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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Tank 50 Simulant Grout and Toxicity Characteristic Leaching Procedure (TCLP) Results for Methyl Mercury Waste Acceptance Criteria (WAC) Limit

Testing of simulated Tank 50 salt solution grout, spiked with methyl mercury (MeHg) and ionic mercury, used the Toxicity Characteristic Leaching Procedure (TCLP) to evaluate leaching performance with respect to Hg and the Waste Acceptance Criteria (WAC) limits for the Saltstone Production Facility (SPF). This report describes the test parameters for simulant preparation and confirmatory analysis, grout preparation, TCLP leach testing and subsequent leachate analyses. These scoping tests were designed to provide an initial evaluation of the effect of increased MeHg and ionic Hg on the TCLP and were requested by Savannah River Remediation LLC (SRR) through a Technical Assistance Request (TAR). It is expected that this preliminary testing will likely lead to future, more detailed, testing involving the mercury (Hg) WAC and Hg limits with respect to the Tank 50 TCLP for mercury. The TCLP concentrations for total Hg have approached 0.06 mg/L in recent years for Tank 50 radioactive solutions containing up to 105 mg/L of Hg in the form of ionic (Hg(I/II), elemental (Hg(0)) and organo-mercury such as MeHg. In discussions with SRR personnel, it was decided for this non-baseline work to target Hg spike concentrations, using predominately MeHg, in the range of 150 to 350 mg/L total Hg to investigate corresponding Hg TCLP leaching behaviors.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Nutrient Exposure Alters Microbial Composition, Structure, and Mercury Methylating Activity in Periphyton in a Contaminated Watershed

The conversion of mercury (Hg) to monomethylmercury (MMHg) is a critical area of concern in global Hg cycling. Periphyton biofilms may harbor significant amounts of MMHg but little is known about the Hg-methylating potential of the periphyton microbiome. Therefore, we used high-throughput amplicon sequencing of the 16S rRNA gene, ITS2 region, and Hg methylation gene pair (hgcAB) to characterize the archaea/bacteria, fungi, and Hg-methylating microorganisms in periphyton communities grown in a contaminated watershed in East Tennes(see United States). Furthermore, we examined how nutrient amendments (nitrate and/or phosphate) altered periphyton community structure and function. We found that bacterial/archaeal richness in experimental conditions decreased in summer and increased in autumn relative to control treatments, while fungal diversity generally increased in summer and decreased in autumn relative to control treatments. Interestingly, the Hg-methylating communities were dominated by Proteobacteria followed by Candidatus Atribacteria across both seasons. Surprisingly, Hg methylation potential correlated with numerous bacterial families that do not contain hgcAB, suggesting that the overall microbiome structure of periphyton communities influences rates of Hg transformation within these microbial mats. To further explore these complex community interactions, we performed a microbial network analysis and found that the nitrate-amended treatment resulted in the highest number of hub taxa that also corresponded with enhanced Hg methylation potential. This work provides insight into community interactions within the periphyton microbiome that may contribute to Hg cycling and will inform future research that will focus on establishing mixed microbial consortia to uncover mechanisms driving shifts in Hg cycling within periphyton habitats.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Fungal necromass presents a high potential for Mercury immobilization in soil

Past industrial activities have generated many contaminated lands from which Mercury (Hg) escapes, primarily by volatilization. Current phytomanagement techniques aim to limit Hg dispersion by increasing its stabilization in soil. Although soil fungi represent a source of Hg emission associated with biovolatilization mechanisms, there is limited knowledge about how dead fungal residues (i.e., fungal necromass) interact with soil Hg. This study determined the Hg biosorption potential of fungal necromass and the chemical drivers of passive Hg binding with dead mycelia. Fungal necromass was incubated under field conditions with contrasting chemical properties at a well-characterized Hg phytomanagement experimental site in France. After four months of incubation in soil, fungal residues passively accumulated substantial quantities of Hg in their recalcitrant fractions ranging from 400 to 4500 μg Hg/kg. In addition, infrared spectroscopy revealed that lipid compounds explained the amount of Hg biosorption to fungal necromass. In conclusion, based on these findings, we propose that fungal necromass is likely an important factor in Hg immobilization in soil.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Materials Data on Na3Hg2 by Materials Project

Na3Hg2 crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are three inequivalent Na sites. In the first Na site, Na is bonded in a 6-coordinate geometry to six equivalent Hg atoms. There are two shorter (3.16 Å) and four longer (3.30 Å) Na–Hg bond lengths. In the second Na site, Na is bonded in a distorted square co-planar geometry to four equivalent Hg atoms. All Na–Hg bond lengths are 3.40 Å. In the third Na site, Na is bonded in a 6-coordinate geometry to six equivalent Hg atoms. There are two shorter (3.19 Å) and four longer (3.34 Å) Na–Hg bond lengths. Hg is bonded in a 10-coordinate geometry to eight Na and two equivalent Hg atoms. Both Hg–Hg bond lengths are 3.07 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg6S4Br3Cl by Materials Project

Hg6S4Br3Cl crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are four inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two S2-, two Br1-, and one Cl1- atom. Both Hg–S bond lengths are 2.46 Å. There are one shorter (3.14 Å) and one longer (3.54 Å) Hg–Br bond lengths. The Hg–Cl bond length is 2.84 Å. In the second Hg2+ site, Hg2+ is bonded to two equivalent S2- and three Br1- atoms to form distorted HgS2Br3 square pyramids that share corners with two equivalent HgS2Br4 octahedra, edges with two equivalent HgS2Br4 octahedra, and an edgeedge with one HgS2Br3 square pyramid. The corner-sharing octahedral tilt angles are 66°. Both Hg–S bond lengths are 2.46 Å. There are a spread of Hg–Br bond distances ranging from 2.97–3.29 Å. In the third Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to two equivalent S2-, two Br1-, and one Cl1- atom. Both Hg–S bond lengths are 2.45 Å. There are one shorter (3.34 Å) and one longer (3.39 Å) Hg–Br bond lengths. The Hg–Cl bond length is 2.83 Å. In the fourth Hg2+ site, Hg2+ is bonded to two S2- and four Br1- atoms to form distorted HgS2Br4 octahedra that share corners with four equivalent HgS2Br4 octahedra, a cornercorner with one HgS2Br3 square pyramid, edges with four equivalent HgS2Br4 octahedra, and an edgeedge with one HgS2Br3 square pyramid. The corner-sharing octahedra tilt angles range from 0–4°. Both Hg–S bond lengths are 2.44 Å. There are a spread of Hg–Br bond distances ranging from 3.20–3.48 Å. 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 6-coordinate geometry to six Hg2+ atoms. In the second Br1- site, Br1- is bonded in a square co-planar geometry to four equivalent Hg2+ atoms. In the third Br1- site, Br1- is bonded in a 7-coordinate geometry to five Hg2+ atoms. In the fourth Br1- site, Br1- is bonded in a distorted body-centered cubic geometry to eight Hg2+ atoms. Cl1- is bonded in a distorted trigonal planar geometry to three Hg2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg2IO by Materials Project

Hg2OI crystallizes in the monoclinic C2/c space group. The structure is two-dimensional and consists of two Hg2OI sheets oriented in the (1, 0, 0) direction. there are two inequivalent Hg+1.50+ sites. In the first Hg+1.50+ site, Hg+1.50+ is bonded in a 6-coordinate geometry to three equivalent O2- and two equivalent I1- atoms. There are two shorter (2.20 Å) and one longer (2.62 Å) Hg–O bond lengths. There are one shorter (3.09 Å) and one longer (3.17 Å) Hg–I bond lengths. In the second Hg+1.50+ site, Hg+1.50+ is bonded in a single-bond geometry to one O2- atom. The Hg–O bond length is 2.17 Å. O2- is bonded to four Hg+1.50+ atoms to form a mixture of edge and corner-sharing OHg4 tetrahedra. I1- is bonded in a 2-coordinate geometry to two equivalent Hg+1.50+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg5(SbI3)2 by Materials Project

Hg5(SbI3)2 crystallizes in the orthorhombic Pna2_1 space group. The structure is three-dimensional. there are five inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a distorted rectangular see-saw-like geometry to one Sb2- and three I1- atoms. The Hg–Sb bond length is 2.75 Å. There are a spread of Hg–I bond distances ranging from 2.78–3.28 Å. In the second Hg2+ site, Hg2+ is bonded in a 1-coordinate geometry to one Sb2- and two I1- atoms. The Hg–Sb bond length is 2.73 Å. There are one shorter (2.73 Å) and one longer (3.41 Å) Hg–I bond lengths. In the third Hg2+ site, Hg2+ is bonded in a distorted rectangular see-saw-like geometry to one Sb2- and three I1- atoms. The Hg–Sb bond length is 2.74 Å. There are a spread of Hg–I bond distances ranging from 2.84–3.55 Å. In the fourth Hg2+ site, Hg2+ is bonded in a rectangular see-saw-like geometry to one Sb2- and three I1- atoms. The Hg–Sb bond length is 2.75 Å. There are a spread of Hg–I bond distances ranging from 2.98–3.14 Å. In the fifth Hg2+ site, Hg2+ is bonded in a 5-coordinate geometry to one Sb2- and four I1- atoms. The Hg–Sb bond length is 2.78 Å. There are a spread of Hg–I bond distances ranging from 2.83–3.87 Å. There are two inequivalent Sb2- sites. In the first Sb2- site, Sb2- is bonded in a 3-coordinate geometry to two Hg2+ and one Sb2- atom. The Sb–Sb bond length is 2.89 Å. In the second Sb2- site, Sb2- is bonded in a tetrahedral geometry to three Hg2+ and one Sb2- atom. There are six inequivalent I1- sites. In the first I1- site, I1- is bonded in a distorted L-shaped geometry to two Hg2+ atoms. In the second I1- site, I1- is bonded in a water-like geometry to two Hg2+ atoms. In the third I1- site, I1- is bonded in a distorted L-shaped geometry to two Hg2+ atoms. In the fourth I1- site, I1- is bonded in a distorted trigonal non-coplanar geometry to three Hg2+ atoms. In the fifth I1- site, I1- is bonded in a 2-coordinate geometry to three Hg2+ atoms. In the sixth I1- site, I1- is bonded in a 3-coordinate geometry to three Hg2+ atoms.

36 MATERIALS SCIENCE↗
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↗