Environmental Science: Nano Blog

Alumina (Al₂O₃) nanofibers have potential applications as catalyst support structures, reaction substrates, filtrations devices and sensors as a result of their high thermal stability. On the other hand, the fibrous nature of these materials calls for extra caution because of their potency to cause pulmonary diseases.

Fiber respirability and durability are among the dominant factors contributing towards the potential toxicity. The aerodynamic diameter controls the respirability while dissolution is related to the durability. A fiber is considered bio-durable if the rate at which it dissolves via chemical dissolution is slower than the rate of physical removal by the lung by mechanical action.

Therefore, Hyeon Ung Shin, Aleksandr B. Stefaniak, Nenad Stojilovic and George G. Chase from University of Akron, National Institute for Occupational Safety and Health and University of Wisconsin Oshkosh has investigated the dissolution of electrospun Al₂O₃ nanofibers in human artificial lung fluid and free radical generation to determine the influence of physicochemical properties.

These fibers were prepared using different thermal treatments and were characterized extensively for size, surface morphology, crystal structure and surface area. Then dissolution was measured by incubating the fibers in serum ultrafiltrate and phagolysosomal simulant fluid and analyzing the supernatant using ICP-OES at different time intervals. Dissolution rates were calculated assuming constant dissolution velocity:

Where (1-M/M_o) is the mass fraction of material dissolved, t is the time (days), SSA is the specific surface area (cm²g^-1) and k is the chemical dissolution rate constant. The free radical generation was probed using electron spin resonance spectroscopy (ESR).

The study has shown no effect of physicochemical properties on the Al₂O₃ dissolution in artificial human lung fluid indicating the differences in the heat treatments does not affect the solubility within lungs. However, greater dissolution rates were observed for the samples with higher heating ramp rates even though their physicochemical properties were similar. No measurable levels of free radicals were generated by these alumina nanofibers.

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

Comparative dissolution of electrospun Al₂O₃ nanofibres in artificial human lung fluids
Hyeon Ung Shin, Aleksandr B. Stefaniak, Nenad Stojilovic and George G. Chase
Environ. Sci: Nano, 2015, 2, 251-261
DOI: 10.1039/C5EN00033E

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free until the 06/10/2015 through a registered RSC account

Summer is almost over and so is a whirlwind of environmental engineering- and nanotechnology-related conferences. At a previous environmental nanotechnology-related conference, I had the great experience to participate in a lively debate on a very fundamental, albeit not often asked question in our field: is nanotechnology novel?

At first, one may think this question should not even be open for debate, since the very idea of nanotechnology evokes exciting futuristic thoughts about the future of medicine, solar energy, nanorobots, and even science fiction.

In this recently published paper, Hochella, Spencer, and Jones present an overview of this unexpected debate. Jones moderated a discussion in which Hochella and Spencer, two experts in their respective fields of nanogeoscience and electrical engineering/material science, brought their arguments for and against the following statement:

“The magic of nanomaterials is not new: nature has been playing these tricks for billions of years.”

In my view, nature’s nanostructures can be informative of how the environment responds to nanomaterials and their study is instrumental for informing environmental nanoscience and technology. However, the potential existence of natural analogues to engineered nanostructures is no evidence that there is reduced likelihood of adverse environmental effects, since after all, with the exception of a few synthetic compounds (e.g., CFC), most environmental pollutants exist in nature. We just happen to place them where they don’t belong (e.g., lead in the atmosphere).

The untended meadow of nature’s nanostructures and the
English-style garden of engineered nanomaterials

This work takes you around the universe and back to demonstrate the importance of determining whether naturally-occurring nanomaterials are representative of the novel and well-controlled structures engineered by man.

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

Nanotechnology: nature’s gift or scientists’ brainchild?
Michael F. Hochella, Jr., Michael G. Spencer and Kimberly L. Jones
Environ. Sci.: Nano, 2015, 2, 114-119
DOI: 10.1039/C4EN00145A

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About the webwriter

Marina Vance is a PhD research scientist at Virginia Tech and Associate Director of @VTSuN. She is interested in air quality, nanotechnology and health. You can find more information about her in mevance.com.

Graphene oxide (GO) is a precursor material in the preparation of graphene. Despite its name, on the surface of this material there are different types of functional groups including epoxy, hydroxyl and carbonyl groups. As a result, GO is hydrophilic and easily dispersed in water. This has led to a variety of investigations relating to GO as a potential pollutant, as well as a possible treatment to cancer.

The disrupted π-bond structure in GO enables the absorption of significant amounts of light from solar radiation. Therefore, environmental processing of GO can be expected to include photochemical processes. One important outcome of such processing is the generation of reactive oxygen species (ROS). These ROS can include singlet oxygen (¹O₂), superoxide anions (O₂^.–) and hydroxyl radicals (^.OH). Generation of ROS has a significant impact on ecological risks associated with GO and is critical in understanding the transformation pathways of carbon in the GO structure.

Therefore, Yingcan Zhao and Chad T. Jafvert at Purdue University (West Lafayette, USA) has investigated the ability of aqueous dispersions of single layered GO to generate ROS upon exposure to light within the solar spectrum (λ=300-410 nm). The generated ROS was detected using specific chemical probes, UV-vis spectroscopy and Raman spectroscopy.

The findings of this research highlighted that upon exposure to solar radiation there is electron transfer reactions occurring from GO to dissolved O₂, forming O₂^.– and significant quantities of H₂O₂.

Given the fact that these are reduction reactions, this resulted in an overall oxidation of GO. Some of the generated ROS reacted directly with the GO surface and therefore, the oxidation of GO was found to be non-stoichiometric.

The exposure to light also increased the chromophores content or the absorptivity of existing chromophores, as suggested by the increased darker colour of the GO suspensions. However, Raman spectroscopic analysis also indicated an increase in non-aromatic defects.

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

Environmental photochemistry of single layered graphene oxide in water
Yingcan Zhao and   Chad T. Jafvert
Environ. Sci.: Nano, 2015, 2, 136-142
DOI: 10.1039/C4EN00209a

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free until the 21/06/2015 through a registered RSC account

Halloysite nanotubes (HNT) are products of nature. In chemical composition they are similar to kaolin and can be considered as rolled kaolin sheets with inner diameter of 10-20 nm, outer diameter of 40-70 nm and a length of 500-1500 nm. The internal side of halloysite is composed of Al₂O₃ while the external is mainly SiO₂.

These clay tubes are excavated from mines as stone minerals and processed by milling to form fine power of tubes, which is then used to dope a variety of polymers. The polymer doping has been observed to enhance various properties of these polymers including strength, adhesivity and flame retardancy. In addition, the large surface area and oppositely charged inner and out diameter facilitate loading a variety of biomolecules useful in medical applications. Given this wide range of applications there is an inevitable release of these materials back to the environment in this refined forms.

Despite the many reports on in vitro toxicity of HNTs, there is only limited information available with regard to its in vivo toxicity. Therefore, to shed light on this matter., Professor Fakhrullin and colleagues at Kazan Federal University investigated for the first time the in vivo toxicity of HNT using Caenorhabditis elegans nematode as a model organism. The C. elegans are an important tool in molecular biology because its fully sequenced genome is closely homologous to the human genome.

The findings of this research has shown that the primary pathway of the HNT entry into the organism is the intestinal uptake. The toxic effects of HNT uptake was then investigated by comparing the body size, fertility (or the number of eggs laid in other words) and longevity of the nematodes.

These comparisons did not give statistically significant differences between the controls, which suggests that these are potentially environmentally safe materials to work with. This is in fact is in contrast to the toxicities observed with other nanomaterials such as single walled carbon nanotubes (SWCNTS), graphene oxides, TiO₂ nanoparticles and platinum nanoparticles.

Even coating the nematode eggs with the HNT did not result in any significant deviations from the control nematodes. At extremely high doses of HNT did inflict some mechanical stress on the alimentary systems but these levels are highly unlikely to be encountered under environmentally relevant conditions.

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

Toxicity of halloysite clay nanotubes in vivo: A Caenorhabditis elegans study
Gölnur I. Fakhrullina, Farida S. Akhatova, Yuri M. Lvov and Rawil F. Fakhrullin
Environ. Sci.: Nano, 2015, 2, 54-59
DOI: 10.1039/C4EN00135D

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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*Access is free through a registered RSC account.

People in modern societies produce a lot of waste. I propose that you think about it next time you buy something. How much of it is comprised of packaging? How much of that packaging is recyclable? How much of it will become waste after a short while?

With the fast advancement of nanotechnological applications to enhance consumer products, we can expect nanomaterials to become ubiquitous in our domestic waste. So what happens when we burn nanotechnology-enhanced waste (or nanowaste)? Unlike that great Jerry Lee Lewis song that everybody knows, the answer to this question is a little bit more complex.

Most modern incinerator facilities are equipped to minimize the emission of air pollutants from the incineration process, especially particulate matter (also known as fly ash).

But what if some nanomaterials lead to the production of different pollutants during the incineration process? As we know from this blog, nanomaterials are multi-talented. Some have the ability to catalyze reactions, which can lead to the production of potentially toxic combustion by-products.

There are many locations around the world that perform open burning to dispose of waste. Therefore, it is possible that air pollutants generated may be slightly different if the waste contains nanomaterials.

In their most recent work—and ES Nano cover article—Vejerano and colleagues evaluated the toxic response of fly ash from waste that contained a wide variety of nanomaterials, such as nanosilver, titania, ceria, fullerenes, quantum dots, and more.

They found that waste that contained nanosilver, titania, and C₆₀ fullerenes led to a toxic response in human lung epithelial cells, which is signalled by an increase in the production of reactive oxygen species (ROS). But, in addition to that, this study also shows that the presence of nanomaterials in waste is not expected to significantly alter the environmental and health risk of the fly ash emitted from combustion processes.

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

Toxicity of particulate matter from incineration of nanowaste
Eric P. Vejerano, Yanjun Ma, Amara L. Holder, Amy Pruden, Subbiah Elankumaran and Linsey C. Marr
Environ. Sci.: Nano, 2014, 2, 143-154
DOI: 10.1039/C4EN00182F

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About the webwriter

Marina is a PhD research scientist at Virginia Tech and Assoc. Director of @VTSuN. She is interested in air quality, nanotechnology and health. You can find more information about her in her website mevance.com.

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Everyone loves and hates nanoparticle aggregation. Why? Because it is a fascinating phenomenon but it complicates all of our experiments, ranging from in vitro / in vivo studies, all the way to the environmental models. For ease of study, it can be broken down into homoaggregation and heteroaggregation. Investigating the former is relatively easier than the latter (relatively!), but in the real world we are forced to deal with the latter. Simply, heteroaggregation in the environment refers to attachment of ENPs to naturally occurring solids (e.g. soil particles, suspended sediments). This plays a key role in determining ENPs bioavailability and mobility in the environment.

Large-scale fate and transport models have been adapted for modelling of ENPs. Earlier models use mass balance as a framework with partition coefficients (K_d) to describe the soil-water distribution of ENPs, but recent studies argue that particle number-based kinetic models using attachment efficiency (α) are better at this, given that colloidal suspensions never reach an equilibrium state as well as ignore the size dependent properties. Yet no agreement has been established on the best way to treat heteroaggregation in these models.

Therefore, to shed light on this matter, Amy L. Dale (Engineering and Public Policy, Carnegie Mellon University, PA), Gregory V. Lowry (Civil and Environmental Engineering, Carnegie Mellon University, PA), and Elizabeth A. Casman (CEINT, Duke University, NC) discuss in detail the ongoing practical challenges in model formulation, parameterization, and calibration for ENPs in their perspective.

A couple of highlights in this article are:

– Particle balance models are more complex, making it challenging to parameterize ENPs in the environment. Therefore, many assumptions are needed that have been discussed in detail in the perspective.

– Attachment efficiency is agreed to be the most appropriate fate descriptor for small-scale models, but at large-scale these models it is claimed to be relative insensitive to the particulate nature of ENPs.

Given the lack of scientific understanding on ENP heteroaggregation it was suggested that balance models to be the better choice, at least in the short term. Overall rates of sorption and desorption has been suggested to be used in the place of equilibrium partition coefficients to overcome concerns arising from using the equilibrium K_d.

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

Much ado about α: reframing the debate over appropriate fate descriptors in nanoparticle environmental risk modeling
Amy L. Dale, Gregory V. Lowry, Elizabeth A. Casman
Environ. Sci.: Nano, 2015, Perspective
DOI: 10.1039/C4EN00170B

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free through a registered RSC account

Of all nanomaterials that I know and have studied in these past seven years working with environmental nanoscience, Quantum Dots (QDs) have by far been my favorites. They just sound so sci-fi. I mean, just listen to their name: Quantum dots [imagine a low, cinema narrator voice]. Also, they glow in neon multi-colors when exposed to UV light.

This interesting optical property of quantum dots is due to quantum confinement, a phenomenon that takes place when some semiconductor particles are so small that the trajectory of their electrons becomes confined. The level of confinement depends on the size of the particles, which is why QDs of different sizes emit different colors.

QDs present the potential for a wide variety of applications, such as solar cells, lasers, LEDs, medical imaging, and even quantum computing. They are just so cool!

One more thing I have learned in these few years working with environmental nanoscience is that anything with so many potential applications is bound to, somehow, end up in the environment.

Quantum dot dispersions hanging out and emitting their neon quantum confinement glow, no big deal.

A common type of QD is a nanohybrid made of a cadmium selenide (CdSe) core and a zinc sulfide (ZnS) shell (CdSe/ZnS), which has been shown to be toxic to organisms and is a known carcinogen to humans. So, it is important to understand the way in which these QDs will be transported through the environment.

QDs and other nanomaterials are often coated with surfactants or polymers to improve stability—to prevent nanoparticles from sticking to each other, which they love to do. The presence of coatings may deeply affect their interactions with the environment.

M. D. Becker and colleagues recently published a study to improve existing models for the transport of coated QDs through porous media, which is an idealized template for groundwater and soil.

They observed that QDs became increasingly stuck to the porous media as they were transported. Both the coating and the presence of other constituents in the environment (such as natural organic matter) may help QDs “slide” more easily through the porous media. But as these coatings are stripped off over time, particles end up getting stuck.

This behavior could not be explained by traditional nanoparticle transport models, so they developed a new transport model to account for the influence that coatings and other constituents may have in the transport of nanomaterials through porous media.


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

A multi-constituent site blocking model for nanoparticle and stabilizing agent transport in porous media
Matthew D. Becker, Yonggang Wang, Kurt D. Pennell and Linda M. Abriola
Environ. Sci.: Nano, 2015, Advance Article
DOI: 10.1039/C4EN00176A

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About the webwriter

Marina is a PhD research scientist at Virginia Tech and Assoc. Director of @VTSuN. She is interested in air quality, nanotechnology and human health. You can find more information about her in her website mevance.com.

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Graphene and graphene oxide are among the recent attractions in novel nanomaterials for electronic and composite applications. Structure of graphene can simply be viewed as taking a single walled carbon nanotubes and unrolling it to give a sheet.

History of graphene runs all the way back to the 19th century but the very first single layer graphene was synthesized in 2004, by Andre Geim and Kostya Novoselov at The University of Manchester, UK. Graphene can be synthesized to contain a single layer or multiple layers. Nanoscience and nanotechnology community has always been very excited about the remarkable electrical and heat conductivity of these materials and a significant influx of graphene into the composite and electronic markets are being anticipated.

There are raising concerns about environmental and health risks of these materials with this increasing usage as there are no established methods for their extraction from complex matrices and quantification. Therefore, Kyle Doudrick and co-workers from the University of Notre Dame and Arizona State University have successfully developed an extraction and quantification method for graphene and graphene oxide from biomass using in situ reduction method followed by detection with programmed thermal analysis (PTA).

PTA is known to determine the carbon mass based on the thermal stability. In this study, the separation was achieved by subjecting the samples to a time dependent temperature ramp program where the less thermally stable carbon compounds evolved early in the program and the high thermally stable compounds were evolved later. Graphene, which has a high thermal stability was therefore easily separated from rest of the components in the biomass. In order to obtain similar separation for graphene oxide that has a higher oxygen content, which limits the separation, an in situ reduction was conducted using sodium borohydride.

Since this makes the graphene oxides more hydrophobic forcing aggregation an efficient separation and extraction was expected. The results of the study has proved that this technique is capable of recovering 52 ± 8% and 80 ± 6% of few layer graphene (FLG) and graphene oxide (GO) from dried biomass, respectively. Therefore, this technique can be applied to the extraction of graphene from complex organic matrices used in nanotoxicological studies.

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

Quantification of graphene and graphene oxide in complex organic matrices
Kyle Doudrick, Takayuki Nosaka, Pierre Herckes, Paul Westerhoff
Environ. Sci.: Nano, 2015,2, 60-67
DOI: 10.1039/C4EN00134F

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About the webwriter

Imali Mudunkotuwa is a Postdoctoral Scholar and Research Assistant at The University of Iowa. She is interested in nanoscience, physical and surface chemistry. You can find more articles by Imali in her author archive .

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* Access is free through a registered RSC account

When friends and family ask me questions about the safety of nanotechnology, what follows is a conversation more or less like this:

Family member: “Are nanomaterials toxic by nature?”

Me: “It depends, nanomaterials can behave very differently from one another.”

Family member: “So, should I avoid products that have nanoparticles?”

Me: “Maybe. It depends on the type of nanomaterial, and how you will use the product.”

Family member: “But, will or will they not hurt me?”

Me: “Maybe. We don’t have a final answer to that yet, because there might be long-term effects that vary tremendously according to the nanomaterial’s composition, size, shape, and other attributes; like comparing apples and oranges.”

Did you sense a theme in this conversation? Yes, there is a lot of unhelpful uncertainty. But that is why researchers continue to work on understanding the possible effects of nanomaterials to human health and the environment, while concurrently developing novel applications for this great technology.

In a recently published ESN paper, Dr. Navid Saleh and his colleagues explore the topic of nanohybrids and their relevance to environmental health and safety (EHS).

A nanohybrid is commonly defined as a coupling of two or more types of nanomaterials that (1) integrate the unique properties of each nanomaterial to (2) create novel or enhanced properties, usually caused by the interaction between these nanomaterials. Moreover, combining two or more nanomaterials may result in (3) a novel material that has different physical dimensions in terms of their nano-ness (for example, from being “nano-thin” and “nano-long” to being “nano-structured”).

A good example of a nanohybrid is a combination of titanium dioxide (TiO₂) nanoparticles and carbon nanotubes, which allow the TiO₂ to be activated as a photocatalyst by visible light. Usually, the photocatalytic properties of TiO₂ can only be activated by UV light.

If nanohybrids have distinct properties from the nanomaterials that originated them, it is fair to wonder about their potential impacts to environmental health and safety (EHS). Can we safely add the known risks of these nano apples and oranges, when we know that the combination of both may generate novel properties?

This perspective paper by Saleh and colleagues proposes a strategy for tackling this complex issue. Hopefuly the nano-EHS community can use this information as a tool to narrow down the plethora of nanohybrid scenarios to focus on those most likely to pose a risk to health and the environment.

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

Research strategy to determine when novel nanohybrids pose unique environmental risks
Navid B. Saleh, Nirupam Aich, Jaime Plazas-Tuttle, Jamie R. Lead and Gregory V. Lowry
Environ. Sci.: Nano, 2015, Advance Article
DOI: 10.1039/c4en00104d

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About the webwriter

Marina is a PhD research scientist at Virginia Tech and Assoc. Director of @VTSuN. She is interested in air quality, nanotechnology and human health. You can find more information about her in her website mevance.com.

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* Access is free through a registered RSC account

As nanoparticles find their way into more products, consumers and scientists alike are concerned about the impact their spread may have on our health. When answering this question, it is important to consider not just our direct interaction with nanoparticles through consumer products that incorporate them, but also the ways they might indirectly make their way into our environment. For instance, nanoparticles in the soil could be taken up by plants that we might later eat.

As a global food staple, maize is an ideal candidate for a comprehensive investigation of this topic. In a recent study published in Environmental Science: Nano, a team of researchers investigated the extent to which maize plants take up zinc oxide (ZnO) nanoparticles—one of the most widely used nanomaterials—and the pathways by which they do so. Their results suggest that ZnO nanoparticles dissolve into Zn2+ ions to make their way into the epidermis and roots of the plants, but rarely translocate to the shoots.

The researchers grew maize hydroponically, adding different concentrations of ZnO nanoparticles or Zn2+ ions to the water. Unsurprisingly, higher concentrations of zinc in the growth medium correlated with higher concentrations of zinc in the plants. The zinc content in the maize plants was virtually identical whether the plants were grown in ZnO solution or Zn2+ solution, suggesting that most ZnO nanoparticles make their way into maize plants by first dissolving into Zn2+, instead of being taken up whole. Zinc taken up by this pathway tended to form phosphate complexes inside the plants, largely preventing it from moving upwards into the shoots.

However, TEM imaging of plants treated with fluorescently labeled ZnO nanoparticles showed that some intact nanoparticles did find their way into the maize plants. These nanoparticles accumulated mostly in the root cortex, occasionally making their way into the vascular tissue. As with the dissolved zinc, though, the zinc oxide nanoparticles were often biotransformed to zinc phosphate and prevented from moving into the shoots.

It seems that in the case of maize, zinc oxide nanoparticles do not directly impact the parts of the plant that we would eat, but excessive accumulation of zinc compounds could potentially affect the plant’s overall health. It is unclear from this study whether the findings can be generalized to interactions between other crops and other types of nanoparticles, or even whether the pathway holds for soil-grown (as opposed to hydroponic) maize plants. Nevertheless, it provides a first step towards a comprehensive understanding of plants’ responses to and defenses against nanoparticles.

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

Liked this blog post? Read Laurel’s previous entry on how rare earth elements trace nanoparticles through the environment.

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