Environmental Science: Nano Blog

Ceria nanoparticles, also known as nanoceria (cerium IV oxide, CeO₂) are quickly climbing the nanotechnology popularity ladder.  Ten years ago, there were hardly any academic publications using the term “nanoceria” and now there are dozens of publications per year on the subject. However, the consumer market still only has a couple of products that advertise to contain this nanomaterial.

So, could it be that we are finally getting ahead of the curve in attempting to understand environmental impacts of this nanomaterial before it becomes widely popular?

ES Nano recently published a special themed collection on this interesting nanomaterial, whose main property as a catalyst brings promise for a variety of applications. Two other Environmental Science: Nano blog posts have focused on the health effects of nanoceria and its biodistribution in rats.

Nanoceria is a powerful catalyst because its chemical structure shows an oxygen vacancy, so oxygen atoms can move around it while oxidizing and reducing molecules in its vicinity.

It absorbs reactive oxygen species (ROS), also known as free radicals, which brings a potential cosmetic and medical application. This material also absorbs UV radiation, so it might be used to replace titanium dioxide and zinc oxide in sunscreens in the future.

Since nanoceria has the potential to be a widely used in medical and cosmetic applications, it is pivotal to understand its behavior in biologically relevant environments. A recent paper by Sudipta Seal and colleagues discusses the environmental factors that can alter the properties of nanoceria and thus dictate its behavior in biological systems.

According to the authors, properties such as size, surface chemistry, surface stabilizers of nanoceria may affect its behavior in biological systems, but important issues remain to be addressed: Do slight variations in size and physico-chemical properties dictate fundamentally different behaviors? Are observed variations due to fundamentally different nanoparticles or did those particles undergo transformations? How should particles be appropriately prepared for relevant environmental and toxicology studies?

Although these general questions can be asked about a number of other nanomaterials, they are particularly relevant to nanoceria, since so little is known about this trending and promising material so far.

To access the full article, download a copy for free* by clicking the link below:
Behavior of nanoceria in biologically-relevant environments
Amit Kumar, Soumen Das, Prabhakaran Munusamy, William Self, Donald R. Baer, Dean C. Sayle and Sudipta Seal
Environ. Sci.: Nano, 2014, 1, 516-532
DOI: 10.1039/C4EN00052H

Did you like this article?
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You and I are not friends, for you are a fish and I am a clam. We are uneasy neighbours. The river water is your playground, the sediment – my sanctuary. If we were living in the Elk River in West Virginia, both of us would have been worried on January 9, 2014. Something changed in the water that day, as crude 4-methylcyclohexanemethanol (MCHM) poured into the river from a leaky storage tank. Would the MCHM have dissolved in the water or bound to sediment? Which of us would have been in more danger – the resident of the water or the denizen of the sediment?

But you are no fish and I am no clam. So, we could try to answer these questions by doing some batch experiments: Take some sediment sample in a bottle, add some water and MCHM, close the bottle tight and shake it for some time. Then measure the concentrations of MCHM and to figure out whether it loves the water or prefers the sediment. We could also run column experiments: Mix some MCHM in water, flow through a packed column and measure the concentrations at the column inlet and outlet to see how much of the MCHM attaches to the column and how much is still left in water at the outlet.

The information gleaned from these experiments regarding the relative concentrations in the sediment, the water or the packed column, are called fate descriptors. Researchers have calculated fate descriptors for thousands of chemicals to figure out whether they partition into the water or the sediment, or volatilize into the air. Fate descriptors help us predict who faces the greatest danger – the clam, the fish or the dragonfly hovering over the water.

Can we run these batch and column experiments to reliably predict the behaviour of nanoparticles in the environment? The concept of fate descriptors calculated from batch and column experiments was established for molecular chemicals.

But nanoparticles have distinctly different properties and do not behave as single molecules. The use of some previously established fate descriptors to predict the environmental fate and transport of nanoparticles has come under criticism.

In a recent perspective article, Dr. Geert Cornelis has discussed the challenges in developing environmentally relevant fate descriptors for nanoparticles. In the same vein, at the 3^rd Sustainable Nanotechnology Organization Conference, Dr. Mark Wiesner and Dr. Greg Lowry stressed on the need to develop functional assays that provide nano-specific fate descriptors.

Like the batch and column experiments, these functional assays need to be operationally simple and of relatively short duration. Indeed, as mentioned in in the perspective article, “[t]he most appropriate method is most likely a compromise between technical accuracy and operational simplicity…”.

You can read more about these challenges and potential solutions in the full article for free*:
“Fate descriptors for engineered nanoparticles: the good, the bad, and the ugly”
Geert Cornelis
Environ. Sci.: Nano, 2015, Advance Article
DOI: 10.1039/C4EN00122B

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About the webwriter

Paramjeet Pati is a PhD Candidate at the Virginia Tech Center for Sustainable Nanotechnology (@VTSuN).
You can find more articles by him in the VTSuN blog, where he writes using the name coffeemug.

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Multi-walled carbon nanotubes (MWCNT) are the preferred choice of nanotubes for many applications as they has a lower cost than the single walled carbon nanotubes (SWCNT). Therefore the chances of them getting into air, natural water systems and soil is extremely probable. Although many beneficial effects are postulated for MWCNTs direct applications such as incorporation into fertilizer to enhance water uptake, seed germination and cell growth can increase their levels in the environment, especially in soil. Since there is evidence of some negative affects on soil microbial communities as well as plants it is always better to have means of monitoring and controlling their levels in the environment. However, methods to detect and quantify MWCNTs in soil and sediments are still not well established. Therefore, Alexander Gogos and co-workers from the Agroscope, Institute for Sustainability Sciences in Switzerland have developed and evaluated a novel approach using asymmetric field flow fractionation (A4F) coupled with multi-angle light scattering (MALS) to differentiate MWCNTs in soil.

Here the high aspect ratios of MWCNT’s have been exploited to differentiate between MWCNTs, soot and native soil particles. The shape factors (ρ) for these materials were calculated by taking the ratio between the radius of gyration (rg) and the hydrodynamic radius (rh). Simply, the rg corresponds to the weighted average of all possible radii of a particle from its center of mass and rh is approximated for non-spherical particles as the radius of a sphere with same diffusion behavior. Elaborately, presence of MWCNTs in the mixtures resulted in increased ρ-values. The fractions of MWCNTs in the mixtures were calculated using the ρ-values obtained from A4F-MALS. They were cross-validated by comparing with the results obtained from automated electron microscopy analysis and were found to be in reasonable agreement. Since natural soils exhibited lower ρ-values consistently this method can be used in specific identification of MWCNTs as well as other high aspect ratio nanomaterials in soil.

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Capabilities of asymmetric flow field-flow fractionation coupled to multi-angle light scattering to detect carbon nanotubes in soot and soil.
Alexander Gogos, Ralf Kaegi, Renato Zenobi, Thomas D. Bucheli
DOI: 10.1039/C4EN00070F

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Nanoceria (nanoparticle form of CeO₂, cerium(IV) oxide) is quickly becoming a trending topic in Environmental Science. After recently discussing its health effects, today we present a fascinating paper regarding its biodistribution and retention in rats.

Currently, the main use for nanoceria is as an abrasive catalyst, especially important for the industry in silicon integrated circuit fabrication. In addition to that, and thanks to its autocatalytic behaviour, encouraging results have been presented in the past regarding its use as an antineoplastic agent. Nevertheless, there is concern on the topic of its toxicity in organisms.

Dr Robert A. Yokel and colleagues from the University of Kentucky have conducted an extensive investigation on the distribution and retention of several nanocerias after their systemic administration to rats.

The aim of their study was to determine if and how the biodistribution and persistence of nanocerias are modified according to the doses administered.

Additionally, interesting discussions regarding nanoceria shape and its influence on its toxicity, retention and disposition have been presented.

Moving forward, it will be exceptionally exciting to learn more about nanoceria’s clinical properties and effects on animals. In any case, this work is a big step forward in its research, helping us to clarify and consolidate our knowledge of the behaviour of nanocerias in mammalian organisms.

To access the full article, download a copy for free* by clicking the link below:

Nanoceria biodistribution and retention in the rat after its intravenous administration are not greatly influenced by dosing schedule, dose, or particle shape
Robert A. Yokel, Jason M. Unrine, Peng Wu, Binghui Wang and Eric A. Grulke
Environ. Sci.: Nano, 2014, Advance Article
DOI: 10.1039/C4EN00035H

The paper mentioned today is part of our Nanoceria Research themed collection, which is the most comprehensive and current source of information on the chemistry, biology, and beneficial and untoward effects of nanocerias.

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Nanomaterials have shown such great potential to advance science and engineering that sometimes research on their applications can skip ahead of safety tests.

Nanoceria, a commonly used nanomaterial, is one such substance. These fine grains of cerium oxide have been proposed for use in fuels, sunscreens, and even pharmaceutical treatments, but the effects of long-term exposure have not been comprehensively investigated. Now, in a critical review published in Environmental Science: Nano’s themed issue, a team of pharmacists and environmental chemists have compiled and analyzed the available research on nanoceria’s health effects.

Nanoceria appears to have minimal effects when applied to the skin, and is not absorbed into the body through the digestive tract. However, once it makes its way into the bloodstream, whether through inhalation or direct injection, it can travel throughout the body.

Nanoceria is biopersistent, meaning that it does not dissolve or break down in the body, but instead builds up. When it finds its way into certain organs—such as the lungs or the liver—it can take months to completely leave, and can lead to inflammation and abnormal tissue growth. As with many hazardous materials, the risks are greater with higher doses or longer-term exposure.

The researchers propose that nanoceria’s toxic effects occur through inducing oxidative stress, an imbalance between oxidizing molecules and antioxidants that can disrupt biochemical pathways in the body. Because the surface properties of nanomaterials are believed to have the greatest influence on their potential toxicity, the authors suggest that coating the particles with a biologically inert material or altering their surface structure could reduce their impacts.

Nanoceria should not be indiscriminately avoided based on these findings—and some research has found positive biological applications for the substance, and even essential chemicals like water can be toxic in high enough doses. Rather, scientists working with these particles should understand their potential risks and work to minimize them.

To access the full article, download a copy for free* by clicking the link below.

The yin: an adverse health perspective of nanoceria: uptake, distribution, accumulation, and mechanisms of its toxicity
DOI: 10.1039/c4en00039k
R. Yokel et al.

Liked this blog? Find out more about Laurel in her first Environmental Science: Nano blog on rare earth elements.

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You may have heard of a material called asbestos. Asbestos was used as a construction material in the 19^th and 20^th centuries until it became the pivot of a widely-spread health concern in the 1980s and 1990s. The fibers’ long aspect ratio and crystalline makeup can cause serious respiratory illnesses, including lung cancer. This health hazard drove a ban on asbestos products.

Carbon nanotubes (CNTs) also have a high aspect ratio—they are very long and thin, and their atoms are also very neatly arranged in a crystal structure. So it is fair to assume that, if inhaled, CNTs may deposit on the respiratory system and cause a health risk similar to that of asbestos.

Currently there are multiple research efforts aiming at understanding the potential inhalation toxicity of CNTs. One complicated issue of this type of research is being able to discern the toxic effect caused by the CNT and the metal catalysts that are usually present. These metal catalysis are used to help synthesize CNTs and left at the tips of the tubes. The recently published work of Cerasela Zoica Dinu and colleagues examines the toxicity of CNTs that had been stripped clean of their metal catalysts.

Another very complicating factor of examining the inhalation toxicity to nanomaterials in general—but especially fibers—is  exposing lung cell cultures to nanomaterials in the same way that our lung cells would be exposed to these very nanomaterials, in air. While this work didn’t use the air route to expose the lung cells to CNTs, they were able to find interesting results. Their research takes us one step closer to understanding how CNTs interact with human cells, cause changes in multiple cellular processes to result in various degrees of toxicity.

To access the full article, download a copy for free* by clicking the link below.

Towards Elucidating the Effects of Purified MWCNTs on Human Lung Epithelial cells
DOI: 10.1039/C4EN00102H
Chenbo Dong et al.

Liked this blog? Find out more about Marina in her first Environmental Science Nano blog on carbon nanotubes.

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Groundwater contamination is becoming a bigger problem than in the past as a result of ever increasing industries and agricultural practices. Furthermore, a significant percentage of drinking water supply relies on clean ground water such that its efficient and effective remediation is a timely need. Specifically chlorinated solvents and nitroaromatic compounds are oxidized organics, which are frequently found as persistent contaminants in groundwater. As a result of their stability in oxic environments these contaminants can act as transporters to a variety of other pollutants between soil and ground waters phases in addition to endangering humans and wildlife.

The oxidized functional groups in these contaminants can be reduced by Fe(II) associated with iron minerals thus providing means for their degradation that can be incorporated into engineered remediation schemes. Ferrihydrite, goethite, magnetite, hematite and lepidocrocite are examples of some ubiquitous iron containing minerals. In these degradation reactions the number of reactive sites on the minerals are directly related to the specific surface area and thereforethe nanoparticles of these minerals, which inherently has large surface areas hold the greatest potential towards degrading these contaminants. Nevertheless, nanoparticles are highly susceptible to aggregation, which can significantly hinder the efficiency of the reduction process. Therefore, Amanda M. Stemig and co-workers from the University of Minnesota, have conducted an extensive investigation using 4-Chloronitrobenzene (4-ClNB) as a model compound to elucidate the link between the aggregation state of iron oxide nanoparticles and their reactivity.

The study was conducted by using well-characterized goethite nanoparticles  as the iron containing minerals. The results revealed that the size of the goethite nanoparticles are significantly reduced upon the adsorption of transition metals. This is, of course no surprise as the adsorption of transition metals introduces additional surface charge. Furthermore, a comparison between the pseudo first order rate constants of 4-ClNB degradation in a variety of buffers indicated that the buffer type affected the reaction kinetics by controlling the aggregation state and thereby changing the available surface area. It was clearly demonstrated that zwitterionic buffers with spatial charge separations are better at preventing aggregation, giving better degradation rates. In addition buffer concentration also affected the degradation kinetics as higher buffer concentrations resulted in more densely packed aggregates with lowered surface area.

To access the full article, download a copy for free* by clicking the link below.

Goethite nanoparticle aggregation: effects of buffers, metal ions, and 4-chloronitrobenzene reduction

Amanda M. Stemig, Tram Anh Do, Virany M. Yuwono, William A. Arnold and R. Lee Penn

DOI: 10.1039/c3en00063j

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Nanotechnology may be a relatively new field of research, but nanosized materials have been present naturally in our environment since long before scientists started engineering them in the lab. As synthetic nanoparticles find their way into a greater variety of consumer items, however, public concern about their potential health effects has increased. Researchers trying to monitor the spread of engineered nanomaterials now face a challenge: how to distinguish their creations from the background nanomaterials already present in the environment.

A new paper recently published in Environmental Science: Nano, addresses this concern by using rare earth elements (REEs) to label synthetic nanoparticles and trace their path through the environment.

So-called REEs are actually fairly abundant in the earth’s crust, but are typically widely dispersed and are largely absent from background nanomaterials. In this paper, researchers at the University of Zaragoza, Spain, tagged titanium dioxide (TiO₂) nanoparticles with two different REEs: lanthanum (La) and cerium (Ce). REEs were added to the nanoparticles during the synthesis stage so that they would be integrated into the particles’ structure. The incorporation of REEs induced a slight color shift, but did not cause significant structural changes—the labeled nanoparticles looked and behaved much like the non-labeled ones, though small differences in surface area and particle sized were observed at higher concentrations of REEs. However, because REEs are present in in the background in such low concentrations, the labeling technique is very sensitive—only a small amount of the element must be added in order for a signal to be picked up.

Then, the researchers tested whether their labeled nanoparticles were detectable in the environment. To simulate the type of contamination that might result from basic handling, they poured the nanoparticles between two beakers, a common laboratory procedure that has the potential to release particles into the air and deposit them onto the surrounding work surface.

They analyzed their work surface by systematically wiping the testing area and dissolving the wipe along with any particulate matter that it had picked up. Using optical spectrometry, they were able to quantify the amount of nanoparticle

s found near their beakers. The simple transfer procedure had spread nanoparticles across their work surface—a hint that failing to clean up the workspace between experiments could confound future results through cross-contamination!

Although this study found that even simple laboratory techniques can introduce nanoparticle contamination into the environment, it did not assess the potential health effects of these particles. Rather, the labeling technique described here provides an easy and sensitive method to trace engineered nanomaterials in the environment that will facilitate future studies attempting to answer this question.

To access the full article, download a copy for free* by clicking the link below.

Identification of TiO₂ nanoparticles using La and Ce as labels: application to the evaluation of surface contamination during the handling of nanosized matter.
DOI: 10.1039/c4en00060a
V. Gomez et al

About the webwriter

Laurel Hamers is a recent graduate of Williams College and an aspiring science journalist. She has written for the Marine Biological Laboratory, Inside Science News Service, and the Materials Research Society. You can find her on her blog (sciencescope.wordpress.com) or on Twitter (@arboreal_laurel.)

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Silver nanoparticles (AgNPs) are becoming increasingly popular due to their antimicrobial properties. In fact, silver compounds have been used to treat or prevent infections since before penicillin was ever discovered. The ability of AgNPs to kill microorganisms brings great potential for treating drinking water in situations when traditional water treatment is not possible.

Roughly 10% of the world’s population does not have access to safe, clean drinking water because basic sanitation is lacking. In some cases, a point-of-use (aka in-your-home) water treatment method that is easy and affordable might make a great difference in preventing or reducing the incidence of diseases caused by water-borne microbes, such as cholera and poliomyelitis. A water filter that is embedded with a small amount of AgNPs is a great example of a point-of-use treatment method that can be easily distributed to homes in developing countries and used with minimal training.

In this paper, T. Dankovich, from the University of Virginia, presents us an elegant method for creating paper filters that are embedded with silver nanoparticles. Her method can be considered more environmentally friendly than usual silver nanoparticle synthesis techniques because the reducing agent is glucose (that’s right, sugar!) and the heating technique involved nothing more than a domestic microwave oven (that’s right, a kitchen microwave!). In this technique, silver nanoparticles were synthesized directly on the paper filters, as opposed to being synthesized in a liquid suspension and then applied onto the filter. This method avoids the potential pitfall of nanoparticle aggregation during application onto the filter.

The paper filters were successful treating water containing two different types of bacteria (E. coli, and E. faecalis). Moving forward, it will be interesting to know the efficiency of this type of filter in treating real surface water samples and the filtering capacity, or how many liters of water each filter is capable of treating before it needs to be replaced.

To access the full article, download a copy for free* by clicking the link below.

Microwave-assisted incorporation of silver nanoparticles in paper for point-of-use water purification
DOI: 10.1039/c4en00067f
Theresa A. Dankovich

Liked this blog? Find out more about Marina in her first Environmental Science Nano blog on carbon nanotubes.

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Nanocellulose (NC) provides a readily available and biodegradable substrate that can act as a novel template or carrier for a range of different nanomaterials (NMs) including carbonaceous, mineral and metal particles. NC is an ideal platform for inorganic NMs due to its high specific surface area, highly porous structure and high mechanical strength. The resulting NC combines the characteristics of both constituents therefore displaying synergistic properties useful for a variety of uses.

Peter Vikesland and colleagues from Virginia Tech and Duke University, USA provide a tutorial review discussing recent advances in the preparation of NC-based nanocomposites and their potential uses in addressing current and future environmental challenges. This is the first review of its kind to discuss the use of these novel nanocomposites in the context of environmental sciences and engineering applications.

You can download the full review for free* on our publishing platform

The authors describe:

• different forms in which NC is produced,
• how the NC can be derived both from plant materials and bacterial processes,
• how NC can be modified into a number of useful forms.

Furthermore, in-depth discussion of the different methods used in the preparation of NC and different types of composites is provided. This includes a discussion of how the guest NM can be incorporated in/on to the NC structure, guidance regarding the challenges faced in these processes and how researchers have address these problems, and instructions on the best available methods currently known for these procedures.

The review also details the uses of NC-based nanocomposities in key environmental science/engineering applications and summarises the practical considerations and advantages these provide over more conventional NMs. This focuses on four principal areas:

1) The better incorporation of antimicrobial materials such as Ag NMs into NC-based filters for air and drinking water purification.

2) The use of NC as a support for photocatalysts and metal catalysts used in the degradation of organic pollutants in water remediation.

3) The use of Au NP/NC biosensors for monitoring of water-borne pathogens and organic contaminants.

4) The use of NC-based nanocomposites in the design of superior energy conversion devices such as fuel cells, solar cells and Li-ion battery manufacturing.

Finally, potential directions of further research in the field of NC nanocomposites are highlighted. Specifically, researching methods to better control the size and distribution of NMs on or within the NC substrate, investigating how the loading of NMs influence the potential applications, and ways to prolong the lifetime and/or regenerate NMs to ensure their sustainability.

Cellulose is an abundant, cheap and renewable resource. Nanocellulose is shown to form useful nanocomposites with inorganic nanomaterials, which display valuable optical, catalytic, electrical properties. This review provides guidance to researchers in the field of environmental sciences and engineering on the production and uses for this type of nanocomposites to address current and emerging environmental challenges.

Environmental science and engineering applications of nanocellulose-based nanocomposites
Haoran Wei, Katia Rodriguez, Scott Renneckar and Peter J. Vikesland
Environ. Sci.: Nano, 2014,1, 302
DOI: 10.1039/c4en00059e

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