Showing papers by "Pedro J. J. Alvarez published in 2006"

Assessing the risks of manufactured nanomaterials.

Abstract: Although progress has recently been made toward understanding the health and environmental consequences of these materials, challenges ramain for future research.

Antibacterial Activity of Fullerene Water Suspensions: Effects of Preparation Method and Particle Size†

Abstract: Fullerene research in biological systems has been hindered by the compound's relative insolubility in water. However, C60 molecules can be made to aggregate, forming stable fullerene water suspensions (FWS) whose properties differ from those of bulk solid C60. There are many different protocols for making FWS. This paper explores four of these methods and establishes the antibacterial activity of each resulting suspension, including a suspension made without intermediary solvents. The aggregates in each polydisperse suspension were separated by size using differential centrifugation and tested for antibacterial activity using Bacillus subtilis as a test organism. All suspensions exhibited relatively strong antibacterial activity. Fractions containing smaller aggregates had greater antibacterial activity, although the increase in toxicity was disproportionately higher than the associated increase in putative surface area. This suggests the need for improved understanding of the behavior of FWS towards orga...

Improved Pd-on-Au bimetallic nanoparticle catalysts for aqueous-phase trichloroethene hydrodechlorination

Abstract: Groundwater remediation through the catalytic breakdown of the undesired contaminants is a more effective and desirable approach than the conventional physical displacement methods of air-stripping and carbon adsorption. Palladium-on-gold nanoparticles (Pd/Au NPs) have recently been shown to catalyze the hydrodechlorination of trichloroethene in water, at room temperature, and in the presence of hydrogen, with the most active Pd/Au material found to be >70 times more active than Pd supported on alumina on a per-Pd atom basis. The potential of this catalyst as a groundwater remediation technology could be improved by synthesizing Pd/Au NPs with smaller diameters and immobilizing them on a solid support. For this study, we synthesized Pd/Au NPs with a core diameter of 4 nm and with different Pd loadings and studied them in colloidal form for aqueous-phase trichloroethene hydrodechlorination. The most active catalysts were considerably more active (>1900 L/gPd/min) than Pd NPs (55 L/gPd/min) and conventionally synthesized Pd/Al2O3 (47 L/gPd/min). Accounting for a gas–liquid mass transfer effect and converting the Pd loading to Pd surface coverage using a magic cluster model for the Pd/Au NPs, the reaction rates in terms of initial turnover frequencies were >1.4, 4.35 � 10 � 2 , and 3.76 � 10 � 2 s � 1 , respectively. These materials exhibited volcano-like catalytic activity, in which hydrodechlorination rate was maximum near 70% Pd surface coverage. Au appeared to promote catalysis through geometric and electronic effects. Immobilization of the NPs on alumina, magnesia, and silica supports yielded active oxide-supported catalysts. # 2006 Elsevier B.V. All rights reserved.

Comparison of bioaugmentation and biostimulation for the enhancement of dense nonaqueous phase liquid source zone bioremediation.

Abstract: Two 11.7-m 3 experimental controlled release systems (ECRS), packed with sandy model aquifer material and amended with tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL) source zone, were operated in parallel with identical flow regimes and electron donor amendments. Hydrogen Releasing Compound (Regenesis Bioremediation Products, Inc., San Clemente, California), 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 before bioaugmentation, shown by nested polymerase chain reaction with phylogenetic primers, suggests that dechlorinating catabolic potential may be somewhat widespread. Results obtained corroborate that source zone reductive dechlorination 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.

Effect of simulated rhizodeposition on the relative abundance of polynuclear aromatic hydrocarbon catabolic genes in a contaminated soil

Abstract: Microcosms were used to investigate whether soil exposure to mulberry root extracts (rich in phenolic compounds) select for bacteria that degrade polynuclear aromatic hydrocarbons (PAHs). Unlike previous studies with freshly spiked soil, the present experiments were conducted with soils aged for 518 d with [14C]phenanthrene to decrease bioavailability and avoid exaggerating the selective pressure exerted by PAHs relative to the rhizosphere effect. Microcosms simulating contaminated planted soil were exposed to carbon at 20 mg/L/week of mulberry root extract for 211 d to simulate rhizodeposition. Contaminated bulk soils microcosms were amended with a C-free mineral medium to discern the effect of rhizodeposition. Uncontaminated soil controls also were exposed to similar dose regimes. Real-time quantitative polymerase chain reaction was used to enumerate total bacteria and PAH degraders harboring the genes nahAc (coding for naphthalene dioxygenase), todC1 (coding for toluene/benzene/chlorobenzene dioxygenase), bmoA (coding for hydroxylating monooxygenases), and dmpN (coding for phenol hydroxylase). Exposure to root extracts enhanced the growth of total bacteria and PAH degraders in both contaminated and uncontaminated rhizosphere microcosms. The relative abundance of PAH-degrader gene copies (as a fraction of the total bacteria) was similar for different treatments, suggesting that the root extracts did not select for PAH degraders. Overall, these results suggest that rhizodeposition from phenolic releasers contributes to the fortuitous (but not selective) proliferation of PAH degraders, which may enhance phytoremediation.

Nanotechnology in the Environment—The Good, the Bad, and the Ugly

Abstract: Nanotechnology is the ability to work at the molecular level, atom by atom, to create larger structures with fundamentally new molecular organization, novel properties, and functions. Engineered nanomaterials, typically a tenth the size of a human cell, are currently being used for a broad range of novel applications, including drug delivery, tissue engineering, tumor treatment, imaging, catalysis, detectors/sensors, and energy storage and transmission devices. Although some nanomaterials have been synthesized since the 1980s, their widespread production is relatively recent and their market size is expected to reach $1 trillion within 10 to 15 years. Such rapid growth suggests the potential for large environmental footprints, some of which will be good, some bad, and some ugly. On the good side, some nanomaterials hold great promise for reducing waste production, cleaning up industrial contamination, providing potable water, and improving the efficacy of energy production and use. The high potential to improve environmental technologies some of which date back to the Victorian era is intrinsically related to the small size of engineered nanomaterials, which results in significantly different properties than the associated bulk materials. Small size translates into a large surface to volume ratio, which implies greater opportunity to interact with environmental pollutants. In a sense, nanomaterials are “all surface.” This can be a highly desirable property for water, wastewater, and hazardous waste treatment. Some nanomaterials can be superior adsorbents or catalysts that remove pollutants more efficiently and at a substantially lower cost than current materialintensive approaches such as ion exchange resins and activated carbon adsorption. Nanotechnology also offers the potential for multifunctional materials, such as nano-architectured membranes for water treatment that incorporate chemically reactive nanomaterials to accomplish both separation and degradation of pollutants and enhance antifouling properties. The good news is that many of our colleagues are making significant progress toward the development of environmental nanotechnologies. These include nanosized iron for reductive treatment of chlorinated solvent DNAPLs, nanomagnetite for the removal of arsenic by sorption and magnetic separation, high-performance nanoscale Pd/ Au catalysts for treating particularly challenging contaminants in water that must be removed to a very low level, and novel advanced oxidation and disinfection approaches, to name a few. We hope to publish more papers in these emerging areas of research in the near future. On the bad side, the environment will be increasingly prone to

Phenanthrene removal by Penicillium frequentans grown on a solid-state culture: effect of oxygen concentration.

Abstract: Phenanthrene removal by Penicillium frequentans was compared under aerobic and microaerophilic conditions in a solid culture amended with low quantities of an agricultural residue. An inoculum of P. frequentans grown on sugarcane bagasse pith was mixed with soil spiked with 200 mg l−1 of phenanthrene, to obtain a final bagasse/soil ratio of 1:16. The C/N ratio was adjusted to 60 and the moisture content to 40%. The oxygen concentrations were adjusted to 20%, 10%, 5%, 2% and close to 0%, in the soil-gas phase for each treatment. There were statistically significant (p<0.05) differences in the metabolic activity at different oxygen concentrations, measured as CO2 production. Phenanthrene removal rates increased with oxygen concentration, reaching 52% removal after 17 days of incubation for the treatment with 20% O2. Nevertheless, oxygen-limited (microaerophilic) conditions did not preclude phenanthrene degradation.