Pollutants in the ground that do not easily mix with water, such as organic solvents, are a continued source of groundwater pollution until they are removed.
"These subsurface pollutants are a particularly difficult problem because there are few reliable technologies to locate and destroy them," said Lowry, a professor of civil and environmental engineering at Carnegie Mellon. "Our team of environmental engineers, chemical engineers, chemists and physicists is developing a process very similar to a targeted drug delivery system to target and destroy these dangerous groundwater toxins," he said.
A team of investigators, including Lowry, Sara Majetich, Krysztof Matyjaszewski, David Sholl and Robert Tilton of Carnegie Mellon and Paul Meakin, George Redden and Harry Rollins of the Energy Department, designed nanoparticles with the potential to reach underground pockets of chlorinated organic solvent called trichloroethylene (TCE). This chemical is still used extensively to remove grease from metal parts. Approximately 60 percent of the 1,400 contaminated sites on the National Priorities List, the nation's most hazardous waste sites, are contaminated with this suspected carcinogen, according to Lowry.
TCE separates out from water as droplets, much like oil or water. But underground pockets of this chemical can steadily release droplets into porous soil layers called aquifers, which supply 50 percent of the nation's drinking water. Left untreated, billions of gallons of groundwater stand to be contaminated by TCE, Lowry said.
To make the nanoparticles used in the current research, the investigators started with a core reactive iron that quickly breaks down chlorinated organic solvents into harmless byproducts. The research group of Matyjaszewski, a professor of chemistry and director of the Center for Macromolecular Engineering at the Mellon College of Science, coated these iron molecules with two polymer shells. An outer, "water-loving" shell would enable particles to travel through an aquifer. Once it reached a water-TCE interface, an inner "water-hating" shell would make the particles stick there and allow the particle's reactive core to break down this toxic residue.
The nanoparticles were created by atom transfer radical polymerization (ATRP). This synthetic method was developed by Matyjaszewski to precisely control the formation of polymers at the nanoscale level. Using ATRP, scientists can mass produce high quality materials that combine very different structural and functional properties.
Nanoparticles are ideal agents to treat underground pockets of chlorinated organic solvents because they can move easily through even the smallest pores within soil. The current study is focused on developing particles with field testing as the next segment. This nanoparticle technology also could be adapted to clean up spills of other chlorinated solvents.
It has been estimated that the cost of cleaning up the many U.S. groundwater sites contaminated by TCE could reach $1 trillion, according to the Department of Energy. Current technologies are limited in their effectiveness. Typically, they involve containing the problem by treating a steady plume of organic solvent as it is slowly released from the source. Taking the targeted nanoparticles directly to the source of the contamination would remove it and solve the problem faster, Lowry said. This step would significantly lower cleanup costs. This research also will provide a better understanding of how small particles transport in a subsurface. Researchers from Carnegie Mellon and the Idaho National Engineering and Environmental Laboratory received $1.7 million from the Department of Energy for the three-year study.
An illustration of these nanoparticles is available by contacting either Chriss Swaney at 412-268- 5776 or Lauren Ward at 412-268-7761.