WES plant scientists and environmental engineers, in support of the SERDP Biotreatment Consortium, have completed a 115-day outdoor phytoremediation study at the Volunteer Army Ammunition Plant (VAAP), Chattanooga, TN, to quantify the clean-up ability of native aquatic and wetlands plants. Three underwater species and an emergent, cattail, were planted in sediment and held in above-ground growth tanks, 592-L or 1071-L in volume. Local VAAP groundwater was fed in with a 7-day hydraulic retention time. Explosives removal with plants was compared to that of sediment lacking plants with and without the ultraviolet (UV) component of full sunlight. Studies were conducted from the end of May through September 1996.

The VAAP groundwater initially contained 2.7 mg L^-1 (parts per million) of TNT, along with 95 mg L^-1 of various nitrotoluenes produced by explosive degradation (see table). These concentrations were over a thousand-fold higher than the target clean-up levels for potable water. The three submersed species tested--elodea, coontail, and American pondweed--failed to survive. However, narrowleaf cattail, a common marsh plant, grew well.

Compound	Initial Levels in Groundwater (mg L-1)	Explosives Removal Rates (mg L-1)
.	.	Cattails/ Full Sunlight	No Plants/ Full Sunlight	No Plants/ No UV
TNT	2.7	0.27	0.26	0.17
2,4-DNT	16.7	1.28	0.58	0.17
2,6-DNT	5.2	0.53	0.48	0.17
2-NT	42.6	.	.	.
4-NT	30.5	.	.	.

TNT, 24DNT, 26DNT, 2NT, 3NT 4NT and TNB disappeared steadily from all units, while levels of 2ADNT, 4ADNT, 26DANT, 3DNB and NB fluctuated. Degradation rates of TNT, 24DNT and 26DNT were higher in planted units (see table). Since TNT, 24DNT and 26DNT disappeared more slowly from shielded reactors, it was concluded that UV light in sunlight contributed substantially to photolytic degradation, and may have enhanced biotransformation of these contaminants. TNT was not found in any plant tissues, but products of its chemical reduction--2ADNT and 4ADNT--were present. A component of the initial groundwater, 24DNT, was also found in plant tissue.

Explosives degradation rates found in this field study are higher than those reported from laboratory studies. This is assumed to result from the interaction of plant, microbial, and photolytic mechanisms. While the toxicity to plants of the individual explosives was not evaluated, overall toxicity of the groundwater was seen to be species-dependent.

Product:

Miller, J.L., Best, E.P.H. and Larson, S.L. 1997. Degradation of explosives in groundwater at the Volunteer Army Ammunition Plant in flow-through systems planted with aquatic and wetland plants. Book of Abstacts, 12th Annual Book of Abstracts, 12th Annual Conference on Hazardous Waste Research, May 19-22, Kansas City, MO:9-10.

Webdate: August 1997

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