The nano boom yielded countless commercial benefits—ultra-precise drug delivery systems, improved superconductors. Now, experts are examining the potential for toxic nanoparticles (objects typically smaller than one billionth of a meter) to end up inside plants, animals, or people.
The potential impact of nanoparticles on marine life concerns Southern Methodist University toxicologist Eva Oberdrster, who recently completed a study involving captive large-mouth bass. Oberdrster exposed the fish to various concentrations of a dome-shaped molecule called Carbon-60. After two days, signs of an immune response to the invaders were found inside the fishes' livers. Evidence suggests the molecules may have even breached the cells protecting the brain and central nervous system. Carbon-60 is part of a family of precision-engineered nanoparticles called fullerenes, named after architect R. Buckminster Fuller, famous for his geodesic domes. The structure of the molecules and their resistance to heat, among other properties, make them suitable for use in fuel cells, high-temperature lubricants, and other products that could wind up in landfills, says nanochemist Vicki Colvin, director of the Center for Biological and Environmental Nanotechnology at Rice University, where fullerenes were first discovered. But not all fullerenes are toxic, Colvin points out.The type used in the fish study lacked the protective coating often applied to fullerenes to render them non-toxic to living tissue. "Fullerenes have extremely stable surface coatings," she says. More than merely shellacking the sphere, the coating process chemically bonds the surface material to the carbon. Colvin adds that fullerene pollution will likely pale next to the nanoscopic airborne pollution already in existence, from the carbon particles in car exhaust to the manganese oxide in welding fumes."We're exposed to multi-ton quantities of incidentally created nanoparticles," Colvin says. Oberdrster's father, Gnter Oberdrster, director of the University of Rochester’s EPA-funded Particulate Matter Center, has probed the toxicity of those inadvertent particles for years. His most recent research project shows that rats, like monkeys, may be subject to contamination by inhaled ultrafine particles via the olfactory tract, a pathway also found in humans. Gnter Oberdrster cautions against alarm, too: Nanoparticle toxicity is not a given. "Surface chemistry is very important," he says. "Most of the engineered nanoparticles may be harmless. Of course, we don't know that. We need to find out."There are not many ongoing studies as they relate to nanoparticles in drinking water. Perhaps the most important one revolves around the idea of how nanoparticles could complicate the treatment processes of already existing contaminants in large industrial watershed areas such as the Clark Fork River, the largest EPA Super Fund clean-up site in the U.S. Scientists are discovering that aquatic nanoparticles, from 1 to 100 nanometers, influence natural and engineered water chemistry and systems differently than similar materials of a larger size. "Nanoparticles are in an awkward intermediate state, between elements dissolved in water and minerals that you can hold in your hand," said Michael Hochella Jr., University Distinguished Professor of geosciences at Virginia Tech. "The nanoscale represents a transition zone. For instance, the electronic, magnetic, and optical properties at the atomic, nano, and bulk scales are all different."
"In Montana, we are finding that nanoparticles are important in transporting toxic heavy metals, such as lead and arsenic, down the river," said Hochella. "These particles are incredibly small — 5 to 10 nanometers. Historically, we have not even known the nanoparticles were there. Now we know that lead in solution is different than if it is attached to a particle. But finding the particles is not easy. And the impact on bioavailability is still unknown." He asks, "Are the metals less toxic if they are associated with nanoparticles than if dissolved as atoms in water? If a person, animal, fish, or insect ingests this water, will lead pass harmlessly through if it is associated with a nanoparticle? "What Kelly learns about the role of nanoparticles in metal transport will be applicable to rivers worldwide," Hochella said.
Closer to home, the authors asked, can environmental nanoparticles, which both transport and break down contaminants, affect the quality of our drinking water — despite or because of water treatment processes? As a model system for identifying the mineral phase(s) of nanoparticles extracted from treated waters, Virginia Tech researchers examined tap water from Washington, D.C., which had had a significant problem with dangerously high lead concentrations in drinking water, likely due to leaching from lead-bearing pipes promoted by breakdown products of disinfection agents, according to Marc Edwards, professor of civil engineering at Virginia Tech, who was named a MacArthur Fellow for his work.
The Virginia Tech geosciences group’s TEM data showed the presence of many nanoparticles of various compositions, sizes, and morphologies, some of which contain lead. Wigginton wrote, "Although very few studies have been done to address the origin of nanoparticles in drinking water systems, it is relatively safe to assume one of three mechanisms: 1) the particles themselves (not necessarily the sorbed species that they are carrying) are native to the source water and are resilient enough to withstand chemical processing steps at the treatment facility; 2) nanoparticulate phases precipitate once inside the treatment plant and/or distribution system in response to changing chemical conditions, or 3) corrosion of pipes promoted by disinfectants and/or their degradation byproducts could cause nanoparticles attached to the piping material to detach." He said that preliminary evidence suggests lead transport is influenced by environmental nanoparticles from the source water that have made it through the treatment facility and into the distribution system.
The researchers concluded that "environmental nanoparticle science will have to advance aggressively along at least two research paths: 1) fundamental research on the physical property and chemical reactivity variability of nanoparticles as a function of their size; and 2) the detailed study and understanding of the influence of nanoparticles on aqueous chemical processes." Hochella observed that the Journal of Environmental Monitoring prefers to give engineers and scientists information about processes, "but we are not yet able to tell engineers and scientists in the field where the nanoparticles and metals are and why nanoparticles behave differently. But it certainly is important that they know that recent research is calling assumptions about transport, remediation, and water treatment into question."