FATE AND MASS BALANCES OF [14C]-TNT AND [14C]-RDX IN AQUATIC AND WETLAND PLANTS IN GROUND WATER FROM THE MILAN ARMY AMMUNITION PLANT
|E.P.H. Best1, S.L. Sprecher2, S.L. Larson2, H.L. Fredrickson2, and D.F. Bader2, US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS 39180. 1AScl Corporation, 2US Army Environmental Center||
The present study was performed to elucidate the environmental behavior and fate of TNT and RDX in aquatic and wetland plants collected from the Field-scale wetland demonstration at Milan Army Ammunition Plant where explosives are being degraded in ground water. The mass balance study had three objectives. The first was to establish the physiological capacity of plants to absorb and transport TNT or RDX in the absence of substrates and their sorptive activities.
The second was to elucidate the extent and partitioning of TNT and RDX over the plant parts. The third was to establish the short-term chemical fate of TNT and RDX in plant tissues. The substrates in which these plants were rooted at the Milan field site (sediment, gravel) were also incubated without plants to investigate sorptive activities and to evaluate microbial/chemical transformation of TNT and RDX, that may affect the explosives availability for plants.
Hydroponic batch incubations of plant or substrate treatments with 14C-TNT or 14C-RDX were used to evaluate explosives transformation. The study surveyed seven planl species and two substrates in sequential, independent incubations of 7 and 13 days with TNT and RDX, respectively. Parent compounds and degradation products were determined through chemical analyses of plant tissues, aqueous phases, and substrate extracts. The fate of radiolabel was followed by radioanalytic imaging.
It was found that growth of most plants except parrot-feather, was reduced in ground water containing 1.5 to 3.7 mg TNT L-1 . TNT disappeared completely from ground water incubated with plants in 7 days, but was removed to a lesser extent with substrates, and least in controls. The radiolabel was present in all plants after incubation, in the submersed species concentrated in physiologically active roots and shoots, and in emergent species in roots.
Mineralization to CO2 was very low, and evolution into volatile organic compounds was negligible. TNT residues were extremely low or below chemical detection in the plant tissues. Radioactive degradation products accumulated at the uptake sites and transport were limited. TNT degradation took place via reduction of a single nitro-group.
For RDX, it was found that growth of the submersed plants was normal, but growth was reduced in emergent plants In ground water containing 1.5 mg RDX L-1, RDX disappeared less rapidly than TNT from the incubated ground water. The radiolabel was present in all plants after incubation. Mineralization to CO2 was low, but relatively higher than in the TNT incubation, and evolution into volatile organic compounds was negligible.
Radioactive degradation products accumulated at physiologically active sites, and transport to leaves were substantial. RDX residues were low in most plants, or below detection in the below-ground portions of two emergent species. RDX degradation occurred.
In the substrates residues of both explosives were below detection.
The plant-mediated rapid decrease in TNT and relatively slower decrease in RDX concentrations in ground water and low explosives residues in the plant tissues and substrates suggest that phytoremediation is a promising technology for ground water treatment.
Key words: phytoremediation, bioremediation, nitroaromatics, ground water, cleanup
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