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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Hg3(SeBr)2 by Materials Project

Hg3(SeBr)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are five inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded to two Se2- and three Br1- atoms to form distorted HgSe2Br3 square pyramids that share corners with two HgSe2Br4 octahedra, a cornercorner with one HgSe2Br3 square pyramid, edges with two HgSe2Br4 octahedra, and an edgeedge with one HgSe2Br3 square pyramid. The corner-sharing octahedra tilt angles range from 59–61°. Both Hg–Se bond lengths are 2.59 Å. There are a spread of Hg–Br bond distances ranging from 2.93–3.52 Å. In the second Hg2+ site, Hg2+ is bonded to two equivalent Se2- and four Br1- atoms to form HgSe2Br4 octahedra that share corners with four equivalent HgSe2Br4 octahedra, corners with two equivalent HgSe2Br3 square pyramids, edges with four HgSe2Br4 octahedra, and edges with two equivalent HgSe2Br3 square pyramids. The corner-sharing octahedra tilt angles range from 4–9°. Both Hg–Se bond lengths are 2.56 Å. There are two shorter (3.33 Å) and two longer (3.35 Å) Hg–Br bond lengths. In the third Hg2+ site, Hg2+ is bonded to two equivalent Se2- and four Br1- atoms to form HgSe2Br4 octahedra that share corners with four equivalent HgSe2Br4 octahedra, corners with two equivalent HgSe2Br3 square pyramids, edges with four HgSe2Br4 octahedra, and edges with two equivalent HgSe2Br3 square pyramids. The corner-sharing octahedra tilt angles range from 4–9°. Both Hg–Se bond lengths are 2.56 Å. There are two shorter (3.25 Å) and two longer (3.42 Å) Hg–Br bond lengths. In the fourth Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two equivalent Se2- and three Br1- atoms. Both Hg–Se bond lengths are 2.55 Å. There are a spread of Hg–Br bond distances ranging from 3.12–3.39 Å. In the fifth Hg2+ site, Hg2+ is bonded in a 4-coordinate geometry to two equivalent Se2- and three Br1- atoms. Both Hg–Se bond lengths are 2.56 Å. There are a spread of Hg–Br bond distances ranging from 3.01–3.66 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are four inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 5-coordinate geometry to five Hg2+ atoms. In the second Br1- site, Br1- is bonded in a 4-coordinate geometry to seven Hg2+ atoms. In the third Br1- site, Br1- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the fourth Br1- site, Br1- is bonded in a 5-coordinate geometry to five Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgSb3XeF17 by Materials Project

XeHgSb3F17 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of one XeHgSb3F17 sheet oriented in the (0, 0, 1) direction. Xe is bonded in a single-bond geometry to one Hg atom. The Xe–Hg bond length is 2.86 Å. Hg is bonded in a 5-coordinate geometry to one Xe and six F atoms. There are a spread of Hg–F bond distances ranging from 2.36–2.65 Å. There are three inequivalent Sb sites. In the first Sb site, Sb is bonded to six F atoms to form corner-sharing SbF6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Sb–F bond distances ranging from 1.88–2.07 Å. In the second Sb site, Sb is bonded to six F atoms to form corner-sharing SbF6 octahedra. The corner-sharing octahedral tilt angles are 33°. There are a spread of Sb–F bond distances ranging from 1.88–2.09 Å. In the third Sb site, Sb is bonded in an octahedral geometry to six F atoms. There are a spread of Sb–F bond distances ranging from 1.88–1.97 Å. There are seventeen inequivalent F sites. In the first F site, F is bonded in a single-bond geometry to one Hg and one Sb atom. In the second F site, F is bonded in a distorted single-bond geometry to one Hg and one Sb atom. In the third F site, F is bonded in a single-bond geometry to one Sb atom. In the fourth F site, F is bonded in a bent 120 degrees geometry to one Hg and one Sb atom. In the fifth F site, F is bonded in a single-bond geometry to one Sb atom. In the sixth F site, F is bonded in a single-bond geometry to 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 Sb 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 bent 150 degrees geometry to two Sb atoms. 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 single-bond geometry to one Sb atom. In the fourteenth F site, F is bonded in a distorted single-bond geometry to one Hg and one Sb atom. In the fifteenth F site, F is bonded in a single-bond geometry to one Sb 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 bent 150 degrees geometry to one Hg and one Sb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg3(SBr)2 by Materials Project

Hg3(SBr)2 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are five inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded to two S2- and three Br1- atoms to form distorted HgS2Br3 trigonal bipyramids that share corners with three HgS2Br4 octahedra, a cornercorner with one HgS2Br3 trigonal bipyramid, edges with three HgS2Br4 octahedra, and an edgeedge with one HgS2Br3 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 58–65°. There are one shorter (2.48 Å) and one longer (2.49 Å) Hg–S bond lengths. There are one shorter (2.83 Å) and two longer (3.30 Å) Hg–Br bond lengths. In the second Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with four HgS2Br4 octahedra, edges with two equivalent HgS2Br3 trigonal bipyramids, and faces with two equivalent HgS2Br4 octahedra. The corner-sharing octahedra tilt angles range from 2–11°. Both Hg–S bond lengths are 2.43 Å. There are two shorter (3.26 Å) and two longer (3.44 Å) Hg–Br bond lengths. In the third Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two equivalent S2- and three Br1- atoms. Both Hg–S bond lengths are 2.43 Å. There are a spread of Hg–Br bond distances ranging from 3.08–3.51 Å. In the fourth Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with two equivalent HgS2Br4 octahedra, edges with two equivalent HgS2Br3 trigonal bipyramids, and faces with two equivalent HgS2Br4 octahedra. The corner-sharing octahedra tilt angles range from 61–66°. Both Hg–S bond lengths are 2.45 Å. There are a spread of Hg–Br bond distances ranging from 3.13–3.54 Å. In the fifth Hg2+ site, Hg2+ is bonded to two equivalent S2- and four Br1- atoms to form HgS2Br4 octahedra that share corners with eight HgS2Br4 octahedra, corners with two equivalent HgS2Br3 trigonal bipyramids, edges with four HgS2Br4 octahedra, and edges with two equivalent HgS2Br3 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 2–66°. Both Hg–S bond lengths are 2.44 Å. There are two shorter (3.32 Å) and two longer (3.36 Å) Hg–Br bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second S2- site, S2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are four inequivalent Br1- sites. In the first Br1- site, Br1- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second Br1- site, Br1- is bonded in a 6-coordinate geometry to six Hg2+ atoms. In the third Br1- site, Br1- is bonded in a 5-coordinate geometry to five Hg2+ atoms. In the fourth Br1- site, Br1- is bonded in a 7-coordinate geometry to seven Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZnHg3 by Materials Project

(Hg)2HgZn crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two Hg sheets oriented in the (0, 0, 1) direction and two HgZn sheets oriented in the (0, 0, 1) direction. In each Hg sheet, Hg is bonded in a distorted square co-planar geometry to four equivalent Hg atoms. All Hg–Hg bond lengths are 3.10 Å. In each HgZn sheet, Hg is bonded in a square co-planar geometry to four equivalent Zn atoms. All Hg–Zn bond lengths are 3.10 Å. Zn is bonded in a square co-planar geometry to four equivalent Hg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg4BiSe2Cl5 by Materials Project

Hg4BiSe2Cl5 is Pb (Zr_0.50 Ti_0.48) O_3-derived structured and crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted see-saw-like geometry to one Hg2+, one Se2-, and two Cl1- atoms. The Hg–Hg bond length is 2.64 Å. The Hg–Se bond length is 2.61 Å. There are one shorter (3.31 Å) and one longer (3.51 Å) Hg–Cl bond lengths. In the second Hg2+ site, Hg2+ is bonded in a 6-coordinate geometry to one Hg2+, one Se2-, and four Cl1- atoms. The Hg–Se bond length is 2.62 Å. There are a spread of Hg–Cl bond distances ranging from 3.29–3.60 Å. In the third Hg2+ site, Hg2+ is bonded to two Se2- and three Cl1- atoms to form distorted HgSe2Cl3 square pyramids that share corners with three equivalent BiCl6 octahedra and an edgeedge with one HgSe2Cl3 square pyramid. The corner-sharing octahedra tilt angles range from 45–74°. Both Hg–Se bond lengths are 2.54 Å. There are a spread of Hg–Cl bond distances ranging from 3.14–3.46 Å. In the fourth Hg2+ site, Hg2+ is bonded in a 6-coordinate geometry to two Se2- and four Cl1- atoms. Both Hg–Se bond lengths are 2.55 Å. There are a spread of Hg–Cl bond distances ranging from 3.02–3.53 Å. Bi1+ is bonded to six Cl1- atoms to form BiCl6 octahedra that share corners with two equivalent BiCl6 octahedra and corners with three equivalent HgSe2Cl3 square pyramids. The corner-sharing octahedral tilt angles are 30°. There are a spread of Bi–Cl bond distances ranging from 2.65–2.90 Å. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. In the second Se2- site, Se2- is bonded in a 3-coordinate geometry to three Hg2+ atoms. There are five inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 2-coordinate geometry to three Hg2+ and one Bi1+ atom. In the second Cl1- site, Cl1- is bonded in a 1-coordinate geometry to four Hg2+ and one Bi1+ atom. In the third Cl1- site, Cl1- is bonded in a 4-coordinate geometry to three Hg2+ and one Bi1+ atom. In the fourth Cl1- site, Cl1- is bonded in a bent 150 degrees geometry to two equivalent Bi1+ atoms. In the fifth Cl1- site, Cl1- is bonded in a distorted tetrahedral geometry to three Hg2+ and one Bi1+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg2PO4 by Materials Project

Hg2PO4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Hg+1.50+ sites. In the first Hg+1.50+ site, Hg+1.50+ is bonded in a 2-coordinate geometry to two O2- atoms. There are one shorter (2.19 Å) and one longer (2.60 Å) Hg–O bond lengths. In the second Hg+1.50+ site, Hg+1.50+ is bonded in a 3-coordinate geometry to three O2- atoms. There are a spread of Hg–O bond distances ranging from 2.26–2.49 Å. There are two inequivalent P5+ sites. In the first P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.54 Å) and two longer (1.57 Å) P–O bond length. In the second P5+ site, P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to two Hg+1.50+ and one P5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one P5+ atom. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Hg+1.50+ and one P5+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to one Hg+1.50+ and one P5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ag4Hg4S4BrCl3 by Materials Project

Ag4Hg4S4BrCl3 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are four inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to two equivalent S2- and two Cl1- atoms to form distorted AgS2Cl2 trigonal pyramids that share corners with eight HgS2Cl4 octahedra, corners with two equivalent AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Br2Cl2 octahedra, and an edgeedge with one AgS2Cl2 trigonal pyramid. The corner-sharing octahedra tilt angles range from 45–81°. There are one shorter (2.54 Å) and one longer (2.56 Å) Ag–S bond lengths. There are one shorter (2.55 Å) and one longer (3.14 Å) Ag–Cl bond lengths. In the second Ag1+ site, Ag1+ is bonded to two equivalent S2- and two Cl1- atoms to form distorted AgS2Cl2 trigonal pyramids that share corners with eight HgS2Br2Cl2 octahedra, corners with two equivalent AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Cl4 octahedra, and an edgeedge with one AgS2Cl2 trigonal pyramid. The corner-sharing octahedra tilt angles range from 45–80°. There are one shorter (2.54 Å) and one longer (2.56 Å) Ag–S bond lengths. There are one shorter (2.54 Å) and one longer (3.13 Å) Ag–Cl bond lengths. In the third Ag1+ site, Ag1+ is bonded to two equivalent S2-, one Br1-, and one Cl1- atom to form distorted AgS2BrCl trigonal pyramids that share corners with eight HgS2Br2Cl2 octahedra, corners with two equivalent AgS2BrCl trigonal pyramids, edges with two equivalent HgS2Br2Cl2 octahedra, and an edgeedge with one AgS2BrCl trigonal pyramid. The corner-sharing octahedra tilt angles range from 45–79°. There are one shorter (2.57 Å) and one longer (2.59 Å) Ag–S bond lengths. The Ag–Br bond length is 3.12 Å. The Ag–Cl bond length is 2.56 Å. In the fourth Ag1+ site, Ag1+ is bonded to two equivalent S2-, one Br1-, and one Cl1- atom to form distorted AgS2BrCl trigonal pyramids that share corners with eight HgS2Br2Cl2 octahedra, corners with two equivalent AgS2BrCl trigonal pyramids, edges with two equivalent HgS2Cl4 octahedra, and an edgeedge with one AgS2BrCl trigonal pyramid. The corner-sharing octahedra tilt angles range from 43–80°. There are one shorter (2.52 Å) and one longer (2.55 Å) Ag–S bond lengths. The Ag–Br bond length is 2.65 Å. The Ag–Cl bond length is 3.17 Å. There are four inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded to two S2-, two equivalent Br1-, and two equivalent Cl1- atoms to form HgS2Br2Cl2 octahedra that share corners with four equivalent HgS2Br2Cl2 octahedra, corners with eight AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Br2Cl2 octahedra, edges with two equivalent AgS2Cl2 trigonal pyramids, and faces with two equivalent HgS2Br2Cl2 octahedra. The corner-sharing octahedra tilt angles range from 58–60°. There are one shorter (2.42 Å) and one longer (2.43 Å) Hg–S bond lengths. There are one shorter (3.22 Å) and one longer (3.25 Å) Hg–Br bond lengths. There are one shorter (3.34 Å) and one longer (3.35 Å) Hg–Cl bond lengths. In the second Hg2+ site, Hg2+ is bonded to two S2- and four Cl1- atoms to form distorted HgS2Cl4 octahedra that share corners with four equivalent HgS2Cl4 octahedra, corners with eight AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Cl4 octahedra, edges with two equivalent AgS2Cl2 trigonal pyramids, and faces with two equivalent HgS2Cl4 octahedra. The corner-sharing octahedra tilt angles range from 57–59°. Both Hg–S bond lengths are 2.41 Å. There are a spread of Hg–Cl bond distances ranging from 3.16–3.36 Å. In the third Hg2+ site, Hg2+ is bonded to two S2-, two equivalent Br1-, and two equivalent Cl1- atoms to form distorted HgS2Br2Cl2 octahedra that share corners with four equivalent HgS2Br2Cl2 octahedra, corners with eight AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Br2Cl2 octahedra, edges with two equivalent AgS2BrCl trigonal pyramids, and faces with two equivalent HgS2Br2Cl2 octahedra. The corner-sharing octahedra tilt angles range from 58–60°. Both Hg–S bond lengths are 2.42 Å. There are one shorter (3.37 Å) and one longer (3.42 Å) Hg–Br bond lengths. There are one shorter (3.17 Å) and one longer (3.21 Å) Hg–Cl bond lengths. In the fourth Hg2+ site, Hg2+ is bonded to two S2- and four Cl1- atoms to form distorted HgS2Cl4 octahedra that share corners with four equivalent HgS2Cl4 octahedra, corners with eight AgS2Cl2 trigonal pyramids, edges with two equivalent HgS2Cl4 octahedra, edges with two equivalent AgS2BrCl trigonal pyramids, and faces with two equivalent HgS2Cl4 octahedra. The corner-sharing octahedra tilt angles range from 57–59°. Both Hg–S bond lengths are 2.41 Å. There are a spread of Hg–Cl bond distances ranging from 3.19–3.41 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded to two equivalent Ag1+ and two Hg2+ atoms to form corner-sharing SAg2Hg2 trigonal pyramids. In the second S2- site, S2- is bonded to two equivalent Ag1+ and two Hg2+ atoms to form corner-sharing SAg2Hg2 trigonal pyramids. In the third S2- site, S2- is bonded to two equivalent Ag1+ and two Hg2+ atoms to form corner-sharing SAg2Hg2 trigonal pyramids. In the fourth S2- site, S2- is bonded to two equivalent Ag1+ and two Hg2+ atoms to form corner-sharing SAg2Hg2 trigonal pyramids. Br1- is bonded in a 1-coordinate geometry to two Ag1+ and four Hg2+ atoms. There are three inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 1-coordinate geometry to two Ag1+ and four Hg2+ atoms. In the second Cl1- site, Cl1- is bonded in a 1-coordinate geometry to two Ag1+ and four Hg2+ atoms. In the third Cl1- site, Cl1- is bonded in a 1-coordinate geometry to two Ag1+ and four Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Contrary effects of phytoplankton Chlorella vulgaris and its exudates on mercury methylation by iron- and sulfate-reducing bacteria

Mercury (Hg) is a pervasive environmental pollutant and poses serious health concerns as inorganic Hg(II) can be converted to the neurotoxin methylmercury (MeHg), which bioaccumulates and biomagnifies in food webs. Phytoplankton, representing the base of aquatic food webs, can take up Hg(II) and influence MeHg production, but currently little is known about how and to what extent phytoplankton may impact Hg(II) methylation by itself or by methylating bacteria it harbors. This study investigated whether some species of phytoplankton could produce MeHg and how the live or dead phytoplankton cells and excreted algal organic matter (AOM) impact Hg(II) methylation by several known methylators, including iron-reducing bacteria (FeRB), Geobacter anodireducens SD-1 and Geobacter sulfurreducens PCA, and the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans ND132 (or Pseudodesulfovibrio mercurii). Here our results indicate that, among the 4 phytoplankton species studied, none were capable of methylating Hg(II). However, the presence of phytoplankton cells (either live or dead) from Chlorella vulgaris (CV) generally inhibited Hg(II) methylation by FeRB but substantially enhanced methylation by SRB D. desulfuricans ND132. Enhanced methylation was attributed in part to CV-excreted AOM, which increased Hg(II) complexation and methylation by ND132 cells. In contrast, inhibition of methylation by FeRB was attributed to these bacteria incapable of competing with phytoplankton for Hg(II) binding and uptake. These observations suggest that phytoplankton could play different roles in affecting Hg(II) methylation by the two groups of anaerobic bacteria, FeRB and SRB, and thus shed additional light on how phytoplankton blooms may modulate MeHg production and bioaccumulation in the aquatic environment.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Analysis of biokinetic parameters reveals patterns in mercury accumulation across aquatic species

Mercury (Hg) is a potent neurotoxicant and poses a risk to human health through the ingestion of Hg-contaminated fish. Mercury, especially in its organic form methylmercury (MeHg), biomagnifies up food chains such that even small aqueous concentrations of Hg can result in significant concentrations of total Hg in fish. Understanding the ecological and human health risks associated with Hg and MeHg exposure requires an understanding of the factors that affect its bioaccumulation in aquatic species. We compiled estimates of three biokinetic parameters: uptake rate (k u ), assimilation efficiency (AE), and efflux rate (k e ). These parameters describe contaminant uptake from aqueous (k u ) and dietary (AE) exposure and the rate of excretion (k e ). We found parameter values for 38 and 34 different species of fish and aquatic invertebrates, respectively, and collected 502 parameter values in total. Here, we used a machine learning technique to establish the relationships between experimental and physiological variables and these parameter values. We found differences in which variables were associated with biokinetic parameter values for fish and aquatic invertebrates. The form of Hg was the most impactful variable, influencing values of all parameters except k u for invertebrates, for which aqueous exposure time was the only significant predicator variable. The parameter k e were the only values significantly influenced by more than one variable, with water type (freshwater, brackish, or marine), organism weight, and form of Hg significantly impacting parameter values for fish and/or invertebrates. To our knowledge, this study represents the most extensive review of biokinetic parameters of Hg and MeHg accumulation in aquatic organisms. Environmental parameters found to significantly impact Hg and MeHg bioaccumulation in past studies were not identified as important in our analyses across aquatic ecosystems and species. Our dataset and analysis reveal novel patterns that may help us better understand and manage Hg bioaccumulation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Impacts of Forest Fire Ash on Aquatic Mercury Cycling

Mercury (Hg) is a ubiquitous contaminant in the environment and its methylated form, methylmercury (MeHg), poses a worldwide health concern for humans and wildlife, primarily through fish consumption. Global production of forest fire ash, derived from wildfires and prescribed burns, is rapidly increasing due to a warming climate, but their interactions with aqueous and sedimentary Hg are poorly understood. In this study, we compared the differences of wildfire ash with activated carbon and biochar on the sorption of aqueous inorganic Hg and sedimentary Hg methylation. Sorption of aqueous inorganic Hg was greatest for wildfire ash materials (up to 0.21 μg g ₋1 or 2.2 μg g ₋1 C) among all of the solid sorbents evaluated. A similar Hg adsorption mechanism for activated carbon, biochar made of walnut, and wildfire ash was found that involves the formation of complexes between Hg and oxygen-containing functional groups, especially the ₋COO group. Notably, increasing dissolved organic matter from 2.4 to 70 mg C L ₋1 remarkably reduced Hg sorption (up to 40% reduction) and increased the time required to reach Hg–sorbent pseudo-equilibrium. Surprisingly, biochar and wildfire ash, but not activated carbon, stimulated MeHg production during anoxic sediment incubation, possibly due to the release of labile organic matter. Overall, our study indicates that while wildfire ash can sequester aqueous Hg, the leaching of its labile organic matter may promote production of toxic MeHg in anoxic sediments, which has an important implication for potential MeHg contamination in downstream aquatic ecosystems after wildfires.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Experimental evidence for recovery of mercury-contaminated fish populations

Anthropogenic releases of mercury (Hg) are a human health issue because the potent toxicant methylmercury (MeHg), formed primarily by microbial methylation of inorganic Hg in aquatic ecosystems, bioaccumulates to high concentrations in fish consumed by humans. Predicting the efficacy of Hg pollution controls on fish MeHg concentrations is complex because many factors influence the production and bioaccumulation of MeHg. Here we conducted a 15-year whole-ecosystem, single-factor experiment to determine the magnitude and timing of reductions in fish MeHg concentrations following reductions in Hg additions to a boreal lake and its watershed. During the seven-year addition phase, we applied enriched Hg isotopes to increase local Hg wet deposition rates fivefold. The Hg isotopes became increasingly incorporated into the food web as MeHg, predominantly from additions to the lake because most of those in the watershed remained there. Thereafter, isotopic additions were stopped, resulting in an approximately 100% reduction in Hg loading to the lake. The concentration of labelled MeHg quickly decreased by up to 91% in lower trophic level organisms, initiating rapid decreases of 38–76% of MeHg concentration in large-bodied fish populations in eight years. Although Hg loading from watersheds may not decline in step with lowering deposition rates, this experiment clearly demonstrates that any reduction in Hg loadings to lakes, whether from direct deposition or runoff, will have immediate benefits to fish consumers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
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↗
NASA NTRS2011

Cycle Time Reduction in Trapped Mercury Ion Atomic Frequency Standards

The use of the mercury ion isotope (201)Hg(+) was examined for an atomic clock. Taking advantage of the faster optical pumping time in (201)Hg(+) reduces both the state preparation and the state readout times, thereby decreasing the overall cycle time of the clock and reducing the impact of medium-term LO noise on the performance of the frequency standard. The spectral overlap between the plasma discharge lamp used for (201)Hg(+) state preparation and readout is much larger than that of the lamp used for the more conventional (199)Hg(+). There has been little study of (201)Hg(+) for clock applications (in fact, all trapped ion clock work in mercury has been with (199)Hg(+); however, recently the optical pumping time in (201)Hg(+) has been measured and found to be 0.45 second, or about three times faster than in (199)Hg(+) due largely to the better spectral overlap. This can be used to reduce the overall clock cycle time by over 2 seconds, or up to a factor of 2 improvement. The use of the (201)Hg(+) for an atomic clock is totally new. Most attempts to reduce the impact of LO noise have focused on reducing the interrogation time. In the trapped ion frequency standards built so far at JPL, the optical pumping time is already at its minimum so that no enhancement can be had by shortening it. However, by using (201)Hg(+), this is no longer the case. Furthermore, integrity monitoring, the mechanism that determines whether the clock is functioning normally, cannot happen faster than the clock cycle time. Therefore, a shorter cycle time will enable quicker detection of failure modes and recovery from them.

Burt, Eric A.↗
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↗