THE ENVIRONMENT
The tiny, useful particle that could also be a health problem
May 18, 2008
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Andrew Chung
STAFF REPORTER
For as long as there have been socks, there have been smelly socks, and attempts to try to solve that eternal, noxious problem.
For the last few years, a type of sock has become very popular because it has the solution built right in: infinitesimal particles of silver, naturally anti-bacterial and, thus, anti-odiferous.
The silver, known since ancient times to have disinfectant properties, works so well because particles so small can be vastly more powerful than the same substance at normal size.
It's hard to overstate just how small. "Nano" means one-billionth of a metre. In many cases, this refers to the scale of atoms, which are the smallest units of all matter.
A human hair, by comparison, is 80,000 nanometres wide.
But what happens to the particles in the socks? In an experiment reported at the American Chemical Society meeting last month, two Arizona State University scientists, Troy Benn and Paul Westerhoff, washed seven brands of nanosilver socks and then tested the wastewater. All but one pair leaked silver.
That silver, of course, ends up in our sewers, rivers and lakes.
Results like this have strengthened the calls among scientists and environmentalists for a closer examination of nanoparticles and their effects on humans and the environment.
A number of consumer-protection groups have filed a legal petition with the U.S. Environmental Protection Agency to force the agency to halt the sale of consumer products containing nanosilver.
The groups include the Washington-based International Center for Technology Assessment, as well as Greenpeace and Friends Of The Earth.
The interest in nanomaterials is coming at a time of growing awareness of how chemicals – many of which we don't know are manufactured into the products we use on a daily basis – may be causing us harm.
Last month, the Canadian government said that it would declare bisphenol-A – a chemical commonly found in hard, clear, plastic water and baby bottles, and the linings of tin cans – a toxic substance. Retailers around the world pulled products containing the chemical from their shelves.
The Project on Emerging Nanotechnologies (PEN), also Washington-based, says it has inventoried more than 600 consumer products in 20 countries with nano-scale materials, and "new nanotech products are hitting the market at the rate of three to four per week."
The most prevalent nanoparticle product contains nanosilver. Over 60 per cent are "health and fitness" products, according to the project, an initiative of Woodrow Wilson International Center for Scholars.
You can find nanosilver in products from clothing and shoes to mattresses and pillows to appliances like Samsung's SilverCare washers, and Conair's Infiniti Nano Silver hair straighteners. The TTC also intends to paint the stanchions in its new subway cars with antimicrobial silver.
Friends of the Earth found more than 100 nanomaterials in food and food packaging, including Miller beer bottles that have nano clay, making them less likely to shatter.
Titanium dioxide is found in sunscreens. Fullerenes and alumina nanopowders in cosmetics. Zinc oxide in food additives.
These new uses for nanomaterials have some scientists worried.
"The new controversy is, should it be incorporated into sweatshirts and shoes?" wonders Kevin Robbie, a physics professor at Queen's University in Kingston and the Canada Research Chair in Nanostructured Materials. "Generally it's not a very good idea."
Last December, in the journal Biointerphases , Robbie and two researchers published a comprehensive review of nanoparticle toxicity, mostly to ensure they understood the risks of the materials they work with every day. As a result, they have tightened their cleaning procedures and now store their nanoparticles in fluid, to prevent them from becoming airborne.
The problem is that little is known about how nano-sized elements will act in living organisms and the environment.
When something gets that small, it begins to take on unexpected properties. It can dissolve where the bulk size could not. Or it can begin to conduct electricity. "Even though we know that gold has certain characteristics as a chunk of gold," Robbie explains, "when you make it into nano gold, it's hard to predict what it's going to do."
Research on nanoparticles has raised some concern among scientists.
Nano-scale titanium dioxide, used in some sunscreens, has been found to cause inflammation in rat lungs. "If rats breathe them in, you find that the smaller you make them, the more harmful they are," says Andrew Maynard, PEN's chief science advisor and a nanotechnology expert.
Studies have so far been inconclusive, however, as to whether nanoparticles can penetrate healthy skin.
Nano-sized carbon and manganese-oxide have been found, when inhaled, to make its way up to the brain.
As for nanosilver, its ability to kill cells is well known, hence its use as a germicide.
However, the concern is that it doesn't discriminate between good cells and bad cells.
A recent study found that nanosilver inhibits the growth of beneficial bacteria in wastewater-treatment plants, which remove harmful ammonia from the effluent. Meanwhile, silver is highly toxic to fish, sparking worry about the element at the nano scale.
Also, new research is looking at how nanosilver and other nanoparticles might disrupt cellular metabolism. After all, DNA and the essential proteins they encode are nano-sized.
"If you put a nanoparticle into a nucleus of cell, is it like throwing a wrench into it?" Maynard asks. "Early indications are that nanoparticles can interfere with biological processes at that level."
Why are manufacturers embracing nanomaterials with such vigour? Couldn't they just use larger sized versions of the same chemicals and avoid all this worry?
The fact is that nano-scale materials can be much more effective and, because less material is used, cost-effective too.
For instance, the sun blocker titanium dioxide can paint the skin white. That's okay if you're a beach lifeguard. For the rest of us, manufacturers know that the tinier the particle, the more transparent the sunscreen will be. Similarly, it'd be hard to impregnate the fabric with silver and keep it soft. But with nanosilver, you can give the wool or cotton antimicrobial properties and have it feel like wool or cotton.
Of course, we need to remember that humans have been exposed to nano-scale elements in nature throughout evolution. Think of fine carbon particles from fires, or superfine dust, or even salt particles in sea spray.
"There's a distinction between those and the ones we're fabricating," says Dr. Ivan Pacheco, co-author of the Queen's review, and an expert in gastrointestinal physiology. "Now we're engineering them, so the nanoparticles we're making are quite different in morphology, and we still don't know what properties they have and what they're doing to our health.
"Most," he says, "are not being screened properly."
Our bodies have adapted over millions of years to many natural elements. The worry is how they'll react to these new ones.
"That's the obvious question: If we're putting these things into consumer products that we've not been exposed to before, are there any serious problems there?" says Maynard.
Is banning them from products the answer? Robbie says probably not. Take the use of nanosilver in bandages used on burn victims. They've become essential to medicine, he argues.
"So banning something like nanosilver would be a bad idea."
The scientists say that regulation and research are what's needed.
Canada deals with nanomaterials under current legislation. The Canadian Environmental Protection Act requires any new chemical to undergo a human health and environmental risk assessment.
Since last year, new nanomaterials – including the nano-scale form of a substance already in use "if it has unique structures or molecular arrangements" – must be registered.
In the U.S. the picture is similar. Any substance or device that claims to kill germs is to be registered as a pesticide. Nanosilver is theoretically captured here, and the government last year forced Samsung's washers to register in this way.
But considering how quickly the market is expanding worldwide, the scientists doubt that current regulations are sufficient. They also point out the lack of regulations that specifically address nanoparticles and say that not enough is being spent on their health effects.
Companies are reacting to the growing concern. Last January Dupont was the first firm to provide its nanomaterial product information to the EPA. In a position statement, it says it believes in the "development of responsible safety standards and test methods; the coordination of research to generate reliable, peer reviewed data based on good science; and the adoption of appropriate regulations as needed."
Not all companies are as forthcoming on their intentions. "The worry about new nanomaterials is completely justified," Robbie says, "because manufacturers have been producing more and more, and a broader range, of constituents than ever known before, and launching them into the marketplace with minimal tests."
Toronto Star