This article was generated with the assistance of artificial intelligence. However, all content has been thoroughly reviewed and curated by a human editor before posting to guarantee accuracy, relevance, and quality.
Forensic DNA analysis has traditionally relied on biological samples like blood, saliva, or semen to link individuals to crime scenes. However, as technology advances, a new and powerful tool is emerging—human environmental DNA (eDNA). This groundbreaking approach allows forensic scientists to detect DNA that individuals unknowingly leave behind in their environments, from touch DNA on surfaces to DNA floating in the air or embedded in indoor dust. In a 2024 study published in Forensic Science International: Genetics, Chiara Fantinato and her team explore how eDNA can be used to investigate human presence in specific locations, offering new possibilities for forensic casework.
By collecting and analyzing DNA from surfaces, air, and dust in indoor settings, this research expands the capabilities of forensic investigators, particularly in cases where traditional biological evidence is lacking or degraded. As the use of eDNA in forensic genetics gains traction, the study also sheds light on its potential, limitations, and best practices for its application in real-world scenarios.
What Is Environmental DNA?
Environmental DNA refers to the traces of human DNA that are deposited into an environment through direct contact with surfaces or indirect transfer, such as through air or indoor dust. This DNA can come from skin cells, hair, or bodily fluids that individuals shed as they interact with their surroundings. Unlike conventional forensic DNA sources, eDNA is often more diffuse and can be more challenging to isolate and analyze.
Fantinato and her colleagues focused their study on office environments, collecting samples from commonly touched surfaces such as computer mice, keyboards, door handles, and light switches. They also collected air and dust samples to determine how eDNA from these sources compared to that found on surfaces. Their results suggest that combining DNA from these different environmental sources can provide a more complete picture of who was present in a particular location and when.
Harnessing eDNA as an Investigative Tool
The value of eDNA lies in its ability to capture DNA from individuals who may not have left behind more conventional types of biological evidence. As the study points out, this type of evidence can be particularly useful in indoor environments where direct DNA evidence may be sparse or absent. The researchers found that eDNA from surfaces can reliably identify occupants of a space, while DNA from dust and air samples can complement these findings to give a broader view of how DNA may have transferred in the environment.
For example, the study demonstrated that DNA collected from personal surfaces—such as a computer mouse or a desk—most frequently matched the primary user of the space. However, shared surfaces like door handles or light switches were more likely to contain mixed DNA from multiple individuals. This pattern makes it possible to identify the most frequent users of a space, as well as occasional visitors.
One of the study’s key findings was the power of combining eDNA from multiple sources. By analyzing DNA from air, dust, and surfaces in parallel, investigators can gain a clearer understanding of the occupants of a space and potential DNA transfer events. In one example, the researchers showed how DNA from a regular occupant of an office persisted on surfaces long after they had left, while DNA from a more recent visitor was found on the door handle. This approach is particularly useful for tracking recent activity at a crime scene.
Extraction Methods: The Key to Maximizing eDNA Recovery
To effectively use eDNA as a forensic tool, it is critical to optimize the methods for extracting DNA from different sources. Fantinato’s team compared two extraction methods—one for DNA-only extraction (E1) and a DNA/RNA co-extraction method (E2). The results were clear: the co-extraction method (E2) yielded significantly higher quantities of DNA and more complex profiles, making it the preferred approach for maximizing DNA recovery from surfaces.
This finding underscores the importance of using robust extraction techniques to obtain as much DNA as possible from trace evidence. DNA samples collected from surfaces such as keyboards and door handles provided valuable leads, but the amount of DNA recovered varied greatly depending on the extraction method used. The use of more advanced extraction protocols will likely play a crucial role in increasing the reliability of eDNA in forensic investigations.
The Potential for Indirect DNA Transfer
One of the challenges in using eDNA for forensic purposes is the possibility of indirect DNA transfer. DNA can be transferred to surfaces not only through direct contact but also via air and dust, which can complicate the interpretation of results. Fantinato’s study provides valuable insights into this issue, demonstrating that DNA can persist in an environment and transfer between surfaces over time.
For instance, in one case, the DNA of a person who had been absent from an office for over 30 days was still detected on both surfaces and in the air. This suggests that DNA can remain in an environment long after the individual has left, either through direct deposition or via indirect transfer mechanisms like air circulation. Understanding these dynamics is crucial for forensic scientists who need to determine whether the presence of DNA at a crime scene is relevant to the crime or simply a result of background DNA transfer.
The Use of eDNA in Crime Scene Investigations
The ability to detect and analyze eDNA has important implications for forensic investigations. For example, in cases where suspects had lived with victims but were no longer present at the time of a crime, eDNA can help establish whether the suspect’s DNA was deposited recently or is simply background DNA from previous contact. This information can be crucial for distinguishing between relevant evidence and innocuous DNA left behind from prior interactions.
The study’s findings also suggest that eDNA could be particularly useful in high-traffic areas or shared spaces, such as meeting rooms or office buildings, where multiple individuals may have left traces of their DNA. By targeting surfaces like door handles and light switches, investigators can identify who has recently accessed a room and potentially uncover valuable leads.
Challenges and Future Directions
While eDNA holds great promise as a forensic tool, there are still several challenges to address. One of the biggest concerns is the potential for background DNA to obscure relevant evidence. In busy environments, DNA from multiple individuals may accumulate over time, making it difficult to determine who left the DNA and when. This issue is further complicated by the possibility of indirect transfer, where DNA is moved between surfaces without direct contact.
Additionally, the study highlights the importance of developing better methods for interpreting complex DNA mixtures. As eDNA samples often contain DNA from multiple individuals, forensic scientists will need to continue refining their techniques for separating relevant DNA profiles from background noise.
Looking forward, future research will likely focus on improving the sensitivity and specificity of eDNA analysis, as well as developing more effective protocols for handling and interpreting complex DNA samples. As this field continues to evolve, eDNA has the potential to become an indispensable tool in forensic investigations, offering new ways to solve cases that might otherwise go cold.
Conclusion
The use of environmental DNA in forensic genetics represents an exciting new frontier in the field. By capturing DNA from surfaces, air, and dust, forensic investigators can gain critical insights into who was present at a crime scene and when. Fantinato and her team have demonstrated that eDNA is a valuable investigative tool, particularly in indoor environments where direct biological evidence may be scarce.
As extraction techniques improve and our understanding of DNA transfer deepens, eDNA will likely play an increasingly important role in forensic casework. By combining data from multiple DNA sources, investigators can piece together a more comprehensive picture of the events surrounding a crime, ultimately helping to bring more offenders to justice.
Citations
Fantinato, C., Gill, P., & Fonneløp, A.E. (2024). Investigative use of human environmental DNA in forensic genetics. Forensic Science International: Genetics, 70, 103021. https://doi.org/10.1016/j.fsigen.2024.103021
