A former Energy Dept. uranium-conversion complex outside Ashtabula, Ohio, is an environmental nightmare, its soil laced with deadly uranium. Cleaning it up would ordinarily mean carting away thousands of tons of polluted dirt at great expense. Now, hope for a better, cheaper approach is blooming--literally. In a small greenhouse on the factory grounds, scores of sunflowers are sucking the uranium out of contaminated water pumped from the soil.
The idea of enlisting nature's flora to cleanse polluted soil is called phyto-remediation--and it's spreading faster than fertilized kudzu. "It's an incredible technology," raves DuPont Co. scientist Scott Cunningham. "Not only does using plants to clean up the world's environmental excesses make sense, it's a heck of a lot prettier than engineering solutions."
NEW NICHE. Cunningham's own experiments show that common crops such as corn or Bermuda grass may be able to yank nearly a ton of lead per acre from contaminated soil each year--just the ticket for lead-polluted DuPont facilities and thousands of other U.S. sites. A variety of plants, including trees, are proving adept at cleaning London sewage sludge, TNT-laden ground at a Tennessee munitions factory, and radioactive fields near Chernobyl. "We are just beginning to explore the possibilities," says University of Missouri biochemist Douglas D. Randall.
Already, a handful of companies--such as Phytotech in Monmouth Junction, N.J., Phytokinetics in Logan, Utah, and Applied Natural Sciences in Hamilton, Ohio--have sprouted to commercialize the new approach. The biggest lure: cost. Burt Ensley, an Amgen Inc. veteran who founded Phytotech in 1993, estimates that plants may do the job of environmental engineers for one-tenth the price. That advantage, Ensley figures, should win him a nice piece of the $12 billion-per-year hazardous-waste-remediation industry. And it could lower costs enough for companies and governments to tackle contaminated areas without prodding from regulators. Insurers, too, are intrigued. Phyto-remediation could be "a significant new strategy," says Stuart Ferguson, vice-president of AM-RE Services Inc., a subsidiary of American Re-Insurance Co.
The big environmental firms are still on the sidelines, waiting for proof that nature can do the job. "We haven't seen enough data for us to go out and apply it yet," says Roger Olsen, vice-president at Camp Dresser & McKee Inc.
Researchers acknowledge that they have more work to do, but they believe convincing data is on its way. Take the progress with heavy metals. Back in 1990, Rutgers University biochemist Ilya Raskin was looking for a biological method to clean up lead, zinc, and other metals. He knew that many plant species can accumulate staggering amounts of these elements, but that most are too small to do much good. So he screened thousands of metal-munching plants before finding a few, such as Indian mustard, that are both large and able to vacuum up metals. Once grown, the plants can be harvested and put into a smelter to recover the metals (diagram) or disposed of appropriately in approved landfills. Even if the metals aren't recovered, the amount of waste--in the form of contaminated plants rather than dirt--is reduced by 98%.
Raskin's work is now being sponsored by $1.2 million from Phytotech. The company's tests in Ukraine suggest Indian mustard could clean up strontium-laden soils near Chernobyl within five years.
The plants are only part of the story. By adding chemicals that grab on to metals in the soil, scientists can boost uptake a thousandfold. DuPont's Cunningham is trying such a strategy with lead. He uses ordinary plants such as corn or peas that don't normally extract metals and adds chemicals to the soil that flush the lead into the surrounding water. The plants then readily suck up the metal.
GENE-TWEAKING. Genetic engineering promises further gains. At the University of Georgia, geneticist Richard Meagher added a bacterial gene to a mustard relative named Arabidopsis. The resulting transgenic plant can take up a dangerous form of mercury from soil, transform it into a less harmful form, and allow it to evaporate into the atmosphere. "Everyone told me it wouldn't work," says Meagher. "But now we have something really spectacular to offer." Scientists are creating transgenic plants that target other metals, too. "The technical breakthroughs in the whole field are coming a mile a minute," says Cunningham.
Still, even phyto-remediation's most ardent boosters admit the technology is not a panacea. Plants won't be able to tackle all sites, such as those where toxins lurk deeper than roots can reach. And since metal-containing plants are themselves hazardous waste, they must be off-limits to grazing animals. Despite these limitations, phyto-remediation still has enormous promise, scientists say. The high-tech cleanups of tomorrow may simply be a matter of letting a thousand flowers bloom.