PHYTOREMEDIATION OF PCP- AND PAH-CONTAMINATED SOIL
|B. Pivetz, R. Cochran, and S. Huling, ManTech Environmental, US Environmental Protection Agency, Research Services Corporation, National Risk Management Research Laboratory, 919 Kerr Research Drive, Subsurface Protection and Remediation Division, Ada, OK 74820||
Phytoremediation may be a treatment option or final cover/capping alternative at wood preserving waste sites containing soils contaminated by pentachlorophenol (PCP) and polycyclic aromatic hydrocarbons (PAHs). A vegetative cover established on contaminated soil will minimize fugitive dust/contaminant emissions, surface soil erosion and contaminant runoff, and exposure pathways, and may enhance rhizodegradation (enhanced biodegradation of soil contaminants in the root zone).
However, PCP has been used in the past as a herbicide and may have an inhibitory effect on phytoremediation attempts at these waste sites. The study evaluated contaminant impact on the germination and growth of different grass species over a wide PCP and PAH concentration range and whether or not rhizodegradation was enhanced by the vegetative cover. The identified grass species may be useful to enhance PCP and PAH biodegradation or to establish a vegetative cap.
A greenhouse study indicated that germination of prairie grasses in soil obtained from a woodpreserving waste site was strongly inhibited at 400 to 4200 mg/kg PCP and 1450 to 16,700 mg/kg PAHs. An inverse relationship was observed between the PCP and PAH concentrations and the seed germination and growth. Germination and growth were greatest at the lowest concentration of 38 mg/kg PCP and 75 mg/kg PAHs; however, germination and growth did occur at concentrations up to 840 mg/kg PCP and 3100 mg/kg PAHs.
A laboratory study examined rhizodegradation and growth rates of eight species of prairie grasses, fescues, and wheatgrasses in soils contaminated with PCP (55 to 320 mg/kg) and PAHs (270 to 1200 mg/kg). Contaminant concentrations and microbial numbers were monitored to determine which grasses best enhanced microbial degradation. Germination rates decreased with increasing contaminant concentration. Fescues generally had the highest germination rates, tallest plants, and greatest biomass. Significant PCP and PAH loss occurred in all vegetated soil and non-vegetated control soil.
Lower concentrations occurred in some of the soils with vegetation; however, rhizodegradation was not conclusively demonstrated, perhaps due to a need for a longer time period to establish an extensive rhizosphere. Grasses can be successfully established as a cover in soils contaminated with relatively low PCP and PAH concentrations and may have contributed to somewhat greater contaminant biodegradation.
Note: This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.
Key words: phytoremediation, rhizodegradation, pentachlorophenol, grass, PAH
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