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Poplars Disarm Pollutants




Scientists since the early '90s have seen the potential for cleaning up contaminated sites by growing plants able to take up nasty groundwater pollutants through their roots. Then the plants break certain kinds of pollutants into harmless byproducts that the plants either incorporate into their roots, stems and leaves or release into the air.
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Using plants, or phytoremediation, often hasn't made sense given the timetables required by regulatory agencies at remediation sites. Scientists led by the University of Washington's Sharon Doty, reporting in this week's Proceedings of the National Academy of Sciences, say that genetically engineered poplar plants being grown in a laboratory were able to take as much as 91 percent of trichloroethylene, the most common groundwater contaminant at U.S. Superfund sites, out of a liquid solution. Unaltered plants removed 3 percent. The poplar plants all cuttings just several inches tall growing in vials also were able to break down, or metabolize, the pollutant into harmless byproducts at rates 100 times that of the control plants.

Federal regulations do not allow the commercial growing of transgenic trees.

The work being published this week raises the interesting question of the potential for using transgenic trees on sites where toxic plumes of pollutants are on the move in groundwater.

"Small, volatile hydrocarbons, including trichloroethylene, vinyl chloride, carbon tetrachloride, benzene, and chloroform, are common environmental pollutants that pose serious health effects. Some of these are known carcinogens," Doty, an assistant professor of forest resources, said.

Both unaltered poplars and the transgenic poplar plants produce the enzymes to break down trichloroethylene, C2HCl3, into chloride ions -- harmless salt that the plant sheds -- and recombines the carbon and hydrogen with oxygen to produce water and carbon dioxide.

Along with the trichloroethylene tests, the new results also found improved rates of uptake from solutions of chloroform, the byproduct of disinfecting drinking water; carbon tetrachloride, a solvent; and vinyl chloride, a substance used to make plastics.

Because there is concern that transgenic trees might get into regular forests, Doty and her colleagues believe poplars may be a good choice, she said.

Poplars are fast growing and can grow for several years without flowering, at which time they could be harvested to prevent seeds from generating. And unlike some other kinds of trees, branches of the hybrid poplar being studied do not take root in soils when branches fall to the ground.

"Commercial use of these trees requires federal regulatory approval and monitoring, and regulations are becoming increasingly strict for transgenic plants intended for biopharmaceutical or industrial purposes, including phytoremediation," the co-authors write in their paper. Other co-authors are from the UW, Oregon State University and Purdue University.

For more information: Doty, 206 616-6255, sldoty@u.washington.edu.


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October 17, 2019, 7:04 am PDT

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