Pioneering Interdisciplinary Approaches to Phytoremediation | National Institute of Environmental Health Sciences

Pioneering Interdisciplinary Approaches to Phytoremediation | National Institute of Environmental Health Sciences
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Pioneering Interdisciplinary Approaches to Phytoremediation
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By Adeline Lopez
Researchers at the NIEHS-funded University of Washington Superfund Research Program Center (UW SRP Center) developed innovative approaches to enhance phytoremediation of chlorinated solvents using poplar trees. Phytoremediation is a process that uses plants to remove, break down, contain, or immobilize contaminants from soil or water.
The team, led by Milton Gordon, Ph.D., and Lee Newman, Ph.D., found that hybrid poplar trees can degrade chlorinated organic solvents in groundwater, including trichloroethylene (TCE), perchloroethylene, and carbon tetrachloride. They were the first to genetically enhance poplar trees to increase removal of TCE, and their approach evolved to become more efficient, sustainable, and cost-effective.
The Problem:
Chlorinated organic solvents are widespread toxic pollutants that tend to rapidly move through the soil and into groundwater. Traditional approaches to clean up these compounds, such as pump and treat, are expensive and time consuming, and may form by-products that are also harmful to human health.
SRP Solutions:
Cleaning Up Toxins with Plants
Poplar trees grow quickly, and their root systems penetrate large volumes of soil from which they draw water to extract nutrients. They also take up organic contaminants during this process, which are metabolized and broken down into harmless products. Phytoremediation is driven by solar power and does not involve the use of other chemicals to degrade pollutants. It also does not require contaminated water or soil to be removed from the site to be cleaned up, making it cost-effective.
For examples of high-impact SRP research on bioremediation, including phytoremediation, see the
list of related SRP Research Briefs
Gordan and Newman, with early collaborators Stuart Strand, Ph.D., and Paul Heilman, Ph.D., brought together interdisciplinary expertise in physiology, agronomy, microbiology, hydrogeology, and engineering. They developed remediation technologies using hybrid poplar trees that clean up contaminants in the environment. This cost-effective strategy reduces the amount and toxicity of pollutants while preserving or restoring the environment and habitats. Their findings also spawned a new field of research.
From the 1980's until 2015, the NIEHS SRP funded cutting-edge phytoremediation research at the UW SRP Center. Initiated by Gordon, this work evolved from identifying plant species best suited to remediation, to understanding the mechanism of detoxification, to genetically enhancing poplars to better metabolize these contaminants.
The UW SRP Center team studied phytoremediation of persistent organic compounds, including TCE,
carbon tetrachloride
, methyl tertiary butyl ether, formaldehyde, trichloroethane,
ethylene dibromide
, chlorobenzenes, and pesticides such as
chlorpyrifos
SRP Trainees conduct greenhouse studies with poplar trees in 2002.
(Photo courtesy of the UW SRP Center)
Since then, Newman, Strand, and former UW SRP Center postdoctoral trainee Sharon Doty, Ph.D., pushed the field of phytoremediation forward through their innovative use of hybrid poplar trees to clean up contaminants. Experiments using the trees moved from the lab to field studies, and they have also been used to clean up hazardous waste sites.
From the Lab to the Field
Poplars break down contaminants
Lab results confirmed in the field
Gordon and Newman's
research was the first
to show conclusively that plants themselves, not just microorganisms associated with plants, are capable of degrading toxic compounds.
They demonstrated that hybrid poplars could take up and degrade TCE in greenhouse and lab studies, showing that
less than 5%
of the TCE removed from the environment was transpired by the plants. Later, they expanded this work to the field, showing that the trees
removed more than 99% of TCE
present in groundwater. The group achieved similar results for
carbon tetrachloride
, with 99% removal and limited transpiration under field conditions.
The phytoremediation system was installed as part of a
clean-up plan
for a Superfund site in Keyport, Washington, to treat TCE-contaminated groundwater leaching from a wetland. The team
continued to study the Keyport site
for several years to improve their understanding of how hybrid poplars take up and metabolize contaminants.
UW SRP Center researchers explored the mechanism by which cells of poplar trees detoxify
carbon tetrachloride
and
TCE
. SRP trainees in Newman’s lab focused on identifying plant genes involved in TCE degradation while Stuart and Doty focused on using mammalian P450, a key enzyme in the metabolism of a variety of compounds, to genetically enhance plants to better degrade TCE.
New Frontiers in Phytoremediation
Genetically enhanced poplars aide TCE breakdown
Endophytes health poplars clean up TCE
Building off their early work, Doty and Strand continued to explore new directions in phytoremediation using
genetically enhanced plants
that could metabolize and degrade TCE more efficiently. They developed
developed genetically enhanced poplars
that overexpress mammalian cytochrome P450.
In laboratory studies
, the enhanced poplars were able to metabolize TCE up to 100-fold greater than controls and remove more TCE from water and air. Their work showed that genetically enhanced plants can improve pollutant detoxification and removal. SRP trainee Jun Won Kang, Ph.D., continued this line of research and identified key
changes in gene expression
in modified plants in response to TCE exposure. A field
trial of the genetically enhanced poplar
demonstrated improved TCE removal, though less extensively than what was observed in laboratory studies.
Doty studies genetically enhanced poplar shoots in the lab.
(Photo courtesy of UW SRP Center)
In a related area of research not funded by SRP, colleagues at Brookhaven National Laboratory
identified a species of endophyte bacteria
only present in plants exposed to TCE. Endophytes are symbiotic microorganisms that exist within plant tissues without harming and potentially benefiting the plants. Newman’s
research with this bacteria
showed that they dramatically enhanced plant root development and TCE degradation in the poplars.
With funding from the National Science Foundation, Doty
identified a species of endophyte bacteria
that naturally colonizes poplars with high rates of TCE degradation. Building on this work, her team also isolated endophytes that
degrade polycyclic aromatic hydrocarbons
, which they successfully demonstrated in a
pilot study on a Superfund site
with outside funding.
Researchers led by SRP-funded small business
Edenspace Systems Corporation
conducted the first large-scale experiment on a Superfund site using poplar trees fortified with the microbial endophyte identified by Doty to clean up TCE-contaminated groundwater. Their work showed that
endophyte assistance boosts
the speed and effectiveness of this natural degradation process while also protecting the plants from harmful effects of TCE. With the added help of endophytes, the technology is a more cost-effective and sustainable method for removing contaminants from the environment.
Innovations Reap Economic Benefits
Collaborating with Another SRP Center
In the 1990’s Gordan and Newman met and collaborated with Jerald Schnoor, Ph.D., at the University of Iowa. Interested in a similar line of research, Schnoor, Gordan, and Newman strategized how to use phytoremediation with hybrid poplars for different groups of contaminants. In fact, one of Schnoor’s students teamed up with the UW SRP team to
identify and characterize endophyte bacteria
on poplar trees in a project supported through the university. When the
University of Iowa SRP Center
was funded in 2006, Schnoor led a project studying the ability of hybrid poplar trees
to degrade polychlorinated biphenyls (PCBs)
In addition to public health benefits resulting from reduced exposure to harmful pollutants, the UW SRP Center’s approach to cleaning up chlorinated organic solvents also has significant
economic benefits
The
Naval Undersea Warfare Center Division estimated
estimated that their use of the UW SRP Center phytoremediation method saved up to $10.5 million compared with traditional methods at the Keyport site. Based on these promising results, the
U.S. EPA used hybrid poplar trees
at the Argonne National Laboratory in Batavia, Illinois and estimated approximately $2.4 million in cost savings.
technology was validated
as part of the U.S. Department of Defense’s Environmental Security Technology Certification Program, which estimated that as many as 1,000 cleanup sites worldwide could use the technology, saving hundreds of millions of dollars.
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Last Reviewed: September 19, 2024