Environmental behavior of explosives in groundwater from the Milan army ammunition plant in aquatic and wetland plant treatments. Removal, mass balances and fate in groundwater of TNT and RDX.

Phytoremediation of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitr o-1,3,5-triazine (RDX) in groundwater using constructed wetlands is a poten tially economical remediation alternative. To evaluate Explosives removal a nd fate was evaluated using hydroponic batch incubations of plant and subst rate treatments with explosives-contaminated groundwater amended with [U-C- 14]-TNT or [U-C-14]-RDX. Plants and substrates were collected from a small- scale wetland constructed for explosives removal, and groundwater originate d from a local aquifer at the Milan Army Ammunition Plant. The study survey ed three aquatic, four wetland plant species and two substrates in independ ent incubations of 7 days with TNT and 13 days with RDX. Parent compounds a nd transformation products were followed using C-14 and chemical (HPLC) ana lyses. Mass balance of water, plants, substrates and air was determined. It was demonstrated that TNT disappeared completely from groundwater incubate d with plants, although growth of most plants except parrot-feather was low in groundwater amended to contain 1.6 to 3.4 mg TNT L-1. Highest specific removal rates were found in submersed plants in water star-grass and in all emergent plants except wool-grass. TNT declined less with substrates, and least in controls without plants. Radiolabel was present in all plants afte r incubation. Mineralization to (CO2)-C-14 was very low, and evolution into C-14-volatile organics negligible. RDX disappeared less rapidly than TNT f rom groundwater. Growth of submersed plants was normal, but that of emergen t plants reduced in groundwater amended to contain 1.5 mg RDX L-1. Highest specific RDX removal rates were found in submersed plants in elodea, and in emergent plants in reed canary grass. RDX failed to disappear with substra tes. Mineralization to (CO2)-C-14 was low, but relatively higher than in th e TNT experiment. Evolution into C-14-volatile organics was negligible. Imp ortant considerations for using certain aquatic and wetland plants in const ructed wetlands aimed at removing explosives from water are: (1) plant pers istence at the explosives level to which it is exposed, (2) specific plant- mass based explosives removal rates, (3) plant productivity, and (4) fate o f parent compounds and transformation products in water, plants, and sedime nts.