Superfund Research Program

Phytoremediation to Degrade Airborne PCB Congeners from Soil and Groundwater Sources

Project Leader: Jerald L. Schnoor
Grant Number: P42ES013661
Funding Period: 2006-2020

Project-Specific Links

Final Progress Reports

Year:   2019  2014  2009 

The goal of this project is to provide engineering research (non-biomedical) to determine whether plants can be used for the in situ bioremediation of PCB congeners from airborne sources and other sources like the proposed Confined Disposal Facility in East Chicago, Indiana. Plants can uptake PCB congeners from air and from contaminated soil and groundwater. Microbes in the rhizosphere of plants, together with the plants themselves, can break-down PCBs to much less toxic or completely non-toxic products. Confined Disposal Facilities (CDFs) represent one possible source for contamination of air and for exposure of nearby human populations which could be mitigated by plantations of poplars at or near the site. Research results from this project in previous years include the following:

• Hybrid poplar plants can uptake PCBs (PCB-3, 15, 28, 52, and 77) from hydroponic solution and translocate some congeners, PCB-3 and 15, to stem and leaf tissues.
• Transformation of PCB-77 within whole poplar roots was documented for the first time.
• Several genes involved in poplar detoxification of PCBs were identified (cytochrome monoxygenases and glutathione-S-transferase genes).
• A hydroxyl-metabolite of PCB-35 was synthesized and shown to be a strong growth inhibitor for E. Coli bacteria (4’-OH PCB35).
• A sophisticated method (T-RFLP) for determining the community of bacteria active in PCB transformations was utilized to identify families present with bph gene clusters.

Highlights of the research in the past year include:

• Identification of several hydroxylated metabolites of PCB-77 and PCB-3 that have never been reported before in whole plants, indicating plants themselves can rapidly transform these PCB congeners.
• Development of a new method for analyzing environmental samples of hydroxyl-metabolites of PCB-3.
• Dechlorination of PCB-77 in the root zone of poplar plants in (both) hydroponic solution and in real soils which suggests that the ultimate project goal (mineralization of PCBs through progressive redox cycles in the root zone) is a realistic possibility for the intervention and treatment of PCB " hot-spots" like dredge disposal sites.
• Scavenging of PCBs from air was demonstrated in enclosed plant exposure chambers. PCB-15, 28, 52, and 77 were the most efficiently scavenged, but the most volatile congener tested, PCB-3, was not substantially removed by sorption to the aerial portions of the plant.

The research team has made progress on all four of the Specific Aims in the original proposal (below):

Specific Aim 1. To test the hypothesis that plants can uptake and transform lower-chlorinated PCB congeners to much less toxic residuals.

Specific Aim 2. To test the hypothesis bacteria in the rhizosphere of plants can reductively dechlorinate higher PCB congeners and can mineralize resulting intermediates under oxidizing conditions.

Specific Aim 3. To test the hypothesis that phytoremediation will allow for significant reductions in the airborne transfer of PCBs from waste disposal sites and will mitigate exposure to humans and ecosystems.

Specific Aim 4. To test the hypothesis that residues of PCB transformation products in plant tissues are non-toxic or of greatly reduced toxicity.

Three new research papers and one new book chapter have been submitted in the past year. A total of six research articles and one book chapter have been published (or in press) specifically regarding the four specific aims from this project; four articles have already been published in leading journals (Environmental Science and Technology, Chemosphere, and Environment International); and these have been produced and co-authored by project personnel working together with other members of the team in the Synthesis Core, Analytical Core, and the Atmospheric Sources of PCB Congeners project. Future research will concentrate on the new Specific Aims outlined in the team’s competitive renewal proposal.