Nano Technology Abstracts 0 - Z
Nanotechnology for Site Remediation
The Technology Innovation and Field Services Division (TIFSD) of the U.S. Environmental Protection Agency’s (EPA’s) Office of Solid Waste and Emergency Response recently published a fact sheet on the use of nanotechnology for site remediation. (see http://clu-in.org/542F08009.). Nanotechnology holds promise in remediating hazardous waste sites cost-effectively and in addressing challenging site conditions, such as where dense nonaqueous-phase liquids (DNAPLs) are present in contaminated aquifers. Nanoscale iron is already in use in full-scale projects with an encouraging measure of success.
EPA has collected information on 26 sites where nanoscale zero-valent iron has been tested for site remediation. The presentation summarizes EPA’s findings to date, including both successes and limitations encountered in the field applications and also questions about fate, transport, and toxicity of nanomaterials. The presentation also includes a summary of how EPA’s various program offices are addressing issues regarding the applications and implications of nanotechnology.
Adsorption of Sulfamethoxazole on Carbon Nanotubes as Affected by Phosphate
Nanotechnology has become one of the most promising new technologies in the 21st century. Engineered nanomaterials will inevitably be released into the environment during manufacturing, application or disposal, and may become a very important component of the environment. Unfortunately, carbon nanotubes (CNTs) have been demonstrated to be toxic to various organisms. In addition, the strong interaction between CNTs and various pollutants significantly alters the mobility, bioavailability, and toxicity of both CNTs and pollutants. Therefore, the wide spread of CNTs can lead to unforeseen health and environmental risks. Evaluation of their environmental risk requires our extensive understanding of CNT-pollutant interaction mechanisms. However, research on this area is still very limited, especially in a system with different types of pollutants. This study is aimed at understanding CNT adsorption mechanisms in a bi-solute (Sulfamethoxazole and phosphate) system.
Quantum Dot Transformation Under Simulated Environmental Conditions
Once released into the environment, engineered nanomaterials may be transformed by microbially mediated redox processes altering their toxicity and fate. Little information is currently available on engineered nanomaterial transformation under environmentally relevant conditions. We have developed in vitro biomimetic assays to investigate nanomaterial transformation under simulated environmental conditions. One assay is based on the extracellular hydroquinone-driven Fenton’s reaction used by lignolytic fungi. We demonstrate the utility of the assay using CdSe quantum dots (QDs) encapsulated in a ZnS shell, functionalized with PEG ligands and/or wrapped with an amphiphilic polymer. Quantum dot transformation was assessed by UV-Visible spectroscopy, inductively-coupled plasma-optical emission spectroscopy, dynamic light scattering, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS). PEG-thiol functionalized QDs were readily degraded under simulated oxidative environmental conditions: the ZnS shell eroded and cadmium was released from the QD core. TEM, electron diffraction analysis and EDS of transformed QDs revealed formation of amorphous Se aggregates. The biomimetic hydroquinone-driven Fenton’s reaction degraded QDs to a larger extent than did H2O2 and classical Fenton’s reagent (H2O2 + Fe2+). Amphiphilic polymer wrapping conferred stability against the oxidation by the hydroquinone-driven Fenton’s reaction. This assay provides a method to characterize transformations of nanoscale materials expected to occur under oxidative environmental conditions.
Bioaccumulation Potential of Radioactively Labeled Nanotubes by Terrestrial
and Aquatic Organisms
Despite extensive research on carbon nanotubes’ (CNTs) material properties and intended applications, the risks they pose to the welfare of humankind and the environment are not well understood. To characterize these risks, we have developed a methane chemical vapor deposition method for producing C14-labeled single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs), a technique that allows for direct quantification of unmodified nanotubes in biological and environmental samples. This approach overcomes many of the limitations of current techniques with regards to quantifying modified or unmodified single- or multi-walled carbon nanotubes. The nanotubes were purified and extensively characterized with raman spectroscopy, transmission electron microscopy, scanning electron microscopy, and thermal gravimetric analysis to ensure high purity with regard to the ratio of carbon nanotubes to amorphous carbon and also to catalyst impurities.
Uptake and depuration behaviors of these carbon-14 labeled nanotubes were then tested using representative organisms from terrestrial, sediment, and aquatic ecosystems: earthworms (Eisenia foetida), oligochaetes (Lumbriculus variegatus), and water fleas (Daphnia magna), respectively. Organism mortality caused by exposure to nanotubes was not observed under any exposure condition. Earthworms and oligochaetes were not found to accumulate SWNTs or MWNTs. The calculated accumulation factors in the organisms did not vary based on the duration of exposure or the composition of the soil or sediment, and the calculated nanotube concentration in the organisms was consistently small. Substantially different behaviors were found with the daphnia. After 24 hours of exposure to nanotube solutions, bioconcentration factors were substantially greater than typically found for hydrophobic organic chemicals. Additionally, daphnia were unable to excrete nanotubes after 24 hours of depuration in clean artificial freshwater or filtered Lake Kontiolampi water (20.9 mg/L dissolved organic carbon). The addition of algae to the water during the depuration period, however, caused roughly half of the nanotubes to be removed within the first few hours, but little excretion was observed thereafter. Light microscopy results suggest that the vast majority of the nanotubes present are in the guts of the organism, and not absorbed into organism tissues. Overall, there was a similar lack of nanotube absorption into tissues by each of the organisms, but the potential for toxicological risks seems highest for daphnia given their difficulty exhibited in excreting the CNTs. Ongoing research related to the accumulation and ecotoxicity of nanotubes modified to have positive, negative, or neutral surface charges is discussed.
Semi-Empirical Correlation to Predict the Collision Efficiency of
Natural Organic Matter (NOM) - and Polymer-coated Nanoparticles in
Assessing the potential risks of natural or engineered nanoparticles to the environment and human health requires the ability to predict their mobility in porous media such as groundwater aquifers or sand filters used in water treatment. Semi-empirical correlations to predict the collision efficiency of electrostatically stabilized nanoparticles are available; however, they are not likely to be applicable to nanoparticles coated with natural organic matter (NOM) or engineered with polymeric surface coatings because the exisitng correlations do not account for the electrosteric repulsions afforded by coatings that can inhibit attachment to surfaces. In this study regression analysis of published data on the collision efficiency of NOM-coated latex and hematite particles, and for new data on poly(styrene sulfonate)- and polyaspartate-coated hematite nanoparticles is used to develop a semi-empirical correlation to predict the collision efficiency of NOM- and polymer-coated nanomaterials that includes the adsorbed layer-electrokinetic parameter (NLEK) representing electrosteric repulsions afforded by adsorbed NOM or polyelectrolyte. Despite the large variation in particle type, coating type, and solution conditions, a single semi-empirical correlation with three dimensionless parameters can predict their measured collision efficiency. This study emphasizes the importance of including the adsorbed NOM and polymer layer properties for predicting the collision efficiency of NOM- and polymer-coated natural and manufactured nanomaterials in porous media and offers a functional form of a semi-empirical parameter for such predictions. This modified semi-empirical correlation allows the preliminary estimation of the migration of nanoparticles in porous media once the adsorbed layer properties of surface coatings on the surface of nanoparticles is known.
Evaluation of Ensemble Techniques to Facilitate Monitoring Fate of
Nanoparticles in Three Southern California Wastewater Effluents
With the increasing use of manufactured nanomaterials in everyday products, potential exists for their release in industrial and municipal wastewaters. Existing analytical techniques need to be modified or augmented to selectively monitor the fate of nanoparticles in complex wastewater effluents. For example, sample preparation steps (e.g. acid digestion) for chemical composition analyses such as ICP-MS or TOC analyses may render selective monitoring of nanoscale particles in wastewater ineffective. Multiple pre-filtration steps using nanoscale filters may be required to overcome this limitation. Use of ensemble techniques in conjunction with chemical composition techniques can be a viable alternative.
Kennedy/Jenks Consultants and University of California, Irvine is involved in projects to evaluate fate of biogenic and manufactured nanoscale materials in three wastewater treatment plants in Southern California. Two of the treatment plants use activated sludge process and the third plant uses trickling filter process for wastewater treatment. As part of the project, the applicability of ensemble techniques to detect nanomaterials in wastewater was evaluated. A Malvern Zetasizer Nano-ZS (Westborough, MA) was used to characterize nanoscale materials. This instrument uses a Non-Invasive Back Scattering (NBIS) technology to detect nanoscale particles distribution.
Preliminary analyses of wastewater effluents indicated that a pre-filtration process as well as extension of sample equilibration time was required to analyze biogenic nanoscale particles. Subsequently, replicate analyses of undiluted effluents passed all instrumentation quality criteria. The standard deviations for average particle size and particle count were less than 5% for the wastewater samples. Furthermore, a linear relationship existed (R2 > 0.98) on number of nanoscale particles in samples diluted with varying amounts of DI water. Initial data from TOC analyses of trickling filter effluent indicated that nearly 20% of the filtrate TOC was contributed by biogenic nanoscale suspended particles.
Initial studies using nanoscale alumina and silica yielded insights on their fate in wastewater streams. While nano alumina precipitated and formed sedimenting particles, nano silica formed stable suspensions in the effluents. Efforts are currently in progress to optimize analytical conditions to obtain bimodal distribution of biogenic and manufactured nanomaterials, and relate the particles distribution data to chemical composition.
Effects of Different Surface Modifications on the Transport of Nanoscale
Iron Particles in Porous Media
This paper investigates the transport of nanoscale iron particles (NIP) modified with different surface modifiers (dispersants) in soils. Three types of lactate (aluminum lactate, sodium lactate, ethyl lactate), two types of polymers (polyacrylic acid, aspartic acid) and three types of cyclodextrins (methyl β-cyclodextrin, β-cyclodextrin and hydroxyl propyl-β-cyclodextrin) at different concentrations were selected as dispersants. The porous media used was natural fine to coarse sand. During the experiments, the sand was homogeneously packed in a glass vertical column, and a slug of NIP amended with selected dispersant was immediately placed on top of the sand. About 20 pore volume of simulated groundwater was flushed through sand column under a pressure of 30 psi. Effluent samples were collected at different time periods. The permeability, iron concentration, pH, electrical conductivity and total dissolved solids of the elute were determined. Visual observations also helped in determining the extent of NIP transport in the soil. With the bare NIP, only about 50% of iron was eluted from the soil media. The results showed that different dispersants effected transport of the NIP differently. It also showed that different concentration of the various dispersants showed different characteristics in their transport abilities. Aluminum lactate at 2% showed about 55% elution and 10% aluminum lactate showed about 92% elution. Aspartic acid and ethyl lactate showed low amount of iron elution (35-40%). The pH and ionic strength of dispersants affected the zeta potential of NIP. Overall, these results demonstrated that aluminum lactate can increase the stability of NIP suspension and enhance their transport in porous media. Furthermore, lactate is environmentally safe, relatively inexpensive, and practical to use for in-situ applications.
* This study is a part of project funded by the U.S. National Science Foundation
Regulatory and Industry Acceptance of nZVI Technology
With nearly 10 years of experience, Golder Associates Inc. (Golder)
is a leader in the manufacture and implementation of nano-scale zero-valent
iron (nZVI) for environmental remediation applications. As presented
at the October 2008 International Environmental Nanotechnology Conference:
Applications and Implications, Golder has designed and implemented nZVI
injections in the United States, Canada, Europe and Australia, projects
that have led to several significant advancements in the technology including,
verifying the need to include palladium (Pd) as a catalyst for in situ
treatment using mechanically crushed material, verifying the need to
include a surface modifier to enhance the mobility of nZVI in the subsurface,
and establishing the enhanced treatment potential of combined nZVI/enhanced
Nanotechnological Solutions for Monitoring and Treatment of Drinking
Water and Groundwater
The objective of the EU Water Framework Directive is to prevent further deterioration and to protect and enhance the status of aquatic ecosystems, to promote sustainable water use based on a long-term protection of available water resources, to enhance protection and improvement of the aquatic environment through the reduction of discharges, emissions and losses of priority substances and new emerging pollutants, and to ensure the progressive reduction of pollution of groundwater and prevent its further pollution.
Development of sensitive analytical methods and monitoring tools for multi-residue detection of water pollutants is required to implement and verify compliance with this legislation. Advances in nanotechnology research can enable integrated solutions to complex problems. Potential applications include provision of clean drinking water, remediation of contaminated aquifers and wastewater treatment. Improved water quality monitoring techniques based on biosensor, optical, microfluidic and information technologies will lead to radical changes in our ability to perceive, understand and manage the aquatic environment. Intelligent biosensor networks could perform the task of monitoring water quality, as well as localized detection of sources of pollution. Current research at the interface between nanotechnology, biotechnology and information technology is enabling the solutions tailored to specific problems that were previously irresolvable due to their high degree of complexity.
Present day filtration and purification plants used to supply drinking water tend to be of limited effectiveness because of the relative inefficiency of the active materials. Due to their greater specific surface area, nanoparticles and nanoporous membranes are more effective as filtration media. Nanofiltration and phototocatalytic degradation methods are applied for the removal of organic and inorganic water pollutants for drinking water and groundwater treatment. Other promising technologies include enzyme or hydrophilic coatings on nanofibrous electrospun membranes to reduce fouling and enhance water flow in wastewater treatment, and iron nanoparticles injected directly into the aquifer or contained in permeable reactive barriers for adsorption and reductive degradation of groundwater contaminants. Highly selective filters based on biomimetic structures such as synthetic protein water channels embedded in polymer membranes and filters fabricated from carbon nanotubes are being developed for drinking water purification.
A Collaborative Effort to Address Nanotechnology in Massachusetts
Massachusetts has an expanding nanotechnology industry with approximately 100 companies working with nanomaterials and 11 major nanotechnology research centers. There are many potential nanotech applications in the energy and environmental area such as making solar power more affordable, treating water to reduce contaminants and producing greener and safer products. State Officials encourage the growth of Massachusetts’ nanotechnology companies and research endeavors. State agencies are also collaborating with the nanotech sector to promote innovation and to identify and develop approaches to identify and address potential sources of environmental releases and workplace exposures.
Best management practices (BMPs) and good current practices (GCPs) provide practical opportunities for the expanding nanotech industry to protect workers, public health and the environment. In addition, measurement capabilities can provide information on whether releases or exposures are taking place. In early 2009, the Massachusetts Department of Environmental Protection held a conference to provide a forum for research and development companies, nanomanufacturers, academic researchers, environmentalists, state and federal agencies to discuss opportunities and challenges to protect workers, public health and the environment via the application of BMPs and GCPs. This conference also explored evolving techniques to measure nanoparticles in the environment and workplace.
At this meeting, selected BMPs and GCPs for companies and research laboratories
were reviewed and discussed in terms of the opportunities they present
to protect human health and the environment. During breakout sessions,
participants determined how the BMPs and GCPs could be applied to the
lifecycle of specific products such as cosmetics and paint and provided
feedback on their applicability as well as gaps that need to be filled.
The session on the state-of-the-art techniques for measuring nanoparticles
provided information on how nanoparticles in various media can be used
to measure potential exposures and releases.
Solubilization of Carbon Nanomaterials in Soil and Natural Waters:
The Role of Humic Acid
Carbon nanomaterials are among the most common materials employed in nanoscience and nanotechnology research. Their unique physicochemical properties make them an attractive and versatile class of materials for a wide range of applications. At present there is very little knowledge of the fate of carbon nanomaterials discharged into the environment. Such exposure may take place in waste management at the site of production or from consumer product waste. Concerns of the solubility and transport of carbon nanomaterials in soil and natural waters have often been dismissed on the basis of their hydrophobicity. However, there have recently been numerous reports in the literature of efficient solubilization of fullerenes and carbon nanotubes by amphiphilic substances [e.g., E. Salonen et al., Small (2008) in press].
We have carried out a joint computational and experimental study of the solubilization of carbon nanomaterials by humic acid (HA), one of the major components of natural organic matter. Our computational research has featured atomistic molecular dynamics simulations of the interaction of fullerenes, isolated nanotubes (both single- and multi-walled), as well as bundles of nanotubes with HA. As a representative model for the latter, we have used the Temple-Northeastern-Birmingham (TNB) molecular model, which corresponds to the elemental and chemical functional group compositions of HAs found in soil and natural waters. The computational part of the research is complementd by UV-vis spectrophotometry measurements of the interaction of TNB and carbon nanomaterials. We illustrate how the self-assembly of the TNB molecules leads to the solubilization of carbon nanomaterials. This is made possible by the stacking of the aromatic rings of TNB on the nanomaterial surface via hydrophobic effect and van der Waals interactions, while the polar hydroxyl, carbonyl and carboxylate groups provide a hydrophilic layer at the nanomaterial-water interface. We assess the importance of polarization (zeta potential) on the stability of the carbon nanomaterial suspensions. Finally, we illustrate the role of salinity on the self-assembly of carbon nanomaterial-TNB aggregates in view of understanding the fate of nanomaterials transported in waste water, freshwater and seawater.
Nanomaterials in consumer products – do they pose a hazard?
A brief overview of what is known about the hazard potential of engineered nanomaterials and the potential for human and environmental exposure as a result of their use in consumer products (e.g., personal care products, foods and food packaging, medical devices, and pharmaceuticals) will be presented. Because nanomaterials may have different toxicological properties and exposure potentials than the substances in bulk form or in some cases, they may be totally new substances, there have been concerns regarding the need for increased research to evaluate their safety and exposure potential. There have been recent position statements and frameworks developed for conducting safety and risk assessments of nanomaterials and it is likely that certain components and aspects of the safety assessment process will need to be modified to account for the differences of nanomaterials from “conventional” chemicals and/or particles. In particular, modifications to existing toxicological study protocols may be necessary to include rigorous physicochemical characterization and to account for potential changes in dosimetrics and toxicokinetics. Because of the diversity of the target populations and the consumer products that may contain nanomaterials, carefully designed toxicological studies and exposure assessments with appropriate defaults will be needed for conducting robust risk assessments and to ensure safety of consumer products containing engineered nanomaterials.
Identifying and Complying with Nanotechnology Workplace Safety Requirements
As more companies incorporate aspects of nanotechnology in manufacturing
and operational capacities, a more detailed consideration of potential
workplace exposures is advisable. Such potential exposures can
trigger workplace safety compliance issues. The presenter analyzes workplace
exposure risks associated with nanotechnology; discusses and evaluates
the effectiveness of current workplace safety regulations, engineering
controls, administrative controls and workplace safety equipment as they
relate to nanotechnology and nanomaterials. Further, the opportunity
for companies to utilize the ASTM International “Standard Guide for Handling
Unbound Engineered Nanoscale Particles in Occupational Settings” as a
means for minimizing the risks that nanomaterials may pose to workplace
environments is discussed.
A Nano-Selenium Reactive Barrier Technology for Controlling Mercury
Mercury vapor exposures occur following spills or the accidental breakage of devices that include thermometers, barometers, gas meters, and fluorescent lamps. As part of a recent study of mercury vapor emission from compact fluorescent lamps, a panel of 28 new nanosorbents and commercial reference sorbents were evaluated for their ability to sequester and stabilize Hg-vapor under conditions (release time, temperature and Hg-concentration) relevant to lamp breakage. The presentation describes a detailed study of the most promising sorbent from that panel, uncoated amorphous nano-selenium, and its formulation into reactive barriers designed to prevent human exposure to mercury vapor.
New data is presented on the properties and size distributions of nano-selenium, and on economic routes for large-scale synthesis. Nano-selenium is shown to have a complex phase behavior that can lead to aging phenomena under the influence of water vapor. Based on the detailed materials properties, impregnated reactive-barriers were designed as practical engineered solutions for important exposure scenarios that include (i) remediation of sites where fluorescent lamps or spills occur on porous substrates such as carpets, and (ii) bags or boxes for retail, shipping, collection, and recycling of multiple lamps or other Hg-containing devices. Data on the landfill stability (TCLP) on nano-selenium and its reaction products will be presented, and material safety issues discussed. At this stage, prototypes have been developed and tested, and the prospects for commercialization of this environmental nanotechnology are discussed.
Financial support from the NIEHS Superfund Basic Research Program is acknowledged.
Synergistic nanomaterial features that influence oxidative stress and inflammatory response
Nanotechnology is not only an emerging field of study, it is now an industry. Because of this, we now see an abundance of nanomaterials in numerous medicinal applications and consumer goods.
Nanotechnology: Risk Perception Versus Developing Science
Two recent articles offer a vexing point and counterpoint: one calls
for more regulations due to the potential for nanoscale silver to poison
wastewater treatment plants; the other urges no new regulatory controls
based on quantitative modeling of the possible distribution of nano silver
in the environment, which concludes that it presents no significant ecological
Such contradictory conclusions regarding the potential risks of nanotechnology
can confuse even the technically-trained. But to the highly impressionable
general public, the impression left by dramatic headlines will affect
the market for nanotechnology-based products and likely inspire additional
environmental regulatory controls for years to come.
Nano-Enabled Pesticides, Chemistry, Environmental Fate and Transport
Risk Assessments: Regulatory and Scientific
The Office of Pesticides Programs (OPP) is EPA’s one of the largest Programs. It requires scientific data submissions, reviews the data, conducts the risk assessment for the environment, health and safety of the chemical, registers it and acts as a watch dog for compliance when these pesticides enter in to commerce. This is mandated by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and its amendment of Food Quality Protection Act (FQPA), which demands the determination of safety for children and infants. As part of its mission, OPP conducts risk assessments for three classes of pesticides: agricultural, antimicrobials and biopesticides.
Overall risk assessment of any pesticide includes determination of likely hazard to mammals, animal and terrestrial and aquatic organisms and possible exposure to the pesticide from various environmental media like water and soils. Some major disciplines of science that act as tools to conduct risk assessment are: Mammalian toxicology; eco effects on the terrestrial (like plants, insects) and aquatic organisms (fish); environmental fate and transport of a pesticide environmental media like water, soils, sediments, and air; workers and post-applicator exposures to humans and pesticide residues from food (fruits, vegetables).
In the last few years a number of manufactured nanomaterials (MNs) have entered into consumer market like cosmetics, plastic food wraps etc. This is mostly due to lack of appropriate regulations for new and unique chemicals or loop holes in the existing regulations This presenter will discuss the regulatory and scientific issues likely associated with the nano-enabled antimicrobials and will address the uncertainties in regard to chemistry and environmental and transport data requirements as well as risk assessments for MNs or nano-enabled pesticides.
Risk Analysis: State of the Science and Regulatory Implications for
The rapidly expanding development and use of materials in the nanoscale
range and technological advances at the nanoscale have generated new
challenges to the application of current risk analysis methods for environmental,
health, and safety concerns, and regulatory decision making. The unique
properties for some of these materials potentially have significant implications
for current approaches to the hazard identification, exposure assessment
and dose-response components of the traditional risk assessment paradigm
that informs risk management decisions, and may confound the accurate
assessment of potential risks as well as require changes to the way such
risks are communicated to stakeholders and managed by policymakers.
These issues were deliberated at a workshop, NanoRisk Analysis: Advancing the Science for Nanoscale Material Risk Management, that was held on September 10-11, 2008, in Washington, DC. More than 80 experts in risk analysis, nanotechnology researchers, environmental and health scientists, other key stakeholders and members of the public interested working in or responsible for risk analysis, risk communication, and nanotechnology gathered to identify approaches for risk analysis that assess the unique aspects of nanotechnology and nanomaterials. Five topical white papers were prepared in advance of the workshop, each co-authored by a combination of nanotechnology and risk experts, and were presented on topics of: hazard identification and uncertainty; toxicology; exposure assessment; risk characterization; and risk communication. These papers were vetted in plenary and facilitated deliberative discussion sessions and will be published, along with other ideas generated during the workshop, as a series of reference papers advancing the science of risk analysis for nanomaterials and nanotechnology. A panel discussion on data gaps and needs for sound decision making vetted views of representatives from international governmental authorities, industry, and non-governmental organizations.
Several themes emerged from the workshop. Several participants highlighted the need for adopting a life cycle approach to risk analysis for nanotechnologies. Repeatedly, presenters suggested that engineered nanomaterials may present unique attributes, but share challenges with other emerging environmental substances and technologies in terms of assessing their risks. Many stressed the need for proactive and effective communications about the risks of nanotechnology and nanomaterials, that must explain the complexity and not oversimplify the messaging, while also responding to people’s main concerns. Other workshop outcomes include forming new networks among multidisciplinary experts, junior and international researchers and international governmental, academic and industry leaders in risk analysis and nanotechnology.
Antimicrobial Bio-nanosilver Produced by Lactobacillus sp.
Microorganisms are associated with many problems such as persistent chronic infections, bio-corrosion and food contamination. As a result the worldwide demand for biocides to control microbial contaminations is increasing rapidly. Silver has a long history as an antimicrobial. As nanoparticles have different properties then bulk material, the interest to use nanosilver as a biocide is growing. Many chemical and physical methods exist to synthesize nanoparticles but recent years there is a demand for more eco-friendly production methods. We developed a biological mediated method using Lactobacillus sp. to produce silver nanoparticles. This method is non-enzymatic and allows the application of high pH which accelerates the reduction reaction of Ag(I) to Ag(0). The capacity of Lactobacillus sp. to reduce silver was compared with other lactic acid bacteria, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. Only the lactic acid bacteria were able to reduce silver and some Lactobacillus sp. reached efficiencies of more than 80%, as determined by AAS and XRD.
Transmission electron microscopy showed that the size of the nanosilver
precipitated on the cell wall ranged between 1 and 7 nm, while the nanosilver
inside the cells was significant larger (20-200 nm). The anti-microbial
action of bio-nanosilver was tested on Gram positive and negative bacteria,
yeast, and fungi. Compared with ionic silver, similar Minimal Inhibition
Concentrations were obtained. The antiviral properties of bio-nanosilver
were determined as well using bacteriophages as a model for viruses in
water. Bio-nanosilver removed all viruses in less than two hours. In
conclusion, this method using Lactobacillus sp. allows the eco-friendly
production of silver nanoparticles with a highly antimicrobial efficiency
against a broad range of microorganisms.
Influence of Surface Chemistry on the Deposition and Transport Properties
of Carbon Nanotubes
The environmental health and safety risks posed my nanomaterials will be intimately dependent upon their colloidal transport properties in porous media. In this presentation, I will describe how changes in the surface composition of multi-walled carbon nanotubes (MWCNTs) influence these transport properties and what measurable properties provide the best predictive metrics.
The surface of carbon nanotubes, one of the most widely used class of engineered nanomaterials, often contains oxygen-containing functional groups (surface oxides) as a result of either deliberate or incidental exposure to aggressive oxidizing conditions. Surface oxidized MWCNTs (O-MWCNTs) were prepared by treating the pristine nanomaterials with different oxidants (e.g. HNO3 and HNO3/H2SO4). Stable colloidal suspensions were subsequently prepared by sonicating the O-MWCNTs in milli-Q water. The transport properties of O-MWCNTs were then assessed using model columns, containing ~350 µm silica spheres. Step-input deposition profiles were collected for each O-MWCNT as a function of electrolyte (NaCl and CaCl2) concentration and pH. To limit the extent of O-MWCNT self aggregation during deposition experiments, input MWCNTs concentrations were < 500 ppb; the effluent concentration was monitored in real time with UV-VIS using a 5 cm flow-through cell.
Information gathered from deposition profiles was used to calculate critical deposition concentrations (CDC) for each O-MWCNT studied. The extent to which functional relationships could be developed between the CDC and various surface properties (e.g., surface composition, oxygen-functional group distribution, surface charge and electrophoretic mobility) will be discussed and compared with data gathered during our previous aggregation studies. Information from these transport studies will help to understand the environmental fate of surface oxidized CNTs discharged from waste facilities or manufacturing effluents. This data may also be used to generate robust predictive models capable of describing an idealized aquatic life cycle (manufacture, discharge, and interaction with other aquatic species) for MWCNTs as a function of their surface chemistry.
Discovery of Genes that Mediate Toxicity of Functionalized Gold Nano-Particles
Our long-term goal is to determine mechanisms by which manufactured
nanomaterials may cause cytotoxicity in realistic environments of exposure.
In order to assess potential toxicity and to establish mechanisms through
which one such material may elicit toxic responses, cell growth and survival
of the yeast Saccharomyces cerevisiae were determined in the presence
of functionalized gold nanoparticles.
Yeast growth, as assessed by cell yield after 48 hours in synthetic
medium, was unaffected by exposure to 100 micrograms/ml of functionalized
Au nanoparticles (Au-TMAT) comprised of an 11-atom core 0.8 nm in diameter
with 10 positively-charged functional groups. In contrast, yeast survival
in water over 24 hours was reduced by exposure to Au-TMAT concentrations
of less than 1 microgram/ml. A specific amount of these particles appeared
to kill a fixed number of cells rather than a fixed fraction of cells.
For example, 1 microgram killed about 100,000 cells regardless of the
number of cells exposed. In contrast, the same size gold particles
carrying either no charge or a negative charge exhibited no cytotoxicity
at the same concentrations.
In order to identify genes and mechanisms implicated in Au-TMAT-mediated killing, a yeast gene deletion library was screened in pools for resistant mutants. Six resistant clones were isolated from the initial screen of 2,500 mutants, which constitute about half of the library. Loss of GYL1, YMR155W, DDR48, and YGR207C was found to result in Au-TMAT resistance, suggesting that these genes play roles in mediating Au-TMAT toxicity. The wild type alleles are currently being cloned back into the respective deletion mutants to confirm that the mutants regain wild type sensitivity. Putative resistant isolates from the remainder of the library continue to be characterized.
Anti-Microbial Kinetics of Carbon Nanotubes
The current paradigm of nanoparticle toxicity maintains that oxidative stress via the production of reactive oxygen species (ROS) is responsible for their negative impacts. Carbon-based nanomaterials such as fullerenes, multi-walled carbon nanotubes (MWNTs), and single-walled carbon nanotubes (SWNTs) are reported to have anti-microbial properties. Initial results suggest membrane stress may be a greater anti-microbial factor than oxidative stress for carbon nanomaterials. Here, we use bacterial membrane depolarization kinetics, determined by time-dependent fluorescence of a membrane potential sensitive fluorophore, to investigate the anti-microbial mechanism of carbon nanotubes. Bacterial membranes are polarized due to a proton gradient across the membrane which induces the formation of a negative potential of ~ -100 mV. The potential can be disrupted by electron transfer from the bacteria to the nanomaterial or by physical perturbation of the membrane under high [K+]aq. The depolarization kinetics are measured as a function of bacterial surface structure, type/functionalization of carbon nanotubes, and oxidant concentration. Extent and rate of membrane depolarization are determined under the various conditions and carbon nanotube microbial toxicity mechanisms are discussed.
Mechanisms of Transport and Retention of Silica Nano Particles in Saturated Soils
Engineered (nano particles) and natural (bacteria) mobile colloids are suspected to be a threat for the environment. Mechanisms of transport, deposition and remobilization of colloids in natural porous media such as aquifers are complex and depend on many factors. These factors are flow velocity, nature of electrolyte, physical and chemical properties of porous grain and colloids. The complexity is still increased for bacteria because the deposition and the removal of these micro-organisms are still poorly known. In order to understand transport mechanisms of colloids in porous media and the link between these mechanisms and the microscopic properties of colloids, it is necessary to control a maximum of the dominant factors. In this study some silica nano particles are used as colloid tracers with controlled properties to determine the influence of two factors (size and concentration) on the transport and retention in porous media. Laboratory column experiments conducted with nanotracers are carried out. Both breakthrough curves and spatial distributions are studied.
Retention due to geometrical aspects, namely straining is highlighted establishing conditions unfavorable to attachment and using tracers with different sizes. Colloids are retained in the straining sites until these sites are filled and then are further transported. This phenomenon (blocking effect) has also been observed with two bacterial strains and is emphasized by changing input concentration of colloids. The volume of strained colloid is also assessed. A microscopic-scale study of the pore space geometry has been led to emphasize the link between the volume of straining sites and the pore size distribution.
Toxicity of Nanoparticulate and Bulk ZnO, Al2O3 and
TiO2 to the Nematode Caenorhabditis Elegans
Although the use of metal oxide nanoparticles (NPs) and their release to the aquatic and terrestrial environments are increasing, there is a remarkable lack of information on the environmental behavior and associated potential risk of metal oxide NPs. In this research, toxicity of nanoparticulate and bulk ZnO, Al2O3 and TiO2 was examined to the nematode Caenorhabditis elegans. The 24-h median lethal concentration (LC50) and sublethal endpoints (growth, number of eggs inside the worm body and number of offspring per worm) were assessed. Meanwhile, a comparative experiment with their bulk counterparts and free metal ions was also conducted, and concentration- and time-dependent aqueous solubility of nanoparticulate and bulk ZnO and Al2O3 were further investigated to elucidate if the toxicity was due to nanoparticles (NPs) per se or dissolved metal ions. The results demonstrated that: (1) both the three NPs and bulk particles exerted toxic effects on the nematode, inhibiting growth and especially the reproductive capability of the nematode; (2) the 24-h LC50 values for the ZnO NPs (2.2 mg L-1) and bulk ZnO (2.3 mg L-1) were not significantly different (p < 0.05); while there were significant differences between Al2O3 NPs (81.6 mg L-1) and bulk Al2O3 (152.9 mg L-1), and between TiO2 NPs (79.9 mg L-1) and bulk TiO2 (135.8 mg L-1) (p < 0.05), respectively; (3) oxide solubility was found to influence the toxicity of ZnO and Al2O3 NPs, but nanoparticle-dependent toxicity was indeed observed for the three investigated NPs.
Nanotechnology Regulation and the Precautionary Principle
U.S. government agencies are focusing most of the effort to regulate nanomaterials on the Toxic Substances Control Act, also known by its acronym TSCA. TSCA was one of the last major environmental laws to be passed in the U.S., and was intended to enable the U.S. Environmental Protection Agency to gather physical, health, safety and environmental data on commercial chemicals. Commercialization of nanomaterials has outpaced research into the human health and environmental effects that these novel materials may have. This leaves open the policy question of whether the U.S. should presume that new materials are safe or unsafe in the absence of thorough data, and whether precautions should be imposed until specific nanomaterials are proven to be safe.
The precautionary principle is one response to this dilemma. As classically stated it holds that “where there are threats of serious and irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.” This formulation, for example, appears in the 1999 Canadian Environmental Protection Act. The precautionary principle is an established part of the European Union’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) law, but is not incorporated into U.S. law and regulation.
There are mechanisms available under TSCA to require manufacturers to conduct new tests on nanomaterials before they are commercialized, but to date the US has not systematically implemented any of them. There are many circumstances in which new nanoscale substances will not undergo any regulatory review at all. The Environmental Protection Agency has issued a guidance document stating that, in general, the agency will require submissions of existing data before commercializing nanomaterials only if the “molecular identity” is new. Even if there is a new “molecular identity” the submitter does not have to develop any new test data during this process even though nanomaterials may present novel toxicology by virtue of their quantum properties.
Some industry members are voluntarily submitting toxicological data under the “Nanoscale Materials Stewardship Program” established under TSCA by the Environmental Protection Agency in 2008, but only three companies have agreed as of October 2008 to conduct new tests on nanoscale materials. Against this background, local governments, such as Berkeley, California, have stepped in with ordinances intended to implement the precautionary principle although there is no national policy consensus. Other local governments are considering following Berkeley’s lead.
Massachusetts Government Efforts on Nanotechnology and Other Emerging
A number of Massachusetts state agencies have created a roundtable for receiving internal and external input on issues of relevance to the developing nanotechnology sector in Massachusetts. The Departments of Environmental Protection (MassDEP) and Public Health (DPH), Division of Occupational Safety (DOS), Toxic Use Reduction Institute (TURI), and Offices of Technical Assistance (OTA) and Business Development (MOBD) participate to consider nanotechnology issues of concern to Massachusetts, each keeping in mind their agency’s mission. By looking at nanotechnology from multiple angles, the Interagency Nanotechnology Committee can consider a wide range of possible impacts related to the varying agency missions of: ensuring clean air and water and the safe management of toxics and hazards; promoting public health; protecting workers’ safety and health; researching, testing and promoting alternatives to toxic chemicals used in Massachusetts industries and communities; assisting implement effective toxics use reduction and other pollution prevention or resource conservation activities; and developing Massachusetts businesses. The agencies began meeting in a Massachusetts Interagency Nanotechnology Committee in April 2007, and first met with a group of External Advisors in September 2008. External Advisors represent universities, business, environmental groups, municipalities, consultants, and law firms. The Interagency Committee seeks opportunities to educate its members, the public, and stakeholders on issues related to nanotechnology, and in that spirit held an initial workshop, The Big Picture: Safe Development of Nanotechnology, on November 15, 2007. A further goal of the workshop was to identify potential hazards of the technology, as well as potential roadblocks to safe development, in order to work with the nanotechnology sector towards preventing unintended consequences. Follow-on workshops are to be informed by input solicited from previous attendees and External Advisors, and are intended to include topics of practical use to manufacturers, of general interest, and of specific interest to groups of stakeholders.
Quantitative Surface Characterization
of Oxidized Carbon Nanotubes
Quantitative characterization of a nanomaterial’s surface is crucially important if we are to better understand their environmental fate and impact. This is a direct consequence of the fact that all nanomaterials exhibit extremely high surface area to volume ratios compared to bulk materials, and as a result a large fraction of the atoms are at the introduction of oxygen-containing functional groups that occurs as a result of oxidation. CNTs are exposed to aggressive oxidizing conditions during purification procedures that use strong oxidizing acids (e.g. HNO3) to remove amorphous carbon and metal contaminants, by deliberate oxidative treatments used to functionalize the surface and improve the dispersion of CNTs in polar media, or by incidental exposure to oxidizing agents (e.g., O3 or OH·) after their release into the environment.
This presentation details how we have developed and implemented a suite of chemically specific reactions to quantify the distribution of oxygen containing function groups on the CNTs. Each reaction imparts a fluorinated chemical tag in stoiciometric amounts to either hydroxyl, carbonyl or carboxylic acid group on an oxidized CNT. X-ray Photoelectron Spectroscopy can then be employed to quantify the amount of fluorine present and thus the concentration of the targeted surface oxide. We also describe how we have employed this methodology to quantify the effect of different oxidants (e.g., HNO3, HNO3/H2SO4 and O3) and reaction conditions on the surface chemistry of CNTs as well as the influence that the structure of a carbon nanotube (e.g. diameter, single walled vs. multiwalled) play in regulating the effect of different oxidants. In addition, we give selected examples to highlight how this information can be used to develop detailed structure-property relationships that correlate surface chemistry with environmentally relevant properties of CNTs in aquatic environments (e.g., colloidal stability, sorption).
In Vitro Assessment of the Gastrointestinal Biodurability of Engineered Nanomaterials
Titanium Oxide Nanostructure Photocatalysts for Degradation of Organic
Organic chemicals not only occur as the major pollutants in wastewater effluent from industrial manufacturers and households, but also appear in ground water wells, surface water and river water. There is a strong incentive to get rid of organic pollutants due to an increasing environmental legislation. Photocatalysis by titanium oxides are finding an increasing application in removal of organic pollutants. In the present work, titanium oxide nanomaterials including nanoparticles and nanowires are synthesized by hydrothermal processing and further treated by secondary hydrothermal processing. The effects of the processing parameters on the morphology, crystal structure of titanium oxide nanostructures are studied. The relationship between the microstructure and the photocatalytic activity of titanium oxide nanomaterials is investigated. In addition, we have demonstrated that doping nitrogen into titanium oxide nanostructures has extended their absorption wavelength range to visible region, which has resulted in the visible light responsive photocatalysts. Our studies have implication in water pollutant control.
California’s Approach to Nanomaterials: Information Call-in from
The unique properties of nanomaterials enable novel applications in many fields, including electronics, sporting goods, medicine, coatings and other automotive uses, children’s items, cosmetics and others. However, because of their unique properties, nanomaterials also have the potential to adversely affect human health and the environment. The potential risks of nanomaterials are not well known, thus a comprehensive and systematic approach is necessary to understand those impacts.
As the first step to understanding nanomaterials risks, the California Environmental Protection Agency’s Department of Toxic Substances Control (DTSC) has begun to request information from manufacturers of carbon nanotubes (CNTs), pursuant to California law. DTSC is exercising its authority under California’s Health and Safety Code, Chapter 699, Sections 57018-57020. Under this authority, DTSC has begun the call-in of information regarding analytical test methods, fate and transport in the environment and other relevant information from manufacturers on carbon nanotubes. Carbon nanotubes are of interest to DTSC because they are currently used in many available commercial products, new applications are being developed almost daily, and because data on analytical methods, toxicity, physicochemical properties, or fate and transport are largely unavailable.
To begin to address this emerging issue, DTSC has identified manufacturers who produce or import carbon nanotubes in California and will coordinate with those and other manufacturers to develop an equitable and resource-efficient approach to filling key information gaps. To the extent practicable, DTSC will minimize the cost burden on individual manufacturers. It is contemplated that the list of companies involved will be expanded beyond those who only produce carbon nanotubes in their chemical form, to include manufacturers who incorporate carbon nanotubes into products or who import such products.
DTSC will collaborate with manufacturers throughout the process to identify
and prioritize information gaps, and develop strategies to address those
gaps. DTSC also intends to include carbon nanotubes manufacturers outside
California in these discussions. The first phase of the call-in is expected
to be carried out over the next year.
In-situ Immobilization of Mercury in Sediment by Stabilized
Iron Sulfide (FeS) Nanoparticles
An innovative in-situ mercury (Hg) immobilization technology using stabilized iron sulfide (FeS(s)) nanoparticles was investigated in this study through a series of batch and column experiments. The FeS(s) nanoparticles were prepared using a low-cost and food-grade cellulose (sodium carboxylmethyl cellulose, CMC) as the stabilizer. The particle size of freshly prepared FeS(s) nanoparticles was measured to be 38.5 nm with a standard deviation of 5.4 nm. Batch tests showed that the stabilized FeS(s) nanoparticles effectively immobilized Hg in the sediment. When the Hg-laden sediment was treated by stabilized FeS(s) nanoparticles with a FeS(s)/Hg molar ratio of 26.5, the Hg concentration leached out in the aqueous phase was reduced by 96.8 percent and the TCLP (toxicity characteristic leaching procedure) tests showed that the Hg leachability was reduced by 99.1 percent. Column tests proved that the stabilized FeS(s) nanoparticles reduced the mercury leachability of the Hg-laden sediment by as much as 66.7 percent and the extracted Hg in TCLP solutions was reduced by 76.9 percent when the sediments was treated with 0.5 g/L stabilized FeS(s) nanoparticles. Column tests also proved that stabilized FeS(s) nanoparticles were highly mobile in a clay loam sediment and ~100 percent of FeS(s) nanoparticles passed through the sediment with 18.4 PV (pore volume) of 0.5 g/L stabilized FeS(s) nanoparticles.
Toxicity of Carbon Nanotubes to the Activated Sludge Process: Protective
Ability of Extracellular Polymeric Substances
The discharge of carbon nanotubes (CNTs) from industrial waste or disposal of such materials from commercial and/or domestic use will inevitably occur with increasing production and enter into wastewater treatment facilities with unknown consequences. Therefore, a better knowledge of the toxicity of CNTs to biological processes in wastewater treatment will be critical. The present study examined the toxicity that multi-walled carbon nanotubes (MWCNTs) incur on the microbial communities present in activated sludge. A comparative study using the activated sludge respiration inhibition test was performed on both sheared mixed liquor and unsheared mixed liquor to demonstrate the potential toxicity posed by MWCNTs and to better understand the extent of extracellular polymeric substances (EPS) in protecting the microorganisms from the toxicity of CNTs. Greater respiration inhibition was observed for the sheared mixed liquor compared to the unsheared mixed liquor. The result suggests that EPS did appear to provide protection to the microbial communities in the activated sludge upon exposure to MWCNTs. The toxicity observed by the respiration inhibition test was determined to be dose-dependent; the highest concentration of MWCNTs exhibited the highest respiration inhibition. Scanning Electron Microscopy (SEM) images demonstrated direct physical contact between MWCNTs and bacteria/activated sludge flocs.
Quantum Dot Based Detection of BTEX
Sensor based detection of petroleum by-products with a high degree of sensitivity and selectivity remains a challenge for the cost efficient detection of hydrocarbons in soil and water samples. As quantum dot materials are intrinsically sensitive to their surroundings we have developed a research program aimed at harnessing and controlling this sensitivity through the tailored design of the quantum dot surface chemistry. CdSe semiconductor quantum dots (QDs) were synthesized with selected surface modifying agents to enhance their response towards the detection of aromatic hydrocarbons. The sensing characteristics of unmodified QDs using trioctyl phosphine oxide (TOPO) plus stearic acid (SA) surface groups were compared with QDs having additional benzoic (BA), pentafluorobenzoic acid (FBA) or naphthylamine (NA) surface modifying agents. Both QD types were encapsulated into poly(methyl methacrylate) (PMMA) thin films by drop coating QD-PMMA solutions onto silicon substrates. Reversible PL enhancement was observed at low target gas concentrations, with the onset of a reversible quenching process for each of the films being dependent on the target gas type and its concentration. Unmodified QD/PMMA films had detection limits for xylenes and toluene of 250 and 500 ppm, respectively. While detection limits of 15 ppm xylenes and 50 ppm toluene in a balance of nitrogen were achieved with the FBA and BA modified QD/PMMA films. A comparison of the sensitivity and selectivity of the QD-BA, FBA and NA films was made for 50 ppm toluene and 50 ppm xylenes in N2 exposures which revealed that the QD-FBA film had the best overall performance. Furthermore, by reducing the NA surface group coverage by a factor of 10 the detection limit of the QD-NA films was reduced by a factor of ~3. By depositing the QD materials on anodized aluminum oxide we have been able to surmount the quenching problem found with the QD/PMMA system and have achieved a dynamic range of BTEX detection from 10ppm to 9400ppm in the presence of an air carrier gas. A description of initial sensing array studies which utilize a cost effective optical approach is outlined and the development of next generation QD based hydrocarbon sensing materials is detailed.
Bioavailability and Biodistribution of
Functionalized Gold Nanoparticles Using Mass Spectrometry
Engineered nanomaterials from consumer products will inevitably be released into the environment during their manufacture, use and/or disposal. Studies on the environmental fate, behavior, transport, bioavailability, and toxicity of nanoparticles have appeared, but some of these studies draw conflicting conclusions, likely due to poor control over physical and chemical properties of the materials used in these studies. Moreover, existing reports have also been questioned due to inadequate measurement techniques. Here we employ functionalized gold nanoparticles (AuNPs) as nanoparticle models and develop a new laser desorption/ionization mass spectrometry (LDI-MS) approach to study bioavailability and biodistribution of nanoparticles in complex biological and environmental systems.
The AuNPs used in this study feature a 2 nm core and an alkanethiolate monolayer. End groups of monolayer can be designed with well-defined chemical (e.g. hydrophobic, hydrophilic) and/or physical (e.g. charge) properties, which will facilitate work to understand how these properties influence the fate and bioavailability of nanomaterials. The AuNP core very efficiently absorbs laser light (337 nm). Upon laser irradiation of these AuNPs, the laser energy that is absorbed by the AuNP core is readily transferred to desorb/ionize the surface monolayers. The mass of these monolayer molecules, i.e. “mass barcodes”, can be easily read out by LDI-MS, thus providing characteristic peaks for sensitive identification of the AuNPs. The advantage of such a LDI-MS approach is the ability to simultaneously analyze many different functionalized AuNPs from very complicated matrices.
First, we applied the new LDI-MS approach for multiplexed analysis of nanoparticle uptake by cells. Multiple AuNPs were simultaneously cultured with monkey kidney (COS-1) cells. AuNPs taken up by cells were collected by centrifuge from cell lysate, and then subjected to LDI-MS analysis. We demonstrate that the cellular uptake of the AuNPs with cationic or neutral monolayers can be simultaneously identified and quantified by measuring “mass barcodes” of each AuNP. Subtle changes to AuNP monolayers can lead to measurable changes in cellular uptake propensities. Neutral AuNPs are less readily taken up than cationic AuNPs. Among the cationic AuNPs, hydrophobicity is an important factor controlling cellular uptake. Furthermore, we have extended the LDI-MS approach to study biodistributions of AuNPs in a freshwater fish, Japanese medaka (Oryzias latipes). Fish are exposed to AuNPs that are added to water in which they swim. After a given exposure time, the fish are sacrificed and dissected. Organs such as the brain, gills, liver, gonads and muscles are collected, and analyzed for AuNPs. We also present the results from these studies.