Biomedical subjects

Manuel Valiente

Publications and source records attributed to Manuel Valiente.

8 recordsLinked to original sources

PubMed2006

Microprobe techniques for speciation analysis and geochemical characterization of mine environments: the mercury district of Almadén in Spain.

Metallurgic calcines with very high mercury and methylmercury content from the Almadén mining district were analyzed by synchrotron-based microprobe techniques. Information about mercury speciation was obtained by micro-EXAFS (microscopic extended X-ray absorption fine structure) spectroscopy, whereas elemental associations were evaluated by micro-XRF (microscopic X-ray fluorescence analysis) mapping. Complementary characterization methodologies, including X-ray diffraction (XRD), inductively coupled plasma-optical spectroscopy (ICP-OES), as well as a sequential extraction scheme (SES), were used to predict the potential availability of mercury. Analysis of total metal content revealed extremely high concentrations of mercury and iron (between 7 and 35 and 65-70 g kg(-1), respectively) and high zinc concentrations (2.2-2.5 g kg(-1)), whereas other metals such as copper, nickel, and lead were found at low concentration levels (30-300 mg kg(-1)). Micro-EXAFS results indicate that cinnabar (HgS(red)) is one of the main species within the studied mercury-rich particles (5-89% of total mercury content), together with more soluble mercury compounds such as Hg3(SO4)02 (schuetteite) and HgO (5-55% of total mercury content). Additionally, element-specific micro-XRF maps of selected mercury-rich particles in the studied samples revealed an evident correlation among Hg-Pb-Ni (and S), indicating a possible geochemical linkage of these elements. Correlations were also found among Fe-Mn and Hg, which have been attributed to sorption of mercury onto oxyhydroxides of Fe and Mn. This finding was supported by results from a sequential extraction scheme, where a significant

Environmental Monitoring↗

PubMed2005

Analysis of sorption and bioavailability of different species of mercury on model soil components using XAS techniques and sensor bacteria.

The present work studies the adsorption behaviour of mercury species on different soil components (montmorillonite, kaolinite and humic acid) spiked with CH3HgCl and CH3HgOH at different pH values, by using XAS techniques and bacterial mercury sensors in order to evaluate the availability of methyl mercury on soil components. The study details and discusses different aspects of the adsorption process, including sample preparation (with analysis of adsorbed methyl mercury by ICP-OES), the various adsorption conditions, and the characterization of spiked samples by XAS techniques performed at two synchrotron facilities (ESRF in Grenoble, France and HASYLAB in Hamburg, Germany), as well as bioavailability studies using mercury-specific sensor bacteria. Results show that XAS is a valuable qualitative technique that can be used to identify the bonding character of the Hg in mercury environment. The amount of methyl in mercury adsorbed to montmorillonite was pH-dependent while for all soil components studied, the bond character was not affected by pH. On the other hand, clays exhibited more ionic bonding character than humic acids did with methyl mercury. This interaction has a higher covalent character and so it is more stable for CH3HgOH than for CH3HgCl, due to the higher reactivity of the hydroxyl group arising from the possible formation of hydrogen bonds. The bioavailability of methyl mercury adsorbed to montmorillonite, kaolinite and humic acids was measured using recombinant luminescent sensor bacterium Escherichia coli MC1061 (pmerBR(BS)luc). In case of contact exposure (suspension assays), the results showed that the bioavailability was higher than it was for exposure to particle-free extracts prepared from these suspensions. The highest bioavailability of methyl mercury was found in suspensions of montmorillonite (about 50% of the total amount), while the bioavailabilities of kaolinite and humic acids were five times lower (about 10%). The behaviour of methyl mercury in the presence of montmorillonite could be explained by the more ionic bonding character of this system, in contrast to the more covalent bonding character observed for humic acids. Thus, XAS techniques seem to provide promising tools for investigating the mechanisms behind the observed bioavailabilities of metals in various environmental matrices, an important topic in environmental toxicology.

Adsorption↗

PubMed2005

Characterisation of Almadén mercury mine environment by XAS techniques.

This manuscript describes the analysis and evaluation of mercury species present in three different types of samples (ore, slag and soil) belonging to the abandoned mining area of Almadén (Spain), by means of X-ray Absorption Spectroscopy (XAS) techniques. The applied methodology includes the analysis of possible interfering compounds by ICP-OES and the characterisation of solid samples by identification of heterogeneities using SEM-EDS technique prior to measurements at the synchrotron facilities (ESRF in Grenoble, France and HASYLAB in Hamburg, Germany) and subsequent analysis of data. Results show that cinnabar is the main species both in ore and soil samples, its concentration ranging from 41 to 77% of the total mercury content. On the other hand, metacinnabar (a polymorph of cinnabar) is shown to be the main species in slag samples (42-88%). Other mercury forms have been found in minor proportions (<30%), such as slightly soluble mercury salts (HgCl(2) and HgSO(4)) and HgO. This is the first time that Almadén-type mercury ores have been characterised by a synchrotron-based spectroscopic technique for a direct determination of mercury species. The conclusions presented in this report show the important similarities between Almadén and hot-spring type mercury mineral deposits, despite its different geological origin.

Environmental Monitoring↗

PubMed2005

Cytotoxicity of a new toothpaste based on an ion exchange resin mixture.

PURPOSE: To evaluate the effects for cytotoxicity of two dentifrices: a toothpaste commercially available (Crest Extra-Whitening toothpaste) and a new experimental toothpaste based on a mixture of ion-exchange resins (named NMTD) that supplies calcium, fluoride, phosphate and zinc ions. METHODS: Cultures of mouse fibroblasts cells L929 were used in a MTT assay for in vitro cytotoxicity of the dentifrices. Cells were cultured in Eagle's minimal essential medium supplemented with 10% fetal bovine serum. Cultures were incubated at 37 degrees C in a humidified atmosphere of 5% CO2 and collected by tripsinization (0.05% trypsin/0.5mM EDTA). A 96-well microplate method was employed for the MTT colorimetric assay. Positive control consisted of 10 microl of phenol in 5 ml of 6% media, a dose that produces zero percent cell survival. Negative control was prepared by adding 0.5 ml of HBSS to 4.5 ml of 6% media. The plates were incubated for 24 and 48 hours at 37 degrees C in a 5% CO2 atmosphere. RESULTS: Means and standard deviations of absorbance values for each group and percentage inhibitory dosage (%ID) for each test material were calculated. None of the dentifrices resulted in a percentage of inhibition higher than 50% and did not observe marked increases in cytotoxicity with time of incubation. The positive control gave almost zero percent cell survival, whereas the negative control gave a hundred percent cell survival. Analysis of the results indicated that test dentifrice dose had no significant effect towards the cell viability (P<0.05).

Animals↗

PubMed2004

Remineralization potential of a new toothpaste formulation: an in vitro study.

The aim of the present study was to determine the ability of a dentifrice containing a mixture of ion-exchange resins (named NMTD), which supplies calcium, fluoride, phosphate, and zinc ions, to promote remineralization and/or inhibit demineralization of dental human enamel in a pH cycling model in vitro. A fluoride toothpaste was used as the control. The enamel specimens were tested for microhardness before and after 10 days and 16 days of the demineralizing and remineralizing treatments. The results of this study showed both dentifrices were effective in limiting in vitro enamel demineralization although the effects were not significantly different from each other. Inclusion of calcium and phosphate ion-exchange resins in the dentifrice containing a fluoride ion-exchange resin maintained a similar net outcome of the conventional dentifrice in the demineralization/remineralization process under the experimental conditions employed.

Analysis of Variance↗

PubMed2004

Cleaning power and abrasivity of a new toothpaste based on ion-exchange resins.

PURPOSE: To compare the stain removal efficacy and enamel abrasivity of a new experimental dentifrice based on an ion-exchange resin mixture that releases calcium, fluoride, phosphate and zinc ions (named NMTD1), to four commercially available dentifrices: Crest Extra-whitening toothpaste, Crest Tartar Protection toothpaste, Crest Cavity Protection toothpaste and Colgate Fluoride Cavity Protection toothpaste. Calcium pyrophosphate was used as a control for the efficacy of the staining removal experiment. METHODS: Cleaning power evaluation was made following the method developed by Stookey et al. The abrasion of the toothpastes was determined by means of a brushing machine, using 2000, 4000 and 8000 strokes and a 250g toothbrush load. Bovine specimens were prepared and abrasion was measured by a surface profilometer system. RESULTS: The new experimental dentifrice did not remove stains whereas Crest Extra-whitening and Crest Cavity Protection dentifrices produced statistically significant stain removal when compared with the calcium pyrophosphate control. Abrasion studies demonstrated that abrasion was linearly correlated to the number of strokes and the abrasion rates proved to be non significant for Colgate and the new experimental dentifrices, but significant for Crest Extra-whitening, Crest Tartar Protection and Crest Cavity Protection. CLINICAL SIGNIFICANCE: This study demonstrated that the use of a dentifrice based on an ion-exchange mixture was not effective at removing stains and abrasion was most insignificant when compared to other commercially available toothpastes.

Animals↗

PubMed2003

Determination of phytic acid in urine by inductively coupled plasma mass spectrometry.

An ICPMS method for the determination of phytic acid in human urine based on the total phosphorus measurement of purified extracts of phytic acid is described. Pretreatment of the sample is required to avoid interference in the ICPMS detection from other phosphorus compounds accompanying phytic acid in urine such as phosphate or pyrophosphate. This treatment consists of a simple filtration of the urine sample followed by complete separation of phytic acid from the mentioned phosphorus components using an anion-exchange solid-phase extraction. Separation/recovery conditions, optimized for standards of phytic acid prepared in water and artificial urine, were successfully applied to natural urine samples, resulting in adequate accuracy and precision. Linear range (0.02-0.6 mg of phytic acid L(-)(1)) and limit of detection (5 microg L(-)(1) phytic acid) are adequate for analysis of the usual amounts of phytic acid present in urine. Phosphate, pyrophosphate, and pH of urine samples at concentrations exceeding their normal physiological ranges do not affect the determination of phytic acid. Because of the simplicity, low sample requirement, and relatively high sample throughput (10 to 6 min per sample for runs between 50 and 100 samples, respectively), the present method presents the best alternative to current methods for phytic acid determination in urine. Results also show that the method is adequate for the differentiation of levels of phytic acid excretion from patients suffering from oxalocalcic urolithiasis and healthy controls, suggesting that low phytic acid concentrations in urine lead to elevated risk of oxalocalcic urolithiasis.

Case-Control Studies↗

PubMed2002

Arsenic adsorption by Fe(III)-loaded open-celled cellulose sponge. Thermodynamic and selectivity aspects.

Nowadays there is a great concern on the study of new adsorbent materials for either the removal or fixation of arsenic species because of their high toxicity and the health problems associated to such substances. The present paper reports a basic study of the adsorption of arsenic inorganic species from aqueous solutions using an open-celled cellulose sponge with anion-exchange and chelating properties (Forager Sponge). Consequences of preloading the adsorbentwith Fe(III) to enhance the adsorption selectivity are discussed and compared with the nonloaded adsorbent properties. The interactions of arsenic species with the Fe(III)-loaded adsorbent are accurately determined to clarify the feasibility of an effective remediation of contaminated waters. Arsenate is effectively adsorbed by the nonloaded and the Fe(III)-loaded sponge in the pH range 2-9 (maximum at pH 7), whereas arsenite is only slightly adsorbed by the Fe(III)-loaded sponge in the pH range 5-10 (maximum at pH 9), being that the nonloaded sponge is unable to adsorb As(III). The maximum sorption capacities are 1.83 mmol As(V)/g (pH approximately 4.5) and 0.24 mmol As(lII)/g (pH approximately 9.0) for the Fe(III)-loaded adsorbent. This difference is explained in terms of the different acidic behavior of both arsenic species. The interaction of the arsenic species with the Fe(III) loaded in the sponge is satisfactorily modeled. A 1:1 Fe:As complex is found to be formed for both species. H2AsO4- and H3AsO3 are determined to be adsorbed on Fe(III) with a thermodynamic affinity defined by log K = 2.5 +/- 0.3 and log K = 0.53 +/- 0.07, respectively. As(V) is, thus, found to be more strongly adsorbed than As(III) on the Fe(III) loaded in the sponge. A significant enhancement on As(V) adsorption selectivity by loading Fe(III) in the sponge is observed, and the effectiveness of the Fe(III)-loaded sponge for the As(V) adsorption is demonstrated, even in the presence of high concentrations of interfering anions (chloride, nitrate, sulfate, and phosphate).

Adsorption↗