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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Hg Accumulation by Single-Cell Sulfate-Reducing Bacteria Methylating Mercury

Methylmercury (MeHg) is a potent neurotoxin that poses risks to ecosystems and human health. MeHg is produced by microbes following saturating-like kinetics. We hypothesize that this saturation reflects a limited intracellular mercury (Hg) accumulation. Here, in this study, we investigated Hg accumulation in Pseudodesulfovibrio hydrargyri BerOc1, a sulfate-reducing model strain able to methylate Hg. Cells were incubated with 0.5 and 2 μM of mercury (HgCl 2 ), and mercury localization was studied using synchrotron-based nano-X-ray fluorescence and high-resolution analytical electron microscopy. For both concentrations, Hg was detected in the bacterial cytosol, in addition to extracellular (Hg, S)-containing nanoparticles. Intracellular Hg levels were slightly higher at 2 μM than at 0.5 μM (1.61 vs 1.40 pg.mm –2 ), suggesting a regulated accumulation. However, the population exhibited heterogeneity in Hg accumulation, particularly at the highest Hg exposure, with some cells being Hg hyperaccumulators. Correlative imaging between Hg localization and cell viability revealed that these hyperaccumulating cells were non-active. Our results suggest that active cells regulate Hg accumulation. From an analytical perspective, a minor subpopulation of hyperaccumulating cells can bias bulk measurements and should be considered in interpreting Hg accumulation in microorganisms. Environmentally, these cells can impact Hg cycling by acting as a metal sink.

Intracellular accumulation↗
DOE OSTI2020

Reduction of Hg(II) by Fe(II)-Bearing Smectite Clay Minerals

Aluminosilicate clay minerals are often a major component of soils and sediments and many of these clays contain structural Fe (e.g., smectites and illites). Structural Fe(III) in smectite clays is redox active and can be reduced to Fe(II) by biotic and abiotic processes. Fe(II)-bearing minerals such as magnetite and green rust can reduce Hg(II) to Hg(0); however, the ability of other environmentally relevant Fe(II) phases, such as structural Fe(II) in smectite clays, to reduce Hg(II) is largely undetermined. We conducted experiments examining the potential for reduction of Hg(II) by smectite clay minerals containing 0–25 wt% Fe. Fe(III) in the clays (SYn-1 synthetic mica-montmorillonite, SWy-2 montmorillonite, NAu-1 and NAu-2 nontronite, and a nontronite from Cheney, Washington (CWN)) was reduced to Fe(II) using the citrate-bicarbonate-dithionite method. Experiments were initiated by adding 500 µM Hg(II) to reduced clay suspensions (4 g clay L−1) buffered at pH 7.2 in 20 mM 3-morpholinopropane-1-sulfonic acid (MOPS). The potential for Hg(II) reduction in the presence of chloride (0–10 mM) and at pH 5–9 was examined in the presence of reduced NAu-1. Analysis of the samples by Hg LIII-edge X-ray absorption fine structure (XAFS) spectroscopy indicated little to no reduction of Hg(II) by SYn-1 (0% Fe), while reduction of Hg(II) to Hg(0) was observed in the presence of reduced SWy-2, NAu-1, NAu-2, and CWN (2.8–24.8% Fe). Hg(II) was reduced to Hg(0) by NAu-1 at all pH and chloride concentrations examined. These results suggest that Fe(II)-bearing smectite clays may contribute to Hg(II) reduction in suboxic/anoxic soils and sediments.

58 GEOSCIENCES↗
DOE OSTI2020

Materials Data on Hg by Materials Project

Hg crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a 4-coordinate geometry to four equivalent Hg atoms. There are two shorter (3.34 Å) and two longer (3.38 Å) Hg–Hg bond lengths. In the second Hg site, Hg is bonded in a 7-coordinate geometry to seven Hg atoms. There are a spread of Hg–Hg bond distances ranging from 3.32–3.42 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Comparison of mercury (Hg) bioaccumulation with mono- and mixed Lemna minor and Spirodela polyrhiza cultures

Mercury (Hg) is a prevalent and harmful contaminant that persists in the environment. For phytoremediation, it is important to discover which plants can bioaccumulate meaningful amounts of Hg while also tolerating its toxicity. Additionally, increasing biodiversity could create a more resilient and self-sustaining system for remediation. This study explores whether mixed populations of Lemna minor and Spirodela polyrhiza can better bioaccumulate and tolerate Hg than monocultures. Mono- and mixed cultures of L. minor and S. polyrhiza were grown in mesocosms of 0.5 μg/L or 100 μg/L Hg ( HgCl2) spiked water for 96 h. Change in weight of duckweed was used to assess Hg tolerance. Diffusive gradients in thin-films (DGTs) were used as surrogate monitoring devices for bioavailable levels of Hg. For biomass growth, the mixed culture of the L. minor was greater than the monoculture at the high dose. The L. minor accumulated more Hg in the mixed culture at the low dose while the S. polyrhiza was higher in the mixed at the high dose. Hg speciation in water was modeled using Windermere Humic Aqueous Model 7 (WHAM7) to compare the bioavailable species indicated by the DGTs. Potentially due to the controlled conditions, the WHAM7 output of bioavailable Hg was almost 1:1 to that estimated by the DGTs, indicating good predictive capability of geochemical modeling and passive sampler DGT on metal bioavailability. Altogether, the mixed cultures statistically performed as well as or better than the monocultures when tolerating and bioaccumulating Hg. However, there needs to be further work to see if the significant differences translate into practical differences worth the extra resources to maintain multiple species.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2020

Materials Data on Hg(BrO4)2 by Materials Project

Hg(O4Br)2 crystallizes in the orthorhombic P2_12_12_1 space group. The structure is one-dimensional and consists of two Hg(O4Br)2 ribbons oriented in the (0, 1, 0) direction. Hg is bonded in a 6-coordinate geometry to six O atoms. There are a spread of Hg–O bond distances ranging from 2.06–2.62 Å. There are eight inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to one Br atom. The O–Br bond length is 1.68 Å. In the second O site, O is bonded in a single-bond geometry to one Hg atom. In the third O site, O is bonded in a single-bond geometry to one Hg atom. In the fourth O site, O is bonded in a single-bond geometry to one Br atom. The O–Br bond length is 1.66 Å. In the fifth O site, O is bonded in a water-like geometry to one Hg and one Br atom. The O–Br bond length is 1.70 Å. In the sixth O site, O is bonded in a 1-coordinate geometry to two equivalent Hg and one Br atom. The O–Br bond length is 1.73 Å. In the seventh O site, O is bonded in a bent 120 degrees geometry to one Hg and one Br atom. The O–Br bond length is 1.71 Å. In the eighth O site, O is bonded in a single-bond geometry to one Br atom. The O–Br bond length is 1.67 Å. There are two inequivalent Br sites. In the first Br site, Br is bonded in a trigonal non-coplanar geometry to three O atoms. In the second Br site, Br is bonded in a trigonal non-coplanar geometry to three O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-resolution imaging of Hg/Se aggregates in the brain of small Indian mongoose, a wild terrestrial species: insights into intracellular Hg detoxification

Human activities result in the emission of 2000 metric tons of mercury compounds annually. Mercury (Hg) biomagnification has been characterized in marine mammals and predatory fish; however, little is known about mercury accumulation in brains of wild terrestrial species. Elevated Hg content, of 1.27 μg/g wet wt.—found in the brain of wild small Indian mongoose, prompted us to use synchrotron X-ray fluorescence imaging for simultaneous, quantitative mapping of biologically relevant and neurotoxic elements with high spatial resolution. X-ray fluorescence combined with immunohistochemistry revealed ~0.5–1.9 micron Hg-rich aggregates in cells of the choroid plexus and astrocytes of the subventricular wall in the mongoose brain. Hg content within aggregates correlated with selenium. Hg aggregates did not co-localize with lysosomes. The low Hg density inside aggregates indicated diffuse Hg binding to a Se-containing biomolecule, rather than much denser HgSe nanoparticles proposed to form in other species. Our data show the susceptibility of the small Indian mongoose population to Hg pollution and highlight the vulnerability of the brain as an organ targeted by mercury. Data also provide evidence on the adaptation in the form of a Se-based detoxification mechanism sequestering Hg into intracellular aggregates.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg(ClO3)2 by Materials Project

Hg(O3Cl)2 crystallizes in the monoclinic P2_1 space group. The structure is one-dimensional and consists of two Hg(O3Cl)2 ribbons oriented in the (0, 1, 0) direction. Hg is bonded in a 4-coordinate geometry to four O atoms. There are a spread of Hg–O bond distances ranging from 2.25–2.54 Å. There are six inequivalent O sites. In the first O site, O is bonded in a distorted L-shaped geometry to one Hg and one Cl atom. The O–Cl bond length is 1.50 Å. In the second O site, O is bonded in a water-like geometry to one Hg and one Cl atom. The O–Cl bond length is 1.56 Å. In the third O site, O is bonded in a bent 120 degrees geometry to one Hg and one Cl atom. The O–Cl bond length is 1.60 Å. In the fourth O site, O is bonded in a water-like geometry to one Hg and one Cl atom. The O–Cl bond length is 1.50 Å. In the fifth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.49 Å. In the sixth O site, O is bonded in a single-bond geometry to one Cl atom. The O–Cl bond length is 1.48 Å. There are two inequivalent Cl sites. In the first Cl site, Cl is bonded in a trigonal non-coplanar geometry to three O atoms. In the second Cl site, Cl is bonded in a trigonal non-coplanar geometry to three O atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Interaction of Soil Microbes with Organoclays and their Impact on the Immobilization of Hg under Aerobic Conditions

Immobilization of mercury (Hg) leaching from bank soils of East Fork Poplar Creek (EFPC) is considered part of remediation strategies to mitigate the amount of Hg entering the creek. Different approaches are currently being evaluated, such as utilizing engineered sorbents to immobilize Hg species in EFPC bank soils. However, the influence of environmental microbes on the immobilization of Hg by sorbents is unknown. Organocation-modified phyllosilicate clay minerals (organoclays) are widely used as sorbents for the immobilization of contaminants. This study evaluates the interactions of Serratia marcescens and Burkholderia thailandensis with the sorbent Organoclay PM-199 and their impact on the immobilization of Hg under aerobic conditions. We evaluated the competitive binding of Hg between sorbents and selected microorganisms in a series of pure culture studies using bacterial strains identified in EFPC bank soil samples. Our results suggest that Hg sorption by Organoclay PM-199 is not significantly impacted by common soil bacteria present in EFPC, specifically Serratia marcescens and Burkholderia thailandensis, which are known to form biofilms. These findings suggest that sorbent amendments are an effective strategy for the remediation of Hg contamination in natural ecosystems.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1990

Isotopic Hg in an Allende carbon-rich residue

A carbon-rich residue from Allende subjected to stepwise heating yielded two isotopically resolvable types of Hg: one with an (Hg-196)/(Hg-202) concentration ratio the same as terrestrial (monitor) Hg; the other enriched in Hg-196 relative to Hg-202 by about 60 percent. Hg with the 202 isotope enriched relative to 196, as is found in bulk Allende, was not observed. Whether the result of mass fractionation or nucleosynthesis, the distinct types of Hg entered different carrier phases and were not thermally mobilized since the accretion of the Allende parent body.

Reed, G. W., Jr.↗
DOE OSTI2020

Materials Data on Hg(OF)2 by Materials Project

Hg(OF)2 crystallizes in the orthorhombic Pbcn space group. The structure is two-dimensional and consists of two Hg(OF)2 sheets oriented in the (0, 0, 1) direction. Hg is bonded in a 8-coordinate geometry to four equivalent O and four equivalent F atoms. There are two shorter (2.29 Å) and two longer (2.39 Å) Hg–O bond lengths. There are two shorter (2.39 Å) and two longer (2.46 Å) Hg–F bond lengths. O is bonded in a water-like geometry to two equivalent Hg atoms. F is bonded in a water-like geometry to two equivalent Hg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg by Materials Project

Hg is beta structured and crystallizes in the cubic P4_132 space group. The structure is three-dimensional and consists of twelve mercury molecules and one Hg framework. In the Hg framework, Hg is bonded in a distorted trigonal planar geometry to three equivalent Hg atoms. All Hg–Hg bond lengths are 3.24 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg by Materials Project

Hg crystallizes in the cubic Pm-3n space group. The structure is one-dimensional and consists of two mercury molecules and three Hg ribbons oriented in the (0, 1, 0) direction. In each Hg ribbon, Hg is bonded in a linear geometry to two equivalent Hg atoms. Both Hg–Hg bond lengths are 3.15 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Length and Seed Current Scaling of a Mark X HG driven, 8 inch PBX9501 RancheroS FCG system: II

This report is intended to examine the ultimate operating limits of the combined Pt. 88 capacitor bank (CB) + MarkX Helical Generator (HG) driving a RancheroS Flux Compression Generator (FCG) with various physics experiment load inductances. As such, many degradation mechanisms are neglected in this study. In actual use, degradation of the HG output current delivered to the FCG will probably occur. Internal changes in the HG can occur due to both Ohmic heating in the generator leading to a time varying series resistance [R(t)] such as that seen in the first trial (Shot 0) of the MarkX, as well as any misbehavior, such HG internal turn to turn shorts such as seem to have occurred in subsequent MarkX tests. Both reduce the output current from the HG that is used to seed the FCG. The results discussed here are intended to probe the limits of the RancheroS driving various loads, in an ideal situation in which none of the HG or system degradation mechanisms prior to the FCG armature first motion (FM) reduce the seed current. The HG is modeled simply as a time varying inductance [L(t), as measured in Shot 0], with a constant internal resistance [R(t) = 0.2mOhm]. The RancheroS itself is fully modeled, including all FCG and load degradation mechanisms, thus probing the ultimate capabilities of the full system, independent of problems upstream of the FCG.

47 OTHER INSTRUMENTATION↗
NASA NTRS1981

Defect chemistry and characterization Hg(1-x)Cd(x)Te

Iodine doped single crystal samples of mercury cadmium telluride were annealed at temperatures varying from 450 C to 600 C in Hg vapor and quenched to room temperature. Hall effect measurements at 77 K on the crystals cooled to room temperature indicate the samples to be n-type after anneals at high Hg pressures whereas they turn p-type after anneals at low Hg pressures; the electron concentration increases with increase in Hg pressure. The results are explained on the basis that the crystals are saturated with (Hg,Cd)I2, with a fraction of the iodine being present as donor occupying tellurium lattice sites and a fraction being present as acceptors resulting from the iodine on tellurium lattice sites pairing with the doubly ionized native acceptor defects. The solubility of the donor species increases with increase in Hg pressure, whereas that of the acceptor species increases with decrease in Hg pressure. Equilibrium constants for the incorporation of the iodine species as well as the pairing reaction were established.

Vydyanath, H. R.↗
NASA NTRS1983

Mode of incorporation of phosphorus in Hg(0.8)Cd(0.2)Te

Selim and Kroeger (1977) have studied the mode of incorporation of phosphorus in CdTe. According to their findings, phosphorus behaves amphoterically in CdTe acting as an acceptor interstitially and on Te lattice sites, and as a triple donor on Cd lattice sites. The present investigation is concerned with the role of phosphorus in Hg(0.8)Cd(0.2)Te, taking into account Hall-effect and mobility measurements on phosphorus-doped crystals quenched from a temperature in the range from 450 to 600 C subsequent to anneals in different partial pressures of Hg. It is found that the behavior of phosphorus in Hg(0.8)Cd(0.2)Te is similar to that established for CdTe, except that all the electrically active phosphorus defect centers in Hg(0.8)Cd(0.2)Te appear to be only singly ionized. At low Hg pressure, phosphorus is incorporated as a single donor occupying Hg lattice sites, and at high Hg pressure, as a single acceptor on interstitial sites and Te lattice sites.

Vydyanath, H. R.↗
NASA NTRS1985

The thermal release of Hg from chondrites and their thermal histories

A quantitative treatment and implications of isothermal and linear heating data on Hg in meteorites are given as a sequel to a more qualitative analysis of meteorite thermal histories (Reed and Jovanovic, 1968). Studies of Hg in terrestrial metamorphic rocks establish that thermal events to which meteorites were subjected fall in the same temperature range, of 400-900 C, as exists during terrestrial metamorphism. Hg diffusion parameters based on data from the linear and isothermal heating experiments are calculated. The conclusions are: (1) Meteorites experienced thermal events of the same magnitude as those measured by primarily mineralogical metamorphic indicators reviewed by Dodd (1969); (2) no correspondence with mineralogical-petrological metamorphic grade is evident; (3) Hg data for some chondrites correlate with shock facies (non-thermal) indicators (Dodd and Jarosewich, 1979); (4) small Hg activation energies (6-14 kcal/mole) require that the meteorites must have been stored in closed systems until low temperatures were attained. Hg must be presented as an involatile mineral(s) or as a substituent in a host phase at temperatures below 100 C. Consistent with this interpretation is the fact that despite diffusion times of 100-1,000,000 years at 200 K, Hg was retained in small objects over cosmic ray exposure periods of a hundred-million years.

Jovanovic, S.↗
DOE OSTI2020

Materials Data on Hg by Materials Project

Hg is Magnesium structured and crystallizes in the orthorhombic Cmcm space group. The structure is one-dimensional and consists of two Hg ribbons oriented in the (0, 0, 1) direction. Hg is bonded in a distorted bent 120 degrees geometry to two equivalent Hg atoms. Both Hg–Hg bond lengths are 3.40 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hg by Materials Project

Hg crystallizes in the orthorhombic Cmce space group. The structure is two-dimensional and consists of two Hg sheets oriented in the (1, 0, 0) direction. Hg is bonded in a 1-coordinate geometry to three equivalent Hg atoms. There are one shorter (3.24 Å) and two longer (3.35 Å) Hg–Hg bond lengths.

36 MATERIALS SCIENCE↗