George Redden studies colloidal suspensions in the laboratory. Eventually, he hopes to send colloids underground to investigate and treat the subsurface.
Subsurface Scientist—Three years ago, George Redden came to the U.S. Department of Energy's Idaho National Engineering and Environmental Laboratory to help plumb the depths of the subsurface. With a background in both engineering and chemistry, Redden tries to understand the underground jostling of minerals, contaminants and bacteria by studying the junction between solids and liquids. He says a chemical tug-of-war occurs at the liquid-solid boundary that may govern the movement of subsurface particles. Eventually, Redden wants to use his understanding to affect what happens underground—to stop the spread of a contaminant or disperse a helpful molecule.
Redden's task is not simple. Subsurface scientists use every means they can to observe and treat soil hundreds of feet underground. Complex water-mineral-bacteria interactions are difficult to study without fundamentally altering them—without disturbing the layers of soil underground or exposing them to atmosphere and light that can change their composition. It is also difficult, says Redden, to construct models in the laboratory that realistically mimic a natural underground environment.
But the tall mustached Redden has an idea that may make things a whole lot easier. He wonders whether it would be possible to send small man-made particles into the groundwater to inspect the depths for him.
Redden got the idea from studies about small natural particles called colloids. Colloids are bits of dirt, oil or bacteria that can stay suspended in groundwater without settling out. "Anything that doesn't settle out by gravity, but is larger than what we would call a molecule, is a colloid," says Redden. Fine clay particles in murky water are colloids, as are the pigments in household paint and the oil droplets in Italian salad dressing.
Underground, colloids move with the subsurface water. They can pick up dissolved materials, drop off what they pick up, or stick to passing surfaces. Like wandering dust mites that collect hair, pollen or dirt in the air, colloids can pick up metal or organic contaminants in the groundwater. "Many scientists think colloids might explain why underground pollutants move further than we expect. In some cases, the colloids themselves might be the pollutant in solid form," said Redden.
Redden reasons that if colloids can carry contaminants away from a site, they can also bring beneficial molecules to a site. His unique twist on colloid research is to eventually use new, engineered colloids like shipping vessels to transport wanted molecules into the subsurface.
Redden's groundwork research involves understanding the basic physics and chemistry of natural colloids. Surface charge is very important in colloid chemistry, he says. On something so small, the electrostatic interactions can overwhelm almost all other forces.
Think of a traveling dust mite. It's small enough that gravity has little pull and it wafts easily on air currents. But the surface charge of static cling powerfully attracts a dust mite. Correspondingly, a colloid will travel freely in the water until it encounters a charge. If a rock it passes has the same charge, the colloid will be repelled and continue traveling with the water. But if a colloid and a rock have opposite charges, the colloid will be attracted and slow down or stop altogether.
Some of Redden's research involves looking into what exactly happens when colloids attract, repel or collide with other soil components. Will the colloid drop its load? Will it stick to the soil? Will it careen in another direction? What if it collides with some built-up momentum as opposed to tapping an obstacle slowly? Currently, says Redden, scientists don't understand enough about the effects of colloid collisions or where contaminants go.
As Redden and his colleagues answer these questions, they can begin to tailor synthetic colloids to perform highly specialized functions. Redden envisions sending colloids into contaminated soil carrying molecules that can be used by microorganisms to break down pollutants. The strategy is similar to sending a drug through the bloodstream to cure diseased tissue. Scientists could also use colloids to remove, immobilize or degrade things in the soil, such as metals, radionuclides or organic solvents. Colloids with metal-grabbing chelators may pick even trace metals out of the soil. Or colloids could be used to plug up groundwater pathways—to make a wall so that pollutants can't spread, like a clot blocks the flow of an artery.
Redden also wants to use colloids to simply better understand the subsurface. He envisions attaching fluorescent tags to colloids and recording where the colloids go. Along with Jack Slater in the physics department, he's also trying to figure out how to send colloidal magnets underground and track them to characterize the underground landscape. The magnets would follow the flow of the water, allowing magnet-tracking instruments to trace the water's path.
Eventually, Redden would like to create "smart" colloids that are active only in desired parts of the soil. A bacterial colony that grows up around a pollutant may trigger a synthesized colloid to release its drug load. Or a colloid could carry a uniquely-shaped protein—an antigen—that sticks to only one type of bacterial antibody.
Most of Redden's manufactured colloids are still far from reality. But he's laying the groundwork now to create them later. He knows some applications may not eventually pan out, but he thinks he hasn't begun to exhaust the possible uses for engineered colloids. "It's risky, but the potential is too good to pass up," he says.
Redden thinks INEEL is an especially good place for synthetic colloid research. Subsurface science at INEEL, he says, is in a uniquely powerful position to apply cutting edge and cross-disciplinary research to solve real-world environmental troubles. His preliminary research is funded by INEEL's Laboratory Directed Research and Development fund, as well as the Environmental Systems Research and DOE's Environmental Management Science Program. Though the Subsurface Science Initiative at INEEL is only a few years old, Redden thinks the seeds that researchers plant now will bear fruit later. When speaking to Redden about colloids, it's easy to see why he likes the quote tacked up on his door by cyberpunk author William Gibson: The future is already here. It's just unevenly distributed.
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