Imagine this scenario: a woman as gone missing in a dense forest area during a time of heavy rains. She is suspected to be deceased, but investigators do not know for sure. Given the weather, it is too dangerous for forensic specialists to go in to try to recover a body, and given the thick vegetation, ground-based searching is proving challenging. Thus, investigators decide to take to the skies.
They deploy a drone that has been configured to scan plants for specific fluorescence or reflectance signals that indicate human remains. In less than an hour, the wide-searching drone has detected an uncommon signal, pointing the forensic team right to the cadaver.
This situation may be somewhat farfetched at this time, but Neal Stewart Jr., and his team at the University of Tennessee are taking the first research steps toward making this technology a reality. The impact of decomposition of human remains on surrounding plant life has been tragically under-researched—until now.
“More obvious and easier-to-study biological interactions with cadavers may have been a higher priority than plants.,” Stewart Jr. told Forensic. “For example, indicator insects, microbial mixing among bodies and soils, and animals that may eat bodies. This has not been on the radar of plant scientists. Since we had the University of Tennessee Body Farm literally in our back yard, we started thinking about plants can be used to remotely detect human decomposition.”
Stewart Jr., a plant science professor, and his team are placing donor bodies in research plots at the UT Body Farm where they’ve identified and mapped out all the trees and shrubs. They will then assess how the cadaver decomposition islands change the metabolites and chemicals of the soil and nearby plants.
For example, as the team explains in their paper published in Trends in Plant Science, the average-sized American contains 2.6 kg nitrogen, much of which is converted to ammonium during the course of decomposition. Given a human decomposition island of approximately 3 m2, the amount of increased nitrogen in the area increases 50-fold. While high soil ammonium concentrations can be toxic to plants, researchers might also expect to see an obvious “greening effect” in the area by the body since leaf nitrogen content is associated with increased chlorophyll production.
In addition to an influx of nitrogen, Stewart Jr., and his team will study how personal human history and experiences may yield a unique spectral signature in plants. For example, an individual who frequently smoked cigarettes, had a career in manufacturing, or lived in a location with high environmental contamination may have increased exposure to cadmium. In plants, accumulation of cadmium has been shown to affect photosynthesis—altering the spectral characteristics of the plant enough to allow spectroscopic detection.
Once diagnostic spectra are compiled, the researchers said they can begin to think about scale up.
“Once we identify key responders to decomposition and the changes in leaves (which wavelengths), our plan is to perform controlled studies with replicated plants in a controlled environment,” Stewart Jr. said. “When you start to think about deploying drones to look for specific emissions, now we can think of the signals more like a check engine light—if we can quickly fly where someone may have gone missing and collect data over tens or even hundreds of square kilometers, then we'd know the best spots to send in a search team.”
Photo: Dense vegetative cover, like seen in the Great Smoky Mountains National Park, obscures items on the forest floor. Researchers with UTIA have a theory on how to help forensic scientists in searches for human remains. Credit: P. McDaniels, UTIA