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Phytoremediation of organics moving rapidly into field trials.

Several chemical and petroleum companies are contemplating an offer by EPA's Technology Innovation Office (TIO) to form partnerships between the public and the private sector to exploit emerging phytoremediation technologies of organics and hydrocarbons. Surface planting is already in use for remediation of metal contaminants, and methods for the removal of organics—until now the domain of microbial bioremediation—are passing greenhouse and laboratory tests. The partnerships would evaluate their effectiveness in the field. Some researchers, however, are hesitant about such field trials. University of Oklahoma researcher John Fletcher believes that phytoremediation requires the right plant species for the job, and failures of large studies that use the wrong plants could dampen phytoremediation in the eyes of regulators. "[Failures using] species that were never looked at closely enough in the laboratory could be a fatal blow to phytoremediation " said Fletcher. Phytoremediation of nonhydrophobic contaminants, including chlorinated solvents and some petroleum hydrocarbons, has produced encouraging results in the field; but hydrophobic contaminants such as polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), which bind tightly to soil and resist uptake by plants, continue to elude efforts at phytoremediation. At an EPA-sponsored workshop on phytoremediation of organics in Fort Worth, Tex., in December, Fletcher outiined his research approach. He studied the root-associated microbial community nurtured by carbon sources emitted from the plants. According to the team's findings, PCB and PAH-degrading bacteria favor coumarins and flavonoids as carbon sources, and these compounds are released by the root structures of apple, mulberry, and Osage orange trees. Fletcher suspects that these trees alter the microbial environment favoring the microbes that feed primarily on the counicirins a.nd flavonoids and, evidence suggests, the structurally similar PCBs and PAHs. Plants also extract water-soluble compounds from the soil and store, metabolize, or release them into the air; their roots may hem in contaminated groundwater, preventing it from seeping into surrounding areas. Sheldon Nelson presented data on a Chevron project in which the company planted oneor two-year-old poplar trees over a site with gasoline-contaminated groundwater. Calculations suggested that each plant pumped about 1.5 gallons of groundwater per day, and the water level dropped one to two inches. To satisfactorily control the groundwater, Nelson believes that each tree would have to pump 8.5 gallons per day. In unrelated research, a 5-year-old poplar has been shown to pump as much as 40 gallons per day.