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News Article

Probiotics help poplar trees clean up toxins


Toxins in groundwater broken up at Superfund site

Phytoremediation is the process by which plants and trees are used to decontaminate pollution in soil or water by removing or breaking down contaminants. Trichloroethylene (TCE) is a widespread environmental pollutant common in groundwater plumes associated with industrial manufacturing areas. Researchers from the University of Washington and several small companies have investigated how to boost metabolism of TCEs by poplar trees at a polluted Superfund site (polluted locations in the USA requiring a long-term response to clean up hazardous material contaminations). They suggest that a probiotic bacteria can promote the cleanup by helping protect trees from the toxic effects of the pollutants and break down the toxins plants bring in from contaminated groundwater.

A paper published online in Environmental Science & Technology reports on a successful three-year field trial of endophyte-assisted phytoremediation on the Middlefield-Ellis-Whisman Superfund Study Area TCE plume in the Silicon Valley of California. Where the groundwater had flowed into the NASA Research Park at NASA's Ames Research Center, the researchers planted rows of young poplar trees on a field above a known groundwater plume contaminated with TCE. Some of the rows of trees were inoculated with a natural bacterial endophyte, Enterobacter sp. strain PDN3, of poplar trees, that had been found to rapidly metabolize TCE, releasing chloride ions.

The inoculated poplar trees exhibited increased growth and reduced TCE phytotoxic effects with a 32% increase in trunk diameter compared to mock-inoculated control poplar trees. The inoculated trees excreted 50% more chloride ion into the rhizosphere, indicative of increased TCE metabolism in planta. Data from tree core analysis of the tree tissues provided further supporting evidence of the enhanced rate of degradation of the chlorinated solvents in the inoculated trees.

After only a year, the trees given the microbe were bigger and healthier than the poplars with no special treatment. After three years, the inoculated trees were still more robust, and a sample of tree trunks revealed greatly reduced levels of TCE inside the trees. Additionally, the researchers found that groundwater samples taken directly downstream from the test site showed much lower levels of the toxin, compared with higher levels up-gradient from the testing area.

The successful field trial could be a game changer to quickly and effectively clean up Superfund sites around the country and polluted sites abroad that have high levels of TCE, the authors say. 

"These results open the door," said corresponding author Sharon Doty, a UW professor in the School of Environmental and Forest Sciences. "We have known about this process for a long time from our laboratory research, but it hasn't been used in practice because there were no field results. Now, engineering companies can start using this in real life."

Subscribers to Environmental Impact can find over seventy bibliographic records on trichloroethylene AND phytoremediation. A number of the papers are on the use of tree species, including poplars. Weyens et al. (2015) examined the potential of the endophyte Pseudomonas putida W619-TCE to improve phytoremediation of Ni-TCE co-contamination using poplars. Inoculation with P. putida W619-TCE resulted in a 45% increased Ni uptake in roots as well as a slightly significant reduction in TCE concentration in leaves and TCE evapotranspiration to the atmosphere. These results indicate that endophytes equipped with the appropriate characteristics can assist their host plant to deal with co-contamination of toxic metals and organic contaminants during phytoremediation. Odom et al. (2013) report on tissue sampling to monitor the efficiency of TCE phytoremediation using hybrid poplars. See the Further Reading list below for a small selection of other relevant papers.

Journal Reference

Sharon L. Doty, John L. Freeman, Christopher M. Cohu, Joel G. Burken, Andrea Firrincieli, Andrew Simon, Zareen Khan J. G. Isebrands, Joseph Lukas, and Michael J. Blaylock. Enhanced Degradation of TCE on a Superfund Site Using Endophyte-Assisted Poplar Tree Phytoremediation. Environmental Science and Technology, 2017. DOI: 10.1021/acs.est.7b01504

Article details

  • Author(s)
  • David Simpson
  • Date
  • 17 August 2017
  • Source
  • University of Washington
  • Subject(s)
  • Pollution