Period Covered by Report:
Date of Report:
EPA Grant Number: R827015-01-0
Title: Using Plants to Remediate Petroleum-Contaminated Soil
Investigators: Greg Thoma, Duane Wolf, Craig Beyrouty
Institutions: University of Arkansas
EPA Project Officer: Bala Krishnan
Project Period: September 1, 1999 to August 31, 2000 (N/C Ext. to June 3 0, 2001)
Project Amount: $134,949
Research Category: Phytoremediation
This report covers the April 1, 2001 to June 30, 2001 period and summarizes our current IPEC phytoremediation studies that consist of an on-site field project in southern Arkansas, greenhouse studies, and a mathematical modeling project.
The field site in El Dorado, AR is located in a bermed area that is the site of an intentional spill in 1997 by vandals. The experimental plots consist of four replicates of the following treatments: (1) nonvegetated-nonfertilized control, (2) fescue (Festuca arundinacea Schreb.) - ryegrass (Lolium multiflorum L.) + fertilizer, and (3) fescue-bermudagrass (Cynodon dactylon (L.) Pers.) + fertilizer. Each field plot has 12 microplots (>soil socks=) that contain homogenized soil that allow monitoring of the field treatments, on a smaller scale, with less effect of field variability of the contaminant levels.
On 20-23 May 2001, 17 months after establishment of vegetation at the site, soil and plant samples were collected from the plots. Plant shoot biomass and root biomass, length, surface area, volume, and plant cover for each of the treatments were determined. All plant species appeared to be exhibiting adequate plant growth. The Total Petroleum Hydrocarbon (TPH) and biomarker (hopane) analyses of the soil samples collected 17 months after plot establishment (t=17) are currently being conducted.
The addition of fertilizer and vegetation establishment significantly increased total bacterial and Polycyclic Aromatic Hydrocarbon (PAH) degrader numbers. Control, fescue-ryegrass, and bermudagrass-fescue treatments had PAH degrader numbers of 3.36, 3.71, and 3.78 log MPN/g dry soil, respectively, and bacterial numbers of 6.09, 6.87, and 6.80 log CFU/g dry soil, respectively. Additionally, root surface area levels were higher in the samples collected at 17 months compared to 6 months. The results suggest that agronomic practices are important considerations when developing systems to phytoremediate crude oil-contaminated sites.
We are continuing to improve the estimate of rhizosphere volume through the analysis of fractal root structures. The code has been validated with respect to multiple, separated roots as a function of the spatial orientation of the root segments. We have a limited ability to test analytically the overlapping of adjacent rhizosphere zones (limited to spheres and parallel cylinders only), and the accuracy testing has been acceptable. We have also proposed a sub model for the idealized behavior of roots through out the growing season. The parameters in this sub model can be determined from easily observed field parameters that characterize root growth. These are: maximum rooting depth, maximum standing biomass, fractional turnover on an annual basis, and average root lifespan.
Abstracts and titles that have been submitted for presentation as posters or presentations in the future include:
Thoma, G.J., T.B. Lam, D.C. Wolf, and C.A. Beyrouty. 2001. A Mathematical Model of Phytoremediation of Crude Oil Contaminated Soils. In The Sixth International In Situ and On Site Bioremediation Symposium, San Diego, CA. 4 7 June 2001. Battelle, Columbus, OH.
W.D. Kirkpatrick, White, P.M., G.J. Thoma, D.C. Wolf, C.M. Reynolds, and E.E. Gbur. 2001. Plant response to N addition in petroleum-contaminated soil. In 2001 Agronomy abstracts. ASA, Madison, WI. (abstract submitted)
White, P.M., W.D. Kirkpatrick, G.J. Thoma, D.C. Wolf, C.M. Reynolds, and E.E. Gbur. 2001. Field study to evaluate phytoremediation of petroleum-contaminated soil. In 2001 Agronomy abstracts. ASA, Madison, WI. (abstract submitted)
White, Jr., P.M., W.D. Kirkpatrick, D.C. Wolf, G.J. Thoma, R.M. Reynolds. 2001. Phytoremediation of crude oil-contaminated soil. In 8th Annual International Petroleum Environmental Conference 6-9 November 2001. Houston, TX. (abstract submitted)
Arkansas (AR), petroleum, phytoremediation, EPA Region 6, rhizosphere