Página 11 dos resultados de 5533 itens digitais encontrados em 0.013 segundos

Determination of the surface charge density of a mercury electrode by extrusion: a new method for correction of the faradaic component

Brito, Maria S. L.; Angnes, Lúcio; Brett, Christopher M. A.; Gutz, Ivano G. R.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.84%
The accurate determination of the surface charge density at the mercury | solution interface by the method of extrusion of mercury drops is impaired by the faradaic current caused by traces of electroactive species. This paper describes a new design of a hanging mercury drop electrode with accurate control of the extruded electrode area, to within 0.1%, together with a new and reliable procedure for correction of the faradaic current. The procedure is based on first obtaining the correction parameters in the presence of increasing amounts of electroactive species and then using these parameters for correction of the faradaic component so as to obtain the surface charge density of the electrode. Implementation of the method with a microcomputer controlled system provides automatic acquisition of corrected electrode charge density values as a function of the electrode potential. The results obtained with this new method are in excellent agreement with those obtained by other methods, as illustrated for aqueous sodium fluoride solution.; http://www.sciencedirect.com/science/article/B6TGB-3WS6M1X-4/1/959396100ce50f29fe3e81cc9a422423

Pattern and pathways for mercury lifespan bioaccumulation in Carcinus maenas

Coelho, J. P.; Reis, A. T.; Ventura, S.; Pereira, M. E.; Duarte, A. C.; Pardal, M. A.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.84%
Carcinus maenas is an important and exploited natural resource in temperate estuaries, being consumed by local populations and also used as fish bait. Through bioaccumulation and bioamplification processes occurring in polluted estuarine ecosystems, this species may directly or indirectly represent a major pathway for Human contamination. No information is available on the overall lifespan bioaccumulation pattern of mercury for this species, which would be an invaluable tool for assessing the risks associated with C. maenas harvest in contaminated areas. Taking that in mind, the main objectives of this work were to clarify the lifespan bioaccumulation pattern of mercury for this species.; http://www.sciencedirect.com/science/article/B6V6N-4SDFSCK-3/1/b855ee8cbb8c51a429f283cd5a318efc

Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

CARVALHO, Gabriel G. A. de; FERES JR., Mario A.; FERREIRA, Jose R.; KENNEDY, Valerie H.
Fonte: TAYLOR & FRANCIS LTD Publicador: TAYLOR & FRANCIS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.84%
A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO(4) solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl(2) solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl(2) solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g(-1) for total Hg and 4.3 ng g(-1) for inorganic Hg. The relative standard deviation for a 1.0 mu gL(-1) CH(3)Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 mu gL(-1) Hg(2+) standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4 degrees C.; CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)[110751/2005-1]

Low nanomolar concentration of mercury chloride increases vascular reactivity to phenylephrine and local angiotensin production in rats

Wiggers, Giulia Alessandra; Stefanon, Ivanita; Padilha, Alessandra Simao; Peçanha, Franck Maciel; Vassallo, Dalton Valentim; Oliveira, Edilamar Menezes
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.84%
Exposure to mercury at nanomolar level affects cardiac function but its effects on vascular reactivity have yet to be investigated. Pressor responses to phenylephrine (PHE) were investigated in perfused rat tail arteries before and after treatment with 6 nM HgCl2 during 1 h,,in the presence (E+) and absence (E-) of endothelium, after L-NAME (10(-4) M), indomethacin (10(-5) M), enalaprilate (1 mu M), tempol (1 mu M) and deferoxamine (300 mu M) treatments. HgCl2 increased sensitivity (pD(2)) without modifying the maximum response (Em) to PHE, but the pD(2) increase was abolished after endothelial damage. L-NAME treatment increased pD(2) and Emax. However, in the presence of HgCl2, this increase was smaller, and it did not modify Emax. After indomethacin treatment, the increase of pD(2) induced by HgCl2 was maintained. Enalaprilate, tempol and deferoxamine reversed the increase of pD(2) evoked by HgCl2. HgCl2 increased the angiotensin converting enzyme (ACE) activity explaining the result obtained with enalaprilate. Results suggest that at nanomolar concentrations HgCl2 increase the vascular reactivity to PHE. This response is endothelium mediated and involves the reduction of NO bioavailability and the action of reactive oxygen species. The local ACE participates in mercury actions and depends on the angiotensin 11 generation. (c) 2007 Elsevier Inc. All rights reserved.

Viabilidade do uso do eletrodo de mercúrio como indicador, no estudo da formação de complexos, no sistema Hg(II)/S2O32+, em meio aquoso (OU) Viabilidade do uso do eletrodo de mercurio, no estudo da formação de complexos, no sistema Hg(II)/tiossulfato; Viability of use of a mercury electrode in the study of complex formation in the Hg(II)Thiosulphate system

Tavares, Marina Franco Maggi
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 22/12/1986 PT
Relevância na Pesquisa
36.84%
O presente trabalho procura dar continuidade a uma das linhas de pesquisa desenvolvida pelo Grupo de Química Analítica do Instituto de Química da Universidade de são Paulo: o estudo da formação de complexos. O sistema Hg(II) / S2O2-3 foi analisado potenciometricamente, com a finalidade de identificar o número de complexos formados, assim como estimar as constantes de estabilidade envolvidas no fenônemo de complexação. Tal equilíbrio foi levado a termo a 25,0 ± 0,1°C, e força iônica 2,00M, sendo detectados quatro espécies complexas. O modelo matemático que melhor se ajustou aos dados experimentais fornecidos pelo sistema, conta com os seguintes valores para as constantes globais de formação: β1 1 = x 1024 M-1 (valor atribuído) β2 = (8,0 ± 2,8) x 1027 M-2 β3 = (1,71 ± 0,03) x 1030 M-3 β4 = (3,07 ± 0,77) x 1030 M-4. Na região de baixa concentração analítica de ligante, 5mM, o acesso experimental foi limitado pela precipitação de sulfeto mercúrico sendo impossível obter informaçôes sobre a primeira espécie. O comportamento do mercúrio no sistema Hg(II) / S2O2-3 foi estudado de uma forma mais abrangente, sendo estendido ao meio não complexante, onde o equilíbrio de dismutação do cátion mercuroso governa. Nas mesmas condições de temperatura e força iônica anteriores...

Impacto neurotóxico do mercúrio avaliado no sistema nervoso central por testes neuropsicológicos e no sistema nervoso autônomo por pupilometria; Neurotoxic impact of Mercury on the Central Nervous System evaluated by neuropsychological tests and on the Autonomic Nervous System evaluated by dynamic pupillometry

Milioni, Ana Luiza Vidal
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 16/06/2015 PT
Relevância na Pesquisa
36.84%
O mercúrio é um metal tóxico, que pode causar diversas alterações no organismo humano. O presente estudo teve como objetivo investigar a ocorrência de disfunções neuropsicológicas em ex-trabalhadores de fábricas de lâmpadas fluorescentes que foram expostos a vapor de mercúrio, anos após a interrupção da exposição, além de investigar os efeitos dessa exposição sobre o Sistema Nervoso Autônomo a partir do método não-invasivo da pupilometria dinâmica. A avaliação neuropsicológica foi realizada através do Inventário Beck de Depressão e da bateria neuropsicológica computadorizada CANTABeclipse, utilizando-se subtestes que avaliam memória operacional (Spatial Span), memória espacial (Spatial Recognition Memory), memória visual (Pattern Recognition Memory), percepção visual (Delayed Matching to Sample), planejamento de ações (Stockings of Cambridge) e tomada de decisão (Information Sampling Task). A avaliação do Sistema Nervoso Autônomo, por sua vez, foi realizada através da pupilometria dinâmica, que provê informações acerca do funcionamento de ambas as funções simpática e parassimpática. Foram utilizados flashes de 631nm (luz vermelha) com 1 s de duração, com luminância de 1, 10 e 100 cd/m². Os escores de depressão foram significativamente mais altos entre os indivíduos com histórico de exposição em comparação aos sujeitos do grupo controle (p=0...

Selective sorption of mercury(II) from aqueous solution with an organically modified clay and its electroanalytical application

Dias, N. L.; do Carmo, D. R.; Rosa, André Henrique
Fonte: Taylor & Francis Inc Publicador: Taylor & Francis Inc
Tipo: Artigo de Revista Científica Formato: 733-746
ENG
Relevância na Pesquisa
36.84%
The organo-clay used in this work was prepared from a Na-montmorillonite (Wyoming-USA deposit) by treatment with water solution of hexadecyltrimethylammonium cations. As organo-clays exhibit strong sorptive capabilities for organic molecules, 2-mercapto-5-amino-1,3,4-thiadiazole organofunctional groups, with potential usefulness in chemical analysis, were incorporated on its solid surface. The physically adsorbed reagent did not present any restrictions in coordinating with several metal ions on the surface. The resultant organo-clay complex exhibited strong sorptive capability for removing mercury ions from water in which other metals and ions were also present. The purpose of this work is to study the selective separation of mercury(II) from aqueous solution using the organo-clay complex, measured by batch and chromatographic column techniques, and its application as preconcentration agent in a chemically modified carbon paste electrode for determination of mercury(II) in aqueous solution.

Mercury Redox Chemistry in the Negro River Basin, Amazon: The Role of Organic Matter and Solar Light

Jardim, Wilson F.; Bisinoti, Marcia Cristina; Fadini, Pedro Sergio; da Silva, Gilmar Silverio
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica Formato: 267-278
ENG
Relevância na Pesquisa
36.84%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pristine water bodies in the Negro River basin, Brazilian Amazon, show relatively high concentrations of mercury. These waters are characterized by acidic pH, low concentrations of suspended solids, and high amounts of dissolved organic matter and are exposed to intense solar radiation throughout the year. This unique environment creates a very dynamic redox chemistry affecting the mobility of mercury due to the formation of the dissolved elemental species (Hg-0). It has been shown that in this so-called black water, labile organic matter from flooded forest is the major scavenger of photogenerated H2O2. In the absence of hydrogen peroxide, these black waters lose their ability to oxidize Hg-0 to Hg2+, thus increasing Hg-0 evasion across the water/atmosphere interface, with average night time values of 3.80 pmol m(-2) h(-1). When the dry period starts, labile organic matter inputs gradually diminish, allowing the increasing concentration of H2O2 to re-establish oxidative water conditions, inhibiting the metal flux across the water/atmosphere interface and contributing to mercury accumulation in the water column.

Determination of sulfur compounds in gasoline using mercury film electrode by square wave voltammetry

Serafim, Diana Maria; Stradiotto, Nelson Ramos
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 1007-1013
ENG
Relevância na Pesquisa
36.84%
A sensitive method based on square wave voltammetry is described for the quantitative determination of elemental sulfur, disulfide and mercaptan in gasoline using a mercury film electrode. These sulfur compounds can be quantified by direct dissolution of gasoline in a supporting electrolyte followed by subsequent voltammetric measurement. The supporting electrolyte is 1.4 mol L-1 sodium acetate and No acetic acid in methanol. Chemical and optimum operational conditions for the formation of the mercury film were analyzed in this study. The values obtained were a 4.3 mu m thickness for the mercury film, a 1000 rpm rotation frequency, -0.9 V applied potential and 600 s depositing time. Voltammetric measurements were obtained using square wave voltammetry with detection limits of the 3.0 x 10(-9), 1.6 x 10(-7) and 4.9 x 10(-7) mol L-1 for elemental sulfur, disulfide and mercaptan, respectively. (C) 2007 Elsevier Ltd. All rights reserved.

Analytical procedure for total mercury determination in fishes and shrimps by chronopotentiometric stripping analysis at gold film electrodes after microwave digestion

Augelli, M. A.; Munoz, R. A. A.; Richter, E. M.; Cantagallo, M. I.; Angnes, L.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 579-584
ENG
Relevância na Pesquisa
36.84%
A method for the total mercury determination in fish and shrimps employing chronopotentiometric stripping analysis on gold film electrodes is described. Fish and shrimp tissues were digested using a microwave oven equipped with closed vessels. We developed a microwave heating program which decomposed all the samples employing diluted nitric acid and hydrogen peroxide. The proposed method was validated by analyzing a certified reference material and then applied for different fish species from fresh water and seawater acquired in local markets of São Paulo city, Brazil. The Brazilian legislation establishes 0.5 and 1 mg per kilogram of fish as upper limit of mercury for omnivorous and predator species, respectively. Except for blue shark tissues, the mercury content was situated below 0.5 mu g g(-1) for all the analyzed samples. The detection limit of the proposed method was calculated as 5 ng g(-1) of sample utilizing 5 minutes of electrodeposition (+300 mV vs. Ag/AgCl) on the gold electrode. (c) 2006 Elsevier Ltd. All rights reserved.

Re-evaluation of antibiotic and mercury resistance in Escherichia coli populations isolated in 1978 from Amazonian rubber tree tappers and Indians

Nascimento, Andréa M. A.; Campos, Claudia E. P.; Campos, Evanil P.; Azevedo, João L.; Chartone-Souza, Edmar
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 407-411
ENG
Relevância na Pesquisa
36.84%
A study was carried out to assess the stability of antimicrobial susceptibility of wild isolates upon long-term storage using fifty-three Escherichia coli strains isolated in 1978 from feces of healthy children from the Amazon region in Brazil, exposed to low levels of antimicrobial agents, and examined for resistance to mercury and four antibiotics. All of the strains were kept in Lignieres medium at room temperature and were transferred to fresh media four times during this period. Thirty-five out of the 53 strains analyzed in 1978 were viable. Upon recovery, antibiotic and mercury resistance was estimated. All of the 35 strains maintained their original phenotype in a stable fashion, except for one multiresistant strain which became susceptible to kanamycin. Fifty-four percent of the strains exhibited a resistance phenotype, among which 47% had conjugative plasmids.

Determination of mercury in agroindustrial samples by flow-injection cold vapor atomic absorption spectrometry using ion exchange and reductive elution

Gomes Neto, José A.; Zara, Luís F.; Rocha, Julio C.; Santos, Ademir; Dakuzaku, Carolina S.; Nóbrega, Joaquim A.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 587-594
ENG
Relevância na Pesquisa
36.84%
A flow-injection system with a Chelite-S® cationic resin packed minicolumn is proposed for the determination of trace levels of mercury in agroindustrial samples by cold vapor atomic absorption spectrometry. Improved sensitivity and selectivity are attained since mercuric ions are on-line concentrated whereas other potential interferents are discarded. With on-line reductive elution procedure, concentrated hydrochloric acid could be replaced by 10% w/v SnCl2, in 6 M HCl as eluent. The reversed-intermittent stream either carries the atomic mercury, to the flow cell in the forward direction or removes the residue from reactor/gas liquid separator to a discarding flask in the opposite direction. Concentration and volume of reagent, acidity, flow rates, commutation times and potential interfering species were investigated. For 120 s preconcentration time, the proposed system handles about 25 samples h-1 (50.0 500 ng l-1), consuming about 10 ml sample and 5 mg SnCl2 per determination. The detection limit is 0.8 ng l-1 and the relative standard deviation (RSD) (n = 12) of a 76.7 ng l-1 sample is about 5%. Results are in agreement with certified value of standard materials at 95% confidence level and good recoveries (97-128%) of spiked samples were found. (C) 2000 Elsevier Science B.V.

Preparation of a clay-modified carbon paste electrode based on 2-thiazoline-2-thiol-hexadecylammonium sorption for the sensitive determination of mercury

Dias Filho, Newton L.; Do Carmo, Devaney R.; Gessner, Fergus; Rosa, André H.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 1309-1316
ENG
Relevância na Pesquisa
36.84%
A montmorillonite from Wyoming-USA was used to prepare an organo-clay complex, named 2-thiazoline-2-thiol-hexadecyltrimethylammonium-clay (TZT-HDTA-clay), for the purpose of the selective adsorption of the heavy metals ions and possible use as a chemically modified carbon paste electrode (CMCPE). Adsorption isotherms of Hg 2+, Pb 2+, Cd 2+, Cu 2+, and Zn 2+ from aqueous solutions as a function of the pH were studied at 298 K. Conditions for quantitative retention and elution were established for each metal by batch and column methods. The organo-clay complex was very selective to Hg(II) in aqueous solution in which other metals and ions were also present. The accumulation voltammetry of Hg(II) was studied at a carbon paste electrode chemically modified with this material. The mercury response was evaluated with respect to the pH, electrode composition, preconcentration time, mercury concentration, cleaning solution, possible interferences and other variables. A carbon paste electrode modified by TZT-HDTA-clay showed two peaks: one cathodic peak at about 0.0 V and an anodic peak at 0.25 V, scanning the potential from -0.2 to 0.8 V (0.05 M KNO 3 vs. Ag/AgCl). The anodic peak at 0.25 V presents excellent selectivity for Hg(II) ions in the presence of foreign ions. The detection limit was estimated as 0.1 μg L -1. The precision of determination was satisfactory for the respective concentration level. 2005 © The Japan Society for Analytical Chemistry.

Disposal of elemental mercury via sulphur reaction by milling

López Gómez, Félix Antonio; Alguacil, Francisco José; Roman, C. P.; Tayibi, Hanan; López-Delgado, Aurora
Fonte: Conselho Superior de Investigações Científicas Publicador: Conselho Superior de Investigações Científicas
Tipo: Comunicación de congreso Formato: 611444 bytes; application/pdf
ENG
Relevância na Pesquisa
36.91%
The formation of HgS (metacinnabar) from elemental mercury and pure sulphur, in non stoichiometric conditions, by means of the mechanical energy provided by a ball mill was studied. The effect of milling time in the completeness of the reaction was also studied. The formation of metacinnabar (HgS black) was observed even at short milling time (15 min), but several drops of un-reacted liquid mercury could be seen at that time. Liquid mercury was not detected for milling time of 90 min. The mechanism of the reaction was observed by SEM. This indicated that the reaction of formation of metacinnabar by mechanical dispersion starts with the diminishing of the size of the mercury drops; as reaction time increases the sulphur molecules form an interface with the microspheres of Hg and yield the formation of metacinnabar. The mercuric sulphide obtained passed the TCLP tests, yielded 2.0 x10-3 mg/l of Hg in the leachate.; LIFE06 ENV/ES/PRE/03

The Clear Creek mine, San Benito County, California: A unique mercury locality

Dunning, Gail E.; Hadley, Ted A.; Magnasco, John; Christy, Andrew; Cooper, Joseph F
Fonte: Mineralogical Record Inc Publicador: Mineralogical Record Inc
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.91%
From the first discovery in 1959 until the present, the abandoned Clear Creek mine has yielded an exceptional suite of rare and unusual mercury-bearing minerals unequaled in the world. Among those recently described as new are aurivilliusite, clearcreekite, deanesmithite, edgarbaileyite, edoylerite, hanawaltite, peterbaylissite, wattersite, szymańskiite, tedhadleyite and vasilyevite. In addition, seven new mercury-bearing species are currently under study. Other mercury-bearing minerals identified from the mineralized veins include montroydite, schuetteite, calomel, gianellaite, mosesite, terlinguaite, eglestonite, metacinnabar, cinnabar, native mercury and the second world occurrence of donharrisite.

Teores de chumbo e mercúrio em cabelo de crianças residentes em Cubatão, na região sudeste do Brasil; Lead and mercury in the hair of children living in Cubatão in the Southeast Region of Brazil

Santos Filho, Eladio; Silva, Rebeca de Souza e; Sakuma, Alice M.; Scorsafava, Maria Anita
Fonte: Universidade de São Paulo. Faculdade de Saúde Pública Publicador: Universidade de São Paulo. Faculdade de Saúde Pública
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; ; ; ; ; Formato: application/pdf
Publicado em 01/04/1993 POR
Relevância na Pesquisa
36.91%
A study was carried out in 6 districts of Cubatão county, S. Paulo State, Brazil on a sample of 251 children aged between 1 and 10. The concentration of heavy metals (lead and mercury) in hair was tested. The lead concentration in the hair of 229 children was tested, and in 189 (82.5%) levels varying from 2.5 to 71.4 µg/g were detected. The average concentration of the lead found in hair was of 7.25 ± 8.51 µg/g. The concentration of mercury in the hair of 217 children was checked and all of them were found to have levels varying from 0.2 to 3.0 µg/g. The average concentration of mercury was of 0.82 ± 0.48 µg/g. No statistical difference (p >; 0.05) was observed between the averages found for lead and mercury in the hair of those who consumed and those who did not consume aquatic organisms.; Realizou-se estudo de tipo seccional onde concentrações de chumbo e mercúrio foram determinadas pela técnica de espectrofotometria de absorção atômica em cabelo de 251 crianças de um a 10 anos de idade, residentes em seis bairros situados às margens dos principais rios do Município de Cubatão, SP, (Brasil). Verificou-se concentrações de chumbo em cabelo de 229 crianças, sendo que em 189 delas (82,5%) detectou-se teores que variaram de 2...

Mercúrio: da Antiguidade aos Dias Atuais; Mercury: from Antiquity to Nowadays

Luciano T. Costa; Universidade Federal Fluminense; Giane B. Damas; Universidade Federal de Alfenas; Bruno Bertoldo; Universidade Federal de Alfenas
Fonte: Revista Virtual de Química Publicador: Revista Virtual de Química
Tipo: ; Formato: binary/octet-stream
Publicado em 27/06/2014 PT
Relevância na Pesquisa
36.91%
O elemento mercúrio possui uma importância histórica para a química. Desde os tempos antigos, quando relatos mostram que este elemento podia ser obtido a partir do cinábrio, HgS, o mercúrio esteve sempre presente em importantes descobertas e transformações químicas, como nas experiências com HgO realizadas independentemente por Karl Wilhelm Scheele (1742-1786) e Joseph Priestley (1733-1804), culminando com a descoberta do oxigênio. Utilizado do século XV até o início do século XX para tratamento de sífilis, o mercúrio encontra hoje diversas aplicações, que incluem o uso em amálgamas odontológicas, lâmpadas fluorescentes, em processos industriais e atividades de extração de ouro. Contudo, por ser um elemento altamente tóxico, o descarte incorreto e a contaminação de efluentes e solos por mercúrio causam problemas às populações que fazem uso dos recursos disponíveis na região contaminada.  DOI: 10.5935/1984-6835.20140063; Mercury (Hg) has a historical importance to chemistry. Since old age, when it was obtained from the cinnabar, HgS, mercury was presence in important chemical discoveries and transformations, as in the experiments with HgO carried out independently by Karl Wilhelm Scheele (1742-1786) e Joseph Priestley (1733-1804)...

Adsorption of Mercury(II) onto activated carbons derived from Theobroma cacao pod husk

Kede,Charles M.; Ndibewu,Peter P.; Kalumba,Makonga M.; Panichev,Nikolay A.; Ngomo,Horace M.; Ketcha,Joseph M.
Fonte: South African Journal of Chemistry Publicador: South African Journal of Chemistry
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
Relevância na Pesquisa
36.91%
Activated carbon prepared from Theobroma cacao pod husk was used as a low-costbiosorbent for the removal of mercury(II) from aqueous solutions. The influence of pH and contact time on the adsorption was investigated by conducting a series of batch adsorption experiments. The equilibrium data were fitted to the Langmuir and Freundlich isotherm models. The Langmuir isotherm was found to best describe the experimental data. The amount adsorbed increased with increasing temperature. The maximum adsorption capacity of mercury was found to be 10(5) ng g-1 for an initial mercury concentration of 100 ppb. The kinetics of adsorption were modelled by means of the Lagergren-first-order and pseudo-second-order models. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. It was also found that pore diffusion played an important role in the adsorption, and intra-particle diffusion was the rate-limiting step during the first 30 min. A FTIR study revealed that the carbonyl and sulfur functional groups present on the surface of the adsorbing material were involved in chemical interaction with mercury(II).

Mercury in hair as a biomarker of exposure in a coastal Venezuelan population

Rojas,Maritza; Nakamura,Kunihiko; Seijas,David; Squillante,G; Pieters,Maria Alejandra; Infante,Saba
Fonte: Universidad del Zulia Publicador: Universidad del Zulia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2007 EN
Relevância na Pesquisa
36.91%
To assess mercury exposure and potential risk, total mercury (THg-H) and methylmercury (MeHg-H) in hair were studied in 160 adults. The study group consisted of 60 individuals living in the north central coast of Venezuela. A section of the area was known to be contaminated with mercury from a chlor-alkali plant installed near one of the tributary rivers of the Caribbean Sea. The study group was selected from 4 inclusion criteria points. The control group was composed of 100 individuals selected from Carabobo state with no known exposure to Hg. A questionnaire was designed to collect demographic, health information, work activities and fish consumption habits. Hair samples were analyzed for THg. Samples with THg-H > 5 µg/g were also analyzed for MeHg. The mean THg-H was 1.88 ± 1.50 and 0.99 ± 0.87 µg/g for the study and control groups, respectively. The study group was statistically higher than control individuals, however, no statistical differences of THg-H were found between each of the 4 categories of both groups. Mean MeHg-H value was 3.67 ± 1.25 µg/g. Associations were made between Hg-H and several variables. No significant relationship was noted between Hg-H levels and clinical symptoms. R analyses and t-tests were used to determine associations between questionnaire variables and THg-H. The main predictors of THg-H levels in the study group were fish consumption and frequency. As both groups presented relatively low values for THg-H and MeHg-H...

Performance on neurological development tests by riverine children with moderate mercury exposure in Amazonia, Brazil

Tavares,Lydia Maria Bocayuva; Câmara,Volney Magalhães; Malm,Olaf; Santos,Elisabeth C. de Oliveira
Fonte: Escola Nacional de Saúde Pública Sergio Arouca, Fundação Oswaldo Cruz Publicador: Escola Nacional de Saúde Pública Sergio Arouca, Fundação Oswaldo Cruz
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2005 EN
Relevância na Pesquisa
36.91%
The nervous system can be damaged when the population is exposed to methyl mercury (MeHg) by ingesting fish, and children deserve special attention due to their increased susceptibility as compared to adults. A comparative cross-sectional study was performed in order to investigate the use of a battery of neurological development tests in two groups of 209 riverine children from 3 to 7 years old: a group exposed to moderate levels of MeHg (n = 75) and a control group (n = 134). The study included a questionnaire, the collection of scalp hair samples for determination of total mercury concentration, and performance on a test for evaluating neurological function in children. Riverine children presented higher exposure to MeHg (mean hair Hg = 5.37 ± 3.35µg.g-1) in comparison to the control group (mean Hg = 2.08 ± 1.37µg.g-1). Both groups showed a high proportion of children with what was considered "non-normal" performance, suggesting that the results could not be related to mercury exposure and that this type of test presented limitations for use with river-dwelling Amazon communities.