P. Fernandez-Lomelin

National Autonomous University of Mexico, Ciudad de México, The Federal District, Mexico

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Publications (9)11.17 Total impact

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    ABSTRACT: This paper reports on the effect of aqueous and nano-particulated Pb on oxidative stress (lipid peroxidation), cytoxicity, and cell mortality. As determined by the Thiobarbituric Acid Reactive Substances (TBARS) method, only 6h after incubation aqueous suspensions bearing nano-sized PbO(2), soluble Pb(II), and brain-homogenate only suspensions, were determined to contain as much as ca. 7, 5, and 1 nmol TBARS mg protein(-1), respectively. Exposure of human cells (central nervous system, prostate, leukemia, colon, breast, lung cells) to nano-PbO(2) led to cell-growth inhibition values (%) ca. ≤18.7%. Finally, as estimated by the Artemia salina test, cell mortality values were found to show high-survival larvae rates. Microscopic observations revealed that Pb particles were swallowed, but caused no mortality, however.
    Chemosphere 06/2011; 84(10):1329-35. · 3.14 Impact Factor
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    ABSTRACT: This paper reports arsenic methylation in betaine-nontronite clay-water suspensions under environmental conditions. Two nontronites (<0.05 mm), NAu-1 (green color, Al-enriched) and NAu-2 (brown color, Al-poor, contains tetrahedral Fe) from Uley Mine - South Australia were selected for this study. Betaine (pK(a)=1.83) was selected as methyl donor. The reaction between 5 g L(-1) clay, 20 ppm As(III), and 0.4M betaine at 7< or =pH(0)< or =9 under anoxic conditions was studied. The presence of nontronite clays were found to favor As(III) conversion to monomethylarsenic (MMA). Arsenic conversion was found to be as high as 50.2 ng MMA/ng As(III)(0). Conversion of As was found to be more quantitative in the presence of NAu-2 ((Na(0.72)) [Si(7.55) Al(0.16)Fe(0.29)][Al(0.34) Fe(3.54) Mg(0.05)] O(20)(OH)(4)) than NAu-1 ((Na(1.05)) [Si(6.98) Al(0.95)Fe(0.07)][Al(0.36) Fe(3.61) Mg(0.04)] O(20)(OH)(4)). The inherent negative charge at the nontronite tetrahedral layer stabilizes positively charged organic intermediate-reaction species, thereby leading to decreases in the overall methylation activation energy. The outcome of this work shows that nontronite clays catalyze As methylation to MMA via non-enzymatic pathway(s) under environmental conditions.
    Journal of hazardous materials 01/2010; 178(1-3):450-4. · 4.14 Impact Factor
  • Geochmica et Cosmochimica Acta 07/2008; 72(12).
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    ABSTRACT: Microorganisms and higher plants produce biogenic ligands, such as siderophores, to mobilize Fe that otherwise would be unavailable. In this paper, we study the stability of arsenopyrite (FeAsS), one of the most important natural sources of arsenic on Earth, in the presence of desferrioxamine (DFO-B), a common siderophore ligand, at pH 5. Arsenopyrite specimens from mines in Panasqueira, Portugal (100–149 μm) that contained incrustations of Pb, corresponding to elemental Pb as determined by scanning electron microscopy–electron diffraction spectroscopy (SEM–EDX), were used for this study. Batch dissolution experiments of arsenopyrite (1 g L−1) in the presence of 200 μM DFO-B at initial pH (pH0) 5 were conducted for 110 h. In the presence of DFO-B, release of Fe, As, and Pb showed positive trends with time; less dependency was observed for the release of Fe, As, and Pb in the presence of only water under similar experimental conditions. Detected concentrations of soluble Fe, As, and Pb in suspensions containing only water were found to be ca. 0.09 ± 0.004, 0.15 ± 0.003, and 0.01 ± 0.01 ppm, respectively. In contrast, concentrations of soluble Fe, As, and Pb in suspensions containing DFO-B were found to be 0.4 ± 0.006, 0.27 ± 0.009, and 0.14 ± 0.005 ppm, respectively. Notably, the effectiveness of DFO-B for releasing Pb was ca. 10 times higher than that for releasing Fe. These results cannot be accounted for by thermodynamic considerations, namely, by size-to-charge ratio considerations of metal complexation by DFO-B. As determined by SEM–EDX, elemental sample enrichment analysis supports the idea that the Fe–S subunit bond energy is limiting for Fe release. Likely, the mechanism(s) of dissolution for Pb incrustations is independent and occurs concurrently to that for Fe and As. Our results show that dissolution of arsenopyrite leads to precipitation of elemental sulfur, and is consistent with a non-enzymatic mineral dissolution pathway. Finally, speciation analyses for As indicate variability in the As(III)/As(V) ratio with time, regardless of the presence of DFO-B or water. At reaction times <30 h, As(V) concentrations were found to be 50–70%, regardless of the presence of DFO-B. These results are interpreted to indicate that transformations of As are not imposed by ligand-mediated mechanisms. Experiments were also conducted to study the dissolution behavior of galena (PbS) in the presence of 200 μM at pH0 5. Results show that, unlike arsenopyrite, the dissolution behavior of galena shows coupled increases in pH with decreases in metal solubility at t > 80 h. Oxidative dissolution mechanisms conveying sulfur oxidation bring about the production of {H+}. However, dissolution data trends for arsenopyrite and galena indicate {H+} consumption. It is plausible that the formation of Pb species is dependent on {H+} and {OH−}, namely, stable surface hydroxyl complexes of the form (pH50 5.8) and for pH values 5.8 or above.
    Geochimica et Cosmochimica Acta 01/2008; · 3.88 Impact Factor
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    ABSTRACT: Mexico is a leader in the production of lead. Exposure of soils contaminated with lead ore waste, ingestion of contaminated waters, or inhalation of suspended particles, among others are examples of common routes of exposure. Solubility often becomes limiting for Pb bioavailability, therein the need to further characterize natural processes that contribute to its mobility in the environment. In oxic environments, such as highly weathered soils or surficial seawater, microorganisms and higher plants produce biogenic ligands such as siderophores to mobilize Fe that otherwise would be unavailable. Siderophores ligands facilitate the dissolution of natural particles that represent a primary reservoir of iron. On the other hand, lead sorbs strongly to minerals, particularly to those bearing high contents of iron. Siderophore ligands have been identified to influence the adsorption behavior of Pb(II) on iron mineral surfaces. Yet, little is known on how siderophore ligands may affect the stability of Pb(0). In this paper we study the stability of Pb(0) in the presence of desferrioxamine (DFO-B), a common siderophore ligand. Batch dissolution experiments of Pb(0) (1 g L-1) in the presence of DFO-B ([DFO-B]0 ? 200M) at pH 5 were conducted for 7 days. The adsorption behavior of DFO-B was also characterized. Corresponding experiments in the absence of DFO-B for the purpose of comparison were also conducted. Analyses for soluble Pb were conducted by AA and ICP-AES. Solid characterization was conducted by XRD and SEM-EDX. Analyses for soluble Pb reveal concentrations of up to ca. 40 ppm. White small-sized particles were identified after reaction, regardless of the presence of DFO-B. The suspension chemical composition influenced colloidal stability. In the presence of DFO-B, forming solids showed small aspect ratio ( < 2m), while remained suspended in supernatant solutions. In the absence of DFO-B, solids formed showed varied in size. The were found to remain associated with the Pb(0). Flocculation was observed to occur notingly if in the absence of DFO- B. Intermolecular forces at the mineral-water interface are sought to account for these observatons. As revealed by XRD and SEM-EDX, solid composition is attributed to various lead oxide and hydroxides. The presence of DFO-B influence the solid composition. Thermodynamic considerations lead the authors to suggest that sideophore ligands could act as templates for preferential nucleation of secondary phases, while effectively abating the reaction activation energy of formation.
    AGU Spring Meeting Abstracts. 05/2007;
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    ABSTRACT: Cerium is the most abundant lanthanide and generally the only one to undergo redox reactions at the Earth's surface. Although rarely studied in natural environments, the redox chemistry of cerium may regulate metal toxicity. Unlike Ce(III) or other lanthanide ions, Ce(IV) has shown a remarkably efficacy to hydrolyze DNA. While Ce(IV) has been recognized as an important candidate to occupy peptidases catalytic centers, Ce(III) is virtually inactive for peptide hydrolysis. The selectivity of Ce as Ce(IV) relates to the specific coordination of water molecules and their orientation. Ce(IV) may bind selectivity to biomolecules to instigate conformation changes or cleavage of complexes, which affect metabolic pathways pivotal to growth and survival. For instance, Ce(IV) promotes the selective cleavage of RNA-type substrates, cyclic monophosphates, peptides, or monocleotides such as AMP, leading to mixtures of nucleosides and nucleobases. Association constants for Ce(IV)-DNA complexes are reported to be higher in magnitude for single stranded than double stranded DNA, while cleavage rates for either complexes are comparable. Complexation of Ce(IV) with mitoxantrone results in the intercalation of such complex into DNA, enabling mitoxantrone to bind effectively with DNA, along with concomitant conformational changes in the DNA double helix and inhibition of DNA synthesis. To the authors' knowledge, however, little information is available on the reactivity as it relates to toxicity of Ce-bearing nanoparticles widely used in nanotechnological applications. Here, we study molecular interactions between small-sized CeO2 and biomolecules(e.g., DNA, RNA, proteins) using carbon and cerium spectroscopy. Suspension stability as determined by aggregation kinetics was studied by Dynamic Light Scattering (DSL) and UV. In addition, acidophiles and fungi cultures were analyzed by nephelometry to estimate population density and growth rate values. Results show a progressive increase in the transformation of biomolecules (as % carbon) with decreasing CeO2 particle diameter (13 < d < 84 Å), which substantiates an intimate relation between CeO2 unit cell expansion and reactivity towards organics susceptible to undergo redox transformations. As shown by C and Ce spectroscopy, organic polymers that form because of oxidation are distributed next to the mineral surface and its occurrence is coupled to Ce reduction-oxidation. As evidenced by DSL and UV experiments conducted for the pH 2 to 8 range, the aggregation behavior of nanoCeO2 is susceptible to pH variations imposed because the presence of biological moieties itself over solid concentration.
    AGU Spring Meeting Abstracts. 05/2007;
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    ABSTRACT: Arsenopyrite is one of the most important natural sources of Arsenic on Earth. Arsenopyrite is relatively insoluble in pure water. That is not the case if it is exposed to environmental conditions. Notably, arsenopyrite surfaces exposed to biological activity undergo changes in lattice energy, surface morphology, particle size, and other properties, typical of mineral dissolution. Iron biogeochemical cycling is pivotal to electron transferring in nature. Therein, the need to further scrutinize on the mechanism of arsenopyrite dissolution induced by biological activity. In oxic environments, such as highly weathered soils or surficial seawater, microorganisms and higher plants produce biogenic ligands such as siderophores to mobilize Fe that otherwise would be unavailable. Siderophores ligands facilitate the dissolution of natural particles that represent a primary reservoir of iron. In this paper we study the stability of arsenopyrite in the presence of desferrioxamine (DFO-B), a common siderophore ligand, at pH 5. Arsenopyrite specimens from mines from Panasqueira, Portugal, were used for this study. Batch dissolution experiments of arsenopyrite (1 g L-1) in the presence of DFO-B ([DFO-B]0 - 200 ?M) were conducted for 7 days. The initial pH was adjusted to 5. Samples were stirred at 150 rpm. Sieving was conducted to homogeneized the particle size 0.149-0.1mm before conducting the dissolution experiments. Corresponding experiments in the absence of DFO-B for the purpose of comparison were also conducted. Analyses for soluble metals were conducted by AA and ICP-AES. Surface characterization was conducted by XRD and SEM-EDX. Incrustations of Pb(0) were detected in the arsenopyrite samples used for this study. In the presence of DFO-B, releases of Fe, As, and Pb showed positive trends with time. A shallower dependency was observed for release of Fe, As, and Pb in the presence of water only under similar experimental conditions. Detected concentrations of Fe, As, and Pb, after 100 h of reaction time in the presence of DFO-B were 0.3, 0.26, and 0.13 ?M, respectively. Concentrations of Fe, As, and Pb, in the presence of water only were ca. 0.06, 0.13, and 0.01 ?M, correspondingly. Hence, the effectiveness of DFO-B for releasing Pb was almost three times higher than that for releasing Fe (further details on Pb dissolution as affected by DFO-B are provided in Cornejo et al.). These results cannot be accounted for by size¡Xto-charge considerations prevailing in metal complexation by DFO-B only. Elemental sample enrichment as evidenced by SEM-EDX supporte the idea the Fe-S subunit bond energy is limiting for Fe release, while likely, the mechanism(s) of dissolution for Pb is independent and occurs concurrently to than for Fe and As.
    AGU Spring Meeting Abstracts. 05/2007;
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    ABSTRACT: Cuitzeo is located in Central Mexico. The Cuitzeo lake is very low, it has seven islands and a highway four kilometers long that crosses the lake. Detected concentrations of arsenic average 30-40 mg kg-1. In the salted waters a lot of "charal" (a small fish), main ingredient in many regional dishes, and ducks can be found. This study reports the effect of organic matter on As partitioning. Complexation of As with organic biomolecules that may contribute to detoxification pathways in Cuitzeo are discussed.
    AGU Spring Meeting Abstracts. 05/2007;
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    ABSTRACT: A method for ameliorating the toxicity of As has been developed. Succesive methylation of arsenic has been reported to represent an important detoxification pathway in aquatic systems. Clays are natural porous materials bearing high surface areas and interlayer spacing that allows entrapment of small-sized particles. Thus, clays are natural nanomaterials that can serve as efficient catalysts in natural or engineered systems. In this paper we study the kinetics of transformation of inorganic arsenic to arseno-organic complexes as affected by the following clay samples: Montmorillonite [SWy-2] from Crook Country, Wyoming, USA, and Hectorite [SHCa-1] from San Bernardino. Country, California, USA, and Nontronite [NG-1] from Australia. The effect of environmental factors, arsenic inicial concentration and speciation is discussed.
    AGU Spring Meeting Abstracts. 04/2007; -1:01.