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Showing papers by "Pedro J. J. Alvarez published in 2012"


Journal ArticleDOI
TL;DR: This work suggests that AgNP morphological properties known to affect antimicrobial activity are indirect effectors that primarily influence Ag(+) release, and antibacterial activity could be controlled by modulating Ag(+ release, possibly through manipulation of oxygen availability, particle size, shape, and/or type of coating.
Abstract: For nearly a decade, researchers have debated the mechanisms by which AgNPs exert toxicity to bacteria and other organisms. The most elusive question has been whether the AgNPs exert direct “particle-specific” effects beyond the known antimicrobial activity of released silver ions (Ag+). Here, we infer that Ag+ is the definitive molecular toxicant. We rule out direct particle-specific biological effects by showing the lack of toxicity of AgNPs when synthesized and tested under strictly anaerobic conditions that preclude Ag(0) oxidation and Ag+ release. Furthermore, we demonstrate that the toxicity of various AgNPs (PEG- or PVP- coated, of three different sizes each) accurately follows the dose–response pattern of E. coli exposed to Ag+ (added as AgNO3). Surprisingly, E. coli survival was stimulated by relatively low (sublethal) concentration of all tested AgNPs and AgNO3 (at 3–8 μg/L Ag+, or 12–31% of the minimum lethal concentration (MLC)), suggesting a hormetic response that would be counterproductive t...

1,785 citations


Journal ArticleDOI
TL;DR: The kinetic comparison of SnP/silica and TiO(2) photocatalyst in real wastewater effluents showed that photosensitized singlet oxygenation of pharmaceuticals was still efficiently achieved in the presence of background organic matters, while significant interference was observed for photocatalyzed oxidation involving non-selective OH radical.
Abstract: This study evaluates the potential application of tin porphyrin- and C60 aminofullerene-derivatized silica (SnP/silica and aminoC60/silica) as 1O2 generating systems for photochemical degradation of organic pollutants. Photosensitized 1O2 production with SnP/silica, which was faster than with aminoC60/silica, effectively oxidized a variety of pharmaceuticals. Significant degradation of pharmaceuticals in the presence of the 400-nm UV cutoff filter corroborated visible light activation of both photosensitizers. Whereas the efficacy of aminoC60/silica for 1O2 production drastically decreased under irradiation with λ > 550 nm, Q-band absorption caused negligible loss of the photosensitizing activity of SnP/silica in the long wavelength region. Faster destruction of phenolates by SnP/silica and aminoC60/silica under alkaline pH conditions further implicated 1O2 involvement in the oxidative degradation. Direct charge transfer mediated by SnP, which was inferred from nanosecond laser flash photolysis, induced s...

168 citations


Journal ArticleDOI
25 Jun 2012-ACS Nano
TL;DR: Results show that bacteria can mitigate QD toxicity by turning on energy-dependent heavy-metal ion efflux systems and by mediating the precipitation of dissolved metal ions as less toxic and less bioavailable insoluble NPs.
Abstract: The growing use of quantum dots (QDs) in numerous applications increases the possibility of their release to the environment. Bacteria provide critical ecosystem services, and understanding their response to QDs is important to assess the potential environmental impacts of such releases. Here, we analyze the microbial response to sublethal exposure to commercial QDs, and investigate potential defense and adaptation mechanisms in the model bacterium Pseudomonas aeruginosa PAO1. Both intact and weathered QDs, as well as dissolved metal constituents, up-regulated czcABC metal efflux transporters. Weathered QDs also induced superoxide dismutase gene sodM, which likely served as a defense against oxidative stress. Interestingly, QDs also induced antibiotic resistance (ABR) genes and increased antibiotic minimum inhibitory concentrations by 50 to 100%, which suggests up-regulation of global stress defense mechanisms. Extracellular synthesis of nanoparticles (NPs) was observed after exposure to dissolved Cd(NO3)...

89 citations


Journal ArticleDOI
TL;DR: The results highlight the importance of environment-induced changes in nC₆₀ surface chemistry in its fate and transport in aquatic environments.
Abstract: Nanoparticle transport in natural settings is complex due to interactions with the surrounding environment. In this study, the impact of UVA irradiation and humic acid (HA) on deposition of aqueous fullerene nanoparticles (nC60) on a silica surface as a surrogate for natural sediments was studied using packed column experiments and quartz crystal microbalance with dissipation monitoring under various solution conditions. Surface oxidation of nC60 induced by UVA irradiation greatly retarded its deposition due to the increased negative surface charge and hydrophilicity. Dissolved HA, once adsorbed onto the nC60 surface, also hindered its deposition mainly through steric hindrance forces. The extent of this effect depended on the properties and the amount of HA adsorbed, which is a function of ionic strength and HA concentration. HA has limited adsorption on UVA-irradiated nC60 and is expected to play a less important role in its stability. HA immobilized onto the silica surface had a variable effect on nC60 deposition, depending on the complex interplay of Derjaguin−Landau−Verwey−Overbeek (DLVO) and non-DLVO interactions such as electrostatic interaction, steric hindrance, and hydrogen bonding as well as HA molecular conformation. These results highlight the importance of environment-induced changes in nC60 surface chemistry in its fate and transport in aquatic environments.

59 citations


Journal ArticleDOI
TL;DR: Simulations with the analytical vapor intrusion model "Biovapor" corroborated the low explosion risk associated with ethanol fuel releases under more generic conditions and indicated the importance of methanotrophic activity near the water table to attenuate methane generated from dissolved ethanol plumes.
Abstract: Fuel ethanol releases can stimulate methanogenesis in impacted aquifers, which could pose an explosion risk if methane migrates into enclosed spaces where ignitable conditions exist. To assess this potential risk, a flux chamber was emplaced on a pilot-scale aquifer exposed to continuous release (21 months) of an ethanol solution (10% v:v) that was introduced 22.5 cm below the water table. Despite methane concentrations within the ethanol plume reaching saturated levels (20–23 mg/L), the maximum methane concentration reaching the chamber (21 ppmv) was far below the lower explosion limit in air (50,000 ppmv). The low concentrations of methane observed in the chamber are attributed to methanotrophic activity, which was highest in the capillary fringe. This was indicated by methane degradation assays in microcosms prepared with soil samples from different depths, as well as by PCR measurements of pmoA, which is a widely used functional gene biomarker for methanotrophs. Simulations with the analytical vapor i...

50 citations


Journal ArticleDOI
Yu Yang1, Jing Wang1, Huiguang Zhu1, Vicki L. Colvin1, Pedro J. J. Alvarez1 
TL;DR: Whether this surprising stimulation of nitrogen cycling activities reflects the need to generate more energy to overcome toxicity or to synthesize organic nitrogen to repair or replace damaged proteins remains to be determined.
Abstract: Little is known about the potential impacts of accidental or incidental releases of manufactured nanomaterials to microbial ecosystem services (e.g., nutrient cycling). Here, quantum dots (QDs) coated with cationic polyethylenimine (PEI) were more toxic to pure cultures of nitrogen-cycling bacteria than QDs coated with anionic polymaleic anhydride-alt-1-octadecene (PMAO). Nitrifying bacteria (i.e., Nitrosomonas europaea) were much more susceptible than nitrogen fixing (i.e., Azotobacter vinelandii, Rhizobium etli, and Azospirillum lipoferum) and denitrifying bacteria (i.e., Pseudomonas stutzeri). Antibacterial activity was mainly exerted by the QDs rather than by their organic coating or their released QD components (e.g., Cd and Zn), which under the near-neutral pH tested (to minimize QD weathering) were released into the bacterial growth media at lower levels than their minimum inhibitory concentrations. Sublethal exposure to QDs stimulated the expression of genes associated with nitrogen cycling. QD-PE...

44 citations


Journal ArticleDOI
TL;DR: Targeting the lysosome for optimal treatment of oxysterol-mediated cytotoxicity is suggested, and the use of introducing novel catalytic function into theLysosomes for therapeutic and research applications is supported.
Abstract: Ketocholesterol (7KC) is a cytotoxic oxy- sterol that plays a role in many age-related degenerative diseases. 7KC formation and accumulation often occurs in the lysosome, which hinders enzymatic transformations that reduce its toxicity and increase the sensitivity to lysosomal membrane permeabilization. We assayed the potential to mitigate 7KC cytotoxicity and enhance cell viability by overexpressing 7KC-active enzymes in human fibroblasts. One of the enzymes tested, a cholesterol oxidase engineered for lysosomal targeting, significantly increased cell viability in the short term upon treatment with up to 50 mM 7KC relative to controls. These results suggest targeting the lysosome for optimal treatment of oxysterol-mediated cy- totoxicity, and support the use of introducing novel catalytic function into the lysosome for therapeutic and research applications. Biotechnol. Bioeng. 2012;109: 2409-2415.

18 citations