Research Project 5: Original Proposal

Phytoremediation to Degrade Airborne PCB Congeners from Soil and Groundwater Sources

This proposal investigates the working hypothesis that phytoremediation can be used to degrade airborne PCB congeners from soil and groundwater sources. Plants stimulate the microbial community in the root zone and contribute to microbial degradation of RGBs (rhizodegradation). Higher-chlorinated PCBs are dechlorinated under reducing (anaerobic) conditions; resulting lesser-chlorinated congeners can undergo oxidative mineralization under aerobic conditions. Alternating reducing and oxidizing conditions in the rhizosphere makes the plant-soil system a natural two-stage bioreactor for initial PCB transformation. Lesser-chlorinated PCBs can also be taken-up and transformed inside plan tissues.

The specific aims of the project are:

(1) to test the hypothesis that poplar plants can take up and detoxify lesser-chlorinated PCB congeners by identifying metabolic pathways of PCBs and genes that encode for catabolic enzymes,

(2) to test the hypothesis that bacteria in the rhizosphere can reductively dechlorinate higher-chlorinated PCBs and can mineralize resulting lesser-chlorinated congeners under oxidizing conditions; this will be tested using anaerobic and aerobic batch bioreactors with rhizosphere soils contaminated with PCBs,

(3) to test the hypothesis that phytoremediation will allow for significant reductions in the airborne transfer of PCBs from waste disposal sites and mitigate exposure to humans and ecosystems; this innovative cleaning up strategy (based on hypotheses 1 and 2) will be tested at the bench scale and by pot-studies in the greenhouse,

(4) to test the hypothesis that residues of PCBs in plant tissues are non-toxic or of greatly reduced toxicity to biota by conducting an eco-toxicological evaluation of the phytoremediation process using a battery of toxicity tests, and

(5) to test the hypothesis that higher plants play a significant role in the environmental cycling of airborne PCBs by field analyses of PCB accumulation on vegetation. The significance of this project is that it provides an intervention and remedy for contaminated waste sites that will help to break the continuous cycling of PCBs in the atmosphere and the subsequent exposure to humans.

Project Leader: Jerry L. Schnoor, PhD
Dr. Schnoor will manage the project and guide the research as the Principal Investigator (PI). He has managed over $25 million of research projects since 1980, and has considerable experience as the Editor-in-Chief of Environmental Science and Technology, and serves as the Chair of the EPA-ORD Board of Scientific Counselors. Dr. Schnoor is an international leader in the field of phytoremediation, co-editor of the book Phytoremediation - Transformation and Control of Contaminants (2003), and is the PI of the W.M. Keck PhytoTechnologies Laboratory at the University of Iowa.

Co-Project Leader: Benoit Van Aken, PhD
Dr. Van Aken, the University of Iowa, leads our effort in the laboratory on molecular biological methods for analysis of catabolic enzymes and metabolic pathways of plants and microorganisms in phytoremediation. He has a background in environmental biotechnology and has published several key papers in the area of metabolite identification and enzymatic pathways. Dr. Van Aken led the discovery of a new endosymbiotic bacteria living inside hybrid poplar trees which mineralizes nitramine explosive compounds, Methylobacteriumpopuli. This research was published in the International Journal of Systematics Evolutionary Microbiology and Applied and Environmental Microbiology.