Enhanced Degradation of TCE on a Superfund Site using Endophyte-Assisted Poplar Tree Phytoremediation


Trichloroethylene (TCE) is a widespread environmental pollutant common in groundwater plumes associated with industrial manufacturing areas. We had previously isolated and characterized a natural bacterial endophyte, Enterobacter sp. strain PDN3, of poplar trees, that rapidly metabolizes TCE, releasing chloride ion. We now report findings from 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. 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. Test well groundwater analyses demonstrated a marked decrease in concentration of TCE and its derivatives from the tree-associated groundwater plume. The concentration of TCE decreased from 300 μg/L upstream of the planted area to less than 5 μg/L downstream of the planted area. TCE derivatives were similarly removed with cis-1,2-dichloroethene decreasing from 160 μg/L to less than 5 μg/L and trans-1,2-dichloroethene decreasing from 3.1 μg/L to less than 0.5 μg/L downstream of the planted trees. 1,1-dichloroethene and vinyl chloride both decreased from 6.8 and 0.77 μg/L, respectively, to below the reporting limit of 0.5 μg/L providing strong evidence of the ability of the endophytic inoculated trees to effectively remove TCE from affected groundwater. The combination of native pollutant-degrading endophytic bacteria and fast-growing poplar tree systems offers a readily deployable, cost-effective approach for the degradation of TCE, and may help mitigate potential transfer up the food chain, volatilization to the atmosphere, as well as direct phytotoxic impacts to plants used in this type of phytoremediation.


Civil, Architectural and Environmental Engineering


Research reported in this publication was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under Award Number R44ES020099 to Edenspace Systems Corporation.

Keywords and Phrases

Biodegradation; Bioremediation; Cost effectiveness; Forestry; Groundwater; Groundwater pollution; Pollution; River pollution; Soil pollution control; Soils; Assisted phytoremediation; Bacterial endophytes; Chlorinated solvent; Cis-1 ,2-dichloroethene; Cost-effective approach; Environmental pollutants; Groundwater analysis; Industrial manufacturing; Trees (mathematics); 1,1,2 trichloro 1,2,2 trifluoroethane; 1,2 dichloroethylene; Chloride ion; Chloroform; Cis 1,2 dichloroethene; Dichloroethane; Ground water; Tetrachloroethylene; Trans 1,2 dichloroethene; Trichloroethylene; Unclassified drug; Vinyl chloride; Vinylidene chloride; Bacterium; Core analysis; Deciduous tree; Endophyte; Manufacturing; Phytoremediation; Phytotoxicity; Plume; Pollutant removal; Superfund; Volatilization; Article; Bacterial strain; Chlorination; Concentration (parameters); Controlled study; Cost effectiveness analysis; Enterobacter; Food chain; Ionic strength; Nonhuman; Populus nigra; Tree growth; Volatilization; California; Chemistry; Trees; Water pollutants; Silicon Valley; United States; Bacteria (microorganisms); Enterobacter sp.; Populus; Environmental; Chemical

International Standard Serial Number (ISSN)

0013-936X; 1520-5851

Document Type

Article - Journal

Document Version


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© 2017 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jul 2017