2,439 research outputs found
Mercury sources and bioavailability in lakes located in the mining district of Chibougamau, eastern Canada
No full textThe presence of Hg in the fish of the lakes from the Cu–Zn–Au mining region of Chibougamau (Canada)
represents a serious source of concern for the health of local sports and subsistence fishers. This study focuses on identifying the origin of Hg present in the sediments of lakes with mine wastes stored in tailing facilities located on their shores. In addition to C/N ratios and determination of total Hg, Methyl Hg and other metals, a series of lignin biomarkers were used to contrast the history of the mining contamination with the nature and the intensity of terrigenous organic matter (TOM) inputs from the watersheds to the sampled lakes. It appears that sediments located nearest to mine tailings are as expected most enriched in total Hg and other metals (Cu, As, Al, Fe, Pb). Nevertheless, the presence of only small amounts of refractory TOM in these contaminated sediments could explain why only a very small fraction of Hg is found as Methyl Hg. In sediments with little or no impact by mining activities, a relationship was observed between logging activities in the lake watershed and increased TOM derived from inorganic gymnosperms soils horizons and increased Hg transport to the lakes. Nevertheless, it appears that the additional TOM transported to logged lakes is refractory enough not to promote high levels of Methyl Hg. The highest fractions of Methyl Hg relative to total Hg in lake sediments of the studied area were thus observed in relatively pristine environments where least degraded TOM is brought from the watersheds
Experimental studies of Hg(II)-Hg(0) transformations and their effects on Hg isotope fractionation
No full textUnderstanding the redox transformations of inorganic forms of mercury (Hg) is necessary for understanding the fate of mercury in environmental systems. In this study, the interactions of Hg(0) and Hg(II) with organic and inorganic substances were characterized using mercury stable isotopes. Interactions of a mixed Hg(0)-Hg(II) solution with thiol and humic substances were observed, with no net changes to redox speciation. In the presence of mercaptoacetic acid (MCA), an equilibrium isotope enrichment factor (ε202Hg = δ202HgHg(II) - δ202HgHg(0)) of 1.34‰ between the Hg(II) and Hg(0) fractions was observed, similar with previously published values for Hg(0) oxidation by thiols. The equilibrium ε202Hg values similarly determined for 2-mercaptopropionic acid (MPA) and Suwannee River humic acids were 2.03‰ and 1.50‰, respectively. Reduction of mercury by siderite (FeCO3) was also characterized with respect to isotope fractionation over the course of the reaction. This reaction resulted in an 87% reduction of Hg(II) over 30 minutes, with change in mercury isotope ratios of the reactant. Kinetic ε202Hg values for the reduction of Hg(II) by siderite (ε202Hg = δ202HgHg(0) - δ202HgHg(II)) were determined by closed-system model (-1.59‰) and Rayleigh distillation model (-1.07‰; product enrichment in light isotopes). The final equilibrium state exhibited an equilibrium ε202Hg of -0.67‰. The results from the experiments conducted suggest that there is equilibrium isotope exchange between thiol-bound Hg(II) and dissolved Hg(0), and that the reduction by siderite is rapid and may involve multiple processes through the reaction.M.S.Includes bibliographical reference
Hg sample descriptions by system and species.
No full textMercury (Hg) is a concerning contaminant due to its widespread distribution and tendency to accumulate to harmful concentrations in biota. We used a machine learning approach called random forest (RF) to test for different predictors of Hg concentrations in three species of Colorado reservoir sport fish. The RF approach indicated that the best predictors of 864 mm northern pike (Esox lucius) Hg concentrations were covariates related to salmonid stocking in each study system, while system-specific metrics related to productivity and forage base were the best predictors of Hg concentrations of 381 mm smallmouth bass (Micropterus dolomieu), and walleye (Sander vitreus). Protecting human and ecological health from Hg contamination requires an understanding of fish Hg concentrations and variability across the landscape and through time. The RF approach could be applied to identify potential areas/systems of concern, and predict whether sport fish Hg concentrations may change as a result of a variety of factors to help prioritize, focus, and streamline monitoring efforts to effectively and efficiently inform human and ecological health.</div
Liquid structure of Rb-Hg alloys studied by neutron diffraction
No full textThe structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10 at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20 at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60 at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species
Holocene peat Hg anomalies
No full textThis project examines the major explosive volcanic eruptions recorded in peat. Hg data from three peat profiles, the Hongyuan and Dangxiong peat from the Tibetan Plateau and the Pinet peat record from France, were synthesized here to support our conclusions. All the Hg data and the MATLAB script are prepared for the manuscript entitled "Tibetan peat saw Holocene global major explosive volcanic eruptions".Corresponding author: Haijun PENG, [email protected].</p
MATRIX ISOLATION ESR STUDIES OF Hg RADICALS: , , , and
No full textAuthor Institution: Furman University; University of Western AustraliaAtomic mercury vapor was passed through various rare gas plasma discharges and condensed in neon, argon, and krypton rare gas matrices at cryogenic temperatures for electron spin resonance (ESR) investigations. The first ESR spectrum of , observed in Ne, Ar, and Kr matrices is presented, with determination of its magnetic parameters, which exhibited excellent agreement with gas phase values. The ratio of the values for and is shown to vary slightly from to HgH/HgD. This variation can be attributed to electronic structure differences surrounding the mercury nucleus. Observation of in a Kr lattice also provides information on the required energy gap between the electron affinity of an isolated species and the ionization potential of the matrix host atom. HgH and HgD were observed in experiments where the plasma discharge was doped with a small percentage of gas. The HgH/HgD radicals were observed for the firs t time in a neon matrix, providing a comparison of the various magnetic parameters to earlier argon matrix results. The electronic structure and magnetic parameters of will be analyzed based upon these new matrix results for and HgH
Freedom of choice or force of circumstance? : Eastern European sex-workers in the Republic of Cyprus ; paper for the conference 'Alltag der Globalisierung. Perspektiven einer transnationalen Anthropologie', January 16-18, 2003, Institute of Cultural Anthropology and European Ethnology, Johann Wolfgang Goethe University, Frankfurt am Main
No full textThis paper focuses on Eastern European migrants who, since the beginning of the 1990s, are entering the Republic Cyprus as “artistes”. This is a visa permit status as well as an euphemism for short-term work permits in the local sex industry. In addition to exploring the migrational experiences of these women and their living and working conditions in the Republic of Cyprus, the paper reconstructs, empirically and analyt ically, the connection between immigration and the local sex industry. Here, several categories of social actors and institutions in Cyprus are actively involved. The rhetoric of government representatives, entrepreneurs and clients in the sex business on the one hand is contrasted with the discourse of local NGO representatives concerned with immigrants’ rights on the other hand. The paper comes to the conclusion that all of these discursive positions ultimately do not do justice to the complex process of decisionmaking that women undergo who migrate into the sex industry. Either, freedom of choice is emphasized – such as by entrepreneurs and the government – or the domination of women – as in the public statements of the NGO. In order to analyze the ambivalent tension between freedom of choice and submission to force by which the women’s decision is characterized, the author employs Michel Foucault’s concept of governmentality, which describes forms of political regulation that use the individual’s freedom of action as an instrument to exercise power
Predicted Hg concentrations of 381 mm walleye (<i>Sander vitreus</i>).
No full textEstimated walleye Hg concentrations from empirical data from 26 Colorado reservoirs are plotted as a function of predicted Hg concentrations from the Random Forest (RF) approach. Regions of the plot where RF predictions overestimate and underestimate estimates from empirical data are indicated. Upper 95% confidence intervals are provided for systems with empirical estimates based on five or more samples. The condensed model (Chl a, Elev, Secc, and TP) was used in this analysis. A one-to-one (dotted) line is provided for comparison.</p
Comparison of system architecture and converter topology for a solar powered electric vehicle charging station
No full textAccepted Author ManuscriptOld - EWI-ESE-DC&S DC systems & StoragePhotovoltaic Materials and Device
The land surface mildly contaminated by Hg
No full textThe Hg content in the waters of Jiaozhou Bay was within 0.010-0.060μg/L in May, September and October 1993, which conforms to the seawater quality standards of Class I and II. It indicates that in the entire waters of Jiaozhou Bay, there were some water areas that did not get contaminated by Hg while some areas got mild contamination by Hg in May, September and October. In May, the variation range of Hg content in the waters of Jiaozhou Bay was 0.010-0.046μg/L. In September, it ranged within 0.007-0.011μg/L. And in October, the content of Hg detected in the waters of Jiaozhou Bay was 0.060μg/L. There were three sources to transport Hg content, open sea currents, Licun river and the surface runoff. The Hg content from the transportation of open sea currents was 0.046μg/L, from the Licun river was 0.011μg/L and from the surface runoff was 0.060μg/L. This paper builds a model block diagram to present the different paths and Hg contents that were input in the Jiaozhou Bay. In May, the open sea currents did not get any contamination of Hg; in August, the Licun river did not get any contamination of Hg as well; while in September, the surface runoff was mildly contaminated by Hg. The author concluded two points about the migration of Hg content: 1) Human activities discharge Hg to the land so that the Hg content could directly run to the ocean through the surface runoff. As the Hg content transported by surface runoff was relatively high, it resulted that the nearshore waters got mild contamination of Hg content. On the other hand, the surface runoff transported Hg to rivers, resulting relatively low content of Hg. Then rivers delivered the Hg content to nearshore waters, leading to a non-contaminated condition of rivers. 2) Human activities input Hg content to the ocean in a long period, resulting the increase of Hg content in the ocean. As the accumulation of Hg content in the ocean, the ocean got close to the mild contamination status
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