Criminals can no longer vanish into thin air after scientists discovered humans emit a tell-tale cloud of airborne DNA that could identify who was present at a crime scene.
The accidental discovery was made by a team at the University of Florida who were studying sea turtles using environmental DNA.
When animals move through the world they shed parts of themselves, such as dead skin cells, hair, mucus or faeces, which ends up in the air, water or land around them.
But experts were amazed to find huge amounts of human DNA amid the animal data, and it was of such good quality that it would have been possible to identify individuals.
Even footprints on a sandy beach contain enough DNA to identify who walked there, experts believe.
For ethical reasons the team did not try to find out the identities of the anonymous fragments of human DNA in the wider environment, but carried out an experiment in a veterinary hospital where they showed it was possible to identify staff from the airborne samples present.
The team said the finding could help identify suspects from the DNA floating in the air of a crime scene, or spot undiscovered archaeological sites.
David Duffy, professor of wildlife disease genomics, who led the project, said: “We’ve been consistently surprised throughout this project at how much human DNA we find and the quality of that DNA.
“In most cases the quality is almost equivalent to if you took a sample from a person. The fragments far exceed the minimum length needed to enter a missing person in a DNA database.
“We’re sure the technology exists (to identify anonymous individuals) and the DNA is good enough quality, but because there aren’t ethical frameworks in place we didn’t go to individual identity, but I am certain that could be done in the future.”
In the past, Prof Duffy’s team successfully used environmental DNA to study endangered sea turtles and the viral cancers they are susceptible to by looking at DNA in their tracks in the sand.
The team found quality human DNA in the ocean and rivers surrounding their Whitney Lab, at the University of Florida, as well as in footprints on isolated beaches.
Prof Duffy also carried out testing along the Avoca River passing through Arklow Town, Co Wicklow in Ireland, and found human DNA everywhere except the remote mountain stream where the river began.
Researchers say the discovery could be invaluable for science and forensics but also poses a huge ethical dilemma about how airborne DNA should be used.
Mark McCauley, a contractor for the US Geological Survey and study author, said: “The technology that we used is available in the science community right now.
“I don’t know about its immediate adoption for security of police departments, it will happen in the future. The question is how long it will take to get there and the legal ramifications.”
They warned that experts may be inadvertently scooping up human genetic information during routine sampling which could throw up problems with consent.
Prof Duffy added: “As with any technology, there are potentially worrying uses for human DNA as well.
“For instance, it could be used to harvest genetic information without consent, or knowledge of the people whose DNA you’re recovering. And this is particularly worrying if it was applied to vulnerable populations or ethnic minorities.
“If you take forensics, and trying to prevent or solve crimes, there is also the issue of whether you are going to recover DNA from people who had nothing to do with it. It’s a thorny question and that’s why we are calling for all of these implications to be considered.
“It’s precisely because of these potentially complex ethical issues that we have called for policymakers, scientists and society to consider the issues highlighted by our research and just consider them now.”
The research was published in Nature Ecology and Evolution.