DEGRADATION OF EXPLOSIVES IN GROUND WATER AT THE VOLUNTEER ARMY AMMUNITION PLANT IN FLOW-THROUGH SYSTEMS PLANTED WITH AQUATIC AND WETLAND PLANTS
|J.L. Miller, E.P.H.Best1, and S.L. Larson, US Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS; 1AScl Corporation||
A 115-day study was conducted to quantify the ability of one submersed and one emergent plant species to phytoremediate explosives-contaminated ground water at the Volunteer Army Ammunition Plant (VAAP), when planted in local sediment under flow-through conditions.
Explosives levels of concern were; 2.7 mg L-1 TNT, 16 7 mg L-1 24DNT, 5.2 mg L-1 26DNT, 42.6 mg L-1 2NT, and 30.5 mg L-1 4NT Species evaluated were the submerged Elodea canadensis Rich. in Michx. (elodea) and the emergent Typha angustifolia L. (narrow-leaved cat-tail). Unplanted sediment irradiated by full sunlight or by sunlight without ultraviolet bandwidths served as controls. The hydraulic retention time was 7 days. The study was conducted from end-of-May to end-of-September 1996. Plant health was followed by visual observation.
Of the initial two plant species tested, the submersed elodea failed to grow in VAAP water, but the emergent cat-tail succeeded in forming substantial biomass. Two submerged plant species were then selected for their tolerance for elevated TNT levels to replace elodea in the reactors, Ceratophyllum demersum L (coontail) and Potamogeton nodosus Poir (American pondweed). They were planted in July; however, both failed to survive in VAAP water.
The explosives degradation rates per L per day were generally higher in the reactors with cat-tail planted sediment than with unplanted sediment. The planted sediment reactors in full sunlight removed 22 g TNT, 104 g 24DNT and 38 9 26DNT (592-L system) over the 115-day operational period; the unplanted sediment reactors in full sunlight removed 34 9 TNT,779 24DNT and 62 9 26DNT(1071-L system); and the unplanted sediment reactors in UV-filtered sunlight removed 25 9 TNT, 34 9 24DNT and 26 9 26DNT (1071-L system).
Of the explosives, only 2ADNT and 4ADNT(TNT degradation products), and 24DNT residues were recovered in the plant tissues.
The explosives degradation rates found in the current field study are far higher than those reported for laboratory studies. Mechanisms of explosives degradation have been tentatively identified as plant- and microbe-based. Photolytic degradation of some explosives proved substantial and may have interacted with biotransformation. Overall toxicity of the ground water varied with plant species. Toxicity of the individual explosives compounds was not evaluated in the current study.
Key words: phytoremediation, bioremediation, nitroaromatics, ground water, cleanup
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