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Phytoremediation of Explosives
Abstract
The widespread use of civilian, industrial, and military munitions has led to pollution by explosive compounds in aquatic and terrestrial environments. Each step in the life cycle of a munition from production, transport, storage, distribution, and destruction can introduce explosives as pure liquid or solids via leaching, contaminant spills, trace particles, whole or partial unexploded and exploded ordnance. Remediating explosives is difficult because the behavior of any one explosive compound is rather difficult as a number of factors can vastly alter how it moves, where it binds, and how it is sequestered by organisms. The phytoremediation of explosives focuses largely on sequestering compounds in their parent forms or transforming and degrading the compounds to inert forms using inherent metabolic processes in the plants themselves.
... In this review, we focus on minimizing the environmental risk caused on land by organic contaminants from military activities for two reasons: 1) to account for the most recent developments in environmental analytical chemistry, bioavailability and risk assessment (RA) of organic contaminants, which differ from those of more established, traditional approaches for inorganic (e.g., heavy metals) and radioactive pollution and 2) to account for the specificities of remediation methods for soils, sediments and adjacent waters contaminated by organic contaminants to allow for the development of nature-based approaches based on their biological removal, in line with recent interest in the application of bioeconomic concepts in sustainable land remediation (Francocci et al., 2020). We hope that readers find the approaches described in this review useful from the most recent findings connecting organic contaminants, biological treatments and military activities, which may differ from other reviews published over the last five years on other aspects of military pollution such as the bioremediation (Chatterjee et al., 2017) and phytoremediation (Via, 2020) of explosives, the remediation of inorganic and organic contaminants (Fayiga, 2019), and soil contamination (Broomandi et al., 2020). We also examine public information that has not been published in peerreviewed scientific journals but has been included in different reports, mainly by military institutions. ...
... Even though there have been no successful full scale applications for phytoremediation methodologies (Via, 2020), the ability of several types of plants to remove organic contaminants at levels comparable to those found in military contaminated sites is well documented, mainly for ECs (Table 2). Plants can accumulate or directly metabolize chemicals, by themselves or in combination with microorganisms in both soil and groundwater Hydrocarbon-contaminated and explosive-contaminated soils Siles and Margesin, 2018;Clark and Boopathy, 2007;Raschman and Vanek, 2008 Composting Amendment with biodegradable organic materials, fertilization, and pile maintenance under controlled humidity and aeration ...
As is the case with many other industrial activities, the organic contaminants at military-impacted sites may pose significant hazards to the environment and human health. Given the expected increase in defense investments globally, there is a need to make society aware of the risks of emissions of organic contaminants generated by military activities and to advance risk minimization approaches. The most recent advances in environmental analytical chemistry, persistence, bioavailability and risk assessment of organic contaminants indicate that efficient risk reductions through biological means are possible. This review debates the organic contaminants of interest associated with military activities, the methodology used to extract and analyze these contaminants, and the nature-based remediation technologies available to recover these sites. In addition, we revise the military environmental regulatory frameworks designed to sustain such actions. Military activities that potentially release organic contaminants on land could be classified as infrastructure and base operations, training exercises and armed conflicts; additionally, chemicals may include potentially toxic compounds, energetic compounds, chemical warfare agents and military chemical compounds. Fuel components, PFASs, TNT, RDX and dyphenylcyanoarsine are examples of organic contaminants of environmental concern. Particularly in the case of potentially toxic and energetic compounds, bioremediation and phytoremediation are considered eco-friendly and low-cost technologies that can be used to remediate these contaminated sites. In addition, this article identifies implementing the bioavailability of organic contaminants as a justifiable approach to facilitate the application of these nature-based approaches and to reduce remediation costs. More realistic risk assessment in combination with new and economically feasible remediation methods that reduce risk by reducing bioavailability (instead of lowering the total contaminant concentration) will serve as an incentive for the military and regulators to accept nature-based approaches.
... The ability of these genera to survive in explosive-contaminated soil highlights their potential for phytoremediation. However, it is important to consider the limitations of explosive phytoremediation, as its effectiveness has been demonstrated in laboratory settings but less so in the field [35]. ...
Munition disposal practices have significant effects on microbial composition and overall soil health. Explosive soil contamination can disrupt microbial communities, leading to microbial abundance and richness changes. This study investigates the microbial diversity of soils and roots from sites with a history of ammunition disposal, aiming to identify organisms that may play a role in bioremediation. Soil and root samples were collected from two types of ammunition disposal (through open burning and open detonation) and unpolluted sites in Machachi, Ecuador, over two years (2022 and 2023). High-throughput sequencing of the 16S rRNA gene (for bacteria) and the ITS region (for fungi and plants) was conducted to obtain taxonomic profiles. There were significant variations in the composition of bacteria, fungi, and plant communities between polluted and unpolluted sites. Bacterial genera such as Pseudarthrobacter, Pseudomonas, and Rhizobium were more abundant in roots, while Candidatus Udaeobacter dominated unpolluted soils. Fungal classes Dothideomycetes and Sordariomycetes were prevalent across most samples, while Leotiomycetes and Agaricomycetes were also highly abundant in unpolluted samples. Plant-associated reads showed a higher abundance of Poa and Trifolium in root samples, particularly at contaminated sites, and Alchemilla, Vaccinium, and Hypericum were abundant in unpolluted sites. Alpha diversity analysis indicated that bacterial diversity was significantly higher in unpolluted root and soil samples, whereas fungal diversity was not significantly different among sites. Redundancy analysis of beta diversity showed that site, year, and sample type significantly influenced microbial community structure, with the site being the most influential factor. Differentially abundant microbial taxa, including bacteria such as Pseudarthrobacter and fungi such as Paraleptosphaeria and Talaromyces, may contribute to natural attenuation processes in explosive-contaminated soils. This research highlights the potential of certain microbial taxa to restore environments contaminated by explosives.
... Hazardous compounds are detoxified through phytodegradation by plant enzyme systems and related microorganisms, whereas pollutants are discharged into the atmosphere through phytovolatilization. For the remediation of explosive or other heavy metal-contaminated soil ecosystems, phytoremediation techniques are appropriate (Smith et al. 2015;Via 2020). Explosives like TNT promptly transform in plant tissues and bind with leaves, wood, and stem. ...
Globally, explosive chemicals are widely used in different civil and military operations. During the production, transport, weapon testing, and mining activities, explosives reach to the environment and contaminate it. The problem of explosive contamination in urban environment has been reported in Asia, Sweden, the United States, Germany, and Australia. They readily bind with different components of humus and persist for long periods in soil due to their recalcitrant nature. Explosives are recalcitrant as they are not easily biodegraded by microorganisms in soil and water. Keeping in view their toxicity concerns to living organisms, it is exigent to remove these pollutants from the contaminated environment. The existing physical and chemical methods of removal of explosives from the contaminated environment are costly and not eco-incentive. Also, these methods can be only used under ex situ conditions. For the cleanup of the environment contaminated with harmful substances, such as explosives, phytoremediation is a very successful, well-proven bioremediation technology. In the light of the aforementioned context, present chapter critically assesses the sources of explosives in urban soils, environmental concerns, transport, and various explosive removal techniques in general and phytoremediation. Also, it discusses the mechanism and limitations of phytoremediation of explosives. Finally, it underlines the future prospects of phytoremediation as a prominent, sustainable, eco-incentive technology of removal of explosives from urban soils.
... Several previously selected plants that actively absorb and transform TNT [7][8][9][10][11][12][13][14], and microorganisms with high TNT assimilation capabilities [15][16][17][18][19][20] have commonly been used for cleaning up water and soil contaminated with explosives. Th e joint application of plants and bacteria for the phytoremediation of TNT contaminated soil has also been reported [21]. ...
Phytoremediation is increasingly adopted as a more sustainable approach for soil remediation. However, significant advances in efficiency are still necessary to attain higher levels of environmental and economic sustainability. Current interventions do not always give the expected outcomes in field settings due to an incomplete understanding of the multicomponent biological interactions. New advances in -omics are gradually implemented for studying microbial communities of polluted land in situ. This opens new perspectives for the discovery of biodegradative strains and provides us new ways of interfering with microbial communities to enhance bioremediation rates. This review presents retrospectives and future perspectives for plant microbiome studies relevant to phytoremediation, as well as some knowledge gaps in this promising research field. The implementation of phytoremediation in soil clean-up management systems is discussed, and an overview of the promoting factors that determine the growth of the phytoremediation market is given. Continuous growth is expected since elimination of contaminants from the environment is demanded. The evolution of scientific thought from a reductionist view to a more holistic approach will boost phytoremediation as an efficient and reliable phytotechnology. It is anticipated that phytoremediation will prove the most promising for organic contaminant degradation and bioenergy crop production on marginal land.
Natural selection processes are constantly influencing vegetation community composition. In the presence of anthropogenic contaminants additional forces act as filters controlling persistence of naturally occurring species. Classical species diversity and richness metrics can miss subtle changes under disturbance regimes while species composition and functional characteristics may be able to detect them. Our study was designed to investigate legacy impacts of explosives contaminated soils in an experimental minefield on vegetative communities using ecological metrics. As hypothesized, species diversity and richness showed no change in the presence of explosive compounds while species composition provided clear separation of groups and functional trait dominance was also observed to change. Overall, presence of anthropogenic contaminates have led to community composition and functional shifts for vegetation after initial contamination. The responses in species composition and functional diversity/richness were a result of new tolerant species filling open niches in contaminated plots. More work is needed to confirm this in varied systems and in the presence of diverse contaminants.
New explosive compounds that are less sensitive to shock and high temperatures are being tested as replacements for TNT and RDX. Two of these explosives, DNAN (2,4-dinitroanisole) and NTO (3-nitro-1,2,4-triazol-5-one), have good detonation characteristics and are the main ingredients in a suite of insensitive munitions (IM) explosives that are being, or soon will be, fielded. Both compounds, however, are more soluble than either TNT or RDX; and research has shown that both have some human and environmental toxicity. Data on their fate is needed to determine if DNAN and NTO have the potential to reach groundwater and be transported off base, an outcome that could create future contamination problems on military training ranges and trigger regulatory action. In this study, we measured how quickly DNAN and NTO dissolve in IM formulations and how solutions of these IM explosives interact with different types of soils. Because both dissolution and solution–soil interactions are determined by a suite of parameters, we are using a multifaceted approach to studying these processes. Given a mass of IM compounds scattered on the range, our work will help determine the dissolved IM masses, their subsequent transport and fate, and their likelihood of reaching groundwater.
The ability of agricultural and decorative plants to absorb and detoxify TNT and RDX has been studied. All tested 8 plants, grown hydroponically, were able to absorb these explosives from water solutions: Alfalfa > Soybean > Chickpea> Chikling vetch >Ryegrass > Mung bean> China bean > Maize. Differently from TNT, RDX did not exhibit negative influence on seed germination and plant growth. Moreover, some plants, exposed to RDX containing solution were increased in their biomass by 20%. Study of the fate of absorbed [1- 14C]-TNT revealed the label distribution in low and high-molecular mass compounds, both in roots and above ground parts of plants, prevailing in the later. Content of 14C in low- molecular compounds in plant roots are much higher than in above ground parts. On the contrary, high-molecular compounds are more intensively labeled in aboveground parts of soybean. Most part (up to 70%) of metabolites of TNT, formed either by enzymatic reduction or oxidation, is found in high molecular insoluble conjugates. Activation of enzymes, responsible for reduction, oxidation and conjugation of TNT, such as nitroreductase, peroxidase, phenoloxidase and glutathione S-transferase has been demonstrated. Among these enzymes, only nitroreductase was shown to be induced in alfalfa, exposed to RDX. The increase in malate dehydrogenase activities in plants, exposed to both explosives, indicates intensification of Tricarboxylic Acid Cycle, that generates reduced equivalents of NAD(P)H, necessary for functioning of the nitroreductase. The hypothetic scheme of TNT metabolism in plants is proposed.
Anthropogenic activities have been fundamental for the development of modern societies. However, they have resulted in the increase of environmental pollution which is a serious worldwide problem. Although phytoremediation has emerged as an attractive methodology to deal with contaminants, mainly present in water and soil, there are still some drawbacks to become a widely used practice, such as the problem of soils with diffuse mixed pollution (inorganic and organic). A useful strategy to overcome current limitations of phytoremediation is the use of genetically engineered plants. In this chapter we will discuss the most recent advances which use genetic engineering tools for enhancing phytoremediation of inorganic and organic pollutants. Advantages as well as disadvantages of using transgenic plants will also be discussed. In spite of the controversial aspects of field applications, efforts to minimize risks and reach public acceptance are very significant since the potential and usefulness of phytotechnologies are of great importance to clean up the environment.
Phytoremediation is a technology that is based on the combined action of plants and their associated microbial communities to degrade, remove, transform, or immobilize toxic compounds located in soils, sediments, and more recentlyin polluted ground water andwastewater in treatment wetlands. Phytoremediation could be used to treat different types of contaminants including petroleum hydrocarbons, chlorinated solvents, pesticides, explosives, heavy metals and radionuclides in soil and water. The advantages of phytoremediation compared to conventional techniques are lower cost, low disruptiveness to the environment, public acceptance, and potentiality to remediate various pollutants. The use of plants in conjunction with plant associated bacteria (rhizosphere or endophytic) offers greater potential for bioremediation of organic compounds,and in some cases inorganic pollutants than using plants alone in bioremediation. The implementation of treatment wetlands for phytoremediation of wastewater or polluted water originating from various sources allows removing organic and inorganic pollutants from water in an environmentally friendly and economically feasible way.
Presently, different processes of phytoremediation in treatment wetlands are less studied compared to phytoremediation of polluted soils. Further research is needed to advance the understanding of the pollutant removal mechanisms in treatment wetlands with vegetation, and how based on this information improve treatment wetland design and operational parameters to achieve more efficient treatment processes.This review covers basic processes of phytoremediation with special emphasis on rhizoremediation and plant-microbe interactions in plant–assisted biodegradation in soil and treatment wetlands.
Soils contaminated with explosive compounds occur on a global scale. Research demolition explosive (RDX) (hexahydro-1,3,5-trinitro-1,3,5-triazine) and trinitrotoluene (TNT) (2-methyl-1,3,5-trinitrobenzene) are the most common explosive compounds in the environment. These compounds, by variably impacting plant health, can affect species establishment in contaminated areas. Our objective was to quantify comparative effects of RDX and TNT on a native shrub, Morella cerifera, at two life stages. Morella cerifera seeds and juvenile plants were exposed to soil amended with RDX up to 1500 ppm and TNT up to 900 ppm. Percent germination was recorded for three weeks; morphological metrics of necrotic, reduced, and curled leaves, in addition to shoot length and number were counted and measured at the end of the experiment (eight weeks) for juvenile plants. All concentrations of RDX inhibited seed germination while TNT did not have an effect at any concentration. As contaminant concentration increased, significant increases in seedling morphological damage occurred in the presence of RDX, whereas TNT did not affect seedling morphology at any concentration. Overall the plants were more sensitive to the presence of RDX. Species specific responses to explosive compounds in the soil have the potential to act as a physiological filter, altering plant recruitment and establishment. This filtering of species may have a number of large scale impacts including: altering species composition and ecological succession.
Energetic materials comprise both explosives and propellants. When released to the biosphere, energetics are xenobiotic contaminants which pose toxic hazards to ecosystems, humans, and other biota. Soils worldwide are contaminated by energetic materials from manufacturing operations; military conflict; military training activities at firing and impact ranges; and open burning/open detonation (OB/OD) of obsolete munitions. Energetic materials undergo varying degrees of chemical and biochemical transformation depending on the compounds involved and environmental factors. This paper addresses the occurrence of energetic materials in soils including a discussion of their fates after contact with soil. Emphasis is placed on the explosives 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), and the propellant ingredients nitroglycerin (NG), nitroguanidine (NQ), nitrocellulose (NC), 2,4-dinitrotoluene (2,4-DNT), and perchlorate.
Background and Aims
Explosives released into the environment from munitions production, processing facilities, or buried unexploded ordnances can be absorbed by surrounding roots and induce toxic effects in leaves and stems. Research into the mechanisms with which explosives disrupt physiological processes could provide methods for discrimination of anthropogenic and natural stresses. Our objectives were to experimentally evaluate the effects of natural stress and explosives on plant physiology and to link differences among treatments to changes in hyperspectral reflectance for possible remote detection.
Methods
Photosynthesis, water relations, chlorophyll fluorescence, and hyperspectral reflectance were measured following four experimental treatments (drought, salinity, trinitrotoluene and hexahydro-1,3,5-trinitro-l,3,5-triazine) on two woody species. Principal Components Analyses of physiological and hyperspectral results were used to evaluate the differences among treatments.
Results
Explosives induced different physiological responses compared to natural stress responses. Stomatal regulation over photosynthesis occurred due to natural stress, influencing energy dissipation pathways of excess light. Photosynthetic declines in explosives were likely the result of metabolic dysfunction. Select hyperspectral indices could discriminate natural stressors from explosives using changes in the red and near-infrared spectral region.
Conclusions
These results show the possibility of using variations in energy dissipation and hyperspectral reflectance to detect plants exposed to explosives in a laboratory setting and are promising for field application using plants as phytosensors to detect explosives contamination in soil.
Explosives materials are stable in soil and recalcitrant to biodegradation. Different authors report that TNT (2,4,6-trinitrotoluene), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) and HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) are toxic, but most investigations have been performed in artificial soil with individual substances. The aim of the presented research was to assess the toxicity of forest soil contaminated with these substances both individually as well in combinations of these substances. TNT was the most toxic substance. Although RDX and HMX did not have adverse effects on plants, these compounds did cause earthworm mortality, which has not been reported in earlier research. Synergistic effects of explosives mixture were observed.
The ability of the aquatic plant Eurasian Watermilfoil (Myriophyllum spicatum) to transform 2,4,6-trinitrotoluene (TNT) was investigated in a series of batch assays. The TNT was added to plant cultures in single and multiple consecutive additions, at various initial concentrations, to determine its transformation kinetics, identify products formed, evaluate phytotoxic effects, and to determine the effect of light deprivation on the TNT transformation process. Rapid disappearance of TNT from the plant culture media was observed. The TNT disappearance rate was a function of both plant and TNT concentration (i.e., followed mixed, second-order kinetics). The TNT transformation occurred only in the presence of plants and was inhibited by the addition of sodium azide. Phytotoxicity leading to plant chlorosis was observed in batch plant cultures with an initial TNT concentration above 5.9 μM. Reductive transformation of TNT to aminodinitrotoluenes and lower levels of hydroxylaminodinitrotoluene and diaminonitrotoluenes detected in the plant culture media accounted for less than 10 to 20% of the total TNT mass added. Extraction of plant material at the end of batch incubations when all TNT was depleted from the media yielded low levels of TNT and aminodinitrotoluenes and accounted for only 3.4% of the initially added TNT mass. Light deprivation decreased both the rate and extent of the reductive transformation of TNT.
. Seed germination and early stage seedling growth tests were conducted to determine the ecotoxicological threshold of 2,4,6-trinitrotoluene
(TNT) in two soils of different properties. Soils were amended up to 1,600 mg TNT kg−1 soil and four representative species of higher plants, two dicotyledons (Lepidium sativum L., common name: cress; and Brassica rapa Metzg., turnip) and two monocotyledons (Acena sativa L., oat; and Triticum aestivum L., wheat), were assessed. Cumulative seed germination and fresh shoot biomass were measured as evaluation endpoints. Phytotoxicity
of TNT was observed to be affected by soil properties and varied between plant species. Cress and turnip showed higher sensitivity
to TNT than did oat and wheat. The lowest observable adverse effect concentration (LOAEC) of TNT derived from this study was
50 mg kg−1 soil. In contrast to high TNT concentrations, low levels of TNT, i.e., 5–25 mg kg−1 soil for cress and turnip and 25–50 mg kg−1 for oat and wheat, stimulated seedling growth. Oat was capable of tolerating as much as 1,600 mg TNT kg−1 and demonstrated a potential ability of TNT detoxification in one of the soils tested, suggesting that this plant might be
useful in the bioremediation of TNT contaminated soils.
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Field sampling experiments were conducted at an Air Force live-fire bombing range. The main objective was to assess the effectiveness of using a systematic-random, multi-increment sampling strategy for the collection of representative surface soil samples in areas where bombing practice is conducted with bombs containing high explosives. Replicate surface soil samples were collected within several craters and in different sized grids (1 m x 1 m, 10 m x 10 m, and 100 m x 100 m). One area sampled had been impacted by a low-order 2000-lb bomb detonation and several hundred small chunks of tritonal were present on the surface. Another area sampled had many fewer recognizable chunks of tritonal on the surface. An arroyo located downslope of the heaviest impacted area of this live-fire range where runoff from the area would be captured was also sampled at several locations. TNT was the major energetic compound present within the live-fire bombing area. Short-range heterogeneity in TNT concentrations was very large and the ability to estimate mean concentration using discrete samples even for an area as small as 1 m squared was poor. Much more reproducible estimates of mean concentrations for areas as large as 100 m x 100 m were achieved using multi-increment samples collected with a stratified systematic- random sampling design compared with that achieved using discrete samples. Results from soil profile samples and samples from the arroyo draining this area indicate that the energetic compounds present at the bombing range are not migrating from the site. Another area sampled was a small demolition range where C4 explosive is used to ensure that practice bombs contain no residual explosive prior to removing scrap metal from the range. RDX and HMX were the energetic compounds detected at the highest concentration in surface soil at the demolition range. These compounds originated from the demolition explosive.
Concerns about emerging environmental contaminants have been growing along with industrialization and urbanization around the globe. Among various options for remediating these contaminants, phytotechnology is suggested as a feasible option to maintain the environmental sustainability. The recent advances in phytoremediation, genetic/molecular/omics/metabolic engineering, and nanotechnology are opening new paths for efficient treatment of emerging organic/inorganic contaminants. In this respect, elucidation of molecular mechanisms and genetic engineering of hyperaccumulator plants is expected to enhance remediation of environmental contaminants. This review was organized to offer valuable insights into the molecular mechanisms of phytoremediation and the prospects of transgenic hyperaccumulators with enhanced stress tolerance to diverse contaminants such as heavy metals and metalloids, xenobiotics, explosives, poly aromatic hydrocarbons (PAHs), petroleum hydrocarbons, pesticides, and nanoparticles. The roles of genoremediation and nanoparticles in augmenting the phytoremediation technology are also described in an interrelated framework with biotechnological prospects (e.g., plant molecular nano-farming). Finally, political debate on the preferential use of crops versus non-crop hyperaccumulators in genoremediation, limitations of transgenics in phytotechnologies, and their public acceptance issues are discussed in the policy framework.
The development of methods to remediate soils and groundwaters contaminated with 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octohydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine (HMX), and related explosivemanufacturing byproducts has been an intense research interest for several decades. As discussed in other chapters, the ability of microorganisms to metabolize explosives has been studied extensively, although complete biomineralization of TNT has not been observed.
A study was performed to quantify the ability of 10 submersed and emergent macrophytes to phytoremediate explosives-contaminated groundwater from the Iowa Army Ammunition Plant (IAAP). Species evaluated under hydroponic batch conditions were the submersed Potamogeton nodosus Por. (American pondweed) and Ceratophyllum demersum L.(coontail) and the emergent Alisma subcordatum Raf. (water-plantain), Sagittaria latifolia Willd. (common arrowhead), Carex vulpinoidea Michx. (fox sedge), Scirpus cyperinus (L.) Kunth (woolgrass), Eleocharis obtusa (Wiil.) (blunt spikerush), Phalaris arundinacea L. (reed canary grass), and Typha angustifolia L. (narrow-leaf cat-tail). Parrot-feather (Myriophyllum aquaticum (Veil.) Verde.) was included in the evaluation to provide a comparison between the present study and other similar evaluations. The effects of sediments, native and heat-inactivated, on the explosives in the aqueous phase were also examined. The impact of a decrease in temperature from 25 to 10 °C on contaminant disappearance was assessed in three species and controls. TNT and RDX levels in the tested groundwater were 681 and 12,785 fig L"1.
In every respect, human development and human security are closely linked to the productivity of ecosystems. Our future rests squarely on their continued viability. UNDP, UNEP, World Bank, World Resources Institute: World Resources 2000- 2001. People and Ecosystems. The Fraying Web of Life. 1. OBJECTIVE OF THE BOOK Soil, surface waters/sediments and shallow unprotected groundwater aquifers are interrelated compartments of the environment that are particularly easy to compromise, sensitive to short- and long-term pollution and directly affect sustainability of ecosystems and human health. Routine human activity such as application of fertilizers and pesticides in agriculture and forestry, or wet and dry deposition of atmospheric pollutants emitted from industrial plants, waste disposal and other practices adversely affect soil and water quality that already increasingly suffers from mismanagement in many areas. The predominant sources of pollution result in non-point contamination that is particularly difficult to reduce and control. Wars, accidents and natural emergency cases such as catastrophic floods that occur partly due to anthropogenically disturbed global water balance also add to overall increase of diverse contaminant loads in soil and water. Beneficial properties of some bulk waste materials such as biosolids (sewage sludge), biowaste (e. g. municipal waste composts) or fly ash from coal combustion xi xii Preface encourage applying these waste to land as a source of nutrients and organic matter, or as a soil amendment.
The insensitive munitions compound 3-nitro-1,2,4-triazol-5-one (NTO) was recently approved by the U.S. Army to replace cyclotrimethylene trinitramine (RDX) in conventional explosives. As its use becomes widespread, concern about the potential toxicity of NTO increases. NTO can undergo microbial reduction to 3-amino-1,2,4-triazol-5-one (ATO), which is recalcitrant in waterlogged soils. In this study, the acute toxicity of NTO and ATO towards various organisms, including microorganisms (i.e., methanogenic archaea, aerobic heterotrophs, and Aliivibrio fischeri (Microtox assay)), the microcrustacean Daphnia magna (ATO only), and zebrafish embryos (Danio rerio), was assessed. NTO was notably more inhibitory to methanogens than ATO (IC50=1.2mM,>62.8mM, respectively). NTO and ATO did not cause noteworthy inhibition on aerobic heterotrophs even at the highest concentrations tested (32.0mM). High concentrations of both NTO and ATO were required to inhibit A. fischeri (IC20=19.2, 22.4mM, respectively). D. magna was sensitive to ATO (LC50=0.27mM). Exposure of zebrafish embryos to NTO or ATO (750μM) did not cause lethal or developmental effects (22 endpoints tested). However, both compounds led to swimming behavior abnormalities at low concentrations (7.5μM). The results indicate that the reductive biotransformation of NTO could enhance or lower its toxicity according to the target organism.
Quantifying vegetation response to explosive compounds has focused predominantly on morphological impacts and uptake efficiency. A more comprehensive understanding of the total impacts of explosives on vegetation can be gained using a multivariate approach. We hypothesized that multiple variables representing morphological and physiological responses will more clearly differentiate species and treatments than any one variable. Individuals of three plant species were placed in soils contaminated Composition B, which is comprised of 60% RDX and 40% TNT, and grown for two months. Response metrics used included photosynthetic operation, water relations, growth characteristics, as well as nitrogen and carbon concentrations and isotopic compositions. Individual metrics showed high variability in response across the three species tested. Water relations and nitrogen isotopic composition exhibited the most consistent response across species. By comparing multiple variables simultaneously, better separation of both species and exposure were observed. The inclusion of novel metrics can reinforce previously established concepts as well as provide a new perspective. Additionally the inclusion of various other metrics can greatly increase the ability to identify and differentiate particular groups. By using multivariate analyses and standard vegetation metrics, new aspects of the vegetation response to explosive compounds can be identified.
Existing and Potential Standoff Explosives Detection Techniques examines the scientific techniques currently used as the basis for explosives detection and determines whether other techniques might provide promising research avenues with possible pathways to new detection protocols. This report describe the characteristics of explosives, bombs, and their components that are or might be used to provide a signature for exploitation in detection technology; considers scientific techniques for exploiting these characteristics to detect explosives and explosive devices; discusses the potential for integrating such techniques into detection systems that would have sufficient sensitivity without an unacceptable false-positive rate; and proposes areas for research that might be expected to yield significant advances in practical explosives and bomb detection technology in the near, mid, and long term.
The continued interest in improving the safety of munitions towards unintentional insults has led to a significant amount of research in the synthesis of new insensitive energetic compounds. This paper discusses various approaches to the synthesis of insensitive energetic compounds, theoretical modeling and correlations of structural properties that contribute to reducing the sensitivity of energetic compounds, and how synthetic chemists integrate theoretical predictions into the design and synthesis of new insensitive energetic compounds.
The organic compounds trinitrotoluene (TNT), hexahydro4,3,5-trinitro-l,3,5-triazine (RDX) and l,3,5,7-tetranitro-l,3,5,7-tetrazocine (HMX) have all been demonstrated as subject to biological attack to some degree. In fact, RDX and HMX are routinely treated in wastewaters from production facilities by a conventional anaerobic biological process. The presence of the subject compounds in soil, however, has proven a more difficult removal problem for biological processes, especially in the case of TNT, for which biological treatment was not considered possible before 1975. This paper will discuss the origins of soil contamination by explosives and the current efforts to reduce the treatment costs of these soils using biological methods.
This chapter focuses on color reactions that are extensively used in the field of explosives analysis. Their application is easy, the equipment required is simple and inexpensive, their sensitivities are often in the sub-microgram range, and they enable rapid, on-site diagnostic detection of explosive materials. They are also used for preliminary laboratory tests of materials suspected of being explosive and can help in diagnosing impurities and degradation products of explosives. The main drawback of the use of color reactions for the analysis of explosives lies in their low specificity. Polynitroaromatic compounds were reported to undergo color reactions with numerous bases, such as ammonia in methanol and aqueous solution of tetramethyl-ammonium hydroxide. A completely different approach involves the reduction of a nitroaromatic compound to the corresponding aromatic amine in which Zn, SnCl2, and TiCl3 in acidic medium were used as reducing agents. The most important color reaction for nitrate esters and nitramines is based on the formation of nitrite ions (NO2), upon reaction of these compounds with alkalis, which are then detected by the classical Griess reaction. In 1999, Keinan and Itzhaky registered a patent on peroxide explosive tester, which enabled rapid on-site detection of triacetonetriperoxide (TATP). In the presence of organic peroxides, the outcome is a green-blue color and the detection limit is in the sub-microgram level. A simple, fast, and specific color test for urea nitrate was reported recently by Almog et al., which is based on the reaction between urea nitrate and ethanolic solution of p-dimethylaminocinnamaldehyde (p-DMAC) under neutral conditions from a red pigment that is formed within 1 min from contact.
An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, from the products of a chemical reaction involving explosive materials, or from a nuclear reaction that is uncontrolled. In order for an explosion to occur, there must be a local accumulation of energy at the site of the explosion, which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. Modern explosives or energetic materials are nitrogen-containing organic compounds with the potential for self-oxidation to small gaseous molecules (N
In order to select appropriate plant species for phytoremediation of explosive compounds, phytotoxicity, uptake proficiency, capability of the plant to degrade/transform the compounds, and several environmental factors need to be considered. The environmental factors comprise climatic attributes, soil type, the water environment, root penetration depth, contaminant kinetics, and bioavailability. Out of the plant species that have shown efficient TNT uptake, there are only a few that can do so in a variety of environments, which is imperative in case of contaminants that are widespread, such as TNT and RDX. The two most effective species for TNT uptake reported to date are Eurasian water milfoil, Myriophyllum spicatum and vetiver grass, Chrysopogon zizanioides. For RDX phytoremediation, reed canary grass, fox sedge, and rice have shown promise, although degradation of RDX in the plant tissue is limited. Over the past few decades, a considerable amount of information on phytotoxicity and metabolism of TNT and RDX in plants and microorganisms have been collected, which has led to the identification of potential plant species for use in TNT and RDX phytoremediation, as well as candidate genes for developing effective transgenic plants. Recent research has also revealed promising non-transgenic approaches, such as use of chaotropic agents for enhanced solubilization and uptake of TNT, which could prove to be practical and effective for military sites. Field trials of some of these promising new technologies are necessary for the development of effective, low-cost, and environmentally friendly phytoremediation of explosive-contaminated sites.
Unexploded ordnance (UXO) become point contamination sources when their casings fail and their explosive fill dissolve. To determine the modes of failure, we documented the condition of UXO found on military training ranges and sampled soils for explosives beneath 42 in situ UXO. We found that oxidation caused the metal UXO casings to swell and fail catastrophically. Unlike previous work, pitting of the metal casings was not found to be an important release route for explosives. Of the 42 UXO sampled, eight were leaking explosives into the soil and of these, four had perforated or cracked casings, three were corroded and one was a partially detonated round. We estimated a surface density of 74 UXO per hectare for a subset of UXO sampled. We used the relative concentrations of explosives and their transformation products in the soil to determine if the explosives had recently dissolved or were from past military training.
Published by Elsevier B.V.
Referee: Dr. C. Neal Stewart, Jr., Department of Plant Science and Landscape Systems, The University of Tennessee, 2431 Center Drive, Knoxville, TN 37996-4561 There is major international concern over the widescale contamination of soil and associated groundwater by persistant explosives residues. The development of methods to remediate these contaminants has been a significant research interest for several decades. In the last 10 years, phytoremediation has emerged as a focus for explosives remediation because of its low cost, low energy requirements, and promising research observing explosives removal from contaminated groundwater and soil. More recent work has focused on the modes of transformation and metabolism of energetic compounds by plants. These biochemical studies and the experimental conditions enabling the degradation and uptake of explosives by different plant species are discussed.
In this study, the effect of monopotassium phosphate (MKP) on the reduction in mobility and bioavailability of 2,4,6-trinitrotoluene (TNT) was tested. In the test soil, collected from an active firing range, of which cation binding sites were mostly exchanged with H(+) or Al(3+), potassium ions in MKP exchanged the existing cations and hence significantly increased TNT sorption. In addition, a competitive sorption experiment with hexafluorobenzene and 2,4-dinitrotoluene suggests that TNT was specifically sorbed through cation-polar interaction in the test soil. The unit-equivalent Freundlich sorption coefficient of TNT in MKP-amended soil (1370.96mg-TNT/kg-soil) was about 13 times higher than that in untreated soil (106.23mg-TNT/kg-soil). Finally, modified synthetic precipitation leaching procedure and hydroxypropyl-β-cyclodextrin extraction result revealed that MKP application could reduce both the leachability and bioavailability of soil TNT. The leachable and extractable fraction of TNT in untreated soil were 87.63% and 94.47% of the initial TNT, respectively, whereas these fractions decreased to 49.15% and 54.85% of the initial TNT in the presence of MKP, respectively. MKP application can be a benign technology which can reduce both mobility and bioavailability of TNT in soil.
Unexploded explosives that include royal demolition explosive (RDX) and trinitrotoluene (TNT) cause environmental concerns for surrounding ecosystems. Baccharis halimifolia is a plant species in the sunflower family that grows naturally near munitions sites on contaminated soils, indicating that it might have tolerance to explosives. B. halimifolia plants were grown on 100, 300, and 750 mg kg(-1) of soil amended with composition B (Comp B) explosive, a mixture of royal demolition explosive and trinitrotoluene. These concentrations are environmentally relevant to such munitions sites. The purpose of the experiment was to mimic contaminated sites to assess the plant's physiological response and uptake of explosives and to identify upregulated genes in response to explosives in order to better understand how this species copes with explosives. Stomatal conductance was not significantly reduced in any treatments. However, net photosynthesis, absorbed photons, and chlorophyll were significantly reduced in all treatments relative to the control plants. The dark-adapted parameter of photosynthesis was reduced only in the 750 mg kg(-1) Comp B treatment. Thus, we observed partial physiological tolerance to Comp B in B. halimifolia plants. We identified and cloned 11 B. halimifolia gene candidates that were orthologous to explosive-responsive genes previously identified in Arabidopsis and poplar. Nine of those genes showed more than 90 % similarity to Conyza canadensis (horseweed), which is the closest relative with significant available genomics resources. The expression patterns of these genes were studied using quantitative real-time PCR. Three genes were transcriptionally upregulated in Comp B treatments, and the Cytb6f gene was found to be highly active in all the tested concentrations of Comp B. These three newly identified candidate genes of this explosives-tolerant plant species can be potentially exploited for uses in phytoremediation by overexpressing these genes in transgenic plants and, similarly, by using promoters or variants of promoters from these genes fused to reporter genes in transgenic plants for making phytosensors to report the localized presence of explosives in contaminated soils.
Surrounding vegetation is exposed to a variety of potentially toxic compounds due to unexploded ordnances leaching explosive compounds into the soil. These compounds are absorbed by roots, transported through the vascular system, and distributed throughout plant tissues. Research Demolition Explosive (RDX) (hexahydro-1,3,5-trinitro-1,3,5-triazine) and trinitrotoluene (TNT) (2-methyl-1,3,5-trinitrobenzene) are the most studied; however, mixtures of explosives are widespread in conventional munitions. Composition B (Comp B), a mixture of RDX and TNT, is the most common mixture. Our study objective was to quantify the comparative effects of RDX, TNT and Comp B on the physiology of an evergreen shrub, Morella cerifera. Adult M. cerifera plants were exposed for 7 weeks to soil amended with RDX up to 1500 mg kg−1 dry soil, TNT up to 500 mg kg−1 dry soil, and Comp B up to 750 mg kg−1 dry soil. Stomatal conductance, photosynthesis, leaf water potential, leaf fluorescence, and contaminant uptake values were measured at the end of the experiment. As contaminant concentration increased, significant declines in photosynthesis and leaf fluorescence occurred for all compounds. Overall responses varied between contaminants and impacts of Comp B were largely reduced compared to either RDX or TNT. Of all physiological parameters, photosynthesis was most impacted, making it a sensitive indicator for the detection of explosives. Yet, the intricate relationships within normal physiological processes appear to be severed in the presence of explosives. These disparate responses in plant physiology may serve as a method for explosive contamination stress detection. Our results highlight the importance of studying real world munition mixtures.
One of the most dramatic ways humans can affect soil properties is through the performance of military activities. Warfare-induced disturbances to soil are basically of three types – physical, chemical, and biological – and are aimed at causing direct problems to enemies or, more often, are indirect, undesired ramifications. Physical disturbances to soil include sealing due to building of defensive infrastructures, excavation of trenches or tunnels, compaction by traffic of machinery and troops, or cratering by bombs. Chemical disturbances consist of the input of pollutants such as oil, heavy metals, nitroaromatic explosives, organophosphorus nerve agents, dioxins from herbicides, or radioactive elements. Biological disturbances occur as unintentional consequences of the impact on the physical and chemical properties of soil or the deliberate introduction of microorganisms lethal to higher animals and humans such as botulin or anthrax. Soil represents a secure niche where such pathogens can perpetuate their virulence for decades.
Using plants as phytosensors could allow for large-scale detection of explosives and other anthropogenic contamination. Quantifying physiological, photosynthetic and hyperspectral responses of plants to hexahydro-1,3,5-trinitro-l,3,5-triazine (RDX) contamination, provides the basis for understanding plant signals for remote detection. Plants of the woody shrub Baccharis halimifolia (a generalist species common on many military installations) were potted in soil concentrations of RDX ranging from 100 – 1500 mg kg-1. Physiological measurements of stomatal conductance and photosynthesis were significantly affected by RDX exposure at all treatment levels, with no overall effect on water potential. However, declines in photosynthesis and stomatal conductance were markedly different from those that occur under natural stress. Quantum use efficiency (F′v/F′m) and electron transport rate (ETR) indicated that photosystem II (PSII) of RDX treated plants was functional, with active photosynthetic reaction centers. Thus, declines in photosynthesis resulted from biochemical dysfunction in light-independent processes. Reflectance indices in the near-infrared region (R740/R630, R750/R710, and derivative indices) were most affected and may reflect the pathway in which RDX is contained within plants by being compartmentalized in the vacuole, cell wall or lignin. These results demonstrate the potential for using plants as phytosensors to identify explosives exposure at remote distances.
To evaluate the contribution of seed bank to natural revegetation, a soil seed bank study was carried out at different phases on three quarries in Hong Kong. A total of 2188 seedlings from 57 species were found, among which 36 species were herbaceous and graminoid plants while 21 were woody species. The soil seed banks were dominated by a few annual species, i.e. Ageratum conyzoides, A. houstonianum, Cynodon dactylon, Digitaria longiflora and Kyllinga brevifolia, which accounted for more than 35% of the total abundance. With ecological development, greater species number as well as seed density and diversity were recorded at older rehabilitated sites, which indicated that the process favors the increase in species richness. However, non-woody species predominated in all phases including those that were even more than 10 years after rehabilitation. The result of DCA showed that only 21 woody species which included 15 native species were better represented on the older quarry sites, which may still be insufficient to initiate natural succession at the later successional stage. As most native species in the soil seed banks were dispersed by birds, management strategies should take into account the possibility of enrichment planting with native species in the early stage and sowing some late successional species in the later stage for quarry rehabilitation.
Eleven plant species (five dicotyledonous, six monocotyledonous species) were cultivated for eight weeks in standard soil under identical conditions in the greenhouse. The soil was contaminated with 10, 100 or 500 mg TNT/kg, respectively.
Plant roots were extracted using dichloromethane with acid hydrolysis followed by alkalinisation. The main TNT-metabolites measured by GC-ECD were 2-aminodinitrotoluene and 4-aminodinitrotoluene. There was a positive correlation between soil contamination and the concentrations of extractable nitroaromatics in the roots. A species-dependent contamination level of extractable nitroaromatics was shown. In soil supplemented with 10 mg TNT/kg, the highest concentration of all species tested in this soil was found in the roots of Medicago sativa (2.7 μg NAC/g d. wt.). Medicago sativa was not able to grow in soil contaminated with 100 mg TNT/kg, where Triticum aestivum and Phaseolus vulgaris can develop and their roots contain high levels of TNT-metabolites (98 μg NAC/g d.wt. and 91 μg NAC/g d.wt., respectively). In the same soil the lowest level of nitroaromatics was detected in the root extract of Lupinus angustifilius (14 μg/g d. wt.). Only Phaseolus vulgaris was able to grow in the presence of 500 mg TNT/kg soil with very high levels of NACs in the roots (460μg/g d.wt.).
General differences between dicotyledonous and monocotyledonous plants in quality or quantity of nitroaromatic compounds were not noticed.
Uptake and/or sequestration of nitroaromatics by plants reduce the level of extractable nitroaromatics in the immediate environment of the root (rhizosphere soil). Several cultivars of Triticum aestivum were cultivated in TNT contaminated soil (50 mg TNT/kg) from a former ammunition site. Four of the six cultivars were able to reduce significantly the TNT concentration in the rhizosphere soil.
As an alternative to other groundwater extraction and surface treatment techniques, phytoremediation systems are currently being evaluated by civilian and military administrators for their ability to enhance removal of potentially toxic or mutagenic munitions materiel such as 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX), and their degradation products. To guide selection of aquatic plants for use in demonstration phytoremediation lagoons at the Milan Army Ammunition Plant (MAAP), Milan, TN, this study evaluated the relative ability of ten species to decrease levels of TNT and RDX explosives and related nitrobodies in contaminated MAAP groundwater.