Interaction of mercury(II) with humic substances from the Rio Negro (Amazonas State, Brazil) by means of an ion exchange procedure

The aquatic humic substances (HS) investigated in this study with respect to their binding capability towards mercury(II) were isolated from the river Rio Negro, Amazonas State - Brazil, by means of the adsorbent XAD 8. Labile/inert fractions of inorganic Hg(II) complexes formed with these HS were characterized using an ion-exchange batch and column technique, respectively, based on Chelite S. This collector exhibits high Hg(II) distribution coefficients, Kd, up to the order of 104 decreasing, however, in the case of small Hg(II)/HS ratios (< 0.1 μg Hg(II) / mg HS). The influence of different complexation parameters (ratio of Hg(II)/HS, pH, contact time, complexing time) relevant for Hg(II) binding in aquatic environments was assessed. The Hg(II) lability in dissolved HS is mainly influenced by the mass ratio of Hg(II)/HS and the ageing of Hg(II)-HS species formed. This is particularly obvious in the case of low Hg(II) loading of HS where slow transformation processes of freshly formed Hg(II)-HS species significantly decrease their lability, leading to incomplete recoveries (< 20%) of the total Hg(II) bound to HS.

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

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.

Oxygen related defects excitation and photoconductivity dependence of SnO2 sol-gel films with several light sources

Since oxygen vacancies act as donors in SnO2, the electrical properties are related to deviation from stoichiometric composition. Depending on stoichiometry SnO2 can be highly insulating or may exhibit fairly high n-type conductivity. Since bandgap transitions are in the ultraviolet range, its photoconductivity is strongly dependent on the excitation source. We have measured variation of photoconductivity excitation with wavelength for tin dioxide grown by dip-coating sol-gel technique using several light sources: tungsten lamp, xenon, mercury and deuterium, and present selected results. The main band is obtained in the range 3-4eV according to light source spectrum in the ultraviolet range. The presence of oxygen in the cryostat also affects the spectrum since electron-hole pairs react with adsorbed oxygen specimens. © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Gordon and Breach Science Publishers imprint.

Morphology changes induced by laser irradiation on disperse red 13 films prepared by physical vapor deposition

Surface morphology changes induced by argon laser irradiation (514 nm) on disperse red 13 (DR13) films prepared by physical vapor deposition (PVD) were investigated. Atomic force microscopy was used to characterize the irradiated sample for different periods of irradiation. Needle-shape structures are observed which are attributed to the symmetry of DR13 molecules. The film becomes increasingly closely packed with the irradiation, with lower root mean square roughness for long exposure times. This is due to photoisomerization of DR13 molecules and probably heating of the sample, which can provide the required mobility for the molecular rearrangement. The rearrangement is such that voids in the film are filled in upon irradiating the sample, thus decreasing the film roughness and increasing the packing.

GPS performance in the quantification of integrated water vapor in Amazonian regions

The Amazonian regions are characterized by large space-time variability in the humidity fields due to the intense convective process in those areas associated with the great humidity potential generated by high temperatures. An experiment denominated RACCI/DRY-TO-WET (RAdiation, Cloud, and Climate Interactions in the Amazonia during the DRY-TO-WET Transition Season) was carried out in the Brazilian Amazonian Region in 2002. The IWV values from GPS and other techniques, such as radiosondes, radiometer and humidity sounding satellites were used in this experiment to supply subsidies to evaluate the aerosols influence in the associated processes modifications to seasonality of atmospheric water vapor. Those regions are one of the most humid of the planet, where IWV (Integrated Water Vapor) average values are in the order of 50 kg/m2. As according the literature the IWV quantification using GPS has not been explored in those circumstances, the objective this paper is to present the preliminary results obtained in the evaluation of the GPS performance in Amazonian Regions when comparing with other techniques. The tendency measurement values indicated that the IWV values from GPS tend to be larger than those from radiosondes and smaller than those from radiometer. On the other hand, IWV values from GPS are very close of the average values supplied by radiosondes and radiometer. Due to the great amount of atmospheric water vapor existent in this region, the results obtained in the experiment in percentile terms are quite better than those found in the literature, which are around of 10%.

Effects of copper vapor laser radiation on the root canal wall of human teeth: A scanning electron microscope study

Objective: The aim of this study is to analyze the effects of copper vapor laser radiation on the radicular wall of human teeth. Materials and Methods: Immediately after the crowns of 10 human uniradicular teeth were cut along the cement-enamel junction, a chemical-surgical preparation of the radicular canals was completed. Then the roots were longitudinally sectioned to allow for irradiation of the surfaces of the dentin walls of the root canals. The hemi-roots were separated into two groups: one (control) with five hemi-roots that were not irradiated, and another (experimental) with 15 hemi-roots divided into three subgroups that were submitted to the following exposure times: 0.02,0.05, and 0.1 s. A copper vapor laser (510.6 nm) with a total average power of 6.5 W in green emission, frequency of 16.000 Hz, and pulse duration of 30 ns was used. Results: The results obtained by scanning electron microscope analysis showed the appearance of a cavity in the region of laser beam impact, with melting, recrystallization, and cracking on the edges of the dentin of the cavity due to heat diffusion. Conclusions: We determined that the copper vapor laser produces significant morphologic changes in the radicular wall of human teeth when using the parameters in this study. However, further research should be done to establish parameters that are compatible with dental structure in order to eliminate thermal damages. © Mary Ann Liebert, Inc.

Preconcentration and determination of mercury(II) at a chemically modified electrode containing 3-(2-thioimidazolyl)propyl silica gel

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO3; ν = 2.0 mV s-1 νs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L-1 was obtained. The detection limit was estimated to be 5 μg L-1. The precision for six determinations of 0.05 and 0.26 mg L-1 Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal. 2005 © The Japan Society for Analytical Chemistry.

Evaluating quality of life in mercury intoxicated people in urban-industrial environments through short-form 36 application

Context and objective: Records of contact with mercury (Hg) exist for more than 3500 years and several problems related to the use of this element can be noticed. Considering inexistence of current reports about it, quality of life perception evaluation was studied in people chronically intoxicated by mercury in an industrial environment. Design and setting: This is a cross-sectional descriptive observational study. Information from 47 urban-industrial workers from lamps manufacturing in São Paulo, clinically diagnosed as intoxicated by mercury and currently followed by the Occupational Health Service of Faculdade de Medicine da Universidade de São Paulo, with average age of 41.7 years old, was considered. Methods: SF36 questionnaire application was performed, with inferences tested by χ-square proof, by Spearman linear correlation and Mann-Whitney non-parametric test, adopting p < 0.05 as significant level. Results: In the eight domains, observed medians are 40% for physical functioning; 0 for physical function; 30% for body pain; 30% for general health; 22.2% for vitality; 50% for social functioning; 0 for emotional role and 36% for mental health. Correlation between age and SF36 domains does not reveal statistical significance, except for physical functioning, indicating that lower scores presented by older people in this domain are not followed by changes on other ones. Conclusions: Values obtained in people chronically intoxicated by mercury are actually lower, in the motor and mental scope components. Some instruments domains are higher for men than for women. Older ages are inversely associated to good performance in physical function domain. © Copyright Moreira Jr. Editora. Todos os direitos reservados.

Seasonal behavior of mercury species in waters and sediments from the Negro River Basin, Amazon, Brazil

Total (HgT), reactive (HgR) and organic (Hg ORG) mercury species have been quantified in non-filtered waters collected from the Negro River Basin, Amazon (from January/2002 through January/2004), in both black and white water bodies. Black waters presented the highest HgT, HgORG and HgR concentration (29.1 ng L-1, 1.63 ng L-1 and 3.9 ng L-1, respectively), while, white waters presented the lowest HgT, Hg ORG and HgR concentration (8.8 ng L-1, 0.49 ng L-1 and 1.2 ng L-1, respectively). An inverse correlation between HgT and the water level over the basin was obtained, although the HgORG concentration has increased in the first rainy months and then decreased as the water level rose. Total mercury in surface sediments (0-10 cm) ranged from 70 to 271 mg kg-1 being the methylmercury 0.47-1.79 % of this stock. The results indicate that HgR and the labile dissolved organic matter were introduced into the aquatic environment during the flooding season, especially in the earlier stages, thus contributing to mercury methylation. ©2007 Sociedade Brasileira de Química.

Voltammetry of mercury (II) based on an organo-clay modified graphite electrode

Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Ps(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.

Stacking faults in SiCf/SiC composite obtained by chemical vapor reaction process

SiC fiber-reinforced SiC matrix composite (SiCf/SiC) is one of the leading candidates in ceramic materials for engineering applications due to its unique combination of properties such as high thermal conductivity, high resistance to corrosion and working conditions. Fiber-reinforced composites are materials which exhibit a significant improvement in properties like ductility in comparison to the monolithic SiC ceramic. The SiCf/SiC composite was obtained from a C/C composite precursor using convertion reaction under high temperature and controlled atmosphere. In this work, SiC phase presented the stacking faults in the structure, being not possible to calculate the unit cell size, symmetry and bond lengths but it seem equal card number 29-1129 of JCPDS.

Mercury, copper, and zinc concentrations in extracted human teeth

Amalgam has been used as a filling material for over 150 years. Mercury, copper, and zinc are present in restoration. The aim of this study was to compare mercury, copper, and zinc concentrations in extracted human teeth with amalgam restorations and teeth without restorations. Thirty-two teeth, 15 restored with dental amalgam and 17 without restorations, were chemically analyzed in an Optima 3300 DV (Perkin Elmer) plasma emission spectrometer. Mercury, copper, and zinc were found in human teeth regardless of the presence of amalgam restorations. The highest mercury concentrations were found in the coronary portions of the teeth with amalgam restorations. Copper concentrations were very high. Zinc concentrations in the teeth without restoration were lower than those seen in the coronary portion of the teeth with restorations. © 2009 Heldref Publications.

Determination of Mg (II) in biodiesel by adsorptive stripping voltammetry at a mercury film electrode in the presence of sodium thiopentone

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Direct simultaneous determination of Pb(II) and Cu(II) in biodiesel by anodic stripping voltammetry at a mercury-film electrode using microemulsions

A mercury film electrode was used to determine direct and simultaneously Pb(II) (at -410 mV) and Cu(II) (at -100 mV) in biodiesel by anodic stripping voltammetry. A linear response was obtained for Pb(II) and Cu(II) in the 2.00 × 10-8-1.00 × 10-7 mol L-1 concentration range and detection limits were 2.91 × 10-9 mol L-1 and 4.69 × 10-9 mol L-1 for Pb(II) and Cu(II), respectively, with recovery around of 100.0%. © 2012 Elsevier Ltd. All rights reserved.

Mercury concentrations in south atlantic swordfish, Xiphias gladius, Caught off the Coast of Brazil

This study evaluated the concentrations of mercury in fillets (anterior, middle, and end regions) from the swordfish, Xiphias gladius, and the relationships between mercury concentration and fish weight, as well as the region of collection. Of a total of 697 swordfish analyzed, 11 had mercury concentrations above 1 mg/kg, 421 were between 0.5 and 1.0 mg/kg, and 265 were below 0.5 mg/kg. The anterior and posterior regions had greater concentrations of mercury than the middle region, and fish caught off the northern coast of Brazil had a higher concentration than those caught off the southern coast. © 2013 Springer Science+Business Media New York.