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Biodisponibilidade de mercurio e outros metais-traço em sedimentos do Rio Cubatão, Sistema Estuarino de Santos-Cubatão (SP); Bioavailability of mercury and other trace-metals in sediments of Cubatão River, Santos-Cubatão Estuarine System (SP)

Fanny Roxana Mamani Matamet
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 29/08/2007 PT
Relevância na Pesquisa
36.52%
Os ecossistemas costeiros da Baixada Santista no Estado de São Paulo encontram-se degradados, em conseqüência da concentração populacional e da instalação de um pólo petroquímico e siderúrgico. Essa degradação iniciou-se na década de 1950, com a construção do mais importante complexo de fábricas da América Latina, o Pólo Industrial de Cubatão. Apesar do controle por órgãos de governo das emissões de efluentes industriais, elevados níveis de mercúrio e outros metais têm sido encontrados nos sedimentos do rio Cubatão, um dos mais impactados do sistema estuarino de Santos-Cubatão. O mercúrio constitui um dos poluentes de maior risco para o equilíbrio ecológico e para a saúde humana, justificado pela elevada toxicidade e potencial de bioacumulação e biomagnificação na cadeia trófica. Este estudo objetivou analisar o risco de biodisponibilidade de mercúrio e outros metais-traço em sedimentos do rio Cubatão e a variabilidade de suas concentrações totais e lábeis no inverno e no verão. Para isso, vários aspectos específicos foram investigados em sedimentos de testemunhos curtos, tais como, os níveis totais de mercúrio e outros metais de interesse; as concentrações de sulfetos volatilizáveis por acidificação (AVS) e metais simultaneamente extraídos (SEM = Ni...

Mercurio e sulfetos volatilizaveis por acidos na bacia do Rio Jundiai, SP; Mercury and acid-volatile sulfides in the Jundiai River basin, SP

Enelton Fagnani
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 03/07/2009 PT
Relevância na Pesquisa
36.36%
O presente trabalho teve por finalidade avaliar alguns aspectos ambientais do Rio Jundiaí e do Ribeirão Piraí, principais mananciais da bacia do Rio Jundiaí, estado de São Paulo, uma sub-bacia do Comitê Piracicaba - Capivari - Jundiaí (PCJ), gerando um importante e inédito inventário para esse início de século, capaz de auxiliar nas tomadas de decisão sobre questões ambientais na região, valendo-se da determinação de parâmetros químicos em amostras de água e sedimento no período 2007-2008. Elegeram-se cinco pontos de coleta de água para a determinação de mercúrio total (HgT) e carbono orgânico dissolvido (COD), sendo três no Rio Jundiaí, um no Ribeirão Piraí e um no Rio Tietê, tomado como referência de locais degradados. As concentrações médias para HgT, em ng L-1, foram de 8,2 +- 6,4; 7,0 +- 6,6 e 5,2 +- 3,6 no Rio Jundiaí, 2,1 +- 1,9 no Ribeirão Piraí e 19,3 +- 13,6 no Rio Tietê. Já as concentrações médias de COD, em mg L-1, foram de 7,1 +- 1,5; 9,4 +- 2,2 e 28,6 +- 17,7 no Jundiaí, 3,3 +- 1,2 no Piraí e 14,9 +- 5,4 no Tietê. Correlações entre HgT e COD mostraram que em áreas menos impactadas, como o Ribeirão Piraí, há uma relação positiva entre o COD e o HgT, sendo que maiores valores de COD implicam na ocorrência de maiores valores de HgT; em áreas mais impactadas do Rio Jundiaí...

Emanações gasosas de mercúrio associadas com mineralizações sulfetadas de zinco. Estudo de caso : depósito de Santa Maria (RS); Gaseous Mercury emanations associated with zinc sulfide deposits. Case study : Santa Maria deposit

Fernanda Cecília Dias Barros
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 13/08/2012 PT
Relevância na Pesquisa
36.47%
O uso da geoquímica de gases ou emanometria é um método com grande potencial em prospecção mineral de depósitos não aflorantes e/ou encobertos por rochas não-mineralizadas, porém ainda é pouco utilizado. A temperatura de formação da mineralização é um fator determinante à presença de alguns elementos- traço, dentre eles o Hg. Existe uma predileção do Hg por depósitos de zinco de baixa temperatura do tipo epitermal e stratabound. O depósito de Zn-Pb-Cu de Santa Maria, localizado na Bacia do Camaquã, município de Caçapava do Sul (RS) contém Hg associado à mineralização e, por isso, foi escolhido como área piloto para testes de emanometria. O objetivo desta pesquisa foi medir a concentração de Hg gasoso in situ e avaliar a sua potencialidade na prospecção de depósitos sulfetados de zinco. A concentração de Hg gasoso no ar foi medida ao longo de um percurso de 11 km com um espectrômetro portátil de absorção atômica a fim de definir a concentração de Hg atmosférico local, que variou de 2 a 10 ng/m3. O Hg gasoso no solo foi medido em buracos escavados em profundidades de 30 e 50 cm e a sucção do ar para o interior do espectrômetro, atingindo valor máximo de 19 ng/m3 acima da mineralização. Amostras de solo e de duas espécies de vegetação também foram analisadas. O tratamento estatístico dos resultados mostrou que o background de Hg medido nas amostras de solo variou entre 3...

Mercury Adaptation among Bacteria from a Deep-Sea Hydrothermal Vent

Vetriani, Costantino; Chew, Yein S.; Miller, Susan M.; Yagi, Jane; Coombs, Jonna; Lutz, Richard A.; Barkay, Tamar
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2005 EN
Relevância na Pesquisa
26.47%
Since deep-sea hydrothermal vent fluids are enriched with toxic metals, it was hypothesized that (i) the biota in the vicinity of a vent is adapted to life in the presence of toxic metals and (ii) metal toxicity is modulated by the steep physical-chemical gradients that occur when anoxic, hot fluids are mixed with cold oxygenated seawater. We collected bacterial biomass at different distances from a diffuse flow vent at 9°N on the East Pacific Rise and tested these hypotheses by examining the effect of mercuric mercury [Hg(II)] on vent bacteria. Four of six moderate thermophiles, most of which were vent isolates belonging to the genus Alcanivorax, and six of eight mesophiles from the vent plume were resistant to >10 μM Hg(II) and reduced it to elemental mercury [Hg(0)]. However, four psychrophiles that were isolated from a nearby inactive sulfide structure were Hg(II) sensitive. A neighbor-joining tree constructed from the deduced amino acids of a PCR-amplified fragment of merA, the gene encoding the mercuric reductase (MR), showed that sequences obtained from the vent moderate thermophiles formed a unique cluster (bootstrap value, 100) in the MR phylogenetic tree, which expanded the known diversity of this locus. The temperature optimum for Hg(II) reduction by resting cells and MR activity in crude cell extracts of a vent moderate thermophile corresponded to its optimal growth temperature...

Mercury in traditional medicines: Is cinnabar toxicologically similar to common mercurials?

Liu, Jie; Shi, Jing-Zheng; Yu, Li-Mei; Goyer, Robert A.; Waalkes, Michael P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.59%
Mercury is a major toxic metal ranking top in the Toxic Substances List. Cinnabar (contains mercury sulfide) has been used in traditional medicines for thousands years as an ingredient in various remedies, and 40 cinnabar-containing traditional medicines are still used today. Little is known about toxicology profiles or toxicokinetics of cinnabar and cinnabar-containing traditional medicines, and the high mercury content in these Chinese medicines raises justifiably escalations of public concern. This minireview searched the available database of cinnabar, compared cinnabar with common mercurials, such as mercury vapor, inorganic mercury, and organic mercury, and discusses differences in their bioavailability, disposition, and toxicity. The analysis showed that cinnabar is insoluble and poorly absorbed from the gastrointestinal tract. Absorbed mercury from cinnabar is mainly accumulated in kidney, resembling the disposition pattern of inorganic mercury. Heating cinnabar results in release of mercury vapor, which in turn can produce toxicity similar to inhalation of these vapors. The doses of cinnabar required to produce neurotoxicity are thousands 1000 times higher than methyl mercury. Following long-term use of cinnabar, renal dysfunction may occur. Dimercaprol and succimer are effective chelation therapies for general mercury intoxication including cinnabar. Pharmacology studies of cinnabar suggest sedative and hypnotic effects...

The Chemical Forms of Mercury in Aged and Fresh Dental Amalgam Surfaces

George, Graham N.; Singh, Satya P.; Hoover, Jay; Pickering, Ingrid J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/2009 EN
Relevância na Pesquisa
26.47%
Mercury-containing dental amalgam is known to be a source of human exposure to mercury. We have explored the use of electron-yield Hg LIII X-ray absorption spectroscopy to characterize the chemical nature of dental amalgam surfaces. We find that the method is practical, and that it shows extensive mercury depletion in the surface of the aged amalgam with significant differences between old and fresh amalgam surfaces. Whereas the fresh amalgam gives spectra that are typical of metallic mercury, the aged amalgam is predominantly β-mercuric sulfide. The toxicological implications of these results are discussed.

Dicaesium hexa­mercury hepta­sulfide

Bugaris, Daniel E.; Ibers, James A.
Fonte: International Union of Crystallography Publicador: International Union of Crystallography
Tipo: Artigo de Revista Científica
Publicado em 09/08/2008 EN
Relevância na Pesquisa
36.47%
The title compound, Cs2Hg6S7, crystallizes in a new structure type that is closely related to that of K2Zn6O7. The structure comprises a three-dimensional mercury sulfide network that is composed of channels. These channels, which are along [001], are of two different diameters. The crystal structure contains one Cs, two Hg, and three S atoms in the asymmetric unit. The Cs, one Hg, and one S atom are at sites of symmetry m, whereas a second S atom is at a site of symmetry 2mm. The Hg atoms are bound to the S atoms in both three- and four-coordinate geometries. The caesium cations occupy the central spaces of the larger diameter channels and exhibit a coordination number of 7.

Rare-earth vs. heavy metal pigments and their colors from first principles

Tomczak, Jan M.; Pourovskii, Leonid V.; Vaugier, Loig; Georges, Antoine; Biermann, Silke
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.47%
Many inorganic pigments contain heavy metals hazardous to health and environment. Much attention has been devoted to the quest for nontoxic alternatives based on rare-earth elements. However, the computation of colors from first principles is a challenge to electronic structure methods, especially for materials with localized f-orbitals. Here, starting from atomic positions only, we compute the colors of the red pigment cerium fluorosulfide as well as mercury sulfide (classic vermilion). Our methodology uses many-body theories to compute the optical absorption combined with an intermediate length-scale modelization to assess how coloration depends on film thickness, pigment concentration, and granularity. We introduce a quantitative criterion for the performance of a pigment. While for mercury sulfide, this criterion is satisfied because of large transition matrix elements between wide bands, cerium fluorosulfide presents an alternative paradigm: the bright red color is shown to stem from the combined effect of the quasi-2D and the localized nature of states. Our work shows the power of modern computational methods, with implications for the theoretical design of materials with specific optical properties.

Microbial colonization and dissolution of mercury sulfide minerals

Vazquez Rodriguez, Adiari Iraida
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation
EN_US
Relevância na Pesquisa
66.78%
Mercury (Hg) is a toxic heavy metal that poses significant human and environmental health risks. Mineral-associated Hg is the largest reservoir of Hg in the environment where it can account for nearly 60% of the global Hg mass inventory. A large fraction of this pool is comprised of mercury sulfide (HgS) minerals, including metacinnabar (beta-HgS). HgS minerals have long been considered insignificant sources of Hg to aqueous or atmospheric pools in all but severely acidic environments due to their low solubility and slow abiotic dissolution kinetics. Little previous work has been conducted investigating the bacterial colonization of HgS minerals and the potential role of these mineral-associated communities in impacting the mobility of mineral-hosted Hg. To address this gap in knowledge, the studies within this dissertation employed a combination of field- and laboratory-based methods. Using culture-independent techniques, this work revealed that sulfur-oxidizing bacteria can extensively colonize metacinnabar within aerobic, near neutral pH, creek sediments, suggesting a potential role for chemolithotrophic bacteria in metacinnabar weathering. Within laboratory incubations, the dominant bacterial colonizer (Thiobacillus thioparus)...

Microbial- and thiosulfate-mediated dissolution of mercury sulfide minerals and transformation to gaseous mercury

Vázquez-Rodríguez, Adiari I.; Hansel, Colleen M.; Zhang, Tong; Lamborg, Carl H.; Santelli, Cara M.; Webb, Samuel M.; Brooks, Scott C.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
56.85%
Mercury (Hg) is a toxic heavy metal that poses significant environmental and human health risks. Soils and sediments, where Hg can exist as the Hg sulfide mineral metacinnabar (β-HgS), represent major Hg reservoirs in aquatic environments. Metacinnabar has historically been considered a sink for Hg in all but severely acidic environments, and thus disregarded as a potential source of Hg back to aqueous or gaseous pools. Here, we conducted a combination of field and laboratory incubations to identify the potential for metacinnabar as a source of dissolved Hg within near neutral pH environments and the underpinning (a)biotic mechanisms at play. We show that the abundant and widespread sulfur-oxidizing bacteria of the genus Thiobacillus extensively colonized metacinnabar chips incubated within aerobic, near neutral pH creek sediments. Laboratory incubations of axenic Thiobacillus thioparus cultures led to the release of metacinnabar-hosted Hg(II) and subsequent volatilization to Hg(0). This dissolution and volatilization was greatly enhanced in the presence of thiosulfate, which served a dual role by enhancing HgS dissolution through Hg complexation and providing an additional metabolic substrate for Thiobacillus. These findings reveal a new coupled abiotic-biotic pathway for the transformation of metacinnabar-bound Hg(II) to Hg(0)...

Metal Sulfide Formation by the Cyanobacterium Synechococcus leopoldiensis as a Mechanism of Toxic Metal Bioremediation

Raykin, Leon
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 943104 bytes; application/msword
EN
Relevância na Pesquisa
46.58%
The contamination of water bodies with toxic metals is an environmental issue that can be addressed through several approaches. One approach is bioremediation, in which living organisms are used to detoxify the contaminant. Recent studies have shown that a number of cyanobacteria are able to detoxify mercury by forming insoluble mercury sulfide precipitates. In this study, one of these organisms, Synechococcus leopoldiensis, was studied to determine whether it also forms metal sulfides with lead, arsenic or cadmium. Lead readily precipitated in the cyanobacteria culture medium. This interfered with biomass measurements and decreased the bioavailability of the metal, complicating the study of lead detoxification by S. leopoldiensis. Application of additional sulfate to the culture medium increased the toxicity of lead to the cyanobacterium, suggesting that a decrease in pH associated with sulfate application was increasing the solubility of the lead precipitates. Growth was initially inhibited in S. leopoldiensis cultures incubated with 15 and 30 ppm arsenic, but the cyanobacteria eventually recovered to a biomass not statistically different from that of control cultures incubated in parallel. The recovery was enhanced in 15 ppm cultures that had additional sulfate added to the culture medium...

Elucidating the heavy metal bioremediation capabilities of Chlamydomonas reinhardtii

Beatty, Joseph
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN
Relevância na Pesquisa
26.76%
Environmental pollution by heavy metals poses a serious threat to human and ecosystem health. Bioremediation using microorganisms offers a potentially more affordable and effective alternative to traditional means of heavy metal remediation. Recent studies have shown that a number of species of freshwater algae are able to biotransform mercury into mercury sulfide precipitates. In this study, the ability of Chlamydomonas reinhardtii to bioremediate varying concentrations of cadmium [Cd (II)], copper [Cu (II)] and zinc [Zn (II)] was assessed. Supplementing C. reinhardtii with 10X the amount of sulfate normally found in the growth media, allowed C. reinhardtii to proliferate at concentrations of Cd (II), Cu (II) and Zn (II) that otherwise proved lethal. C. reinhardtii formed cadmium sulfide and zinc sulfide following exposure to 100 μM Cd (II) and 100 μM Zn (II); however, no appreciable amount of copper sulfide was detected following exposure to 2.5 μM Cu (II). C. reinhardtii may have tolerated high concentrations of Cu (II) by employing an alternative detoxification mechanism. Cysteine desulfhydrase activity was consistently highest in C. reinhardtii cultures pre-treated with 10X sulfate. This higher activity may be due to a greater available pool of intracellular thiols that can be broken down to sulfide in response to heavy metal stress. Serine acetyltransferase and O-acetylserine(thiol)lyase activity was consistently highest in control cultures of C. reinhardtii exposed to each of the three heavy metals. Control cultures received no supplemental sulfate or sulfite. Serine acetyltransferase and O-acetylserine(thiol)lyase are two rate-limiting enzymes responsible for the incorporation of sulfide into cysteine...

Reduced organic sulfur: Analysis and interaction with mercury in the aquatic environment

Chen, Sen
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.54%
Reduced organic sulfur (ROS) compounds are environmentally ubiquitous and play an important role in sulfur cycling as well as in biogeochemical cycles of toxic metals, in particular mercury. Development of effective methods for analysis of ROS in environmental samples and investigations on the interactions of ROS with mercury are critical for understanding the role of ROS in mercury cycling, yet both of which are poorly studied. ^ Covalent affinity chromatography-based methods were attempted for analysis of ROS in environmental water samples. A method was developed for analysis of environmental thiols, by preconcentration using affinity covalent chromatographic column or solid phase extraction, followed by releasing of thiols from the thiopropyl sepharose gel using TCEP and analysis using HPLC-UV or HPLC-FL. Under the optimized conditions, the detection limits of the method using HPLC-FL detection were 0.45 and 0.36 nM for Cys and GSH, respectively. Our results suggest that covalent affinity methods are efficient for thiol enrichment and interference elimination, demonstrating their promising applications in developing a sensitive, reliable, and useful technique for thiol analysis in environmental water samples. ^ The dissolution of mercury sulfide (HgS) in the presence of ROS and dissolved organic matter (DOM) was investigated...

Reduced Organic Sulfur: Analyisis and Interaction with Mercury in the Aquatic Environment

Chen, Sen
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
46.56%
Reduced organic sulfur (ROS) compounds are environmentally ubiquitous and play an important role in sulfur cycling as well as in biogeochemical cycles of toxic metals, in particular mercury. Development of effective methods for analysis of ROS in environmental samples and investigations on the interactions of ROS with mercury are critical for understanding the role of ROS in mercury cycling, yet both of which are poorly studied. Covalent affinity chromatography-based methods were attempted for analysis of ROS in environmental water samples. A method was developed for analysis of environmental thiols, by preconcentration using affinity covalent chromatographic column or solid phase extraction, followed by releasing of thiols from the thiopropyl sepharose gel using TCEP and analysis using HPLC-UV or HPLC-FL. Under the optimized conditions, the detection limits of the method using HPLC-FL detection were 0.45 and 0.36 nM for Cys and GSH, respectively. Our results suggest that covalent affinity methods are efficient for thiol enrichment and interference elimination, demonstrating their promising applications in developing a sensitive, reliable, and useful technique for thiol analysis in environmental water samples. The dissolution of mercury sulfide (HgS) in the presence of ROS and dissolved organic matter (DOM) was investigated...

A preliminary characterization of mercury uptake by the sulfate-reducing bacteria Desulfovibrio desulfuricans

Betancourt, Amaury Pedro, III
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.52%
The focus of this research is to determine if a relationship exists between the stability constant and the initial uptake rate of a mercury species by bacteria. Cultures of the sulfate-reducing bacteria (SRB) strain Desulfovibrio desulfuricans G20 were washed with a bicarbonate buffer solution containing either lactate and sulfate or pyruvate and fumarate. The washed cell solutions were then spiked with either mercury bound to natural organic matter (Hg-NOM) or neutral mercury chloride (HgCl2), followed by sampling over time to provide kinetic data. Despite the significantly different stability constants for Hg-NOM and HgCl2, the calculated initial rate constants for mercury uptake for these two types of complexes appeared to be comparable. Uptake of mercury sulfide species was inconclusive due to possible formation of cinnabar. A simple model that is based on assumptions of passive diffusion and facilitated uptake of mercury by bacteria was evaluated for its potential to simulate the uptake. The model results only agreed with experimental data for HgCl2 uptake.

Mercury characterization in soil collected nearby the Department of Energy Oak Ridge reservation

Cabrera, Julio Cesar
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
Relevância na Pesquisa
36.54%
Total mercury (Hg) concentration provides insufficient information to understand Hg behavior in Hg-contaminated soil systems and to seek potential remediation technologies, because the distribution, mobility, bioavailability, and toxicity of Hg are dependent on Hg forms present in soils. The phase association of Hg in soil is investigated to evaluate potential environmental risk through combination of total Hg determination, soil fractionation, and speciation analysis of Hg in a Hg-contaminated DOE site. Besides total Hg concentration analysis, sequential extraction procedures and thermal desorption techniques were employed to study Hg binding forms in soils in this study. Total mercury concentrations ranging from less than 100 ng/g to more than 30,000 ng/g were detected. The highest form of mercury present in the soil is organically-bound mercury, followed by elemental mercury, and mercury sulfide. Bioavailable and mobile mercury is minimal.

Chronic mercury exposure in Late Neolithic/Chalcolithic populations in Portugal from the cultural use of cinnabar

Emslie, Steven D.; Brasso, Rebecka; Patterson, William P.; Carlos Valera, António; McKenzie, Ashley; Maria Silva, Ana; Gleason, James D.; Blum, Joel D.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 01/10/2015 EN
Relevância na Pesquisa
36.52%
Cinnabar is a natural mercury sulfide (HgS) mineral of volcanic or hydrothermal origin that is found worldwide. It has been mined prehistorically and historically in China, Japan, Europe, and the Americas to extract metallic mercury (Hg0) for use in metallurgy, as a medicinal, a preservative, and as a red pigment for body paint and ceramics. Processing cinnabar via combustion releases Hg0 vapor that can be toxic if inhaled. Mercury from cinnabar can also be absorbed through the gut and skin, where it can accumulate in organs and bone. Here, we report moderate to high levels of total mercury (THg) in human bone from three Late Neolithic/Chalcolithic (5400–4100 B.P.) sites in southern Portugal that were likely caused by cultural use of cinnabar. We use light stable isotope and Hg stable isotope tracking to test three hypotheses on the origin of mercury in this prehistoric human bone. We traced Hg in two individuals to cinnabar deposits near Almadén, Spain, and conclude that use of this mineral likely caused mild to severe mercury poisoning in the prehistoric population. Our methods have applications to bioarchaeological investigations worldwide, and for tracking trade routes and mobility of prehistoric populations where cinnabar use is documented.

Detoxification of mercury, cadmium, and lead in Klebsiella aerogenes NCTC 418 growing in continuous culture.

Aiking, H; Govers, H; van 't Riet, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1985 EN
Relevância na Pesquisa
26.73%
Klebsiella aerogenes NCTC 418 growing in the presence of cadmium under glucose-, sulfate-, or phosphate-limited conditions in continuous culture exhibited sulfide formation and Pi accumulation as the only demonstrable detoxification mechanisms. In the presence of mercury under similar conditions only HgS formation could be confirmed, by an increased sensitivity to mercury under sulfate-limited conditions, among others. The fact that the cells were most sensitive to cadmium under conditions of phosphate limitation and most sensitive to mercury under conditions of sulfate limitation led to the hypothesis that these inorganic detoxification mechanisms generally depended on a kind of "facilitated precipitation". The process was coined thus because heavy metals were probably accumulated and precipitated near the cell perimeter due to the relatively high local concentrations of sulfide and phosphate there. Depending on the growth-limiting nutrient, mercury proved to be 25-fold (phosphate limitation), 75-fold (glycerol limitation), or 150-fold (sulfate limitation) more toxic than cadmium to this organism. In the presence of lead, PbS formation was suggested. Since no other detoxification mechanisms were detected, for example, rendering heavy metal ions innocuous as metallo-organic compounds...

Sources and Biogeochemical Transformation of Mercury in Aquatic Ecosystems

Deonarine, Amrika
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2011
Relevância na Pesquisa
57.21%

Mercury contamination in aquatic ecosystems is a concern as anaerobic aquatic sediments are the primary regions of methylmercury production in freshwater and coastal regions. Methlymercury is a bioaccumulative neurotoxin, and human exposure to methylmercury can result in impaired functioning of the central nervous system and developmental disabilities in children. To minimize the risk of human exposure to methylmercury, it is important to be knowledgeable of the various sources which can supply mercury to aquatic ecosystems as well as have a complete understanding of the biogeochemical processes which are involved in methylmercury production in aquatic systems. In this dissertation work, both mercury biogeochemical speciation in anaerobic aquatic sediments and sources of mercury to aquatic systems were addressed.

The biogeochemical speciation of mercury is a critical factor which influences the fate and transformation of mercury in aquatic environments. In anaerobic sediments, mercury chemical speciation is controlled by reduced sulfur groups, such as inorganic sulfide and reduced sulfur moieties in dissolved organic matter (DOM). The formation of mercury sulfide nanoparticles through stabilization by dissolved organic matter (DOM) was investigated in precipitation studies using dynamic light scattering. Mercury sulfide nanoparticles (particle diameter < 100 nm) were stabilized through precipitation reactions that were kinetically hindered by DOM. To further investigate the interaction between DOM and metal sulfides...

Mechanisms of Microbial Formation and Photodegradation of Methylmercury in the Aquatic Environment

ZHANG, TONG
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2012
Relevância na Pesquisa
26.61%

Methylmercury is a bioaccumulative neurotoxin that severely endangers human health. Humans are exposed to methylmercury through consumption of contaminated aquatic fish. To date, effective strategies for preventing and remediating methylmercury contamination have remained elusive, mainly due to the lack of knowledge in regard to how methylmercury is generated and degraded in the aquatic environment. The goal of this dissertation was to study the mechanisms of two transformation processes that govern the fate of methylmercury in natural settings: microbial mercury methylation and methylmercury photodegradation. The role of mercury speciation (influenced by environmental conditions) in determining the reactivity of mercury in these biological and photochemical reactions was the focus of this research.

Methylmercury production in the aquatic environment is primarily mediated by anaerobic bacteria in surface sediments, particularly sulfate reducing bacteria (SRB). The efficiency of this process is dependent on the activity of the methylating bacteria and the availability of inorganic divalent mercury (Hg(II)). In sediment pore waters, Hg(II) associates with sulfides and dissolved organic matter (DOM) to form a continuum of chemical species that include dissolved molecules...