The Use of Box Lysimeters with Freshly Contaminated Soils To Study the Phytoremediation of Recalcitrant Organic Contaminants

The potential for phytoremediation of soil contaminated by trinitrotoluene (TNT) and 2,2‘,5,5‘-tetrabromobiphenyl (PBB was used as a surrogate for PCBs) was examined in a 2-year study using box lysimeters under field conditions. The treatments were a warm season grass, Johnson grass, and a cool season grass, Canadian wildrye, and a rotation of Johnson grass and wildrye plus a fallow condition. The experiment was conducted using 12 large (1.50 m × 1.50 m × 0.75 m), in-ground, box lysimeters filled with a Weswood silt-loam soil freshly spiked with the TNT and PBB compounds to a concentration of 10 mg kg-1 for each chemical. The lysimeters were sheltered to permit controlled applications of water. A total of five sampling rounds were conducted where soil, herbage, and leachate samples were collected for laboratory analysis. TNT and PBB concentrations were determined using the U.S. EPA approved immunoassay test procedures. In the soil, TNT concentrations dropped below the detection limit of 0.25 mg kg-1 by day 92 and PBB concentrations dropped below the detection limit of 0.50 mg kg-1 by day 184. There were no significant differences in chemical concentrations among any of the vegetated or fallow treatments at a significance level of α < 0.05. However, PBB soil concentrations rebounded above the 0.50 mg kg-1 level by day 720 for all treatments. No detectable concentrations of TNT or PBB were found in any of the herbage samples or in the leachate.