Screening of Aquatic and Wetland Plant Species for Phytoremediation of Explosives‐contaminated Groundwater from the Iowa Army Ammunition Plant

Abstract

The results of this study indicate that the presence of plants did enhance TNT and TNB removal from IAAP groundwater. Most effective at 25 degrees 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 degrees C incubations ranging from 0.038 microgram L-1 h-1 for reed canary grass to 0.012 microgram 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 micrograms L-1. Decreasing incubation temperature to 10 degrees 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 degrees 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 degrees C incubation ranging from 13.45 micrograms L-1 h-1 for reed canary grass to no removal in four species. Based on these kinetics, estimated HRTs to reach 2 micrograms L-1 RDX increased from 39 days. Decreasing the temperature to 10 degrees 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 (microgram 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.

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

“…Aquatic macrophytes seem to be especially resistant to the toxicity of a great variety of organic pollutants at concentrations normally encountered in typical wastewater compositions. In addition, numerous studies have shown the capability of many macrophyte species to reduce the aqueous concentrations of various organic xenobiotics such as explosives [40,[105][106][107], petroleum hydrocarbons [36], pesticides [108][109][110] and more recently on some pharmaceuticals [100,[111][112][113][114][115].…”

Identification of Metabolic Routes and Catabolic Enzymes Involved in Phytoremediation of the Nitro- Substituted Explosives TNT, RDX, and HMX

“…Identified transformation products include hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), 4-nitro-2,4-diazabutanal, formaldehyde, methanol, nitrous oxide, and nitrite Hawari, 2000;Just and Schnoor, 2004;. Unidentified high molecular weight and polar metabolites have also been reported (Best et al, 1997;Larson et al, 1999;Thompson et al, 1999;Just and Schnoor, 2004;. Experiments with [U-…”

“…Active uptake of RDX by both terrestrial and wetland plants is well documented (Harvey et al, 1991;Best et al, 1997;Best et al, 1999;Larson et al, 1999;Thompson, Ramer, and Schnoor, 1999;Bhadra et al, 2001;Price et al, 2002;Just and Schnoor, 2004). Following uptake, RDX is translocated preferentially to the leaves where it undergoes a limited transformation (Harvey et al, 1991;Best et al, 1997;Just and Schnoor, 2004;.…”

“…14 C]RDX showed that a large part of the radioactivity initially taken up remains non-extractable from plant tissues, suggesting binding or incorporation into plant structures (Harvey et al, 1991;Best et al, 1997;Larson et al, 1999;Thompson et al, 1999;Bhadra et al, 2001; (Gorge et al, 1994;Schnoor, 2000). A few transformation products have been identified, predominantly amino-and diamino-nitrotoluenes, (Harvey et al, 1990;Hughes et al, 1997;Thompson et al, 1998b;Larson et al, 1999), but incomplete information is available about the metabolism of TNT inside plant tissues.…”

“…Following uptake, RDX is translocated preferentially to the leaves where it undergoes a limited transformation (Harvey et al, 1991;Best et al, 1997;Just and Schnoor, 2004;. Identified transformation products include hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), 4-nitro-2,4-diazabutanal, formaldehyde, methanol, nitrous oxide, and nitrite Hawari, 2000;Just and Schnoor, 2004;.…”