Evaluation of Monoterpene Producing Plants for Phytoremediation of PCB and PAH Contaminated Soils

EPA Grant Number: R829404
Title: Evaluation of Monoterpene Producing Plants for Phytoremediation of PCB and PAH Contaminated Soils
Investigators: Crowley, David E. , Borneman, James
Institution: University of California - Riverside
EPA Project Officer: Lasat, Mitch
Project Period: November 1, 2001 through October 31, 2004 (Extended to September 30, 2005)
Project Amount: $393,135
RFA: Phytoremediation (2001) RFA Text |  Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


Plants produce a variety of chemicals with structures that are analogous to those of many commercially produced chemicals. Rhizodeposition of these substances can beneficially affect xenobiotic degradation by promoting selective enrichment of degrader organisms, enhancement of growth-linked metabolism, and induction of genes for enzymes that facilitate cometabolism. In previous research, we have exploited the ability of plant monoterpenes to induce bacteria to cometabolize PCBs. Data from the literature and our prior research suggest that terpenes produced in situ by plants also should be effective for promoting degradation of many organic contaminants, including PAHs and other recalcitrant contaminants. The objective of the proposed research is to evaluate monoterpene-producing plant species for use in phytoremediation of PCBs and PAHs, and to investigate the ecology of indigenous xenobiotic degrading bacteria in the rhizosphere of monoterpene producing plants. Experiments will test four hypotheses: (1) the rhizosphere selectively enriches for diverse populations of xenobiotic degrading microorganisms that occur at higher population densities in the rhizosphere as compared to the bulk soil; (2) plant and microbial substances that are released into the rhizosphere enhance the expression and activity of inducible enzymes that work in concert to degrade xenobiotic soil contaminants; (3) monoterpene producing plants selectively enrich for diverse populations of xenobiotic degrading microorganisms that will occur at higher population densities in the rhizosphere as compared to the plants that do not produce these substances; and (4) plant enhanced remediation of PAH and PCBs in the rhizosphere can be enhanced by the addition of earthworms to improve soil aeration for aerobic degradation processes.


Experiments will use selected xenobiotics as growth substrates for substrate induced respiration assays in conjunction with molecular analyses of rhizosphere and non-rhizosphere soils to ascertain the active biomass and species richness of bacteria that degrade PCBs and PAHs. Microbial community analyses will be conducted using 16S rDNA profiles generated by PCR-DGGE and by high resolution methods employing oligonucleotide probing on bacterial clones using a DNA microarray. Monoterpene and nonterpene producing plants will be screened for differences in their abilities to promote xenobiotic degradation, and the rate of degradation will be correlated with microbial biomass and gene expression levels.

Expected Results:

Results of this research will provide fundamental information on the mechanisms by which various plants influence xenobiotic degrading populations in the plant rhizosphere. Previously, most studies of the rhizosphere have relied on culture-based methods that identify relatively few bacterial species as compared to the hundreds or potentially thousands of species that comprise the rhizosphere community. Our experiments will determine the active biomass of bacteria that degrade different model contaminants including PCBs, PAHs, and chlorobenzoates. We will identify the predominant species and ascertain, for the first time, the true extent of the diversity of xenobiotic degraders in the rhizosphere of different species. By comparing the rhizospheres of plants that are grown in clean and contaminated soils, we will be able to determine the importance of soil history in influencing the population size of xenobiotic degraders.

Publications and Presentations:

Publications have been submitted on this project: View all 29 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

bioremediation, biodegradation, rhizosphere, microbial communities, polycyclic aromatic hydrocarbons, soil contamination., Scientific Discipline, Toxics, Waste, National Recommended Water Quality, Remediation, Environmental Chemistry, Contaminant Candidate List, Environmental Microbiology, Bioremediation, Ecological Risk Assessment, Environmental Engineering, plant-based remediation, degradation, microbial degradation, biodegradation, PCBs, microflora, PAH, contaminated soil, Polychlorinated Biphenyls PCBs:, contaminants in soil, recalcitrant hydrocarbons, PCB, earthworm, phytoremediation, plant-microbe system, bacterial degradation

Progress and Final Reports:

  • 2002
  • 2003 Progress Report
  • 2004
  • Final Report