Nanoparticles Are in Our Food, Clothing and Medicine -- And No One Knows for Sure How Dangerous They Might Be
Inside nanotechnology’s little universe of big unknowns.
A pair of scientists, sporting white clean-suits complete with helmets and face masks, approach a prefab agricultural greenhouse in a clearing at Duke University’s Research Forest. Inside are two long rows of wooden boxes the size of large horse troughs, which hold samples of the natural world that surrounds them—the pine groves and rhododendron thickets of North Carolina’s piedmont, which at this moment are alive with bird song.
Looking a lot like the government bad guys in E.T., the two men cautiously hover over a row of boxes containing native sedges, water grasses, and Zebra fish to spray a fine mist of silver nanoparticles over them. Their goal: to investigate how the world inside the boxes is altered by these essentially invisible and notoriously unpredictable particles.
The researchers are part of a multidisciplinary coalition of scientists from Duke, Stanford, Carnegie Mellon, Howard, Virginia Tech, and the University of Kentucky, headquartered at Duke’s Center for the Environmental Implications of NanoTechnology (CEINT), that represents one of the most comprehensive efforts yet to measure how nanoparticles affect ecosystems and biological systems.
So far the questions about whether nanoparticles are an environmental risk outnumber the answers, which is why the Duke scientists take the precaution of wearing clean-suits while dosing the boxes—no one’s sure what exposure to a high concentration of nanoparticles might do. Among the few things we do know about them are that they sail past the blood-brain barrier and can harm the nervous systems of some animals.
The regulation of nanoparticles has been recommended for more than a decade, but there’s no agreement on exactly how to do it. Meanwhile, the lid has already been lifted on nanotechnology. The use of man-made nanoparticles has spread into almost every area of our lives: food, clothing, medicine, shampoo, toothpaste, sunscreen, and thousands of other products.
Regulatory structures, both here and abroad, are completely unprepared for this onslaught of nanoproducts, because nanoparticles don’t fit into traditional regulatory categories. Additionally, companies often shield details about them by labeling them “proprietary”; they’re difficult to detect; we don’t have protocols for judging their effects; and we haven’t even developed the right tools for tracking them. If nanotechnology and its uses represent a frontier of sorts, it’s not simply the Wild West—it’s the Chaotic, Undiscovered, Uncontrollable West.
And yet, when I visit the boxes on a warm spring day filled with the buzzing of dragonflies and the plaintive call of mourning doves, they look perfectly benign and could easily be mistaken for a container garden. But there are hints that more is going on: each “mesocosm” (a middle ground between microcosm and macrocosm) is studded with probes and sensors that continually transmit data to CEINT’s central computer.
As I instinctively squint my eyes to try and locate evidence of the silver nanoparticles inside each box, I realize I might as well be staring down at these research gardens from another arm of the galaxy. The scale of these two worlds is so disparate that my senses are destined to fail me.
As with many things that are invisible and difficult to understand—think subatomic particles such as the Higgs boson, muons, gluons, or quarks—any discussion of nanoparticles quickly shifts into the realm of metaphor and analogy. People working in nanoscience seem to try to outdo each other with folksy explanations: Looking for a nanoparticle is like looking for a needle in the Grand Canyon when the canyon is filled with straw. If a nanoparticle were the size of a football, an actual football would be the size of New Zealand. A million nanoparticles could squeeze onto the period at the end of this sentence.
But what is a nanoparticle? The very simplest explanation is that a nanoparticle is a very small object. It can consist of any bit of matter—carbon, silver, gold, titanium dioxide, pretty much anything you can imagine—that exists on the scale of nanometers. One nanometer equals one-billionth of a meter. A nanoparticle may range in size from one nanometer to one hundred nanometers, although the upper boundary remains a matter of debate among scientists.
Nanoparticles exist in nature, but they can also be manufactured. One way is top-down: grinding up things that are big until they are really, really small, an approach used in nanolithography for electronics. Or you can make them from the bottom up, following instructions that read like a chemistry textbook: mixing one chemical with another by pyrolysis (heating a material in a partial vacuum), or with electrolysis (running a current through a liquid), or by other means.
But what do they look like? Raju Badireddy, a postdoctoral researcher, is happy to satisfy my curiosity. He greets me with a smile at the door to one of CEINT’s basement labs and guides me around his little domain. For much of his work, Badireddy uses a “dark field” microscope that excludes certain wavelengths of light, reducing the “noise” in the image to provide unparalleled clarity. Sensing my anticipation, he doses a slide with silver nanoparticles similar to those in the mesocosm boxes in the forest, and slips it under the lens.
As I look into the scope, it fairly takes my breath away. There are so many dots of light that I’m reminded of staring up at the Milky Way on a trip across the Tibetan Plateau years ago. Yet the silver dots throb and undulate as if alive. Here and there, giant spheres of dust, as large as Goodyear blimps, porpoise through the nanoparticles. I pull back from the oculars, feeling as if I’ve intruded upon something private. This world is so close—it’s even inside me—yet it looks so other, so mysterious.
Scientists don’t really have a full theoretical foundation to explain reality at this scale. But all agree that one of the most important aspects of nanoparticles is that they are all surface. Consider a conventional chemical process: When one element is reacting with another, it’s really just the surface molecules that are involved in the lock-and-key dance of classical chemistry. The vast majority of the molecules remain interior, and stable. But there are many fewer molecules in a nanoparticle, so most of the molecules are on the outside, thus rendering nanoparticles more reactive.
Myriad surface imperfections cause randomness to dominate the nano world. If you hit a billiard ball with a clean shot at the macro level, you can have a good idea where it will go. But at the nano level, a billiard ball might shoot straight up, or even reverse direction. These bits of matter are hot to trot: ready to react, to bond, and to do so in unpredictable ways.
This makes life at the nano scale more chaotic. For instance, aluminum is used everywhere to make soda cans. But in nanopowder form, aluminum explodes violently when it comes in contact with air. At the macro level, gold is famously nonreactive. At the nano level, gold goes the opposite way, becoming extremely reactive. Bulk carbon is soft. But at the nano level, if you superheat it, the molecules bend into a tube that is very strong and semiconductive. In the nano world, gravity fades to the background, becoming less pronounced, the melting temperature of materials changes, and colors shift. At 25 nanometers, spherical gold nanoparticles are red; at 50 nanometers they are green; and at 100 nanometers they’re orange. Similarly, silver is blue at 40 nanometers and yellow at 100 nanometers.
So chemistry and physics work differently if you’re a nanoparticle. You’re not as small as an atom or a molecule, but you’re also not even as big as a cell, so you’re definitely not of the macro world either. You exist in an undiscovered country somewhere between the molecular and the macroscopic. Here, the laws of the very small (quantum mechanics) merge quirkily with the laws of the very large (classical physics). Some say nanomaterials bring a third dimension to chemistry’s periodic table, because at the nano scale, long-established rules and groupings don’t necessarily hold up.
These peculiarities are the reason that nanoparticles have seeped into so many commercial products. Researchers can take advantage of these different rules, adding nanoparticles to manufactured goods to give them desired qualities.
Scientists first realized that nanomaterials exhibit novel properties in 1985, when researchers at Rice University in Houston fabricated a Buckminsterfullerene, so named because the arrangement of sixty carbon atoms resembles the geodesic domes popularized by architect Richard Buckminster Fuller. These “Buckyballs” resist heat and act as superconductors. Then, in 1991, a researcher at the Japanese technology company NEC discovered the carbon nanotube, which confers great strength without adding weight. Novel nano materials have been reported at a feverish pace ever since.
With these engineered nanoparticles—not even getting into the more complex nanomachines on the horizon—we can deliver drugs to specific cells, “cloak” objects to make them less visible, make solar cells more efficient, and manufacture flexible electronics like e-paper.
In the household realm, nanosilica makes house paints and clothing stain resistant; nanozinc and nano–titanium dioxide make sunscreen, acne lotions, and cleansers transparent and more readily absorbed; and nanosilicon makes computer components and cell phones ever smaller and more powerful. Various proprietary nanoparticles have been mixed into volumizing shampoos, whitening toothpastes, scratch-resistant car paint, fabric softeners, and bricks that resist moss and fungus.
A recent report from an American Chemical Society journal claims that nano–titanium dioxide (a thickener and whitener in larger amounts) is now found in eighty-nine popular food products. These include: M&Ms and Mentos, Dentyne and Trident chewing gums, Nestlé coffee creamers, various flavors of Pop-Tarts, Kool-Aid, and Jell-O pudding, and Betty Crocker cake frostings. According to a market report, in 2010 the world produced 50,000 tons of nano–titanium dioxide; by 2015, it’s expected to grow to more than 200,000 tons.
At first some in the scientific community didn’t think that the unknown environmental effects of nanotechnology merited CEINT’s research. “The common view was that it was premature,” says CEINT’s director, Mark Wiesner. “My point was that that’s the whole point. But looking at risk is never as sexy as looking at the applications, so it took some time to convince my colleagues.”
Wiesner’s team at CEINT chose to study silver nanoparticles first because they are already commonly added to many consumer products for their germ-killing properties. You can find nanosilver in socks, wound dressings, doorknobs, sheets, cutting boards, baby mugs, plush toys—even condoms. How common is the application of nanoparticles? It varies, but when it comes to socks, for example, hospitals now have to be cautious that the nanosilver in a patient’s footwear doesn’t upset their MRI (magnetic resonance imaging) machines.
Read the full article at: alternet.org
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