Environmental DNA (eDNA) - A New Stage of Investigative Science in Crime Resolution
Forensic science has traditionally stated that we use the evidence of the traces that people leave behind (for example, fingerprints, footprints, or biological samples), but what happens when the traces are too faint or degraded to analyze? A new method for collecting evidence has the potential to change what we know about how we can recover evidence: Environmental DNA, or eDNA. This process collects pieces of genetic material that organisms leave behind in the environment as a result of shedding their skin cells, saliva, feces, or other biological remains (Cristescu and Hebert.,2018).
eDNA was first developed as a method for ecologists to monitor biodiversity and search for qualitative clues on rare and invasive species. Within the last few years, eDNA has garnered interest in forensic science as a means to search for human presence and reconstruct the environmental context of a crime scene (Lewis, et al., 2024). The concept is simple but powerful, every organism leaves a molecular footprint and those footprints can be recovered, sequenced, and interpreted. Forensic scientists can use molecular techniques to analyze eDNA and determine whether a person or species was at a location recently, even when there is no evidence to examine (Dass et al., 2022).
Conventional DNA profiling methods rely on direct biological evidence, such as blood, hair, or tissue. Oftentimes, there may not be a direct biological material present, or it may be compromised due to the environmental conditions, or decay time has passed and the residual material is no longer intact. Environmental DNA (eDNA) is a way to get around the absence of traditional biological material, detecting genetic fragments that remain in soil, water or even air. Within the realm of criminal investigations, this new frontier of “molecular trace evidence” could allow for discovery from locating drowning victims to tracking illegal wildlife trafficking where often traditional methods have been unsuccessful (Goray et al., 2024). As forensic sciences continue to evolve, eDNA is not just a technological advancement, but represents a paradigm shift in how investigators will assess the biological traces remaining after a crime has occurred.
Deciphering Environmental DNA: Concepts and Mechanisms
Environmental DNA is a broad term designating all genetic material released by organisms into their environment whether this is through purposeful or passive shedding (ex. shedding skin or fur cells, or the decomposition or excretion of genetic material). The resulting fragments of DNA accumulate in environmental matrices (e.g. soils, water, sediments, or air) (Cristescu & Hebert, 2018). eDNA needs to be detected using sensitive molecular tools because it is assumed to be present in very low amounts and highly fragmented. eDNA is collected before it is filtered, stored, and extracted in laboratory conditions to allow for the molecules of DNA to be analysed (Dass et al., 2022).
The two main molecular methods in eDNA processes are quantitative polymerase chain reaction (qPCR) and DNA metabarcoding. qPCR is used to target specific DNA sequences to determine whether or not a particular species or genetic marker are present in a sample. This level of specificity makes it more suited for targeted questions where you need to confirm the presence of one particular species (human or animal) (Dass et al., 2022). DNA metabarcoding on the other hand can be analysed by applying next-generation sequencing (NGS), which enables researchers to identify mixtures of DNA, allowing for the reconstruction of entire biological communities from a single environmental sample (Lewis et al., 2024).
Environmental and chemical conditions influence how long eDNA lasts and how confidence in the detection will be. Examples of the potential factors that affect eDNA degradation include temperature, UV radiation, microbial activity and pH (Cristescu & Hebert, 2018). While in water eDNA may be detectable for hours to days, in soil it can last weeks (depending on moisture and microbial content) (Dass et al., 2022). Understanding these mechanisms has important implications for forensic applications as timing and persistence can be utilized by investigators to provide estimates of when biological material was laid down in a crime scene.
In addition to these technical aspects, the most unique feature of eDNA is the non-invasive aspect of sampling. Investigators are able to recover information from genetic evidence without disturbing the environment. This parallels modern forensic aims of minimizing contamination and maximizing information recovered. As methods get better advances in eDNA can seamlessly bridge the disciplines of ecological science to forensic investigations, ethical reconstructing invisible biological information that connects organisms, people and place.
From Ecosystems to Evidence: eDNA Enters the Forensic Realm
The use of environmental DNA in the forensic sciences is a natural extension of its application in ecology. Originally established to detect rare or invasive species in aquatic ecosystems, the same methodology has been adapted for recovering trace human or animal DNA in investigative forensic contexts (Lewis et al., 2024). The process is simple, if organisms leave genetic material within their environment, humans leave behind traces of themselves as they shed skin cells, hair and bodily fluids whenever they come into contact with soil, water, dust or even air particles, thereby creating an invisible genetic record, albeit slightly more complex (Goray et al., 2024).
Then, in 2022, researchers established human eDNA can be reliably detected in water samples following submersion for several hours, which represents a tremendous advancement for aquatic forensic investigations (Dass et al, 2022). Those findings may apply to investigations with drowning victims, body disposal cases or to verify if someone or something was in contact with a particular body of water. In addition, forensic wildlife crime teams using eDNA have established illegal poaching and/or fish smuggling, again, establishing a genetic record of illegal transportation of protected species (Lewis et al., 2024).
One of the intriguing possibilities for eDNA forensics is geolocation-connecting suspects or evidence to areas of interest using unique biological signatures found in soil and plants. Liu et al. (2021) demonstrated that plant DNA metabarcoding could separate soils from different crime scene sites and could determine where an object or person had been located. This illustrates how eDNA connects ecology and criminology, and further, how natural surroundings can be converted to forensic datasets that reconstruct events that went unseen.
In essence, eDNA provides a biological fingerprint for every landscape-and one that is a passive recording of human interactions with the world.
Technological Advances Driving eDNA Forensics
The rapid growth of eDNA within the forensic context has developed in parallel with advances in molecular biology and sequencing technologies. One of the most transformative tools has been DNA metabarcoding, which concurrently identifies multiple species from mixed environmental samples. The technology leverages next-generation sequence (NGS) technology to do so. While metabarcoding was originally developed to assess ecological biodiversity, the Department of Justice has recently recognized its utility in forensic materials, such as soil, water, or dust (Lewis et al., 2024). The capacity to generate large amounts of genetic data makes metabarcoding valuable evidence, especially as the sample consists of small, degraded, or scarce DNA fragments.
There are other new developments to consider as well, such as airborne eDNA. This method collects DNA that floats in the atmosphere, and studies have determined that there are detectable traces of human, animal, or microbial DNA in air samples. This technology could afford forensic scientists a new way to determine who or what was present in a specific indoor environment (Goray et al., 2024). A similar concept is emerging with indoor dust eDNA, which is genetic material found in household dust. These advances could provide evidence about occupants, their pets, and possibly visitors to the home (Investigative Use of Human Environmental DNA, 2024). Such advancements give forensic scientists new options for investigations absent traditional biological evidence.
The study of bacterial or fungal communities on or around human or environmental surfaces, microbiome forensics, is becoming another pipeline technique that complements eDNA research. There is a unique microbial signature that every individual leaves behind, and it connects an individual, responsible for a particular set of bacteria/fungi, to a location or an object (Lee et al., 2019). eDNA data interpretation can become more rapid and efficient as machine learning and bioinformatics tools are integrated into forensic pipelines (Liu et al., 2021).
These technologies are transforming our approach to collecting and interpreting forensic evidence. eDNA is no longer confined to samples collected from aquatic or soil substrates; it covers air, dust, and even digital archives that plot biological forensic evidence across spaces.
Applications of eDNA in solving crime
The potential of eDNA is more than a theoretical framework, it is being tested in real-world applications that are altering the way we investigate forensic cases.
- Human Trace Detection
Human eDNA has the capacity to detect evidence of presence or activity at a location, regardless of the absence of visible biological materials. Dass et al. (2022) illustrated that DNA fragments from human epidermis and saliva can survive in aquatic habitats—something that could be useful to police investigators in drownings, human trafficking, and even corpse disposal. There are also indoor air sampling and dust sampling techniques to identify whether there were specific individuals present in closed environments (Goray et al., 2024). - Wildlife and Environmental Crimes
Beyond human associated applications, eDNA has also shown to be valuable in addressing wildlife trafficking and environmental crimes. Detectable genetic markers for protected species can be obtained from water or soil samples, without having to capture or disturb the species in question (Lewis et al., 2024). This technique has already been used to identify illegal fish trading operations and poaching syndicates. As Lewis and her co-authors noted (2024), eDNA provides investigators the ability to link wildlife products or residues to geographic sources, which can help strengthen prosecution cases. - Geo-location and Scene Reconstruction
Potentially the most novel eDNA application for aiding crime undersigning is geo-location. Soil, plant and fungus-derived DNA signatures will vary when identified from diverse locations.
Limitations and Future directions
Although it presents an incredible opportunity in the field of forensic science, the use of environmental DNA is not without its limitations. The sensitivity of eDNA that enhances its capacity to perform is also a limitation of eDNA. The first limitation and concern is DNA degradation. Environmental factors including sun exposure, active microorganisms, pH, and temperature contribute to the rapid degradation of DNA molecules, posing challenges to the forensic scientist in determining the longevity of a sample or how representative it is of more recent activity (Cristescu & Hebert, 2018). In some instances, eDNA may represent biological debris from organisms that are days or even weeks past, which raises questions about time in the forensic context (Dass et al., 2022). The second challenge is contamination. eDNA is everywhere and highly sensitive to detection; contamination can happen during collection, transport, or laboratory analysis. The smallest cross-contact or cross-contact from an investigator’s gear or instruments can lead to false positives and misinterpretation (Lewis et al., 2024). Therefore, devising and abiding by standard protocols for sample preservation, negative controls, and contamination prevention is necessary for forensic reliability (The Future of Environmental DNA in Forensic Science, 2019).
There are also considerable hurdles posed by legal and ethical issues. The academic admissibility of eDNA evidence in court remains unresolved as there is no existing body of case law or established parameters for standardized validation. Due to the notion that forensic evidence must satisfy the Daubert standard for scientific fidelity and testability, eDNA applications in the field do not meet this benchmark uniformly. Also, collecting human eDNA from public locations creates serious considerations about privacy and consent (Goray et al., 2024). As humans are continuously shedding DNA into their environments, any eDNA sampling for air, water, or dust could capture genetic material from unrelated individuals in the investigation. These issues illustrate the need for regulatory and ethical guidelines without delay.
Even so, eDNA's future in forensic science looks promising and continues to grow.
Researchers are quickly working to overcome some currently perceived barriers to eDNA technology. There are portable sequencers and sensors capable of real-time eDNA detection. This allows tube shots for the eDNA sample to be screened right at the scene which minimizes time lapse to lab analytical methods. Instant bioinformatics via machine learning and artificial intelligence are also enhancing the data interpretation of eDNA when complex information differentiates between noise and true forensic signals (Liu et al., 2021). Research in air and dust eDNA is also being explored as a means of reconstructing activities in an enclosed area or urban setting to detect recent presence or accomplice movement (Goray et al., 2024).
Cross disciplinary collaboration may be a decisive factor in taking the forensic eDNA science from its infancy and fulfilling its true potential. Ecologists, geneticists, computer sciences as well as criminalistic investigators will also have to work as a team to align protocols and ensure methodological replication using robust practices and with ethical compliance. As this science matures and is used more routinely in forensic applications, eDNA may have the capability to become more than a 'scientific tool' to provide evidence while identifying multiple molecular evidentiary items not visible to the naked eye.
In the years to follow, the very definition of crime scene may evolve from a scene of physical traces to a crime scene of invisible ecosystems multitasking to locate and identify FORWARD.
Conclusion
Environmental DNA (eDNA) is arguably one of the most exciting advances in modern forensic science. Facilitating the recovery and interpretation of genetic remnants from air, soil, water, and dust, eDNA represents an avenue for ecological and criminological research to join forces. eDNA allows for the detection of extremely small, degraded, or indirect biological material, and as such, provides law enforcement with a mechanism to investigate cases where traditional forms of evidence have not been captured. Applications can include documentation of illegal wildlife trafficking, or establishing an association between a suspect and a specific location, while revolutionizing otherwise unremarkable environments into molecular proxies of human and animal behavior (Lewis et al., 2024; Dass et al., 2022).
However, like emergent technology of any kind, eDNA technology should be approached thoughtfully and reflectively. eDNA is extremely sensitive, highly susceptible to contamination, and its legal standing is still ambiguous—all factors requiring continued monitoring and testing and potentially protocols and standards. In particular, ethical frameworks and public trust will need to be questioned, especially regarding privacy and the pivotal aspect of consent in the actualization of biomedical technologies when collecting environmental human DNA (Goray et al., 2024).
As we advance into the future, eDNA represents not only a scientific advancement but also a paradigmatic shift in the ascension of evidence. Where traditional forensic science has focused on perceived (visible) traces, eDNA works to capture the unseen or the biological echoes embedded in every space and last touch. If development, testing, and disciplinary collaboration continue to progress, then environmental DNA may soon be reposited as the next cornerstone of forensic science.
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