UK-led International Team Studies Eco Threats from Nanoparticles

by Alicia P. Gregory
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Size really does matter, especially when you’re manufacturing stink-free socks, self-cleaning windows, and superior sunscreens. All of these items—and hundreds more—contain itty-bitty nanoparticles.

Nanoparticles are pieces of metal or other substances that are engineered to measure less than 100 nanometers in at least one dimension. A nanometer is one-billionth of a meter. Based on their miniscule size, nanoparticles have unusual properties compared to larger objects made from the same materials.

Take nano-sized zinc oxide particles. Their UV-blocking properties are superior to large-scale equivalents in traditional sunscreens. Or take nanosilver. Because it can kill bacteria on contact, six decades ago the EPA approved its large-scale forefather, ionic silver, for a variety of anti-microbial uses (water filters, disinfectants). Engineering silver at the nanoscale allows the particles to be easily attached to plastics and fabrics. Nanosilver is added to hundreds of consumer products, and normal use of these products—like washing your clothes—can release nanoparticles into wastewater.

But what happens when those man-manipulated particles enter the wastewater treatment process—dodging grit screens and gravity chambers to settle into sewage sludge—and end up being spread on our fields for fertilizer? What kind of toxic threat do nanoparticles pose to soil, plants, animals, and humans? Is it possible to design less toxic particles? University of Kentucky scientists and partners around the world have formed a new consortium to answer these vital questions.

Paul Bertsch, director of UK’s Tracy Farmer Institute for Sustainability and the Environment, leads the international consortium known as the Transatlantic Initiative for Nanotechnology and the Environment (TĪNĒ). Created by a four-year, $4 million grant from the U.S. EPA and the United Kingdom’s Environmental Nanoscience Initiative, this consortium is exploring the effects of nanoparticles on terrestrial ecosystems.

Bertsch, a soil scientist who came to UK in 2008, explains the problem: “There are no federal regulations for nanomaterials. What’s happening is nano-scale zinc oxide, titanium dioxide, and silver are being mass-produced at such high quantities that they are showing up in biosolids”—solid material from the wastewater treatment process that, unlike sewage sludge, has been dried and cleaned to remove odors, pathogens and toxins. Biosolids contain essential plant nutrients and organic matter and are recycled as fertilizer.

About 60 percent of the 8 million tons of biosolids annually produced in the United States and the United Kingdom are applied to agricultural lands, often to the same fields year after year. Bertsch notes that 20 percent of biosolids are incinerated and another 20 percent are sent to landfills—usually because the heavy metal concentrations exceed EPA limits. “But with landfill space at such a premium, it’s likely that in the near future 80 percent of biosolids will end up being applied to farmlands. The EPA has a several-thousand-page document on the risks of biosolid application based on metal concentrations, but no regulations on nanomaterials.”

Why aren’t they regulated? Nanomaterials are incredibility complex. Bertsch gives an example: “The properties of zinc oxide nanomaterials change drastically if you have a 100 nanometer particle or a 10 or 5 nanometer particle. It could be exactly the same formulation, same crystal structure, with the same surface modifications but the properties change dramatically just based on size.” That’s the beauty—and the potential danger—of nanoparticles. He adds, “Superimpose on that all of these different proprietary formulations that manufacturers have in terms of surface coatings and crystal structure modifications, and creating a framework for regulation seems daunting.”

But before there can be rules, there must be risk assessment. That task is up to the consortium’s five Kentucky plant and soil scientists (Bertsch, Nadine Kabengi, David McNear, Olga Tsyusko, and Jason Unrine), 11 scientists from the United Kingdom, two from Carnegie Mellon University, and two from Duke University. Their focus is the “fate and transport” of nanoparticles. Bertsch explains, “At the crux of this is the question ‘What controls nanoparticles’ mobility and bioavailability—the extent to which they can be taken up by organisms?’ If we can understand what surface properties control both their mobility and their bioavailability, we can design and manufacture nanomaterials that are less environmentally hazardous.”

Nah, no silver lining

Scientists have learned that 90 to 95 percent of manufactured nanosilver ends up in biosolids. Once in soil, these engineered nanoparticles can be taken up by microorganisms, earthworms or plants, with the potential for transfer up the food chain to animals and humans.

And he points out that history has taught us that heavy metals like silver are trouble. Bertsch says that at the height of the photographic industry in 1978, 65 tons of silver was discharged. “In the ’70s the silver nitrate from the photographic industry was causing a significant environmental impact, that’s why the EPA regulated it. Municipal wastewater treatment plants experienced problems because the silver was toxic to the microorganisms used to treat the water.” Companies like Kodak had to build their own treatment plants. Bertsch reports an estimate that in 2017, 457 tons of silver will be discharged as nanosilver.

Tiny anti-microbial silver particles have been added to hundreds of consumer products like washing machines, refrigerators, toys, and clothes, including the aforementioned odor-reducing socks. Bertsch says these socks, and other fabrics made with nanosilver material, emit significant amounts of nanoparticles. “A number of studies have examined how much of that nanosilver leaches out in a single wash versus multiple washes. In some of these products, 100 percent of the nanoparticles come out in the first wash. In the better products, nanosilver leaches out over time, but even then you’re looking at five to seven washes before the particles are gone.”

Last year a study at the University of Utah revealed that nanosilver can kill and mutate fish embryos, but there’s been little research on soil and land-based animals. That’s where Jason Unrine’s study on earthworms comes in.

Unrine, an environmental toxicologist, and his UK team wanted to know if nanoparticles applied to farm fields eventually made their way into the food chain. In October 2010, Unrine told Chemical & Engineering News: “Because we expected the nanomaterials to aggregate onto soil particles, we were initially very skeptical that organisms could take them up from the soil.”

To find out, Unrine’s team mixed earthworms into artificial soil tainted with gold nanoparticles. Like silver, gold is a noble metal but unlike silver the chemistry is a lot more straightforward. Unrine says, “We used gold nanoparticles because they’re stable, insoluble, and easily detected.”

After 28 days, Unrine’s team detected gold nanoparticles throughout the earthworm’s bodies, with the highest concentrations in their gut. The gold nanoparticles didn’t have much of an impact on worm mortality, but some of the exposed worms produced 90 percent fewer offspring. This gold study can serve as a model for the transport of other nanoparticles, says Bertsch.

The most recent study by Bertch's team revealed an even more interesting effect: the biomagnification of nanoparticles. Biomagnification is a phenomenon that occurs when these manufactured nanoparticles are more concentrated the higher up the food chain they move. In their most recently published paper, in Environmental Science & Technology, the UK researchers reported direct evidence that gold nanoparticles taken up by plants were more highly concentrated in the caterpillars that ate these plants—between six to 12 times more. Bertsch thinks this is because the caterpillars could not shed or eliminate the nanoparticles efficiently, and he worries that chemicals could magnify in organisms even further up the food chain.

A study at the University of California-Santa Barbara, released shortly after UK's study, provides further evidence for biomagnification. That project tested a different nanomaterial in a simple aquatic food chain. Both studies have attracted international attention since the research provides noteworthy evidence that these biomagnified contaminants could affect animals and humans.

Bertsch says, "This is such a difficult area of inquiry we’re trying every option we can to get a handle on what particle-specific effects there might be. One thing that has helped us tremendously is our affiliation with CEINT.” Both Bertsch and Unrine lead projects in the Center for the Environmental Implications of NanoTechnology (CEINT), which is based at Duke University and funded by the NSF and EPA. Bertsch says, “In our proposal for the new international consortium, we leverage CEINT significantly. We’re using the infrastructure CEINT already has in place—materials acquisition, synthesis and characterization, web resources and data management, plus all of the intellectual capital of scientists from Kentucky, Duke, Carnegie Mellon, Howard University, Virginia Tech, and Stanford.

“Our consortium has assembled some of the world’s top scientists working on the fate, transport, bioavailability and toxicity of nanomaterials in terrestrial systems. Together we can find ways to protect our environment while pushing the boundaries of nanoscience.”

photo of earthworms in soil

Jason Unrine’s UK research team mixed earthworms into artificial soil tainted with gold nanoparticles. After 28 days, Unrine’s team detected gold nanoparticles throughout the earthworm’s bodies, with the highest concentrations in their gut. Some of the exposed worms produced 90 percent fewer offspring. This study can serve as a model for how organisms take up other kinds of nanoparticles.

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Photo of Paul Bertsch

UK’s Paul Bertsch leads the Transatlantic Initiative for Nanotechnology and the Environment.

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