Fate of 2,4,6-trinitrotoluene in axenic sand culture systems containing smooth bromegrass

Plants have the potential to metabolize the munition 2,4,6-trinitrotoluene (TNT) in contaminated soils, sediments, and natural waters. However, microbial interference must be eliminated to demonstrate an intrinsic capacity for the metabolism of TNT by plants. An axenic sand culture system for smooth bromegrass (Bromus inermis Leyss) was established to investigate the influence of TNT on smooth bromegrass growth and metabolism. Shoot length growth was inhibited by 40% after 14 d of exposure to TNT at 36 mg/L in the sand solution, whereas photosynthetic and respiration rates were similar to controls. Addition of [¹⁴C]-labeled TNT to the system resulted in the roots containing 21.3% and the shoots containing 3.8% of the radioactivity. The [¹⁴C]TNT in media that contained plants was reduced about 50% compared to media without plants. Trace amounts (0.03%) of the initial [¹⁴C]TNT was converted to ¹⁴CO₂, during a 5-d incubation period. The TNT and its metabolites were observed in root and shoot extracts by radiochromatographic analysis. The major TNT metabolites identified were 2-amino-4,6-dinitrotoluene and 4-amino-2,6-dinitrotoluene. Previous exposure of the plants to TNT did not increase TNT metabolism or prevent reduction of shoot length growth. From these results we concluded that smooth bromegrass is capable of taking up and metabolizing TNT.