Soil contamination—also known as soil pollution—is caused by the presence of manmade chemicals in the natural soil environment. It is often caused by some form of industrial activity, agricultural chemicals or the improper disposal of waste. The most common chemicals involved in soil pollution are petroleum hydrocarbons, pesticides and lead and other heavy metals. Soil contamination can also happen as a result of underground storage tanks rupturing or the leaching of waste from landfills. Mining, fertilizer application, oil and fuel dumping and a multitude of other environmental issues can also cause pollution of the soil.
The biggest concern associated with soil contamination is the harm it can cause to human health. There are significant health risks involved with direct contact with contaminated soil, the vapors from the contaminants and even secondary contamination of water supplies.
A solution to the problem of soil contamination is soil remediation. Soil remediation is a way of purifying and revitalizing the soil. It is the process of removing contaminants in order to protect both the health of the population and the environment. In short, the goal of the process is to restore the soil to its natural, pollution-free state.
Traditionally, there are three main soil remediation technologies: soil washing, bioremediation and thermal desorption. Soil washing is a process that uses surfactants and water to remove contaminants from the soil. The process involves either dissolving or suspending pollutants in the wash solution and separates the soil by particle size. Bioremediation involves the use of living microorganisms, such as bacteria and fungi, to break down organic pollutants in the soil. In thermal desorption, heat is used to increase the volatility of contaminants, so that they can be separated from the solid material. The contaminants are then either collected or destroyed.
Residual contaminants can remain in the environment following defense operations, including
training. Spilled fuel and explosives such as – spilled Jet Propellant-8 (JP-8) and Trinitrotoluene, commonly known as TNT – can significantly degrade local habitats and negatively impact the surrounding communities. DARPA launched Ceres program in Oct 2022 which seeks novel, plant-based approaches to remediate soil contaminated with explosives and aircraft fuel.
While conventional soil bioremediation is effective, it still requires extensive soil preparation, nutrient delivery, and continuous site monitoring, making it too laborious and expensive to scale to the vast tracts of land that require decontamination. Ceres aims to greatly reduce the cost of remediation by generating a platform that requires minimal energy and human intervention, through engineering the behavior of plants and their associated microbial communities.
Ceres aims to engineer modular platforms that demonstrate proof-of-concept capabilities for two specific applications. The “Cleaner” track seeks to develop synthetic plant-root (rhizosphere) microbial communities, where plants, their roots, and microbes act together in a symbiotic way to degrade either TNT or JP-8 down to U.S. Environmental Protection Agency (EPA)-approved levels without dangerous byproducts. The “Beacon” track will develop complementary plant-microbe synthetic communities that provides an overt signal – such as flowers changing color – to indicate that the target contamination has been reduced to similarly safe levels.
Ultimately, the bioremediation platforms developed under Ceres platforms aim to achieve autonomous decontamination and contaminant tracking without the routine addition of power or human intervention.
“Ceres will capitalize on what nature does for free and without intrusive excavation,” said Dr. Paul Sheehan, Ceres program manager. “This could theoretically be performed for no cost beyond planting a seed fortified with microbes engineered to clean the soil.”
Ceres is a four-and-a-half-year long program divided into two 24-months phases, followed by a final six-month demonstration performed by an independent verification and validation (IV&V) team. Proposers are expected to (1) isolate or assemble functional plant-microbe communities, (2) optimize the communities through biological and ecological engineering into synthetic communities, (3) develop controls so that the synthetic communities can be easily removed post remediation, and (4) generate realistic testbeds that mimic field conditions for synthetic community optimizing and testing.
By the end of the program, the IV&V team will perform greenhouse-scale testing using soil from the three major U.S. biomes where U.S. military bases are located – Eastern Woodlands, Great Plains, Mediterranean – for explosive and fuel remediation. Throughout all phases, performers will be expected to conform to U.S. Environmental Protection Agency requirements. Moreover, teams will collaborate with ethical, legal, and societal implications experts to ensure the research addresses any related concerns.
“Biosafety is of utmost importance, and as such a key aspect of this program is building multiple layers of controls for the introduced organisms,” added Sheehan. “That means both controls internal to the organism, using synthetic biology strategies already under development, but also a brand-new class of controls external to the organism using in advances in synthetic ecology.”