Nanoparticles, the nearly invisible high-tech building blocks that could open new ways to generate energy, treat disease and clean up pollution, are also under laboratory scrutiny for a different reason - to find out whether they are novel pollutants in their own right.
Scientists at the U.S. Environmental Protection Agency's Mid-Continent Ecology Division in Duluth have begun studying seven different nanomaterials, hoping to develop the tools regulators will need to determine how risky they will be in lakes, rivers and groundwater.
Because nanotechnology - the use of very tiny engineered particles to create substances that behave in new ways - is a relatively new field, it lacks the years of environmental study the EPA has done on many common chemicals.
"I would say we're just starting to scratch the surface in understanding how toxic these things have the potential to be," said Steve Diamond, who spent years earlier in his career studying toxic chemicals for the EPA.
SOMETIMES HELPFUL, SOMETIMES DANGEROUS
Diamond and his colleagues in Duluth face a couple of significant challenges.
Because nanoparticles are so tiny, it takes a powerful electron microscope to see one. They can change dramatically, depending on their environment. And sometimes the very characteristic that makes them helpful can also render them dangerous.
For example, nanoparticles of titanium dioxide are activated by sunlight. That makes them effective in blocking ultraviolet rays in sunscreen. It also could let them render oil spills less harmful when sprayed on water, breaking up the oil.
But the property might also cause them to destroy anything living in the water.
In the lab, Diamond recently showed a visitor how he exposed tiny water fleas called daphnia to titanium dioxide nanoparticles.
Under a microscope, you could see the tiny crustacean's heart beating. Its intestines were packed with nanoparticles and its body was crusted with blobs of nanoparticles.
"What's remarkable here is the organism is obviously ingesting and coated by titanium dioxide but it's not affecting them at least in terms of how well they survive."
But if takes the same daphnia down the hall and exposes it to a lamp that mimics sunlight, it will die within hours.
That's because titanium dioxide nanoparticles exposed to sunlight give off large amounts of energy, in the form of something called reactive oxygen molecules. They attack any organic matter, whether it's oil in the water or tiny crustaceans or fish.
"So they'll actually disrupt membranes and disrupt tissues and eventually the organism can almost melt if the strength of the reaction is strong enough."
"IT'S LIKE A BOLD NEW WORLD"
By understanding the complex ways these particles interact, researchers might find a way to neutralize them. But right now they can't even accurately measure the particles in a lake or stream. Scientists may never be able to measure some nanoparticles in nature, Diamond said.
It's impossible to know how common nanoparticles are, and, so far, manufacturers aren't required to tell consumers or the government if products contain them. That will change when the EPA requires disclosure.
"The economic benefits, the environmental benefit, there's huge potential there. It's undeniable," Diamond said. "But then on the other hand we're faced with this problem these things do very strange things, that's why they're effective. It makes us very concerned about side effects they might have. It's like a bold new world."
Carl Richards, director of the EPA's mid-continent ecology division in Duluth, said, "A big part of it is making sure we're developing scientists who have sound understanding of the science and all of the issues that are related to regulation of these materials and development of the science to support that kind of regulation."
Diamond said, "We're very aware of what the problems are. But in terms of technology we have some very large hurdles to get over."