Nanotech: Think big by thinking small. That could be nanotechnology’s tagline, if indeed this hot area of science needed a cool slogan — which it doesn’t. That’s because nanotech is already the wunderkind of science and the darling of the industrial world. Embraced by the public and researchers alike, nanotechnology is being touted as the solution to a host of problems: climate change, water and food security, human disease — and that’s not even mentioning the prosaic but (for some) equally worrisome issue of smelly socks and stinky sports jerseys.
Some types of nanoparticles have indeed proven to be revolutionary. For example, zero-valent nanoparticles can be used to break down highly toxic chlorinated hydrocarbons such as DDT into inert compounds. With cancers, nanoparticles can help medical imagers zero in on tumours and may one day provide targeted drug delivery, considered superior to the conventional blitzkrieg of chemotherapy, where healthy tissue becomes collateral damage.
Tyson MacCormack of Mount Allison University researches the effects of nanoparticles on aquatic ecosystems, using the common white sucker fish as his test animal. Photo credit: Mount Allison University
Nanotechnology is the understanding and control of constructs on a nano scale, typically between one and 100 nanometres. Many nanoparticles are made of metals or metal oxides such as silver, titanium, copper, gold and zinc. In development in laboratories around the world since the 1980s, nanoparticles — the term encompasses tens of thousands of formulations — are becoming ubiquitous. A year ago, the Nanotechnology Consumer Products Inventory identified 1,628 consumer products containing nanoscale materials. According to the Washington, DC-based Wilson Center, the most common material used in nanoparticles was silver, while the next most common was titanium.
Although nanoparticles are increasingly being used in manufacturing and consumer goods, little is known about the long-term effects on human health or the environment. The science community acknowledges this as a key research challenge, as it is clear that nanomaterials such as titanium dioxide (TiO2) make their way into the environment, eventually entering surface waters and agricultural land or landfill sites.
Silver nanoparticles (AgNP), are also accumulating. Useful for its antimicrobial properties, nanosilver is commonly found in medical items like bandages and catheters. This same property has made nanosilver popular for reducing odour in sports gear and, in recent years, it’s also been added to teddy bears, face creams, baby blankets and makeup. But concerns are being raised. Studies in rats show that AgNP in aerosols can be inhaled and cross the air-blood-barrier in the lungs to accumulate in secondary organs.
In addition to concerns about human health, there is the question of what happens when nanoparticles leave the laboratory. Do the same antimicrobial properties that keep our socks smelling nice upset the delicate balance of microorganisms in lakes and rivers? Are they bioaccumulating in larger creatures potentially causing unexpected problems? But at only one-billionth of a metre long, how can such minute particles cause problems?
Tyson MacCormack, an assistant professor in the Department of Chemistry and Biochemistry at Mount Allison University in New Brunswick, is assessing the interaction of nanomaterials and biological systems in order to identify potential mechanisms by which they can affect human or animal health. He faces a challenge common to nanoresearch — things at the nano scale can behave very differently than at other scales. The remarkable configuration of nanomaterials not only gives them their unique properties but makes it difficult to predict their reaction with the environment using conventional testing. This is because nanoparticles have more surface area to react; reactions catalysed on the surface are much faster than with bigger particles. Such reactions may turn previously benign chemicals into harmful ones. “There is lots of evidence for toxicity,” says MacCormack.
At his lab at Mount Allison, MacCormack uses the white sucker, a fish common to North America, as the test animal for his research into the effects of nanoparticles on aquatic ecosystems. His work is funded by the Canadian Foundation for Innovation (CFI) and NSERC. A $200,000 CFI grant paid for critical equipment such as a dynamic light scattering instrument, which analyzes the size and surface charge in nanomaterials. “It is important to measure diameter and charge to determine if certain nanoparticle properties contribute to toxicity,” says MacCormack.
The grant also paid for a swim tunnel respirometer, which assesses the metabolic activity of a fish to determine toxic reaction following exposure to nanoparticles.
The white sucker is an ideal test subject as, being a bottom feeder, it would be exposed to nanoparticles that aggregate in silt as well as those suspended in water. MacCormack attaches electrocardiography probes to the fish then places them in the swim tunnel respirometer — the equivalent of a human treadmill — to assess cardiorespiratory performance following exposure to nanomaterials. “The lab equipment is highly sensitive and can pick up minute changes in the environment or fish,” MacCormack says.
Michael Rennie, with the International Institute for Sustainable Development’s Experimental Lakes Area project, reads Passive Integrated Transponder tags on a fish. This method (capture, mark, recapture) is being used to measure indirect responses, such as a reduction in population, in fish swimming in a lake containing experimental nanosilver. Photo credit: Joel Trenaman, IISD
MacCormack has specifically been researching the effects of cerium oxide (CeO2), an additive in diesel fuel that improves combustion efficiency and reduces emissions. He is also analyzing zinc oxide (ZnO), used in large quantities in consumer products. ZnO, for example, is increasingly replacing titanium dioxide (TiO2) in sunscreens. (TiO2 nanoparticles are useful as whiteners and found in products like salad dressing and toothpaste.) In humans, both TiO2 and ZnO are inert. Evidence indicates, however, that ZnO is toxic to the gills of fish, says MacCormack.
How nanoparticles affect gills — the respiratory organ of fish — is important, as it is an indicator of compromised cardiovascular function and oxygen uptake and delivery, which impacts energy metabolism and thus growth, sexual maturity and vigour. MacCormack has also isolated proteins associated with oxidative stress to assess their interaction with nanoparticles on a molecular scale. His studies have shown that nanoparticles interact with these proteins and change their structure and function, MacCormack says. “The sort of molecular-scale mechanisms by which nanoparticles cause a toxic reaction are likely to be the same in humans as they are in fish.”
MacCormack’s research is key to the future production of nanomaterials, which is ramping up across all sectors. “By identifying the mechanisms by which nanomaterials have a negative effect, it may be possible for producers to slightly alter the properties of their particles to keep the beneficial properties while reducing the negative properties.”
The impact of nanoparticles on aquatic environments is being done on an even larger scale in northwestern Ontario under the auspices of the Experimental Lakes Area (ELA), a renowned freshwater research station that is managed by the International Institute for Sustainable Development (IISD). Unique in the world, the ELA undertakes long-term, whole-lake studies of fresh water ecosystems to determine the impact of contaminants. Michael Rennie, an adjunct professor in the University of Manitoba Department of Biological Sciences and a former research scientist with Fisheries and Oceans Canada, is focusing his studies on AgNP’s direct and indirect effects on fish populations. Led by researchers at Trent University, the experiment tracks the dispersal and fate of AgNP in the lake, especially how it affects the phytoplankton and zooplankton that fish eat. (AgNP is increasingly entering waterways from municipal wastewater due to washing clothes containing antibacterial nanoparticles, he adds.)
Complementing Rennie’s field studies are lab experiments by U of M graduate student Laura Murray, who is recording the growth and respiratory impact of AgNP on fish to understand at what concentration in water the particles directly affect fish metabolism. This is complicated by various factors. For example, the smaller an AgNp particle, the more potentially toxic it is, says Rennie. Also, if there are high levels of dissolved organic carbon in the water, these can complex with AgNP, making them distribute more widely in the environment. Finally, AgNP can break down and release silver ions that are more toxic to organisms than the particle itself.
Current wastewater treatment plants are not designed to catch such tiny particles. This may change thanks to research by University of Calgary’s Leland Jackson, who heads the $33-million Advancing Canadian Wastewater Assets (ACWA) project. Jackson, an aquatic ecologist who works on the effects of pollutants, considers nanoparticles, present in wastewater effluent, an environmental contaminant similar to viruses, prions and bacteria “that we would like to remove if possible.”
Even though the City of Calgary’s wastewater treatment system is one of the best in the world, its technology can’t catch all nanoparticles, Jackson says. The system’s ZeeWeed ultrafiltration membranes have a pore size of 20 nanometres wide while a complementary reverse osmosis system has a pore size of two nanometres. Together, these systems capture most bacteria and viruses and even the bigger nanomaterials, but don’t nab the smallest ones, says Jackson. Hence, some nanoparticles are getting into downstream water sources.
An even larger concern is what to do with the large amounts of nanoparticles that are caught by the filter, Jackson says. Sludge recovered from the wastewater system is sprayed on agriculture fields by Calgro, the City of Calgary’s biosolids-to-land program. Jackson says that “quite high amounts” of AgNP are being detected, however it’s not known what the long-term effects will be to soil.
With nanomaterials spread so widely throughout the environment, system-wide thinking is needed to understand and deal with the challenges. Greg Goss of the University of Alberta’s Department of Biological Sciences is working towards such a goal — being able to predict the relative toxicity of manufactured nanomaterials to advance risk prediction and create a foundation for solid regulatory guidelines. Like the other researchers, Goss uses aquatic animals for nanotoxicity testing.
As a designated nanotechnology expert representing Environment Canada at the Organisation for Economic Co-operation and Development (OECD), Goss is helping member nations establish legislation and set guidelines for industry to enhance sustainable and responsible development of the nanotechnology industry as a whole. This is challenging on two fronts: first, nanomaterials are difficult to measure and detect once they are in the environment. Second are the unexpected reactions that “change the toxicity potential,” Goss says.
Industry is beginning to accept greater responsibility to ensure that the nanomaterials they make for use in consumer goods won’t contaminate the environment. It is a significant undertaking. “You have to do a full cradle-to-cradle assessment all the way through development,” says Goss. In about a year, he adds, the OECD will have approved a standard suite of tests and guidance on how nanomaterial testing should be conducted. It is a worthy endeavour. “Nanotechnology is the green revolution; this is the way society is going to solve a lot of our problems.”