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 30, 2001)
Project Amount: $134,949
Research Category: Phytoremediation
This summary reports on our current IPEC phytoremediation study in southern Arkansas. The field site was identified in October, 1999. The site is located in a bermed area that is the site of an intentional spill by vandals approximately three years ago. At the time of the spill, most of the oil was capture and replaced in the storage facility, but a significant amount remained in the soil contained within the berm. In October, the experimental plots were defined and marked at the site. Winter cover grasses were planted at the field plots that consisted of 4 replicates of three treatments. The field plots contain 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 contamination levels. Initial sampling was done and the TPH levels are currently being analyzed at a commercial laboratory and in-house.
Our initial greenhouse study on survivability of plant species on crude oil-contaminated soil with different amendments has identified a number of promising combinations. These results are summarized in Tables 1 and 2.
Table 1 - Species Survival Rates
| Species | % Survival |
| Alfalfa | 61.0 b* |
| Bermudagrass | 100.0 ** |
| Crabgrass | 62.5 b |
| Fescue | 73.0 ab |
| Ryegrass | 80.0 a |
Table 2 - Amendment Effect on Survival
| Amendment | % Survival |
| Control | 70 ab* |
| Inorganic Fertilizer |
80 a |
| Broiler Litter | 66 b |
| Paper Mill Biosolids |
80 a |
| Hardwood Sawdust | 80 a |
*Means with the same letter are not significantly different at the 5% level.
**Bermudagrass not included in statistical analysis as it was sprigged.
Although broiler litter did not have a positive effect on germination compared to the control, it did have a positive effect on the root biomass that the surviving plants produced. Despite the observations that these species can germinate (results not presented) and grow in crude oil-contaminated soils, it has yet to be determined whether the oil-degrader microbial population is stimulated, and that enhanced oil degradation occurs. These measurements will be made at the conclusion of an on-going greenhouse study.
We have also developed a simple mathematical model of the phytoremediation process that is the first model to account for the "exploration" of contaminated soil by plant roots. Unlike pesticides, metals, and explosives that are readily transported to the plant via water movement, and thus exposed to the root-zone-enhanced remediation rates, spilled crude oil is not mobile, so root penetration must be accounted for in the model. Both the volume of soil in contact with the roots (the rhizosphere) and the rate of root turnover are very important in this system. Accurate and precise experimental measurements of the rhizosphere volume are difficult to make, and we are developing tools to estimate these parameters for comparison to available experimental data. At present approximately 2400 lines of source code have been written that are able to analyze ?virtual root systems? generated using a fractal approach. Briefly, a specific root structure is created, and a voxel (volume element) space is imposed upon the structure. Individual voxels are queried as to their proximity to the root, and then the voxel number is summed to give the root and rhizosphere volume. The code has been tested with simple cylinders of known volume, and gives acceptably accurate results. However, for more complex structures, there remains a dependence of the computed root volume on the density of voxels used in the computation. Removal of this density dependence and streamlining the computations are the current focus of the modeling effort.
Bowen, M.L. 1999 A mathematical model of phytoremediation of hydrocarbon impacted soils including an L-system approach to rhizosphere volume estimation, Masters Thesis Univ. Arkansas, Fayetteville
Bowen, M., G. Thoma, D.C. Wolf, and C.A. Beyrouty. 1998. A mathematical model of phytoremediation for hydrocarbon-impacted soils. In K.L. Sublette (ed.) Proc. 5th International Petroleum Environmental Conf., Albuquerque, NM, 20-23 Oct. 1998.
Integrated Petroleum Environmental Consortium, Tulsa, OK. Thoma, G.J., M.L. Bowen, C.A. Beyrouty, and D.C. Wolf. 1999. An L-systems approach to rhizosphere volume estimation. p. 125. In K.L. Sublette, G.J. Thoma, and T.J. Ward (ed.) Proc. 6th International Petroleum Environmental Conf., Houston, TX. 16-18 Nov. 1999. Integrated Petroleum Environmental Consortium, Tulsa, OK.
White, Jr., P.M., L.J. Krutz, W.D. Kirkpatrick, D.C. Wolf, C.M. Reynolds, and G.J. Thoma. 1999. Phytoremediation of petroleum-contaminated soils. p. 392-406. In K.L. Sublette, G.J. Thoma, and T.J. Ward (ed.) 6th International Petroleum Environmental Conf., Houston, TX. 16-18 Nov. 1999. Integrated Petroleum Environmental Consortium, Tulsa, OK.
Continue development of the mathematical model. Begin sampling field location for TPH, microbial populations, and plant available nutrients. Establish greenhouse studies for survival and growth of alfalfa, ryegrass, fescue, bermudagrass, and crabgrass in unamended or soil amended with inorganic fertilizer, broiler litter, hardwood sawdust + inorganic fertilizer, and papermill sludge.
Arkansas (AR), petroleum, phytoremediation, EPA Region 6, rhizosphere