopes across a wide spectrum of freshwater systems.

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

Mercury methylation by metabolically versatile and cosmopolitan marine bacteria

Microbes transform aqueous mercury (Hg) into methylmercury (MeHg), a potent neurotoxin that accumulates in terrestrial and marine food webs, with potential impacts on human health. This process requires the gene pair hgcAB, which encodes for proteins that actuate Hg methylation, and has been well described for anoxic environments. However, recent studies report potential MeHg formation in suboxic seawater, although the microorganisms involved remain poorly understood. In this study, we conducted large-scale multi-omic analyses to search for putative microbial Hg methylators along defined redox gradients in Saanich Inlet, British Columbia, a model natural ecosystem with previously measured Hg and MeHg concentration profiles. Analysis of gene expression profiles along the redoxcline identified several putative Hg methylating microbial groups, including Calditrichaeota, SAR324 and Marinimicrobia, with the last the most active based on hgc transcription levels. Marinimicrobia hgc genes were identified from multiple publicly available marine metagenomes, consistent with a potential key role in marine Hg methylation. Computational homology modelling predicts that Marinimicrobia HgcAB proteins contain the highly conserved amino acid sites and folding structures required for functional Hg methylation. Furthermore, a number of terminal oxidases from aerobic respiratory chains were associated with several putative novel Hg methylators. Our findings thus reveal potential novel marine Hg-methylating microorganisms with a greater oxygen tolerance and broader habitat range than previously recognized.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Anaerobic guilds responsible for mercury methylation in boreal wetlands of varied trophic status serving as either a methylmercury source or sink

Wetlands are common sites of active Hg methylation by anaerobic microbes; however, the amount of methylmercury produced varies greatly, as Hg methylation is dependent upon both the availability of Hg and the composition and activity of the microbial community involved. In this study, we identified the major microbial guilds responsible for Hg methylation along a trophic gradient composed of two sites and three different types of wetlands: a bog–fen peatland gradient and a black alder swamp, serving as net sources and a sink for methylmercury respectively. Iron-reducing bacteria in the Geobacteraceae were important Hg methylators across all wetlands and seasons examined, as evidenced by abundant 16S rRNA and hgcA transcripts clustering with this family. Molybdate inhibited Hg methylation more efficiently in the peatlands than in the swamp, suggesting an increasing role of sulfate-reducing bacteria and/or related syntrophs in the methylation of Hg with decreasing trophic status. Further, sulfate addition failed to increase Hg methylation rates in the peatlands, suggesting that SRBs/syntrophs were instead likely metabolizing alternative substrates such as syntrophic fermentation of organic compounds with methanogens. These results highlight the interconnectivity of anaerobic metabolism and importance of community dynamics on the methylation of Hg in wetlands with different trophic status.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Transcriptional Control of hgcAB by an ArsR-Like Regulator in Pseudodesulfovibrio mercurii ND132

The hgcAB gene pair encodes mercury (Hg) methylation capability in a diverse group of microorganisms, but its evolution and transcriptional regulation remain unknown. Working from the possibility that the evolutionary function of HgcAB may not be Hg methylation, we test a possible link to arsenic resistance. Using model Hg methylator Pseudodesulfovibrio mercurii ND132, we evaluated transcriptional control of hgcAB by a putative ArsR encoded upstream and cotranscribed with hgcAB. This regulator shares homology with ArsR repressors of arsenic resistance and S-adenosylhomocysteine (SAH)- responsive regulators of methionine biosynthesis but is distinct from other ArsR/SahR proteins in P. mercurii. Using quantitative PCR (qPCR) and RNA sequencing (RNA-seq) transcriptome analyses, we confirmed this ArsR regulates hgcAB transcription and is responsive to arsenic and SAH. Additionally, RNA-seq indicated a possible link between hgcAB activity and arsenic transformations, with significant upregulation of other ArsRregulated arsenic resistance operons alongside hgcAB. Interestingly, wild-type ND132 was less sensitive to As(V) (but not As(III)) than an hgcAB knockout strain, supporting the idea that hgcAB may be linked to arsenic resistance. Arsenic significantly impacted rates of Hg methylation by ND132; however, responses varied with culture conditions. Differences in growth and metabolic activity did not account for arsenic impacts on methylation. While arsenic significantly increased hgcAB expression, hgcAB gene and transcript abundance was not a good predictor of Hg methylation rates. Taken together, these results support the idea that Hg and As cycling are linked in P. mercurii ND132. Our results may hold clues to the evolution of hgcAB and the controls on Hg methylation in nature. This work reveals a link between microbial mercury methylation and arsenic resistance and may hold clues to the evolution of mercury methylation genes (hgcAB). Microbes with hgcAB produce methylmercury, a strong neurotoxin that readily accumulates in the food web. This study addresses a critical gap in our understanding about the environmental factors that control hgcAB expression. We show that hgcAB expression is controlled by an ArsR-like regulator responsive to both arsenic and S-adenosylhomocysteine in our model organism, Pseudodesulfovibrio mercurii ND132. Exposure to arsenic also significantly impacted Pseudodesulfovibrio mercurii ND132 mercury methylation rates. However, expression of hgcAB was not always a good predictor of Hg methylation rates, highlighting the roles of Hg bioavailability and other biochemical mechanisms in methylmercury production. This study improves our understanding of the controls on hgcAB expression, which is needed to better predict environmental methylmercury production

RNA-seq↗
DOE OSTI2021

Mercury Remediation Technology Development for Lower East Fork Poplar Creek—FY 2021 Update

Mercury 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, Tennessee, but the greatest environmental risk concern relative to Hg on the Oak Ridge Reservation is likely associated with historical Hg losses at and near the Y-12 National Security Complex (Y-12). Mercury in water and fish from East Fork Poplar Creek (EFPC) downstream of Y-12 exceeds 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 upper EFPC (UEFPC), research and technology development are needed to develop appropriate and longer-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). Whereas previous annual reporting updates for Hg remediation technology development for LEFPC have focused on presenting detailed results from the previous fiscal year, this FY 2021 update takes a comprehensive, higher-level approach to the research and technology development activities conducted since 2014. The report is organized to be consistent with the three tasks defined in the LEFPC strategic plan

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗