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-trinitro-1,3,5-triazine (RDX) in groundwater using constructed wetlands is a potentially economical remediation alternative. To evaluate Explosives removal and fate was evaluated using hydroponic batch incubations of plant and substrate treatments with explosives-contaminated groundwater amended with [U-14C]-TNT or [U-14C]-RDX. Plants and substrates were collected from a small-scale wetland constructed for explosives removal, and groundwater originated from a local aquifer at the Milan Army Ammunition Plant. The study surveyed three aquatic, four wetland plant species and two substrates in independent incubations of 7 days with TNT and 13 days with RDX. Parent compounds and transformation products were followed using 14C and chemical (HPLC) analyses. Mass balance of water, plants, substrates and air was determined. It was demonstrated that TNT disappeared completely from groundwater incubated 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 after incubation. Mineralization to 14CO2 was very low, and evolution into 14C-volatile organics negligible. RDX disappeared less rapidly than TNT from groundwater. Growth of submersed plants was normal, but that of emergent 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 substrates. Mineralization to 14CO2 was low, but relatively higher than in the TNT experiment. Evolution into 14C-volatile organics was negligible. Important considerations for using certain aquatic and wetland plants in constructed wetlands aimed at removing explosives from water are: (1) plant persistence at the explosives level to which it is exposed, (2) specific plant-mass based explosives removal rates, (3) plant productivity, and (4) fate of parent compounds and transformation products in water, plants, and sediments.     

Dendroremediation of trinitrotoluene (TNT) Part 2: Fate of radio-labelled TNT in trees

BACKGROUND, AIM AND SCOPE: Problems of long-term existence of the environmental contaminant 2,4,6-trinitrotoluene (TNT) and necessities for the use of trees ('dendroremediation') in sustainable phytoremediation strategies for TNT are described in the first part of this paper. Aims of the second part are estimation of [14C]-TNT uptake, localisation of TNT-derived radioactivity in mature tree tissues, and the determination of the degree of TNT-degradation during dendroremediation processes. METHODS: Four-year-old trees of hybrid willow (Salix spec., clone EW-20) and of Norway spruce (Picea abies) were cultivated in sand or ammunition plant soil (AP-soil) in wick supplied growth vessels. Trees were exposed to a single pulse application with water solved [U-14C]-TNT reaching a calculated initial concentration of 5.2 mg TNT per kg dry soil. Two months after application overall radioactivity and extractability of 14C were determined in sand/soil, roots, stem-wood, stem-bark, branches, leaves, needles, and Picea May sprouts. Root extracts were analysed by radio TLC. RESULTS: 60 days after [14C]-TNT application, recovered 14C is accumulated in roots (70% for sand variants, 34% for AP-soil variant). 15-28% of 14C remained in sand and 61% in AP-soil. 3.3 to 14.4% of 14C were located in aboveground tree portions. Above-ground distribution of 14C differed considerably between the angiosperm Salix and the gymnosperm Picea. In Salix, nearly half of above-ground-14C was detected in bark-free wood, whereas in Picea older needles contained most of the above-ground-14C (54-69%). TNT was readily transformed in tree tissue. Approximately 80% of 14C was non-extractably bound in roots, stems, wood, and leaves or needles. Only quantitatively less important stem-bark of Salix and Picea and May shoots of Picea showed higher extraction yields (up to 56%). DISCUSSION: Pulse application of [14C]-TNT provided evidence for the first time that after TNT-exposure, in tree root extracts, no TNT and none of the known metabolites, mono-amino-dinitrotoluenes (ADNT), diaminonitrotoluenes (DANT), trinitrobenzene (TNB) and no dinitrotoluenes (DNTs) were present. Extractable portions of 14C were small and contained at least three unknown metabolites (or groups) for Salix. In Picea, four extractable metabolites (or groups) were detected, where only one metabolite (or group) seemed to be identical for Salix and Picea. All unknown extractables were of a very polar nature. CONCLUSIONS: Results of complete TNT-transformation in trees explain some of our previous findings with 'cold analytics', where no TNT and no ADNT-metabolites could be found in tissues of TNT-exposed Salix and Populus clones. It is concluded that 'cold' tissue analysis of tree organs is not suited for quantitative success control of phytoremediation in situ. RECOMMENDATIONS AND OUTLOOK: Both short rotation Salicaceae trees and conifer forests possess a dendroremediation potential for TNT polluted soils. The degradation capacity and the large biomass of adult forest trees with their woody compartments of roots and stems may be utilized for detoxification of soil xenobiotics.     

Fate of RDX and TNT in agronomic plants

Phytoremediation is of great interest to remediate soil contaminated with hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT). The ability of 4 agronomic plants (maize, soybean, wheat and rice) to take up these explosives and their fate in plants were investigated. Plants were grown for 42 days on soil contaminated with [(14)C]RDX or [(14)C]TNT. Then, each part was analyzed for its radioactivity content and the percentage of bound and soluble residues was determined following extractions. Extracts were analyzed by radio-HPLC. More than 80% of uptaken RDX was translocated to aerial tissues, up to 64.5 mgg(-1) of RDX. By contrast, TNT was little translocated to leaves since less than 25% of uptaken TNT was accumulated in aerial parts. Concentrations of TNT residues were 20 times lower than for RDX uptake. TNT was highly metabolized to bound residues (more than 50% of radioactivity) whereas RDX was mainly found in its parent form in aerial parts.     

Degradation of explosives-related compounds using nickel catalysts

We report the ability of nickel-based catalysts to degrade explosives compounds in aqueous solution. Several nickel catalysts completely degraded the explosives, although rates varied. Nearly all of the organic explosive compounds tested, including 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), were rapidly degraded to below detection limits by a powdered nickel on an alumina-silicate support (Aldrich nickel catalyst). Perchlorate degradation was minimal (<25%). Degradation of TNT by Aldrich nickel catalyst resulted in apparent first-order kinetics. Significant gaseous 14C was released and collected in an alkaline solution (most likely carbon dioxide) from [14C]RDX and [14C]HMX, indicating heterocyclic ring cleavage. Significant gaseous 14C was not produced from [14C]TNT, but spectrophotometric evidence indicated loss of aromaticity. Degradation occurred in low ionic strength solutions, groundwater, and from pH 3 to pH 9. Degradation of TNT, RDX, and HMX was maintained in flow-through columns of Aldrich nickel catalyst mixed with sand down to a hydraulic retention time of 4h. These data indicate that nickel-based catalysts may be an effective means for remediation of energetics-contaminated groundwater.     

Removal of TNT and RDX from water and soil using iron metal

Contaminated water and soil at active or abandoned munitions plants is a serious problem since these compounds pose risks to human health and can be toxic to aquatic and terrestrial life. Our objective was to determine if zero-valent iron (Fe(0)) could be used to promote remediation of water and soil contaminated with 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). As little as 1% Fe(0) (w/v) removed 70 mg TNT litre(-1) from aqueous solution within 8 h and removed 32 mg RDX litre(-1) within 96 h. Treating slurries (1:5 soil:water) of highly contaminated soil (5200 mg TNT and 6400 mg RDX kg(-1) soil) from the former Nebraska Ordnance Plant (NOP) with 10% Fe(0) (w/w soil) reduced CH(3)CN-extractable TNT and RDX concentrations below USEPA remediation goals (17.2 mg TNT and 5.8 mg RDX kg(-1)). Sequential treatment of a TNT-contaminated solution (70 mg TNT litre(-1) spiked with (14)C-TNT) with Fe(0) (5% w/v) followed by H(2)O(2) (1% v/v) completely destroyed TNT and removed about 94% of the (14)C from solution, 48% of which was mineralized to (14)CO(2) within 8 h. Fe(0)-treated TNT also was more susceptible to biological mineralization. Our observations indicate that Fe(0) alone, Fe(0) followed by H(2)O(2), or Fe(0) in combination with biotic treatment can be used for effective remediation of munitions-contaminated water and soil.     

Phytotoxicity to and uptake of RDX by rice

Phytoremediation is an emerging strategy to remediate soils contaminated with pollutants like explosives in which plants will uptake, degrade and/or accumulate pollutants. To implement this technology on a site contaminated with RDX, we chose rice, which is able to grow in lagoons, and we tested its ability to grow in soils with high levels of RDX and to decrease RDX concentrations in soil. Rice was grown for 40 days in soil contaminated with increasing [14C]RDX concentrations. Emergence and growth were not affected by RDX. Total chlorophyll content decreased with RDX concentrations of over 500 mg kg(-1). Amounts of chlorophyll were correlated with the appearance of necrosis in leaf extremities. After 40 days, rice translocated 89% of uptaken radioactivity to leaves with 90% in leaf extremities. Analyzes of leaf extracts showed that 95% of radioactivity was RDX in its parent form. Necrosis appears to be a phytotoxic symptom of RDX accumulation.     

Phytotoxicity and phytoremediation of 2,6-dinitrotoluene using a model plant, Arabidopsis thaliana

Biochemical and genetic studies of xenobiotic metabolism in the model plant Arabidopsis have significant potential in providing information for phytoremediation. This paper presents the toxicity of 2,6-dinitrotoluene (2,6-DNT) to Arabidopsis under axenic conditions, the fate and transformation of 2,6-DNT after uptake by the plant, and the effect of a putative glutathione S-transferase (GST), which is highly induced by 2,4,6-trinitrotoluene (TNT) in the previous study, on the detoxification of 2,6-DNT. 2,6-DNT had toxic effects on the growth of Arabidopsis based on whole seedling as well as root growth assays. Using [U- 14C]2,6-DNT, the recovery was over 87% and less than 2% accounted for the mineralization of 2,6-DNT in axenic liquid cultures during the 14d of exposure. About half (48.3%) of the intracellular radioactivity was located in the root tissues in non-sterile hydroponic cultures. 2-Amino-6-nitrotoluene (2A6NT) and two unknown metabolites were produced as transformation products of 2,6-DNT in the liquid media. The metabolites were further characterized by proton NMR spectra and the UV-chromatograms when the plant was fed with either 2,6-DNT or 2A6NT. In addition, polar unknown metabolites were detected at short retention times from radiochromatograms of plant tissue extracts. The GST gene of the wild-type of Arabidopsis in response to 2,6-DNT was induced by 4.7-fold. However, the uptake rates and the tolerance at different concentrations of 2,6-DNT and TNT were not significantly different between the wild-type and the gst mutant indicating that induction of the GST gene is not related to the detoxification of 2,6-DNT.     

Biodegradation pathways of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) by Clostridium acetobutylicum cell-free extract

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a military high explosive, is becoming an increasingly important pollutant in the US. The cleanup of RDX-contaminated soil and groundwater has been a serious challenge due to its recalcitrance in the environment. This study was conducted to determine the biodegradation kinetics of RDX by crude cell extract of Clostridium acetobutylicum (ATCC 824), and to examine whether this bacterium will carry out reductive transformation pathways similar to the transformation of 2,4,6-trinitrotoluene (TNT), 2,4- and 2,6-dinitrotoluenes (DNTs) we have reported previously. Batch studies on the anaerobic transformation of RDX were conducted in serum bottles with U-ring-14C-RDX. RDX and its transformation products were quantified by HPLC and qualified by LC/ MS interfaced to two soft ionization techniques--an atmospheric pressure ionization and an electron spray ionization (API-ES). Results demonstrated that C. acetobutylicum is capable of transforming RDX with H2 as the electron donor. The transformation followed a zero-order kinetics and the rates increased with increasing H2. RDX was transformed into several polar intermediates that could not be separated by reverse-phase HPLC and its molecular ions were unstable under the condition of commonly used electron impact detector. Using a polar and water immiscible solvent (ethyl acetate) and the softer MS ionization techniques, mass spectroscopy detected the presence of several RDX derivatives including mononitroso-, monohydroxylamino-, mononitrosomonohydroxylamino-, monoamino-, diamino-, and triamino-compounds. The presence of hydroxylamino compounds is analogous to the transformation of TNT and DNTs we elucidated previously.     

Distribution of14C-TNT and derivatives in different biochemical compartments ofPhaseolus vulgaris

¹⁴C-TNT was used to quantify the uptake rate and metabolic turnover of TNT inPhaseolus vulgaris. Seventeen plants were analysed by a special cell fractionation method with polar and nonpolar solvents and enzymes. We obtained three cytoplasmic fractions and five cell wall derived fractions. The recovery rate was 72% as measured by liquid scintillation counting.¹⁴C partitioned almost in equal amounts with approximately 50% in the cytoplasm and in the cell wall. The majority of the TNT-metabolites are present in the cytoplasm as was shown by GC/ ECD and thin layer chromatography. The¹⁴C in the cell wall is bound probably resulting in long-term immobilisation of these metabolites. We conclude that plants may also be a model for nitroaromatic turnover and immobilisation in soil components.     

Degradation of 2,4,6-trinitrotoluene by selected helophytes

Four emergent plants (helophytes, synonyms emersion macrophytes, marsh plants, etc.) Phragmites australis, Juncus glaucus, Carex gracillis and Typha latifolia were successfully used for degradation of TNT (2,4,6-trinitrotoluene) under in vitro conditions. The plants took up and transformed more than 90% of TNT from the medium within ten days of cultivation. The most efficient species was Ph. australis which took up 98% of TNT within ten days. The first stable degradation products 4-amino-2,6-dinitrotoluene (4-ADNT) and 2-amino-4,6-dinitrotoluene (2-ADNT) were identified and analysed during the cultivation period. [14C] TNT was used for the detection of TNT degradation products and their compartmentalization in plant tissues after two weeks of cultivation. Forty one percent of 14C was detected as insoluble or bound in cell structures: 34% in roots and 8% in the aerial parts. These results open the perspective of using the above-mentioned plants for the remediation of TNT contaminated waters.     

Simulating uptake and transport of TNT by plants using STELLA

Understanding the uptake and transport of soil organic contaminants by plants is crucial to a successful application of phytoremediation technique. This study investigated the removal of 2,4,6-trinitrotoluene (TNT) from a contaminated sandy soil by a poplar tree (Populus fastigiata) through the examinations of temporal variations of xylem water potential, leaf water transpiration, and root water and TNT uptake. A dynamic model for Uptake and Translocation of Contaminants from a Soil-Plant ecosystem (UTCSP), developed using the STELLA software package, was modified for the purpose of this study. The model was calibrated using laboratory measurements prior to its application. Simulation results showed that about 25% of TNT was removed from the soil by the poplar tree in 90 days. Simulations further revealed that the rates of water and TNT up taken by roots had a typical diurnal variation pattern: increasing during the day and decreasing during the night, resulting from daily variations of xylem water potentials that were caused by leaf water transpiration. In general, the storage of TNT mass in the roots decreased with time and occurred partially because of the low availability of soil TNT as time elapsed and partially because of the biodegradation of TNT in the plant tissues. This study suggests that the UTCSP model could be a useful tool for estimating phytoremediation of soil TNT by a plant.     

Electrolytic transformation of ordinance related compounds (ORCs) in groundwater: laboratory mass balance studies

Electrolytic reactive barriers (e(-) barriers) consist of closely spaced permeable electrodes installed across a groundwater contaminant plume in a permeable reactive barrier format. Application of sufficient potential to the electrodes results in sequential oxidation and reduction of the target contaminant. The objective of this study was to quantify the mass distribution of compounds produced during sequential electrolytic oxidation and reduction of ordinance related compounds (ORCs) in a laboratory analog to an e(-) barrier. In this study, a series of column tests were conducted using RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and TNT (2,4,6-trinitrotoluene) as representative ORCs. The experimental setup consisted of a plexiglass column packed with quartz-feldspar sand to simulate aquifer conditions. A single set of porous electrodes consisting of expanded titanium-mixed metal oxide mesh was placed at the midpoint of the sand column as a one-dimensional analog to an e(-) barrier. Constant current of 20mA (variable voltage) was applied to the electrode set. Initial studies involved quantification of reaction products using unlabeled RDX and TNT. Approximately 70% of the influent concentration was transformed, in one pass, through sequential oxidation-reduction for both contaminants. Following the unlabeled studies, (14)C labeled RDX and TNT were introduced to determine the mass balance. An activity balance of up to 96% was achieved for both (14)C-RDX and (14)C-TNT. For both contaminants, approximately 21% of the influent activity was mineralized to (14)CO(2). The proportion of the initial activity in the dissolved fraction was different for the two test contaminants. Approximately 30% of the initial (14)C-RDX was recovered as unreacted in the dissolved phase. The balance of the (14)C-RDX was recovered as non-volatile, non-nitroso transformation products. None of the (14)C-RDX was sorbed to the column sand packing. For (14)C-TNT approximately 51% of the initial activity was recovered in the dissolved phase, the majority was unreacted TNT. The balance of the (14)C-TNT was either sorbed to the sand packing (approximately 24%) or dissolved/mineralized as unidentified ring cleavage products ( approximately 4%).     

Sequential biodegradation of TNT,RDX and HMX in a mixture

We describe TNT's inhibition of RDX and HMX anaerobic degradation in contaminated soil containing indigenous microbial populations. Biodegradation of RDX or HMX alone was markedly faster than their degradation in a mixture with TNT, implying biodegradation inhibition by the latter. The delay caused by the presence of TNT continued even after its disappearance and was linked to the presence of its intermediate, tetranitroazoxytoluene. PCR–DGGE analysis of cultures derived from the soil indicated a clear reduction in microbial biomass and diversity with increasing TNT concentration. At high-TNT concentrations (30 and 90 mg/L), only a single band, related to Clostridium nitrophenolicum, was observed after 3 days of incubation. We propose that the mechanism of TNT inhibition involves a cytotoxic effect on the RDX- and HMX-degrading microbial population. TNT inhibition in the top active soil can therefore initiate rapid transport of RDX and HMX to the less active subsurface and groundwater.     

Dendroremediation of trinitrotoluene (TNT) part 1: Literature overview and research concept

BACKGROUND, AIM AND SCOPE: For decades, very large areas of former military sites have been contaminated diffusely with the persistent nitroaromatic explosive 2,4,6-trinitrotoluene (TNT). The recalcitrance of the environmental hazard TNT is to a great extent due to its particulate soil existence, which leads to slow but continuous leaching processes. Although improper handling during the manufacture of TNT seems to be a problem of the past in developed countries, environmental deposition of TNT and other explosives is still going on unfortunately, resulting from thousands of unexploded ordnance or low order explosions at munitions test areas and at current battlefields. OBJECTIVE: Sustainable phytoremediation strategies for explosives in Germany, which intend to use trees to decontaminate soil and groundwater ('dendroremediation'), have to consider that most of the former German military sites are already covered with woodlands, mainly with conifer stands. Therefore, parallel investigation of the remediation potential is necessary for both of the selected hybrids of fast growing broadleaf trees, which are waiting for planting and forest conifers, which have already proven for decades that they are able to grow on explosive contaminated sites. MAIN FEATURES: A short literature review is given regarding phytoremediation of TNT with herbaceous plants and some general aspects of dendroremediation are discussed. Furthermore, an overview of our TNT-dendroremediation research network is introduced, which has the strategic goal to make dendroremediation more calculable for a series of potent trees for site-adapted in situ application and for the assessment of tree remediation potentials in natural attenuation processes. RESULTS AND DISCUSSION: Some of our methods, results and conclusions yet unpublished are presented. For a preliminary calculation of area-related annual TNT dendroremediation potential of five-year-old trees, the following values were assessed: Salix EW-13 6.0, Salix EW-20 8.5, Populus ZP-007 4.2, Betula pendula 5.2, Picea abies 1.9 and Pinus sylvestris 0.8 g m(-2) a(-1). For a 45-year-old spruce forest, an annual natural attenuation potential of 4.2 g TNT m(-2) a(-1) was found. CONCLUSION, RECOMMENDATIONS AND PERSPECTIVE: Our main results deliver quantitative proposals for dendroremediation strategies in situ and provide decision aids. Also aspects of growth of raw materials for energy production are considered. Our dendroremediation research concept for TNT and its congeners can be easily completed for other trees of interest and it can also be applied to herbaceous plants. Knowing the current bottlenecks of phytoremediation and considering the known environmental behaviour of other contaminants, elements of our methodological approach may be easily adapted to those pollutant groups, e.g. for pesticides, pharmaceuticals, PAHs, chlorinated recalcitrants and, with some restrictions, to inorganics and to multiple contaminations. Our dynamical dendrotolerance test systems will help to predict tree growth on polluted areas. To provide some light into the black box of TNT dendroremediation, experimental data regarding the uptake, distribution and degradation of [14C]-TNT in mature tree tissues will be reported in the second part of this publication.     

Microtox toxicity test: detoxification of TNT and RDX contaminated solutions by poplar tissue cultures

Poplar (Populus deltoidesxnigra DN34) tissue cultures removed 2,4,6-trinitrotoluene (TNT) from an aqueous solution in five days, reducing the toxicity of the solution from highly toxic Microtox EC value to that of the control. 1,3,5-Trinitro-1,3,5-triazacyclohexane (RDX) was taken up by the plant tissue cultures more slowly, but toxicity reduction of the solution was evident. The measurement of toxicity reduction of aqueous solutions containing TNT and RDX was performed using a novel methodology developed for use with the Microtox testing system. Radiolabeled TNT and RDX were used to confirm removal of explosives from hydroponic solutions containing plant tissue cultures and to verify that toxicity did not change in solutions where no plant cultures were present (positive controls). High Performance Liquid Chromatography (HPLC) and Liquid Scintillation Counter (LSC) measurements confirmed removal of TNT and RDX from solutions containing poplar plant tissue cultures and constancy of the plant-free controls. In addition, metabolites were identified in remediated solutions by HPLC, confirming the mechanism by which plants can remediate groundwater, surface water, and soil solutions.     

Localization of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) in poplar and switchgrass plants using phosphor imager autoradiography

Phosphor imager autoradiography is a technique for rapid, sensitive analysis of the localization of xenobiotics in plant tissues. Use of this technique is relatively new to research in the field of plant science, and the potential for enhancing visualization and understanding of plant uptake and transport of xenobiotics remains largely untapped. Phosphor imager autoradiography is used to investigate the uptake and translocation of the explosives 1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene within Populus deltoides × nigra DN34 (poplar) and Panicum vigratum Alamo (switchgrass). In both plant types, TNT and/or TNT-metabolites remain predominantly in root tissues while RDX and/or RDX-metabolites are readily translocated to leaf tissues. Phosphor imager autoradiography is further investigated for use in semi-quantitative analysis of uptake of TNT by switchgrass.     

The impact of synthetic pyrethroid and organophosphate sheep dip formulations on microbial activity in soil

Sheep dip formulations containing organophosphates (OPs) or synthetic pyrethroids (SPs) have been widely used in UK, and their spreading onto land has been identified as the most practical disposal method. In this study, the impact of two sheep dip formulations on the microbial activity of a soil was investigated over a 35-d incubation. Microbial utilisation of [1-(14)C] glucose, uptake of (14)C-activity into the microbial biomass and microbial numbers (CFUs g(-1) soil) were investigated. In control soils and soils amended with 0.01% sheep dip, after 7d a larger proportion of added glucose was allocated to microbial biomass rather than respired to CO(2). No clear temporal trends were found in soils amended with 0.1% and 1% sheep dips. Both sheep dip formulations at 0.1% and 1% concentrations resulted in a significant increase in CFUs g(-1) soil and [1-(14)C] glucose mineralisation rates, as well as a decline in microbial uptake of [1-(14)C] glucose, compared to control and 0.01% SP- or OP-amended soils. This study suggests that the growth, activity, physiological status and/or structure of soil microbial community may be affected by sheep dips.     

Chemically catalyzed uptake of 2,4,6-trinitrotoluene by Vetiveria zizanioides

The efficiency of vetiver grass (Vetiveria zizanioides) in removing 2,4,6-trinitrotoluene (TNT) from aqueous media was explored in the presence of a common agrochemical, urea, used as a chaotropic agent. Chaotropic agents disrupt water structure, increasing solubilization of hydrophobic compounds (TNT), thus, enhancing plant TNT uptake. The primary objectives of this study were to: (i) characterize TNT absorption by vetiver in hydroponic media, and (ii) determine the effect of urea on chemically catalyzing TNT uptake by vetiver grass in hydroponic media. Results showed that vetiver exhibited a high TNT uptake capacity (1.026 mgg(-1)), but kinetics were slow. Uptake was considerably enhanced in the presence of urea, which significantly (p<0.001) increased the 2nd-order reaction rate constant over that of the untreated (no urea) control. Three major TNT metabolites were detected in the roots, but not in the shoot, namely 1,3,5-trinitrobenzene, 4-amino 2,6-dinitrotoluene, and 2-amino 4,6-dinitrotoluene, indicating TNT degradation by vetiver grass.     

Persistence and fate of 17beta-estradiol and testosterone in agricultural soils

Steroidal hormones are constantly released into the environment by man-made and natural sources. The goal of this study was to examine the persistence and fate of 17beta-estradiol and testosterone, the two primary natural sex hormones. Incubation experiments were conducted under aerobic and anaerobic conditions using [4-(14)C]-radiolabeled 17beta-estradiol and testosterone. The results indicated that 6% of 17beta-estradiol and 63% of testosterone could be mineralized to (14)CO(2) in native soils under aerobic conditions. In native soils under anaerobic conditions, 2% of testosterone and no 17beta-estradiol was methanogenized to (14)CH(4). Essentially, no mineralization of either testosterone or 17beta-estradiol to (14)CO(2) occurred in autoclaved soils under aerobic or anaerobic condition. Results also indicated that 17beta-estradiol could be transformed to an unidentified polar compound through abiotic chemical processes; however, 17beta-estradiol was only oxidized to estrone via biological processes. The TLC results also indicated that testosterone was degraded, not by physical-chemical processes but by biological processes. Results also indicated that the assumed risks of estrogenic hormones in the environment might be over-estimated due to the soil's humic substances, which can immobilize majority of estrogenic hormones, and thereby reduce their bioavailability and toxicity.     

Dissolution and sorption of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT) residues from detonated mineral surfaces

Composition B (Comp B) is a commonly used military formulation composed of the toxic explosive compounds 2,4,6-trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Numerous studies of the temporal fate of explosive compounds in soils, surface water and laboratory batch reactors have been conducted. However, most of these investigations relied on the application of explosive compounds to the media via aqueous addition and thus these studies do not provide information on the real world loading of explosive residues during detonation events. To address this we investigated the dissolution and sorption of TNT and RDX from Comp B residues loaded to pure mineral phases through controlled detonation. Mineral phases included nontronite, vermiculite, biotite and Ottawa sand (quartz with minor calcite). High Performance Liquid Chromatography and Attenuated Total Reflectance Fourier Transform Infrared spectroscopy were used to investigate the dissolution and sorption of TNT and RDX residues loaded onto the mineral surfaces. Detonation resulted in heterogeneous loading of TNT and RDX onto the mineral surfaces. Explosive compound residues dissolved rapidly (within 9 h) in all samples but maximum concentrations for TNT and RDX were not consistent over time due to precipitation from solution, sorption onto mineral surfaces, and/or chemical reactions between explosive compounds and mineral surfaces. We provide a conceptual model of the physical and chemical processes governing the fate of explosive compound residues in soil minerals controlled by sorption-desorption processes.