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

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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.

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

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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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.

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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.

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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

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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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