Abstract:
A method of detecting RDX in soil includes the steps of: planting a plurality of prickly sida plants in a defined area; remotely monitoring the pigmentation of the prickly sida plants using hyperspectral imaging; and identifying one or more areas within the defined area that are contaminated by RDX based on the monitored pigmentation of the prickly sida plants.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application incorporates by reference and claims priority to U.S. Provisional Patent Application No. 61/418,729 filed Dec. 1, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     The present subject matter relates generally to a RDX plant indicator system. More specifically, the present invention relates to a plant indicator system designed to detect contamination of RDX using prickly sida plants as sentinels. 
     The continuous use of explosives on training ranges results in the development of major negative environmental impacts that are difficult to remedy. Also, the costs of environmental compliance, cleanup, pollution reduction, and conservation are significant. Existing methods to test for contamination are also dangerous since the military sites may include land mines and other explosives or explosive residues. Hexahydro-1,3,5-trinitro-1,3,5-triazine, referred to as RDX, is commonly found at military operation sites. RDX is one of the most widely distributed energetic soil contaminants. RDX is the primary energetic used in most military applications from explosives ordnance (bombs, missiles, and shells) to missile propellants and demolition charges. The United States Department of Defense (DoD) has identified more than one thousand sites with explosives contamination. Many sites became contaminated through open detonation and burning of explosives at army depots, evaluation facilities, artillery ranges, and ordnance disposal sites. Before the 1980&#39;s, waste was often dumped in unlined pits, and has now contaminated both soil and groundwater. The use of ordnance continues to pollute soil and water in the U.S. and worldwide. 
     As RDX readily migrates into the surface or near surface soils, it leads to soil and groundwater contamination. Soil contamination by this energetic at military ranges in the United States and Canada is well documented. Furthermore these contaminants have leached into and contaminated groundwater. Their residues are known to accumulate in soils on military ranges. Live fire training and testing ranges are placed at risk by the transport of Off Range Contaminates (ORC) through a variety of environmental pathways. 
     The mobility of energetic residues is a major concern. Mobility is a complex process and has many confounded effects. Among energetics, TNT and RDX are most widely distributed as soil contaminants, and both compounds are often found in the soil at the same site. RDX has a high potential for soil leaching since it does not bind to soil very strongly and can move rapidly into the groundwater. RDX is more soluble than other contaminants, but RDX is not typically absorbed or biodegraded significantly in aerobic soil. Unlike TNT, RDX does not bind to soil particles, and its breakdown products are more likely to move into the groundwater. Energetics and residues are labile in the environment and these changes can be caused through sunlight, soil microbes, and transformation by certain plant processes. 
     RDX does not bioaccumulate or build up in fish or people, but exposure to RDX in large amounts may cause seizures. However, the effects of long-term, low-level exposure to RDX in humans is unknown. Studies have also been made on plants and crops, and many plants have developed an uptake of RDX from contaminated soil and contaminated irrigation water. Technologies such as phytoextraction and phytostabilization has been studied in cases of TNT contamination. Phytoextraction is the use of plants to uptake, accumulate, and remove contaminants from the soil, and phytostabilization is the use of both plants and soil amendments to prevent the contaminants from moving out of the area. These methods may be used to detect contamination on military sites. 
     A large number of studies have been done to evaluate phytoremediation processes for energetics. However, in the studies using plants, the majority of plants are either grasses or species growing in wetland habitats. Little research has been on upland plants. Past research has focused mainly on grasses and found RDX induced inhibition of biomass production. Also, related work has been done where fluorescence was used as an indicator in monitoring uptake of explosives in genetically modified plants that were not commonly found on ranges. This approach may be more expensive, and does not provide a realistic training environment on ranges. 
     Also, in order to test for contamination on military sites, the safety of range personnel is often compromised in order to collect field samples and test for energetics. In areas with dense vegetation, locations of residues are more difficult to visualize and locate. Collecting these samples also disrupt military range activity and put personnel in danger since they may disrupt an unexploded land mine or other explosive. The current methods of collecting sufficient data for a comprehensive environmental assessment are also very costly. 
     Therefore, there is much concern regarding the migration of these contaminants, particularly RDX, to groundwater. Ecosystem components, such as vegetation cover and soil types, play important roles in determining potential pathways a contaminant may take upon leaving a particular range. 
     Accordingly, a need exists for a plant indicator system designed to detect contamination of RDX using naturally occurring plants such as prickly sida as sentinels as described and claimed herein. 
     BRIEF SUMMARY OF THE INVENTION 
     The plant indicator system detects contamination of RDX using prickly sida plants as plant sentinels. When exposed to RDX, the prickly sida plants may respond by having pigmentation discoloration that may be observed using remote hyperspectral imaging. 
     Possible movement pathways of contaminants can be determined through soil leaching and plant uptake. The energetic interaction and other environmental factors stress the plants and may often result in physiological changes, such as stunting and pigmentation discoloration. For example, when the prickly sida plants detect contaminants, their leaves may turn red. While some of the changes are visible to the naked eye, detection by hyperspectral imaging is more efficient, safe, and cost effective. 
     Using plants that grow in the natural range ecosystem to detect these contaminants is beneficial to military ranges as plants are relatively inexpensive. If additional plants are needed on a range they may be planted safely by air seeding or hydro seeding methods over an un-cleared range area. The use of vegetation as sentinels to indicate the presence and/or absence of contaminants may also provide an ideal mechanism for detecting contaminants in a large area. Additionally, forbs and grasses such as the prickly sida plant are commonly maintained on active firing ranges since they provide a realistic training environment and control erosion. 
     Color changes have been observed in a species of plant belonging to the Malvaceae family, Prickly Sida ( Sida spinosa ). This particular member of the Malvaceae family is known to grow well throughout the United States. These plants were one of five species grown in a typical soil from a large military base that had been treated with TNT or RDX soil. Prickly Sida was the only plant that became red in the presence of RDX in the soil. This plant also exhibited interveinal chlorosis and a reduction in biomass and fruit size. The red color change was visible in the leaf margins and not in the same area as the interveinal chlorosis. The red pigment appeared on the top leaf surface. Red coloration may be caused by anthocyanins, which are produced in response to free radicals. When a sida uptakes RDX it triggers an antioxidant reaction in the leaves thus activating the gene expression to up regulate the enzymes involved in the Shimikic pathway leading to production of anthocyanin. 
     Prickly sida is also resilient to RDX contamination. Resilience to physical disturbance and tolerance towards contaminants such as energetics are important determinants in the distribution of plants at contaminated training areas. Resilience is the ability of a vegetative system to recover after disturbance and return to its original state. Military training exercises often destroy the vegetation, which leads to soil erosion, increased runoff, and leaching of explosives. Since prickly sida exhibits resilience to RDX, it is an ideal plant to be used to detect contamination. 
     The method of using plant sentinels to detect soil contaminated with RDX includes the first step of planting the prickly sida plants by air seeding or hydro seeding in a desired operational range or military site where RDX is used. This allows for safe delivery of the plants to the site. The second step is to remotely monitor the prickly sida plants using hyperspectral imaging. The third step is to detect and monitor any appearance of color changes on the leaves of the prickly sida plants indicating soil contaminated with RDX. The fourth step is to use intensity signals of chlorophyll fluorescence to determine the sensitivity of frequency disruption, or days required to observe a response, of the prickly sida plants to RDX. The fifth step is to use spectral measurements to distinguish the appearance of color changes from contamination or any natural stressors. It is necessary to discern that the color change in the prickly sida, if producible, is not caused by any environmental stressors. Stressors such as drought, soil salinity, pH changes, nutrients, and soil type have been evaluated to ensure they have not produced false positives. 
     The sixth step is to determine which parts of the operational range or surrounding areas are contaminated based on which prickly sida plants have red leaves. Remote hyperspectral imaging is used to detect any red leaves on the prickly sida plants. This imaging may inform personnel of the exact location of the red prickly sida plants. Non-invasive remote sensing technologies, such as chlorophyll fluorescence, is used to monitor plant stress and to detect and predict changes in the natural environment. The visible and hyperspectral response to energetics in plants could improve the environmental sustainability of military firing ranges. With this technology, the safety of range personnel would not be endangered by a successful operating remote sensing protocol. The use of remote sensing technology may lower costs of collecting sufficient data for comprehensive environmental assessment and may increase safety since data may not have to be collected by range personnel. Finally, the seventh and final step allows for treatment of the contaminated area. 
     In one example, a method of detecting RDX in soil includes the steps of: planting a plurality of prickly sida plants in a defined area; remotely monitoring the pigmentation of the prickly sida plants using hyperspectral imaging; and identifying one or more areas within the defined area that are contaminated by RDX based on the monitored pigmentation of the prickly sida plants. The step of planting the prickly sida plants may be accomplished by an air seeding or hydro seeding process. The step of remotely monitoring the pigmentation of the prickly sida plants may include monitoring the intensity signals of chlorophyll fluorescence in the plants. Further, the step of remotely monitoring the pigmentation of the prickly sida plants may include using spectral measurements to distinguish the appearance of color changes in response to RDX as opposed to color changes in response to natural conditions. The method may further include the step of treating the identified contaminated areas to remove the RDX contamination. 
     An essential DoD priority includes remote sensing technologies to identify off site contaminant migration without interfering in range activity. Non-invasive remote sensing technologies, such as chlorophyll fluorescence, is used to monitor plant stress and to detect and predict changes in the natural environment. The visible and hyperspectral response to energetics in plants could improve the environmental sustainability of military firing ranges. With this technology, the safety of range personnel would not be endangered by a successful operating remote sensing protocol. 
     An advantage of the plant indicator system is that it may indicate when soil is contaminated with RDX. 
     Another advantage of the plant indicator system is that it may allow for remote detection of RDX contamination using hyperspectral imaging. 
     A further advantage of the plant indicator system is that it allows for safe detection of contaminants on military sites. 
     Yet another advantage of the plant indicator system is that it uses plants that are naturally occurring. 
     Another advantage of the plant indicator system is that it uses low cost hyperspectral imaging. 
     Additional objects, advantages and novel features of the examples will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following description and the accompanying drawings or may be learned by production or operation of the examples. The objects and advantages of the concepts may be realized and attained by means of the methodologies, instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing figures depict one or more implementations in accord with the present concepts, by way of example only, not by way of limitations. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a contaminant transport model illustrating how prickly sida plants respond to contaminants, such as RDX, in the soil. 
         FIG. 2  is a flowchart illustrating an example of a method of using plant sentinels to detect soil contaminated with RDX. 
         FIG. 3   a  is an example of a prickly sida plant that has not been exposed to RDX contamination. 
         FIG. 3   b  is an example of a prickly sida plant that has detected RDX contamination. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an example of a contaminant transport model  12  illustrating how prickly sida plants  14  respond to contaminants, such as RDX, in the location. As shown in  FIG. 1 , the plant indicator system  10  (hereinafter “the system”) includes a plurality of prickly sida plants  14  spread over an area of soil  16  to detect the presence of a contaminant at the site. In one example, an explosive  18 , such as RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine), may be detonated on the ground surface of the soil  16  causing explosive residue  20  to seep into the site, particularly when there is precipitation that assists in transporting the contaminant through the soil  16  and into the groundwater mixing zone  22 . 
     As shown in  FIG. 1 , after the explosive  18  has been detonated, the explosive residue  20  seeps through the soil  16  and enters the groundwater mixing zone  22 . In the example in  FIG. 1 , the groundwater carries the explosive residue  20  in the direction of the groundwater flow  24 . 
     In order to detect the presence of the contaminant in the soil  16 , the plants  14  are spread over the ground surface of the soil  16 . For example, the plants  14  may be planted by air seeding or hydro seeding such that the ground surface of the soil  16  is reasonably well covered by the plants  14 . 
     In the example used in  FIG. 1 , the plant indicator system  10  detects contamination of RDX  18  using prickly sida plants  14  as plant sentinels. When the prickly sida plant (i.e., a species of plant belonging to the Malvaceae family, Prickly Sida,  Sida spinosa )  14  is exposed to RDX  18 , color changes in the plant  14  are visually observable. Specifically, when exposed to RDX  18 , the normally green leaves of the prickly sida plants  14  (shown in  FIG. 3A ) respond by exhibiting a red pigmentation discoloration  60  (shown in  FIG. 3B ). The red pigmentation discoloration  60  appears only on the top leaf surface and not the under leaf. The red pigment discoloration  60  may be observed using remote hyperspectral imaging, which enables the detection of the contamination from a safer location rather than requiring direct contact with the contaminated area. While the pigment changes shown in  FIG. 1  may be visible to the naked eye, detection by hyperspectral imaging may be more efficient, safe, and cost effective. In addition, other physically observable changes may occur in the plats  14  subjected to contamination, such as stunted growth; however, it is believed that the pigmentation coloration is the easiest to identify, particularly remotely. 
     Turning back to  FIG. 1 , as the plants  14  grow in the soil  16 , remote hyperspectral imaging may be used to determine which areas are contaminated by RDX  18  since only the prickly sida plants  14  in the contaminated areas  26  turn red and the prickly sida plants  14  in the uncontaminated areas  28  remain green. Because the plants  14  are able to detect the contaminants  18  beneath the surface of the soil  16  (through soil leaching and plant uptake), the movement pathways of the contaminants can be determined using the plants  14  at the surface. 
     Using plants  14  that grow in the natural range ecosystem to detect these contaminants is beneficial to military ranges as the plants  14  are relatively inexpensive. If additional plants  14  are needed on a range  16  they can be planted safely by air seeding or hydro seeding methods over an un-cleared range area. The use of vegetation as sentinels to indicate the presence and/or absence of contaminants may also provide an ideal mechanism for detecting contaminants in a large area. Additionally, forbs and grasses are commonly maintained on active firing ranges since they provide a realistic training environment and control erosion, so prickly sida plants  14  would look realistic in that environment. 
     Prickly sida  14  is also resilient to RDX contamination. Resilience to physical disturbance and tolerance towards contaminants such as energetics are important determinants in the distribution of plants  14  at contaminated training areas. Resilience is the ability of a vegetative system to recover after disturbance and return to its original state. Military training exercises often destroy the vegetation, which leads to soil erosion, increased runoff, and leaching of explosives. Since prickly sida  14  exhibits resilience to RDX  18 , it is an ideal plant to be used to detect contamination by RDX  18 . 
       FIG. 2  illustrates an example of a method  40  of using plant  14  sentinels to detect soil contaminated with RDX  18 . In the first step  42 , the prickly sida plants  14  are planted by air seeding or hydro seeding in a desired operational range or military site where RDX  18  is used. This allows for safe delivery of the plants  14  to the site. The second step  44  is to remotely monitor the prickly sida plants  14  using hyperspectral imaging. The use of remote sensing technology may lower costs of collecting sufficient data for comprehensive environmental assessment and may increase safety since data may not have to be collected by range personnel. Remote sensing technology is reliable and accurate. For example, remote sensing technology may also be used to distinguish between weeds and crops in a field with a high degree of accuracy. 
     The third step  46  is to detect and monitor any appearance of color changes on the leaves of the prickly sida plants  14  indicating soil contaminated with RDX  18 . The fourth step  48  of the method  40  is to use intensity signals of chlorophyll fluorescence to determine the sensitivity of frequency disruption, or days required to observe a response, of the prickly sida plants  14  to RDX  18 . These measurements are useful in assessing the plant&#39;s physiological state, which show a relationship to RDX exposure. The fifth step  50  is to use spectral measurements to distinguish the appearance of color changes from contamination or any natural stressors. It is helpful to discern that the color change is not caused by other environmental stressors. Stressors such as drought, soil salinity, pH changes, nutrients, and soil type may be evaluated to ensure they have not produced false positives. 
     The sixth step  52  of the method  40  is to determine which parts of the operational range or surrounding areas are contaminated based on which prickly sida  14  plants have red leaves. Once again, remote hyperspectral imaging is used to detect any red leaves on the prickly sida plants  14 . This imaging may inform personnel of the exact location of the red prickly sida plants  14 . Then finally, the seventh and final step  54  of the method  40  treat the contaminated area. 
       FIG. 3A  illustrates a prickly sida plant  14  that has not been exposed to RDX  18 .  FIG. 3B  illustrates a prickly sida plant  14  that has been exposed to RDX  18 . As shown in  FIG. 3B , the prickly sida plant  14  that has been exposed to RDX  18  reacts by expressing a red pigmentation  60 . As shown in  FIG. 3 , most changes to the pigmentation of the plants  14  occur on the leaves of the prickly sida plant  14 , but the stem may also contain some red pigmentation  60  as well. In most cases, the red pigmentation  60  appears only on the top leaf surface and not the under leaf. 
     It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages.