Still, Dr. Landmeyer estimates that probably less than 10 percent of Superfund sites in the country use phytoremediation as a stand-alone cleanup method.
One reason for the limited success is that trees that were planted with good intentions could not survive in areas that were highly polluted. “People were losing faith in phytoremediation because it got expensive to replace dead or sick trees,” said John Freeman, chief scientific officer at Intrinsyx. “It was viewed to be cost prohibitive.”
If the trees remained healthy, phytoremediation would cost about half as much, saving perhaps a half-million dollars per project, compared to traditional engineering methods such as drilling and extracting toxins from soil or groundwater, Dr. Landmeyer said. Trees might take a bit longer for the same job — about five years, he estimates — “but the cleanup goal would be the same.”
Before planting the poplars, Intrinsyx inoculate the poplar cuttings with high concentrations of a microbe called PDN3. This microbe not only gives the poplars an added survival advantage, but helps the trees withstand toxic groundwater by breaking down trichloroethylene, an industrial pollutant from solvents and degreasers.
The technique was developed by Dr. Doty, who in 1995, as a post-doctoral researcher, began studying whether genetically modified poplar trees could clean up pollutants. Poplars are fast-growing and have an extensive root system, which allows them to quickly take up whatever is in the soil groundwater. Poplars could be genetically modified, she reasoned, to speed up their ability to break down chemicals and toxins.
Dr. Doty found that poplars that were engineered with an abundance of one enzyme seemed to make the carcinogen trichloroethylene disappear. The results were “so beautiful” in eliminating trichloroethylene, she said. But because of public concern about genetically modified organisms — for instance, that engineered genes might “jump” into neighboring wild plants — Dr. Doty feared that her technique might never catch on.
Dr. Doty noticed that when she was engineering her poplars, other bacteria in the plant tissue seemed to be contaminating the results. At the time, little was known about the microbiome; Dr. Doty considered these bacteria a nuisance.