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UGA researchers use transgenic trees to help clean up toxic waste site


Can genetically engineered cottonwood trees clean up a site contaminated with toxic mercury? A team of researchers from the University of Georgia - in the first such field test ever done with trees - is about to find out.

The results could make clearer the future of phytoremediation - a technique of using trees, grasses and other plants to remove hazardous materials from the soil. UGA scientists and city officials in Danbury, Conn., planted on July 16 some 60 cottonwoods with a special gene at the site of a 19th-century hat factory in that northeastern city.

"We hope to see a significant difference in the levels of mercury in the soil within 18 months, perhaps as much as a twofold reduction," said Richard Meagher, professor of genetics at UGA.

The field test is a collaboration between UGA, Western Connecticut State University, Applied PhytoGenetics, Inc., of Athens and the City of Danbury.

While the technology now being used in Danbury does not apply to all sites, mercury pollution is a pervasive problem in Georgia as it is elsewhere. The site of a former chemical factory near Brunswick, for example, is polluted with mercury and other toxic chemicals. Mercury contamination has been reported around the sites of former gold mines in north Georgia, and advisories have been issued during the past decade for mercury-contaminated fish in more than 80 streams, lakes and creeks in the state.

Meagher’s team did the first-ever field trial of a genetically engineered plant to sequester mercury when it grew transgenic tobacco in a New Jersey field trial in 2001, but this is the first such trial using trees, whose larger root systems and year-round life cycle makes them better candidates for long-term cleaning of polluted soil.

Phytoremediation is a relatively new field and one gaining international interest. A team of photographers working for National Geographic, for instance, recently spent considerable time with Meagher capturing on film his work as part of a four-part documentary that will be aired some time next winter.

Meagher has for more than a decade been a pioneer in phytoremediation, and he was the first to demonstrate that a gene called merA can be inserted into plants and used to detoxify mercury in the environment. While no plant can break mercury down, since it is an element, less toxic forms can be created, and that has been the goal of Meagher’s lab - to find ways to let plants or trees grow on polluted sites, draw such heavy metals as mercury into the plants themselves and then either transpire the much less toxic forms of the metal into the air where they are quickly diffused or trap the metal aboveground for later harvest.

The project with Danbury came about because Danbury’s environmental coordinator, Jack Kozuchowski, had in 1977 published an early study that showed how native plants could transfer mercury from contaminated soils into the atmosphere. Kozuchowski, aware of Meagher’s work, convinced officials in Danbury that the so-called Barnum Court site in that town would be a perfect site for a field trial of the genetically engineered trees that Meagher and his collaborator Scott Merkle developed.

The city was awarded a grant of some $55,162 from the Environmental Protection Agency to explore use of the technology, and the trial was set up - though most costs for the work are being born by those involved in it.

"It is our hope that the research will lead to a cleansing of the Barnum Court property so the city can transfer the property for development," said Mark Boughton, mayor of Danbury.

Meagher’s mercury phytoremediation technology is exclusively licensed to Applied PhytoGenetics, or APGEN as it is called, and that Athens company has been instrumental in helping set up the field trial. (Meagher is a consultant to and cofounder of APGEN.)

Postdoctoral associate Andrew Heaton of Meagher’s lab and one other of Meagher’s students traveled to Danbury in July to supervise planting the genetically engineered trees on the site in enclosed plastic containers buried on the site.

Because the mercury on the site ranges, depending on location, from five to more than 300 parts per million, trials were set up to measure the effects of the cottonwood trees on progressively more polluted samples of soil. Forty-five plots, most planted with four trees each, are located on the site, which is in a mixed-use urban area and whose total area is less than an acre. (Some 15 plots have four merA trees, 15 are nonengineered or "wild-type" trees and 15 received no trees at all, so there are 120 trees in the field test.)

The form of mercury at the Danbury site is ionic mercury, a species that can be sequestered and transformed into less toxic metallic mercury in the transgenic trees and then transpired into the atmosphere. (Several forms of mercury were used in hat-making in the 19th century, but their toxic effects often sickened workers and led to the phrase "mad hatter," which described the process of neurological degeneration that came from working with the metal. In this part of New England, the symptoms of mercury poisoning were called the "Danbury shakes.")

Meagher’s lab actually has two genes that can effect phytoremediation, merA and merB, but since the merA is active on ionic mercury, the cottonwoods trees chosen for the Danbury trial express the merA gene.

"This is a field test, not a cleanup," said Meagher. "And we will be measuring mercury in both the soil and the trees to see just how much success we have in reducing the mercury levels in the soil. We are very optimistic that this technology will work."

While the trees at the site will have to be watered, the costs of that pale in comparison to traditional clean-up methods - digging up the polluted soil and hauling it off for storage at another site, possibly greater than $1 million.

A team of researchers from Western Connecticut State University will be studying the role of soil microorganisms in the potential clean-up of mercury on the site. According to the City of Danbury, the field test will run through the 2004 growing season, and if results are positive, genetically engineered cottonwood trees will be used to clean the whole site.

Kim Carlyle | EurekAlert!
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