Environmental Science: Nano Blog

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

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

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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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