February 23, 2013 |
This article first appeared at Orion Magazine under the title "Pandora's Boxes." You can enjoy future Orion articles by signing up to the magazine's free trial subscription program.
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.
Wiesner
and his colleagues spent several months designing the experiments that
will help them outline some general ecological principles of the unique
nanoverse. He knew they wanted to test the particles in a system, but a
full-scale ecosystem would be too big, too unmanageable, so they had to
find a way to container-ize nature. They considered all sorts of
receptacles: kiddie pools (too flimsy), simple holes in the ground (too
dirty, too difficult to harvest for analysis), concrete boxes (crack in
winter). Finally, they settled upon wooden boxes lined with nonreactive,
industrial rubber: cheap to build, easy to reuse, and convenient to
harvest.
They built thirty boxes and a greenhouse to hold them.
The large number would make it easier to replicate experiments, and to
answer the spectrum of questions being posed by CEINT’s
interdisciplinary team. The ecologists were interested in community
diversity and how the biomass shifts over time. The biologists wanted to
know whether the nanoparticles become concentrated as they move up the
food chain. The toxicologists wanted to track where the particles went
and how fast they got there. The chemists wanted to know about
reactivity.
Whatever the goal of the experiment it houses, each
mesocosm features a slanted board upon which a terrestrial ecosystem
slowly gives way to an aquatic one. It’s a lot more complicated than a
test tube in a lab, but it remains an approximation. The team had hoped
to run streams through the mesocosms, but the computing power and
monitoring vigilance necessary to track nanoparticles in the streams
proved prohibitive.
In 2011, the team dosed the boxes with two
kinds of nanosilver made on campus: one coated in PVP, a binder used in
many medicines, and the other coated in gum arabic, a binder used in
numerous products, including gummi candies and cosmetics. Both coatings
help to stabilize the nanosilver. In some boxes, the researchers let the
silver leach slowly into the box. In other boxes, they delivered the
silver in one big pulse. In some, they introduced the silver into the
terrestrial part of the box; in others, they put the silver into the
water.
Then the researchers watched and waited.
Reading
through descriptions of nanoparticle applications can make a person
almost giddy. It all sounds mostly great. And the toxicology maxim “Dose
makes the poison” leads many biologists to be skeptical of the dangers
nanoparticles might pose. After all, nanoparticles are pretty darn
small.
Yet size seems to be a double-edged sword in the nanoverse.
Because nanoparticles are so small, they can slip past the body’s
various barriers: skin, the blood-brain barrier, the lining of the gut
and airways. Once inside, these tiny particles can bind to many things.
They seem to build up over time, especially in the brain. Some cause
inflammation and cell damage. Preliminary research shows this can harm
the organs of lab animals, though the results of some of these studies
are a matter of debate.
Some published research has shown that
inhaled nanoparticles actually become more toxic as they get smaller.
Nano–titanium dioxide, one of the most commonly used nanoparticles
(Pop-Tarts, sunblock), has been shown to damage DNA in animals and
prematurely corrode metals. Carbon nanotubes seem to penetrate lungs
even more deeply than asbestos.
What little we know about the
environmental effects of nanoparticles—and it isn’t very much—also
raises some red flags. Nanoparticles from consumer products have been
found in sewage wastewater, where they can inhibit bacteria that help
break down the waste. They’ve been found to accumulate in plants and
stunt their growth. Another study has shown that gold nanoparticles
become more concentrated as they move up the food chain from plants to
herbivores.
“My suspicion, based on the limited amount of work
that’s been done, is that nanoparticles are way less toxic than DDT,”
says Richard Di Giulio, an environmental toxicologist on the CEINT team.
“But what’s scary about nanoparticles is that we’re producing products
with new nanomaterials far ahead of our ability to assess them.”
As
a society, we’ve been here before—releasing a “miracle technology”
before its potential health and environmental ramifications are
understood, let alone investigated. Remember how DDT was going to stamp
out malaria and typhus and revolutionize agriculture? How asbestos was
going to make buildings fireproof? How bisphenol A (BPA) would make
plastics clear and nearly shatterproof? How methyl tertiary-butyl ether
(MTBE) would make gasoline burn cleanly? How polychlorinated biphenyls
(PCBs) were going to make electrical networks safer? How genetically
modified organisms (GMOs) were going to end hunger?
The CEINT
scientists are trying to develop a library that catalogues all the
different kinds of engineered nanoparticles. They’re designing methods
for assessing potential hazards, devising ways to evaluate the impact
nanoparticles have on both terrestrial and aquatic ecosystems, and
creating protocols that will help shape environmental policy decisions
about nanoparticles.
Wiesner says the boxes in the forest provide
“ground truth” for experiments in the lab. Sometimes, he says,
environmental research leads to generalizations that become so
abstracted that they have no relationship to reality. The example he
likes to give is Freon: if you were to study the toxicology of Freon in
the traditional way, you’d never get to the ozone hole. “Nature changes
things,” Wiesner says. “So we need to be able to understand those
transformation processes, and we need to understand them in complex
systems.”
The first large set of CEINT experiments ended about a
year ago, and the team spent most of last year figuring out where the
nanoparticles went, what they did, and how they added up. They
superimposed a grid on each box, then harvested the plants and animals
section by section. They clipped the grasses, sorted them by type, and
ground them up. They took bore samples of the soil, the water, and the
rocks. They anesthetized and flash froze the vertebrates. Then they
started measuring the nanoparticle concentrations in the plants, the
animals, and core-sample slices.
But consider the magnitude of the
scientific problems that face the scientists at CEINT, or anyone else
trying to answer a multitude of questions as nanotech applications
gallop into the market and man-made nanoparticles begin to litter our
world. Just try tracking something a billion times smaller than a meter
in even a modestly sized ecosystem, say, a small wetland or a lake. Do
carbon nanotubes degrade? And if not, then what? And how do you tell the
nanotubes from all the other carbon in your average ecosystem? Even if
we did regulate nanoparticles, how would we detect them? There’s no
“nanoprobe” that could find them today, and given the challenges of
developing such a thing, the team at CEINT considers it unlikely that
there will be one any time soon. Thus, gathering evidence of
nanoparticles’ effects—whether positive or negative—turns out to be a
titanic task. Simply finding them in the experiment samples seems about
as complicated as finding that needle in a haystack the size of the
Grand Canyon.
Lee Ferguson, a chemistry professor who directs the
nanoparticle analysis, meets me in the basement of the CEINT building
and leads me on a tour of all the hulking, pricey instruments the
researchers use. Despite the cutting-edge aura of this machinery, none
of it is fully up to the task of locating and analyzing the proverbial
nanoneedle.
“With nanoparticles, we’re playing catch-up as a
scientific community—not only to ask the right questions, but to have
the right tools to investigate them,” Ferguson says as he pushes through
a door into the first lab. “We were well prepared to answer questions
about PCBs—we’d spent half a century refining the chemistry and the
instruments that were used to analyze the molecules in those chemicals.
But simply measuring nanoparticles is a challenge. It’s one thing if
they’re concentrated, but if you’re looking for nanoparticles in soil,
for instance, you just can’t find them.”
He spends the next hour
showing me how the CEINT team has back-engineered methods to detect and
characterize nanoparticles. The fluorometer aims three lasers at carbon
nanotubes. Another instrument uses ultrasonic waves to flush out its
tiny quarry. Across campus, huge electron microscopes train electron
beams on the nanoparticle samples, projecting their images onto a
charge-coupled device camera, like the ones used on the Hubble
Telescope, and atomic force microscopes form images of them by running a
probe over samples like a hypersensitive, high-tech record player.
As
the team’s methods continue to advance, their experiments have resulted
in some surprising data. “After we dosed the water, we took some of it
to the lab and exposed fish to it,” says Wiesner’s research assistant,
Benjamin Espinasse. “Some of the particles turned out to be more toxic
in the lab. And the reverse also happened: some things didn’t appear to
be toxic in the lab, but they were more toxic in the boxes. It seems
that the organic matter in the mesocosms changed the coatings of the
particles, making them more toxic or less toxic,” Espinasse continues.
“We could never have imagined that.”
While CEINT has only
published the results of the preliminary mesocosm experiments, the team
has been able to make a few conclusions: When the nanoparticles come in a
burst, they tend to stay in the soil. But if they bleed into the system
slowly, they filter into the water column. Regardless, nanoparticles
seem to have a tendency to stick around—that was also the case with DDT.
Meanwhile,
CEINT has begun a new set of experiments in the boxes: testing
nanoparticles that have been combined with various other substances.
“The
materials we most see now are nanomaterials incorporated into other
products: textiles, foams, mattresses, nanotubes in display screens,”
Wiesner explains. “How it will get out into the environment will be very
different than just the pristine particle.”
And then there are
the nanobots to plan for. “As we get closer to even simple nanobots, we
will need to understand how to do research on them, too,” Wiesner says.
Although they remain a marvel of the future, scientists are working
toward nanomachines that may someday be able to replicate red blood
cells, clean up toxic spills, repair spinal cord injuries, and create
weapon swarms to overwhelm an enemy. Researchers are already working on
simple versions of nanobots using the chemical principles of attraction
and repulsion to help nanostructures arrange and build themselves in a
process akin to the way DNA works: a strand of DNA can only split and
rebuild in one particular way, and the desired structure is preserved,
no matter how many times the DNA replicates.
As if trying to
figure out the effects of simple nanoparticles weren’t enough of a
futuristic challenge, concerns surrounding nanobots that replicate like
DNA are so theoretical they’re spoken about in narratives resembling
science fiction. Sun Microsystems founder Bill Joy famously warned that,
if released into the environment, self-assembling and self-replicating
nanomachines could spread like pollen or bacteria, and be too tough and
too small to stop before invading every part of the biosphere, chewing
it up and reducing all life on earth to “gray goo.” In nanotech circles,
this is called the “gray goo problem,” but no one really knows if this
vision is prophetic or simply hysterical.
Down the basement
hallway, postdoc Badireddy motions to me to join him at a computer
monitor next to the dark field microscope in his lab. He clicks on a
movie he’s made from images he’s captured. It shows silver nanoparticles
interacting with bacteria.
At first, the nanoparticles don’t seem
to be doing much. Then, all of a sudden, they start to clump to the
outside of a bacterium. The nanoparticles build up and build up until
the bacterium’s cell membrane bursts. Then the nanoparticle clumps
dissolve into small units before clumping back up again and attacking
more bacteria. “The whole cycle happens in about thirty minutes,”
Badireddy says. “It’s so fast. If you leave the nanoparticles overnight,
when you come back in the morning, all the bacteria are ground mush.”
If
you’re looking for stink-free athletic socks, maybe this is a good
thing. But could that same process someday turn out to have some sort of
nasty biological effect? We just don’t know yet.
“The fact that
they re-cycle suggests they might persist for a long time,” Badireddy
says as we watch the movie a second time. “They might enter the food
chain. And then, who knows what will happen?”
For more on the topic, listen to theaudio recording of the forum Orion hosted with Millar,
a researcher, ethicist, and consumer advocate on the topic, here, which
expanded on several themes Heather didn't have room for in this
article.
Heather Millar has covered science, health, and technology for twenty years, contributing to magazines such as Sierra, Smithsonian, and The Atlantic. She lives with her family in San Francisco.
