1999 Progress Report: Phytoremediation and Modeling of Land Contaminated by HydronsEPA Grant Number: R825414
Title: Phytoremediation and Modeling of Land Contaminated by Hydrons
Investigators: Munster, Clyde , Corapcioglu, Yavuz , Drew, Malcolm
Institution: Texas A & M University
EPA Project Officer: Lasat, Mitch
Project Period: October 28, 1996 through October 27, 1999 (Extended to January 31, 2001)
Project Period Covered by this Report: October 28, 1998 through October 27, 1999
Project Amount: $452,020
RFA: DOE/EPA/NSF/ONR Joint Program on Bioremediation (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:The two primary objectives of this project are to: (1) evaluate the effectiveness of Johnsongrass (Sorghum halapense) and Canada Wild Rye grass (Elymus canadensis) in the phytoremediation of soil contaminated with a mixture of recalcitrant polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and 2,4,6-trinitrotoluene (TNT) using field lysimeters; and (2) use the field lysimeter results to calibrate and validate a recently developed bioremediation computer model that is capable of simulating the removal and degradation of organic chemicals from the soil by plant roots and their rhizosphere.
Our last report described the final project design and reported the data collected from days 30 and 90 after germination of Johnsongrass that was seeded following soil contamination. The purpose of this project is to evaluate the effectiveness of a warm season grass (Johnsongrass) and a cool season prairie grass (Canada Wild Rye) on the phytoremediation of soil contaminated with a mixture of TNT, PCB, 2,2',5,5'-tetrabromobiphenyl, and a PAH (chrysene).
Because the United States has banned commercial production and importation of PCBs, they can only be obtained in small quantities for research and are prohibitively expensive. This combination prevented their use for this large-scale field study. Therefore, to conduct field studies to improve PCB remediation technology, an available and affordable compound was required to simulate the behavior of PCBs in soil. A suitable replacement, polybrominated biphenyls (PBBs), meets these requirements. Polybrominated biphenyls are currently manufactured in the United States for use as flame retardants. The persistence, movement, and plant uptake of PBBs from soil are similar to those of PCBs (Jacobs, et al., 1976; Filonow, et al., 1976; and Rusling and Miaw, 1989), and because they are available and affordable, they were used in this study to simulate the fate of PCBs in soil.
Two types of lysimeters were developed for field testing. Twelve metal box lysimeters, 1.5 m x 1.5 m x 0.75 m (length x width x height) and 72 polyvinyl chloride (PVC) column lysimeters, 0.1 m (diameter) x 1.5 m (height), were fabricated. The box and column lysimeters were placed in the ground to maintain an in situ temperature gradient throughout the soil profile. The lysimeters were filled with virgin Weswood silt loam soil that was mixed with TNT, PBB, and chrysene to a target concentration of 10 mg of each contaminant per kg of soil.
Since last year's report, additional samples were collected for analysis on days 180 (November 17, 1999), and 360 (May 14, 1999). The cool season grass, Canada Wild Rye, was seeded on November 25, 1998, and had germinated by December 7, 1998. Additionally, the progress of this research has been presented at five scientific meetings and published in their respective proceedings.
Chemical losses during the initial 360 days of this experiment were similar for both lysimeters, at all depths, and between vegetated and unvegetated soils. The largest and most rapid loss in soil-chemical concentration was TNT, which decreased to < 10 mg kg-1 after 360 days. Contaminant detection from plant herbage and leachate has been insignificant. Enumeration of soil microorganisms reveals a robust population in both the bulk soil and root rhizosphere, but no significant differences. The simulation results using the phytoremediation computer model are being evaluated. Thus far, simulations with TNT demonstrate that the present model can predict contaminant concentration with time and depth under actual field conditions. Other model parameters are being evaluated, and samples will continue to be collected and analyzed during a 2-year period. The validated and calibrated computer model may provide insight into the selection and optimization of phytoremediation at contaminated sites.