Our Proposed Scenario: Contaminated Sites

At the beginning of our project, we wondered how we could solve the problem of buried chemical weapons in the best way. We decided on plants as the system of our choice, further developed and improved this application scenario in discussions with experts. As a result, we propose to use our system to monitor sites, where leftovers from past wars are suspected. After planting, the change in leaf color to bright red will indicate where immediate intervention is necessary. As it will still take a long time until all areas are cleaned from chemical weapons, in the meantime this will greatly reduce the risk that these chemicals endanger humans and pollute the environment, as removal can start where it is most urgent.

Introduction

To apply our plant-based detection system, we identified five important steps for its implementation. Besides that, one major requirement is the release of genetically modified organisms (GMOs). Therefore extensive safety features are required for these organisms to prevent the uncontrollable release and spread. Until this is ensured, our project can be seen as a good practice example of how engineered plants can be used in the future, where GMOs are part of our everyday life. Currently, the application of genetically modified organisms in the field is restricted in many countries. However, we developed a strategy on how our plants could be engineered as safely as possible so that their use may be possible in the future.

Distribution

First, a detection system needs to reach the location, where it is planned to be used. However, “almost all instrumental techniques that currently unambiguously determine the presence of nerve agents are expensive and nonportable” [1]. This is one major advantage of plants over established technical detection methods. They can be distributed as seeds, which are much smaller than other typical detection devices [1]. This allows our system to cover large areas with relatively small quantities of seeds. In addition, as seeds, our plants can be stored for years. This makes it possible to order seeds from a stock center when needed and transport them even to regions, where transport of larger equipment for example by trucks is not possible.

Areas to use on

Unknown or suspected contaminations

Related to our motivation, one application for our plants are areas where chemical weapon contaminations are suspected or even known. On some areas such as former battlefields and possible storage sites pollutants are distributed over a large area. On those sites, the plant-based detection system can be applied, easily distributed, and identify those contaminations. This enables the precise application of further laboratory analyses for verification and the fast initiation of decontamination procedures.

Contamination monitoring of known chemical weapon storage sites

However, there are several known, but uninvestigated storage sites of chemical weapons, remaining from the past wars, where no decontamination efforts are attempted. At those sites, our system can be applied to monitor for the emergence of leaks and therefore would make these uninvestigated, but known storage sites less dangerous.

Screening of construction sites

In Germany, some thousand tons of explosives from both world wars are found every year on buildings ground, often within the city centers. Evacuations, where thousands of citizens must be evacuated for a safe deactivation or controlled detonation, are required. Unfortunately, some explosives are recognized too late and lives are lost. Our plant could help to prevent those accidents. Before digging on building ground starts, our plants can ensure that it is safe to work there, and therefore can save the lives of construction workers and future inhabitants. However, for some areas, the application of our system is easier than for others. For example, due to lack of light small plants would not work well in areas that are densely overgrown, such as forests and its detection would be difficult. As many relevant sites lie in forests [2] solutions for these areas are of great interest. This can be addressed through the choice of plants to use (Additional Remarks).

Application

Our plants could easily be applied through sowing, either by hand, by conventional techniques, or even by using drones [3] to reach areas that are hard to access, or where the expected noxious chemicals prevent humans from entering the area. As modest plants would be used, they can grow unattended, without further human influence. Another possibility is to use plants that have already grown. This can be useful, if faster results are of interest or if they need to overgrow other plants. However, this also implies more workload and therefore would not be the preferred way of application.

Detection

When the plants are sowed, detection of certain chemicals is possible when the plants are grown and the root system is fully developed. In most cases, this delay should not be a problem, as decontamination usually progresses slowly [4]. As soon as shells or containers become leaky and detectable chemicals are released, their detection is possible. Either with our plants or with conventional methods. Once the plants have changed their leaf color, this signal will be visible at least for several weeks as we tested in further experiments. One of the chemicals we want to detect is Thiodiglycol, which was already found in the groundwater of contaminated areas. It is a degradation product of mustard gas and persists in soil. Another chemical we worked with is Methylphosphonic acid, which is a product of hydrolysis of nerve agents like Sarin and Soman. For an overview of chemicals, we considered, visit our chemicals page. But as our method in receptor design is not limited to the substances we used, other receptors can be designed when needed.
The absence of chemicals does exclude a possible leakage but does not imply that there are no containers of chemical weapon leftovers. Therefore a repetition of such a screening from time to time on suspected areas is inquired, as leakages can develop over time. For screening of areas that are large or difficult to reach, it is an option to determine changes in the plant’s leaf color using drones [5] or even satellite images [6]. Chemicals can be detected up to 1.5 m depth using tobacco [7]. But of course, this can be extended by using different plants which grow deeper into the ground (Additional Remarks).

Decontamination

When the remains of chemical weapons are found, work-intensive and expensive decontamination [4] is required. As different specific receptor proteins can be designed for different pollutants and as there are several independent reporter systems available, it is possible to create plants that can detect several substances and distinguish between them. This would give a clue on what substances were released at this location, to enable comprehensive safety measures, further analysis, and decontamination procedures. As the high costs are the main reason, why decontamination efforts progress slowly [8], finding a more cost-efficient solution for this could accelerate the process. Enzymatic degradation pathways for a few chemical weapons are known [4] opening the possibility for plant-based systems that not only detect but also degrade dangerous chemicals when present. For chemicals that cannot be degraded further such as arsenic, plants could be used to take it up from the ground. It is known, that several plants take up arsenic and are able to withstand its toxic effects to a certain degree [9]. These plants could be harvested and processed further so that these pollutants are taken out of the environment.

Additional Remarks

Plants to be used

Due to time limitations, we chose model organisms to work with according to their properties for lab work. Depending on the application, it is possible to adapt the system to other plants, in order to detect noxious chemicals in regions where N. benthamiana is not suited for the task. This can be due to climatic reasons, rooting depth, or growth height. Using Helianthus annuus L. (Sunflower) for example could increase the detection depth up to three meters [10]. As a comparison: at the deposit location of chemical weapons “Dethlinger Pond” in Germany, the first grenades were found 1.7 meters below the ground [4]. In France, the majority of bombs that did not explode lie less than four meters below the ground [11]. Therefore, three meters of rooting depth are sufficient to detect the majority of chemical weapon remains. In the case of densely overgrown areas, the choice of plants for the application could even be extended to trees. This would allow to plant them when they are already large enough to reach the light. As trees will take some time to grow, even the utilization of trees that already are at sites of interest could be an option. As it can be seen, using a model organism for the proof of application for a plant-based detection system for chemical weapon degradation product detection was the first step, but many can follow.

Costs

The production, distribution, and application of our plants would be relatively cheap, compared to conventional detection systems. Therefore, the most costly part would be the development and authorization of use, as the safety in field use would need to be ensured and proven. However, the costs would be a good investment for the future, in order to prevent harm by the escape of dangerous substances, as it can be feared, that this will occur more often in the future.

Sources:

[1] Kibong Kim, et al. Destruction and Detection of Chemical Warfare Agents. Chemical Reviews 111 (9), 5345-5403 (2011)

[2] https://www.welt.de/geschichte/article160308532/Waffensammler-graben-auf-den-Schlachtfeldern-von-Verdun.html (access 03.10.21)

[3] Jubair, M. Abu, et al. Design and development of an autonomous agricultural drone for sowing seeds. 101-4 (2018).

[4]https://www.heidekreis.de/home/verwaltung-politik/verwaltung/buergerinformationen/informationen-zur-vorbereitung-der-oeffnung-des-dethlinger-teiches-munster-ab-september-2019.aspx (access 10.10.21)

[5] Revanasiddappa, B., et al. Real-time early detection of weed plants in pulse crop field using drone with IoT. Technology 16.5: 1227-1242. (2020)

[6] Wu, Shengbiao, et al. Monitoring tree-crown scale autumn leaf phenology in a temperate forest with an integration of PlanetScope and drone remote sensing observations. ISPRS Journal of Photogrammetry and Remote Sensing 171: 36-48. (2021)

[7] Gier, L. J. Root systems of bright belt tobacco. American Journal of Botany, 780-787 (1940).

[8] https://www.tagesschau.de/inland/chemiewaffen-altlasten-deutschland-101.html (access 01.10.21) https://robindesbois.org/en/comment-la-france-gere-t-elle-les-munitions-chimiques-anciennes/ (access 03.10.21)

[9] Abbas, Ghulam et al. Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects. International journal of environmental research and public health vol. 15,1 59. 2 Jan. (2018)

[10] Dardanelli, Julio Luis, et al. Rooting depth and soil water extraction patterns of different crops in a silty loam Haplustoll. Field Crops Research 54.1: 29-38 (1997).

[11] https://info.arte.tv/de/welche-gefahren-gibt-es-weltweit (access 02.10.21)

Team:Bielefeld-CeBiTec/Implementation