Screening of aquatic and wetland plant species for phytoremediation of explosives-contaminated groundwater from the Iowa Army Ammunition Plant

The results of this study indicate that the presence of plants did enhance TNT and TNB removal from IAAP groundwater. Most effective at 25°C were reed canary grass, coontail and pondweed. Groundwater and plant tissue analyses indicate that in presence of the plants tested TNT is degraded to reduced by-products and to other metabolites that were not analyzed. TNT removal was best modeled using first order kinetics, with rate constants at 25°C incubations ranging from 0.038 μg L-1 h-1 for reed canary grass to 0.012 μg L-1 h-1 for parrot-feather. These kinetics predict hydraulic retention times (HRTs) ranging from 4.9 days to 19.8 days to reach a TNT concentration of 2 μg L-1. Decreasing incubation temperature to 10°C affected reed canary grass more than parrot-feather, increasing estimated HRTs by factors of four and two, respectively. The plant species tested showed a far lower potential for RDX removal from the IAAP groundwater. Most effective at 25°C were reed canary grass and fox sedge. Analyses of plant material indicated the presence of RDX in under-water plant portions and in aerial plant portions, and RDX accumulation in the latter. RDX removal was best modeled using zero order kinetics, with rate constants for the 25°C incubation ranging from 13.45 μg L-1 h-1 for reed canary grass to no removal in four species. Based on these kinetics, estimated HRTs to reach 2 μg L-1 RDX increased from 39 days. Decreasing the temperature to 10°C increased HRT 24-fold for reed canary grass. By using the biomass-normalized K value, submersed plants are identified as having the highest explosives-removing activity (μg explosive L-1 h-1 g DW-1). However, biomass production of submersed plants is normally five to ten times less than that of emergent plants per unit area, and, thus, in plant selection for wetland construction, both, explosives removal potential and biomass production are important determinants.