Submitted to: Environment International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2004
Publication Date: August 15, 2004
Citation: Chekol, T., Vough, L.R., Chaney, R.L. 2004. Phytoremediation of polychlorinated biphenyl-contaminated soils: the rhizosphere effect. Environment International. 30(6):799-804.
Interpretive Summary: Phytoremediation uses plants to aid in biodegradation of xenobiotic (non-natural) organic compounds which require remediation. The present study was conducted to characterize the role of plants and soil microbes in biodegradation of PCBs in amended soils. Initially different grass and legume forage crops were evaluated for their ability to increase the extent of PCB degradation. The two most effective plant species, Reed Canary Grass and Switchgrass, were further evaluated in sterilized and non-sterilized soil, with both unplanted and planted treatments. Sterilization had little effect on the rate of biodegradation, while planting substantially increased the extent of biodegradation of PCBs in this soil. Planting these crops increased the density of soil microbes in the soil, and especially in the rhizosphere soil (soil within about 0.1-0.3 mm of the root surfaces). The present experiment provides a strong illustration of the role of plant species in increasing soil microbial ability to degrade xenobiotic organic compounds which contaminate soils. It is well known that root exudates and lysed root cells supply nutrients which aid growth of soil microbes. Plants may further aid biodegradation by improving soil structure, and improving oxygenation of the rhizosphere. Phytoremediation is increasingly recognized as a method which can achieve required soil remediation at far lower cost than the default soil removal and replacement with clean soil. Effective management of the crop growth and monitoring of the extent of remediation are needed to achieve optimum remediation rate and lowest costs.
The objective in the first phase of this study was to screen alfalfa, flatpea, sericea lespedeza, deertongue, reed canarygrass, switchgrass, and tall fescue for phytoremediation of polychlorinated biphenyl (PCB)-contaminated soil. During the second phase, the focus was rhizosphere characterization to optimize PCB phytoremediation. Aroclor 1248 (PCB) was added to soil at 100 mg kg-1 of soil. In the first phase, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls and the two most effective species were selected for further study. During the rhizosphere characterization study, soil irradiation did not affect PCB biodegradation, but planting significantly increased PCB biodegradation; 38% or less of the initial PCB was recovered from planted pots, compared to more than 82% from the unplanted control soils. Presence of plants significantly increased the biological activity (microbial counts and enzyme activity) of both irradiated and unirradiated soils. Greater bacterial counts and soil enzyme activity were closely related to higher levels of PCB biodegradation. The data showed that Aroclor 1248 biodegradation in soil seem to be positively influenced by the presence of plants and plant-bacteria interactions. Our results suggested that phytoremediation could be an environmentally friendly alternative for PCB-contaminated soils.