Scientists Mine Gold With Alfalfa

As a child growing up in the mining village of Parral in northern Mexico, Jorge Gardea-Torresdey learned quickly about the devastation that resulted from the effort to extract gold and silver from land around his community.

Toxic chemicals, including cyanide and mercury, leached into the soil, leaving it useless for anything else, and even as a kid he figured there had to be a better way.

That's why today he has an alfalfa field growing near his lab at the University of Texas, El Paso.

Don't laugh. Those alfalfa plants are mining gold. And if his research continues to hit pay dirt, someday gold used in everything from medical procedures to high-tech industries might well come from fields of alfalfa.

Using Plants as Tools

So far, his plants have produced only nanoparticles of gold — tiny specks less than a billionth of a meter in diameter — but Gardea thinks they are capable of a much more prodigious output.

"I think we can get 20 percent of the weight of the plant in gold," he says. "That could be possible."

The success he and his colleagues have had so far, he says, amounts to a childhood dream come true. It turns out that he happened to be the right person, at the right place, at the right time.

His passion for chemistry began as a high school student when he worked in the laboratory at one of the mines near his village. Years later, he finished his graduate study just as a new field was emerging. Scientists were experimenting with using trees and plants to extract toxic materials from the ground.

The process, called phytoremediation, relies on the natural ability of some plants to take up materials, even heavy metals, through their roots. Scientists across the country are experimenting with using the process to clean up toxic spills ranging from explosive materials to hydrocarbons.

Gardea plunged into the field nearly a decade ago, working mainly with alfalfa.

"We found that alfalfa can take up metal more than other plants," he says, suggesting that it is probably suitable for cleaning up some highly toxic sites. The plant concentrates the metal in its shoots, making it possible to remove the hazardous material from the area.

But that successful research wasn't enough to satisfy his boyhood dreams.

"Always, in my mind, was gold and silver," he says with a chuckle.

Could it be possible, he wondered, to turn a plant normally grown as cattle food into a gold factory?

Gold-Laced Alfalfa

To find out, Gardea needed some very sophisticated partners. And he needed a chunk of dirt salted with a little gold. And he needed a little cash, which was provided by the Environmental Protection Agency, the Department of Energy, and the National Institutes of Health.

Getting the alfalfa to grow was the easy part. Finding out if it was actually taking up the gold was a bit harder.

So Gardea turned to colleagues at the University of Texas, Austin, and Stanford University.

Miguel Jose Yacaman, a professor of chemical engineering, used a high-resolution transmission electron microscope in his Austin lab to study plants that Gardea had harvested from his gold-enriched soil. It was pay day, big time. Not only had the alfalfa taken up the gold particles, it had stored them throughout its roots and stems.

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