René H. Lara

Bovine serum albumin and chitosan coated silver nanoparticles and its antimicrobial activity against oral and nonoral bacteria

Antimicrobial agents have been developed for drug-resistance infections, which have been rapidly increasing; however, the control of involved microorganisms is still a challenge. In this work, SNP with bovine serum albumin (BSA) and chitosan (CS) coatings were prepared with an aqueous reduction method, characterized using dispersion light scattering, transmission electron microscopy, and thermal analysis. Antibacterial activity was tested on seven oral and nonoral bacteria by microdilution test and scanning electron microscopy. Six different sizes and shapes of coated SNP were prepared and used. Characterization revealed narrow size and good distribution of particles, spherical and pseudospherical shapes, and the presence of coatings on the SNP surfaces. All samples showed antimicrobial activity, although smaller sizes and CS samples had the best inhibition effects. The highest microbial resistance was shown by Gram-positive bacteria. Although coated SNP action depends on particular bacterium, BSA and CS coated SNP could be used for drug-resistance infections.

An experimental study of iron sulfides weathering under simulated calcareous soil conditions

In calcareous sites, hard rock mining activities release pyrite (FeS2), pyrrhotite (Fe1−xS) and other sulfides to soils. The sulfides then undergo weathering processes, generating acid rock drainage and secondary compounds. Despite the potentially important environmental impacts, very few studies have considered the mechanisms of pyrite and pyrrhotite weathering and the transformation of secondary compounds under neutral-alkaline carbonated conditions. In this study, we used an experimental approach combining electrochemical, microscopic and spectroscopic techniques to examine the interfacial processes involved in pyrite and pyrrhotite weathering under simulated calcareous soil conditions. The results showed an initial oxidation step with the formation of variable amounts of surface sulfur compounds (e.g., polysulfides, Sn2−, and elementary sulfur, S0) and acid generation, leading to significant modification of the oxidative behavior of the minerals. The surface changes that occurred as a result of mineral weathering provoked transient enhancement of pyrite reactivity and progressive passivation in the pyrrhotite system. Iron sulfides weathering was found to involve the formation of an intermediate siderite (FeCO3)-like compound, preceding the predominant formation of K-jarosite (K·Fe3(SO4)2(OH)6) and/or ferric oxyhydroxide (α, γ-FeOOH) compounds, depending on the surface acid condition reached in the systems. Mechanisms of pyrite and pyrrhotite weathering in calcareous soils are suggested on the basis of surface characterization and chemical analysis of the leachates generated, and the environmental implications are discussed.

Chemical and surface analysis during evolution of arsenopyrite oxidation by Acidithiobacillus thiooxidans in the presence and absence of supplementary arsenic

Bioleaching of arsenopyrite presents a great interest due to recovery of valuable metals and environmental issues. The current study aims to evaluate the arsenopyrite oxidation by Acidithiobacillus thiooxidans during 240h at different time intervals, in the presence and absence of supplementary arsenic. Chemical and electrochemical characterizations are carried out using Raman, AFM, SEM-EDS, Cyclic Voltammetry, EIS, electrophoretic and adhesion forces to comprehensively assess the surface behavior and biooxidation mechanism of this mineral. These analyses evidence the formation of pyrite-like secondary phase on abiotic control surfaces, which contrast with the formation of pyrite (FeS2)-like, orpiment (As2S3)-like and elementary sulfur and polysulfide (Sn(2-)/S(0)) phases found on biooxidized surfaces. Voltammetric results indicate a significant alteration of arsenopyrite due to (bio)oxidation. Resistive processes determined with EIS are associated with chemical and electrochemical reactions mediated by (bio)oxidation, resulting in the transformation of arsenopyrite surface and biofilm direct attachment. Charge transfer resistance is increased when (bio)oxidation is performed in the presence of supplementary arsenic, in comparison with lowered abiotic control resistances obtained in its absence; reinforcing the idea that more stable surface products are generated when As(V) is in the system. Biofilm structure is mainly comprised of micro-colonies, progressively enclosed in secondary compounds. A more compact biofilm structure with enhanced formation of secondary compounds is identified in the presence of supplementary arsenic, whereby variable arsenopyrite reactivity is linked and attributed to these secondary compounds, including Sn(2-)/S(0), pyrite-like and orpiment-like phases.

Arsenopyrite weathering under conditions of simulated calcareous soil

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., Sn2−/S0) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

Spatial distribution, mobility and bioavailability of arsenic, lead, copper and zinc in low polluted forest ecosystem in North-western Mexico

A geochemical-environmental mapping was carried for a low polluted forest in North-western Mexico (Santiago Papasquiaro mining area), as part of the North American forests accounting for environmental behavior of arsenic (As), lead (Pb), zinc (Zn) and copper (Cu) in soil and tree components (stem wood and aciculums). Spectroscopic and microscopic techniques along with standard protocols were used to determine the mineralogical phases containing these elements, and their corresponding spatial distributions in soil and forests and mobility. In soil, total As, Pb, Zn and Cu ranged from 4.9 to 98.3, 19.6 to 768.6, 19.6 to 407.1, and 1.6 to 63.8 mg kg-1, respectively. Ultrafine particles (<5-10 μm) of arsenopyrite and sphalerite (and complex Zn-Fe phase) were the main As and Zn-bearing phases determined by SEM-EDS, respectively. Complex Pb-Cu-Fe and Cu-O oxide-like phases were the only ones containing Pb and Cu, respectively. Mobility was low for Pb, Zn and Cu, whereas a significant mobility was assessed for As. Concentrations vs. depth profiles suggested progressive accumulations of As, Pb, Zn and Cu in top soil. Total As, Pb, Zn and Cu in pine stem wood varied from 11.5 to 184.5, 98.9 to 7359.8, 3242.7 to 22197.3, 689.2 to 7179.6 μg kg-1, respectively. The respective concentrations in the pine needles ranged from 50 to 624.2, 100 to 16353.1, 120 to 46440.9 and 720 to 7200 μg kg-1, indicating an active bioaccumulation of As, Pb, Zn and Cu. A prospective environmental behavior was discussed for As, Pb, Zn and Cu in the low-polluted forest.