Environmental Science: Nano Blog

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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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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