Predicting the environmental effects of nanomaterials is difficult.

Why It’s So Difficult to Determine the Environmental Effects of Nanomaterials

Why It’s So Difficult to Determine the Environmental Effects of Nanomaterials

The citizen’s guide to the future.
Sept. 29 2016 7:00 AM
FROM SLATE, NEW AMERICA, AND ASU

From Nano to Nature

Predicting the fate of nanomaterials in the environment is no small task.

GummyNinja/Thinkstock.
Comparing natural and engineered nanomaterials is like comparing a pebble to a marble.

GummyNinja/Thinkstock

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Imagine your future self-driving car. You’ll get so much more work done with extra time in your commute, and without a driver, your commute will be safer. Or will it? During your first ride, you probably won’t be able to shake the fear that the software doesn’t know to avoid pedestrians or that you’ll get a ticket because the car ran a light. New technologies are inherently a tangle of exciting possibilities and new risks. We’ve learned from history—and from dinosaurs escaping Jurassic Park—that potential dangers must be evaluated and mitigated before new technologies are released.

Car crashes and T. rex teeth are obvious hazards, but the risks of nanotechnology can be less accessible. Their small size and surprising properties make them difficult to define, discuss, and evaluate. Yet these are the same properties that make nanotechnology so revolutionary and impactful. Nanotechnology is one of the core ideas behind the science of the driverless car and the science fiction of living, 21st-century dinosaurs. Your future self-driving vehicle will likely contain a catalytic converter made efficient by platinum nanomaterials and a self-cleaning paint made possible by titanium dioxide nanomaterials. If electric, the lithium-ion battery may contain nickel magnesium cobalt oxide, or NMC, nanomaterials. If nanotechnology fulfills its promises to reduce emissions, gas requirements, and water use, we will see quality of human life improve, and environmental impacts reduced. But like all progress, nanotechnologies have inherent risk.

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Unfortunately, when discussing nanoscience research and implications, risks can be easily misunderstood and miscommunicated. The Center for Sustainable Nanotechnology recently reported in a journal called Chemistry of Materials that the NMC nanomaterials in some lithium-ion batteries are harmful to a beneficial soil bacteria grown in the lab. As reported in the center’s blog, local news ran a somewhat alarmist headline on the study: “Lithium-Ion Batteries Are Bad for the Environment.” But, the full news story revealed that the results were not so universal.

Rather, this kind of scientific research lays essential groundwork for understanding nanotechnology’s impact on the environment. With this knowledge, the scientific community can establish new design principles to make nanotechnologies more sustainable. But research alone isn’t the answer to every problem here: For instance, in the case of lithium-ion batteries, creative technological design can reduce environmental impact, but creating policies that support battery recycling could do just as much good.

In evaluating and reducing the environmental risks of nanotechnologies, scientists and engineers are taking a variety of approaches. Studies include two broad classifications of nanomaterials: natural and engineered. Natural nanomaterials have evolved with life on this planet. In our daily lives, they are found in ocean spray, campfire smoke, and even in milk as protein/lipid micelles. It is only in the past few decades, however, that scientists and engineers have been able to accurately make, manipulate, and characterize matter at the atomic scale. These “engineered” nanomaterials designed by scientists and engineers are made for specific applications in well-controlled, reproducible processes. Comparing a naturally occurring and an engineered nanomaterial is like comparing a pebble to a marble. Both are roughly the same size, but they are otherwise very different. Like most anything man-made, engineered nanomaterials are designed with a targeted function and their structure is more uniform, pure, pristine, and well-ordered. These two categories of material can behave and react differently.

Once the nanomaterial is released from manufacturer conditions, it can undergo dramatic changes, including physical, chemical, and biological transformations. As engineered nanomaterials enter the environment, they begin to resemble their natural counterparts. Let’s go back to the example of a marble. If you throw one into a stream, the marble may chip, develop imperfections, and change shape from pounding on rocks. Chemical reactions might strip it of its protective plastic coating. Microorganisms may even be able to take hold to form a new biological surface on the marble. By studying these kinds of complexities and imperfections already present in natural nanomaterials, scientists will be able to predict how these complexities change the behavior and impacts of engineered nanomaterials as well.

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The diversity and novel properties of engineered nanomaterials affect the way they react and change in the environment. Every single engineered nanomaterial requires an environmental impact study designed to include a range of sizes, shapes, impurities, and surface properties. Since many nanomaterials are essentially small particles suspended in solution (known as “colloidal suspensions”), they can dissolve, join together (or “aggregate”), and undergo surface changes. We don’t have to consider these factors when it comes to more “traditional” molecular structures that are dissolved, like aspirin or table salt. Suddenly, an environmental impact study becomes an exponentially greater task. Silver nanomaterials, for example, can dissolve to form silver ions in solution. Silver ions are considered nontoxic to humans at reasonable concentrations but can affect the growth of fish embryos. The formation of ionic silver is not only dependent on the engineered properties of the nanomaterial (like size or shape); it’s also dependent on changes from environmental exposure (for instance, coatings of biomolecules or surface imperfections).

Using tools made possible by nanotechnology, scientists and engineers have collaborated to develop new evaluative approaches for engineered nanomaterials in the environment. To screen the many relevant variables in evaluating the impact of nanomaterials, a tool called high throughput screening has been modified from drug discovery research in the late ’80s. This approach uses volumes as small as a drop or two to test hundreds of different variables in one pass. Imagine a rectangular plate the size of your hand that contains a few hundred tiny wells—with one experiment in each well. This is how a range of silver and other nanomaterials of various sizes and surface coatings have been tested for their effects on zebrafish embryos.

When combined with quantitative modeling, high throughput screening can even be used to develop predictive tools. A recent high throughput study took engineered gold nanomaterials of various sizes and surface coatings and examined interactions with biological molecules (that is, hundreds of proteins) and the resulting formation of nanomaterial clumps in solution (aggregation). Then, they evaluated these nanomaterials, which all had new biological coatings, to see if they could get into cells. The work produced a large searchable database of nanomaterial-protein interactions, useful for researchers working with gold nanomaterials but also went further with quantitative analysis to reveal that the binding of specific proteins completely changed cellular response to the gold nanomaterials.

Models like these will eventually predict nanomaterial changes and biological response for other systems. Using this combination of experimental and computational expertise, the scientific community can screen a plethora of materials, then develop predictive tools for the rest.

Roughly three decades after the term nanotechnology was coined and a little more than a decade after formation of early nanotechnology companies, scientists and engineers came together in critical mass to spearhead efforts that will lower the environmental and human health risks of newly developed nanomaterials. A body of knowledge is building to enable sustainable and green approaches to nanotechnology, including simple changes in the making of nanomaterials to include nontoxic chemicals, like vitamin C, coffee, or plants and plant extracts. But more complex questions still require study, including how to best prevent unintended release of engineered nanomaterials and, if released, how to predict changes in engineered nanomaterials as they transition to resemble their natural counterparts. As the foundational science and technology improves, it also must inform public policy on nanomaterials. Nanotechnology will surely improve the quality of our lives, but we need continued research in sustainable approaches to ensure that it lives up to the challenge of also improving the environment.

This article is part of the nanotechnology installment of Futurography, a series in which Future Tense introduces readers to the technologies that will define tomorrow. Each month, we’ll choose a new technology and break it down. Future Tense is a collaboration among Arizona State University, New America, and Slate.

Korin Wheeler is an associate professor of chemistry at Santa Clara University and researcher at the interface of nanoscience and biochemistry.