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DEGRADATION OF TNT AND RDX IN GROUND WATER FROM THE IOWA ARMY AMMUNITION PLANT IN FLOW-THROUGH SYSTEMS PLANTED WITH AQUATIC AND WETLAND PLANTS

Species evaluated were the submersed Ceratophyllum demersvm L.(coontail), Potamogeton nodosus Poir. (American pondweed), and the emergent Sagittaria latifolia Willd. (common arrowhead). Unplanted sediment served as the control. The effects of amendments with nitrogen or with a microbial seed on explosives removal were quantified. TNT and RDX levels in the tested ground water were 0.8 and 10.7 mg L-1 respectively. The hydraulic retention time was 30 days.

The disappearance rates for TNT from ground water were similar in all incubations, including the unplanted control. Most TNT degradation occurred in the beginning of the incubation. Reduction products of TNT were recovered in the incubation water, but not in plants and sediments after 49 days.

RDX disappearance in the ground water was slower than that of TNT. The disappearance rates were more rapid in the incubations of sediment planted with submersed plants than in those of unplanted sediment and of sediment planted with arrowhead. Disappearance was gradual and adsorption to sediment and plant surfaces, therefore, limited. The microbial seed greatly increased RDX removal. RDX degradation products in the incubation water could not be demonstrated, since they were not analyzed for these compounds. RDX was detected in all plants and sediments, and its mono-nitroso-derivative in most plants and only in unplanted sediment after 49 days.

From the results it can be estimated that wetlands planted with the plants tested will remove approximately 0.016 to 0.019 mg TNT L-1 d-1 and 0.133 to 0.29l mg RDX L-1 d-1 at 25(C at steady state. Plant growth was reduced (but still considerable), probably because the IAAP ground water was toxic for the plants selected; toxic ranges of TNT and RDX were estimated to be 5 to 7 mg L-1 (in hydroponic culture).

Key words: phytoremediation, bioremediation, nitroaromatics, ground water, cleanup