Showing papers by "Pedro J. J. Alvarez published in 2009"

Comparative Photoactivity and Antibacterial Properties of C60 Fullerenes and Titanium Dioxide Nanoparticles

Abstract: The production of reactive oxygen species (ROS) by aqueous suspensions of fullerenes and nano-TiO2 (Degussa P25) was measured both in ultrapure water and in minimal Davis (MD) microbial growth medium Fullerol (hydroxylated C60) produced singlet oxygen (1O2) in ultrapure water and both 1O2 and superoxide (O2-*) in MD medium, but no hydroxyl radicals (OH*) were detected in either case PVP/C60 (C60 encapsulated with poly(N-vinylpyrrolidone)) was more efficient than fullerol in generating singlet oxygen and superoxide However, two other aggregates of C60, namely THF/nC60 (prepared with tetrahydofuran as transitional solvent) and aqu/nC60 (prepared by vigorous stirring of C60 powder in water), were not photoactive Nano-TiO2 (also present as aggregates) primarily produced hydroxyl radicals in pure water and superoxide in MD medium Bacterial (Escherichia coli) toxicity tests suggest that, unlike nano-TiO2 which was exclusively phototoxic, the antibacterial activity of fullerene suspensions was linked to ROS production Nano-TiO2 may be more efficient for water treatment involving UV or solar energy, to enhance contaminant oxidation and perhaps for disinfection However, fullerol and PVP/ C60 may be useful as water treatment agents targeting specific pollutants or microorganisms that are more sensitive to either superoxide or singlet oxygen

The water footprint of biofuels: a drink or drive issue?

Abstract: The water consumption and agrochemical use during biofuel production could adversely impact both availability and quality of a precious resource.

Understanding and harnessing the microaerobic metabolism of glycerol in Escherichia coli.

Abstract: Given its availability, low prices, and high degree of reduction, glycerol has become an ideal feedstock for the production of reduced compounds. The anaerobic fermentation of glycerol by Escherichia coli could be an excellent platform for this purpose but it requires expensive nutrients such as tryptone and yeast extract. In this work, microaerobic conditions were used as a means of eliminating the need for rich nutrients. Availability of low amounts of oxygen enabled redox balance while preserving the ability to synthesize reduced products. A fermentation balance analysis showed approximately 95% recovery of carbon and reducing equivalents. The pathways involved in glycerol dissimilation were identified using different genetic and biochemical approaches. Respiratory (GlpK-GlpD/GlpABC) and fermentative (GldA-DhaKLM) routes mediated the conversion of glycerol to glycolytic intermediates. Although pyruvate formate-lyase (PFL) and pyruvate dehydrogenase contributed to the synthesis of acetyl-CoA from pyruvate, most of the carbon flux proceeded through PFL. The pathways mediating the synthesis of acetate and ethanol were required for the efficient utilization of glycerol. The microaerobic metabolism of glycerol was harnessed by engineering strains for the co-production of ethanol and hydrogen (EH05 [pZSKLMgldA]), and ethanol and formate (EF06 [pZSKLMgldA]). High ethanol yields were achieved by genetic manipulations that reduced the synthesis of by-products succinate, acetate, and lactate. Co-production of hydrogen required the use of acidic pH while formate co-production was facilitated by inactivation of the enzyme formate-hydrogen lyase. High rates of product synthesis were realized by overexpressing glycerol dehydrogenase (GldA) and dihydroxyacetone kinase (DhaKLM). Engineered strains efficiently produced ethanol and hydrogen and ethanol and formate from glycerol in a minimal medium without rich supplements.

In situ Synthesis of Metal Nanoparticle Embedded Free Standing Multifunctional PDMS Films.

Abstract: We demonstrate a simple one-step method for synthesizing noble metal nanoparticle embedded free standing polydimethylsiloxane (PDMS) composite films. The process involves preparing a homogenous mixture of metal salt (silver, gold and platinum), silicone elastomer and the curing agent (hardener) followed by curing. During the curing process, the hardener crosslinks the elastomer and simultaneously reduces the metal salt to form nanoparticles. This in situ method avoids the use of any external reducing agent/stabilizing agent and leads to a uniform distribution of nanoparticles in the PDMS matrix. The films were characterized using UV-Vis spectroscopy, transmission electron microscopy and X-ray photoemission spectroscopy. The nanoparticle-PDMS films have a higher Young's modulus than pure PDMS films and also show enhanced antibacterial properties. The metal nanoparticle-PDMS films could be used for a number of applications such as for catalysis, optical and biomedical devices and gas separation membranes.

Research Priorities to Advance Eco-Responsible Nanotechnology

Abstract: Manufactured nanomaterials (MNMs) are rapidly being incorporated into a wide variety of commercial products with significant potential for environmental release, which calls for eco-responsible design and disposal of nanoenabled products. Critical research needs to advance this urgent priority include (1) structure−activity relationships to predict functional stability and chemistry of MNMs in the environment and to discern properties that increase their bioavailability, bioaccumulation, and toxicity; (2) standardized protocols to assess MNM bioavailability, trophic transfer, and sublethal effects; and (3) validated multiphase fate and transport models that consider various release scenarios and predict the form and concentration of MNMs at the point of exposure. These efforts would greatly benefit from the development of robust analytical techniques to characterize and to track MNMs in the environment and to validate models and from shared reference MNM libraries.

Cleaner water using bimetallic nanoparticle catalysts

Abstract: Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air-stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non-chlorinated compounds. Palladium-based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladiumon-gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next-step in the development of a viable hydrodechlorination catalysis technology. c � 2008 Society of Chemical Industry

Photochemical and antimicrobial properties of novel C60 derivatives in aqueous systems.

Abstract: Four novel hexakis C60 derivatives with varying functionalities were synthesized, and their photochemical properties and photodynamic disinfection efficiencies were quantitatively evaluated. All these C60 derivatives generated 1O2 more efficiently than commercial multihydroxylated C60 (fullerol), as assessed by furfuryl alcohol consumption and electron paramagnetic resonance analysis. Despite significant agglomeration/aggregation in the aqueous phase to micrometer-sized particles, nanosecond laser flash photolysis showed that the lifetime of triplet state (a key intermediate for energy transfer responsible for 1O2 production) was comparable to reported values for pristine C60 in organic phase. As a result of facile 1O2 production, the C60 derivatives efficiently inactivated Escherichia coli and MS-2 bacteriophage. Cationic aminofullerene hexakis, which likely exerted electrostatic attraction, exhibited exceptionally rapid virus inactivation even compared to commercial nano-TiO2 photocatalyst. These unique...

Performance Assessment of Bioremediation and Natural Attenuation

Abstract: Bioremediation and monitored natural attenuation are among the most cost-effective approaches to manage soil and groundwater contamination by hazardous organic pollutants. However, these remediation alternatives are not universally applicable and may be marginally effective for recalcitrant pollutants if the necessary microbial catabolic capacity is not present or expressed. Thus, regulatory and public approval of bioremediation and natural attenuation requires documentation of the efficacy of microbial degradation of the target pollutants. Performance assessment generally consists of three components: documented contaminant mass loss, geochemical fingerprints associated with biodegradation, and microcosm studies that show direct evidence of biodegradation. More recently, new molecular and isotope fractionation techniques have emerged to complement existing technologies for the forensic analysis and the demonstration of bioremediation and natural attenuation. This critical review examines the current state-of-art in performance assessment methods and discusses future research directions.

Field metabolomics and laboratory assessments of anaerobic intrinsic bioremediation of hydrocarbons at a petroleum-contaminated site

Abstract: Field metabolomics and laboratory assays were used to assess the in situ anaerobic attenuation of hydrocarbons in a contaminated aquifer underlying a former refinery. Benzene, ethylbenzene, 2-methylnaphthalene, 1,2,4- and 1,3,5-trimethylbenzene were targeted as contaminants of greatest regulatory concern (COC) whose intrinsic remediation has been previously reported. Metabolite profiles associated with anaerobic hydrocarbon decay revealed the microbial utilization of alkylbenzenes, including the trimethylbenzene COC, PAHs and several n-alkanes in the contaminated portions of the aquifer. Anaerobic biodegradation experiments designed to mimic in situ conditions showed no loss of exogenously amended COC; however, a substantive rate of endogenous electron acceptor reduction was measured (55 ± 8 µM SO(4) day(-1)). An assessment of hydrocarbon loss in laboratory experiments relative to a conserved internal marker revealed that non-COC hydrocarbons were being metabolized. Purge and trap analysis of laboratory assays showed a substantial loss of toluene, m- and o-xylene, as well as several alkanes (C(6)-C(12)). Multiple lines of evidence suggest that benzene is persistent under the prevailing site anaerobic conditions. We could find no in situ benzene intermediates (phenol or benzoate), the parent molecule proved recalcitrant in laboratory assays and low copy numbers of Desulfobacterium were found, a genus previously implicated in anaerobic benzene biodegradation. This study also showed that there was a reasonable correlation between field and laboratory findings, although with notable exception. Thus, while the intrinsic anaerobic bioremediation was clearly evident at the site, non-COC hydrocarbons were preferentially metabolized, even though there was ample literature precedence for the biodegradation of the target molecules.

Modeling the natural attenuation of benzene in groundwater impacted by ethanol-blended fuels: Effect of ethanol content on the lifespan and maximum length of benzene plumes

Abstract: [1] A numerical model was used to evaluate how the concentration of ethanol in reformulated gasoline affects the length and longevity of benzene plumes in fuel-contaminated groundwater. Simulations considered a decaying light nonaqueous phase liquid source with a total mass of ∼85 kg and a groundwater seepage velocity of 9 cm d−1 and corroborated previous laboratory, field, and modeling studies showing benzene plume elongation due to the presence of ethanol. Benzene plume elongation reached a maximum of 59% for 20% ethanol content (E20) relative to regular gasoline without ethanol. Elongation was due to accelerated depletion of dissolved oxygen during ethanol degradation and to a lower specific rate of benzene utilization caused by metabolic flux dilution and catabolite repression. The lifespan of benzene plumes was shorter for all ethanol blends compared to regular gasoline (e.g., 17 years for regular gasoline, 15 years for E10, 9 years for E50, and 3 years for E85), indicating greater natural attenuation potential for higher-ethanol blends. This was attributed to a lower mass of benzene released for higher-ethanol blends and increased microbial activity associated with fortuitous growth of benzene degraders on ethanol. Whereas site-specific conditions will determine actual benzene plume length and longevity, these decaying-source simulations imply that high-ethanol blends (e.g., E85) pose a lower risk of benzene reaching a receptor via groundwater migration than low-ethanol blends such as E10.

Pore Water Characteristics Following a Release of Neat Ethanol onto Pre-existing NAPL

Abstract: Neat ethanol (75.7 L) was released into the upper capillary zone in a continuous-flow, sand-packed aquifer tank (8.2 m 3 ) with an average seepage velocity of 0.75 m/day. This model aquifer system contained a residual nonaqueous phase liquid (NAPL) that extended from the capillary zone to 10 cm below the water table. Maximum aqueous concentrations of ethanol were 20% v/v in the capillary zone and 0.08% in the saturated zone at 25 and 30 cm downgradient from the emplaced NAPL source, respectively. A bench-scale release experiment was also conducted for a similar size spill (scaled to the plan area). The concentrations of ethanol in ground water for both the bench- and pilot-scale experiments were consistent with advective–dispersive limited mass transfer from the capillary to the saturated zone. Concentrations of monoaromatic hydrocarbons and isooctane increased in the pore water of the capillary zone as a result of both redistribution of residual NAPL (confirmed by visualization) and enhanced hydrocarbon dissolution due to the cosolvent effect exerted by ethanol. In the tank experiment, higher hydrocarbon concentrations in ground water were also attributed to decreased hydrocarbon biodegradation activity caused by preferential microbial utilization of ethanol and the resulting depletion of oxygen. These results infer that spills of highly concentrated ethanol will be largely confined to the capillary zone due to its buoyancy, and ethanol concentrations in near-source zone ground water will be controlled by mass transfer limitations and hydrologic conditions. Furthermore, highly concentrated ethanol releases onto pre-existing NAPL will likely exacerbate impacts to ground water, due to NAPL mobilization and dissolution, and decreased bioattenuation of hydrocarbons.

Medical bioremediation of age-related diseases

Abstract: Catabolic insufficiency in humans leads to the gradual accumulation of a number of pathogenic compounds associated with age-related diseases, including atherosclerosis, Alzheimer's disease, and macular degeneration. Removal of these compounds is a widely researched therapeutic option, but the use of antibodies and endogenous human enzymes has failed to produce effective treatments, and may pose risks to cellular homeostasis. Another alternative is "medical bioremediation," the use of microbial enzymes to augment missing catabolic functions. The microbial genetic diversity in most natural environments provides a resource that can be mined for enzymes capable of degrading just about any energy-rich organic compound. This review discusses targets for biodegradation, the identification of candidate microbial enzymes, and enzyme-delivery methods.

Potential Environmental and Human Health Impacts of Nanomaterials Used in the Construction Industry

Abstract: Nanomaterials and nanocomposites with unique physical and chemical properties are increasingly being used by the construction industry to enable novel applications. Yet, we are confronted with the timely concern about their potential (unintended) impacts to the environment and human health. Here, we consider likely environmental release and exposure scenarios for nanomaterials that are often incorporated into building materials and/or used in various applications by the construction industry, such as carbon nanotubes, TiO2, and quantum dots. To provide a risk perspective, adverse biological and toxicological effects associated with these nanomaterials are also reviewed along with their mode of action. Aligned with ongoing multidisciplinary action on risk assessment of nanomaterials in the environment, this article concludes by discerning critical knowledge gaps and research needs to inform the responsible manufacturing, use and disposal of nanoparticles in construction materials.

Medical Bioremediation: A Concept Moving Toward Reality

Abstract: A major driver of aging is catabolic insufficiency, the inability of our bodies to break down certain substances that accumulate slowly throughout the life span. Even though substance buildup is harmless while we are young, by old age the accumulations can reach a toxic threshold and cause disease. This includes some of the most prevalent diseases in old age—atherosclerosis and macular degeneration. Atherosclerosis is associated with the buildup of cholesterol and its oxidized derivatives (particularly 7-ketocholesterol) in the artery wall. Agerelated macular degeneration is associated with carotenoid lipofuscin, primarily the pyridinium bisretinoid A2E. Medical bioremediation is the concept of reversing the substance accumulations by using enzymes from foreign species to break down the substances into forms that relieve the disease-related effect. We report on an enzyme discovery project to survey the availability of microorganisms and enzymes with these abilities. We found that such microorganisms and enzymes exist. We identified numerous bacteria having the ability to transform cholesterol and 7-ketocholesterol. Most of these species initiate the breakdown by same reaction mechnism as cholesterol oxidase, and we have used this enzyme directly to reduce the toxicity of 7-ketocholesterol, the major toxic oxysterol, to cultured human cells. We also discovered that soil fungi, plants, and some bacteria possess peroxidase and carotenoid cleavage oxygenase enzymes that effectively destroy with varied degrees of efficiency and selectivity the carotenoid lipofuscin found in macular degeneration.

Nanotechnology-Enabled Water Disinfection and Microbial Control: Merits and Limitations

Abstract: Several natural and engineered nanomaterials, such as silver (nAg), titanium oxide (TiO,), and carbon nanotubes (CNT), are known to have antibacterial properties and are under consideration as disinfecting agents for water treatment systems. Their antimicrobial mechanisms are diverse, including photocatalytic production of reactive oxygen species (ROS) that inactivate viruses and cleave DNA, disruption of the structural integrity of the bacterial cell envelope resulting in leakage of intracellular components, arid interruption of energy transduction. In order for a material to be used for water disinfection, it must exhibit potent antimicrobial activity while remaining harmless to humans at relevant doses. However, other factors can also hinder its viability as a disinfectant. For suspended nanoparticles, these factors include the presence of salts that promote coagulation and precipitation, natural organic matter that coats or sorbs on nanoparticles and reduces their bioavailability, and competing species that consume ROS. Similarly, the efficacy of antimicrobial coatings can be compromised by the deposition of debris (e.g., soluble microbial products, inorganic precipitates, or dead cells) that occlude antimicrobial surface sites and facilitate biofilm formation. Another potential limitation is the need to retain and recycle the nanoparticles to reduce cost and avoid potential health and environmental impacts. Despite these limitations, antimicrobial nanoparticles could overcome critical challenges associated with traditional chemical disinfectants (e.g., free chlorine and ozone) such as harmful disinfection by-products and short-lived reactivity, and they could enhance existing technologies such as ultraviolet inactivation of viruses, solar disinfection of bacteria, and biofouling prone membrane filtration. Furthermore, a potential growth in demand for decentralized or point-of use water treatment and reuse systems will likely stimulate further research and commercialization of nanoparticles to enhance water disinfection applications.

Reductions in DNAPL Longevity through Biological Flux Enhancement

Abstract: : In the first phase of this project (Phase I), two 11.7 cubic meter Experimental Controlled Release Systems (ECRS), packed with sandy model aquifer material and amended with tetrachloroethene (PCE) DNAPL source zones, were operated in parallel with identical flow regimes and electron donor amendments. Hydrogen Releasing Compound-trademark (HRC), and later dissolved lactate, served as electron donors to promote dechlorination. One ECRS was bioaugmented with an anaerobic dechlorinating consortium directly into the source zone, and the other served as a control (biostimulated only) to determine the benefits of bioaugmentation. The presence of halorespiring bacteria in the aquifer matrix prior to bioaugmentation, shown by nested PCR with phylogenetic primers, suggests that dechlorinating catabolic potential may be somewhat widespread. PCR analyses demonstrated that the bacteria present in the culture used for bioaugmentation in the ECRS prevailed for almost a year. Unfortunately, even with Dehalococcoides present, complete dechlorination to ethene was achieved at minimum (<1 micrometer). Results demonstrated that the low concentration of ethene produced in this first phase was not due to washout of the dechlorinating organisms. It was also demonstrated that as long as the electron acceptor was not limiting, there was greater energy flow to the dechlorinating populations than to the methanogens. Overall, the results obtained in the Phase I corroborate that source zone reductive Dechlorinating of PCE is possible at near field scale, and that a system bioaugmented with a competent halorespiring consortium can enhance DNAPL dissolution and dechlorination processes at significantly greater rates than in a system that is biostimulated only.