There are a lot of things we leave behind as we pass through this life. Sometimes we are intentional, sometimes not. We mature, grow up, leave home and leave behind a whole host of things that marked our passage through childhood, the teenage years, and as a young adult. Those are the intentional things. The list of unintentional things is no doubt as long. Did you know you were leaving behind a trail of your DNA?

Of course we might think about all the crime shows we have watched. There are strands of our hair in a brush, saliva samples on a toothbrush, and more. Elizabeth Anne Brown, a science columnist for the NY Times, writes: “Over the last decade, wildlife researchers have refined techniques for recovering environmental DNA, or eDNA — trace amounts of genetic material that all living things leave behind. A powerful and inexpensive tool for ecologists, eDNA is all over — floating in the air, or lingering in water, snow, honey and even your cup of tea. Researchers have used the method to detect invasive species before they take over, to track vulnerable or secretive wildlife populations and even to rediscover species thought to be extinct. The eDNA technology is also used in wastewater surveillance systems to monitor Covid and other pathogens.”

Dr. David Duffy at the University of Florida, a wildlife researcher, had always known about the human strands of DNA that were in his environmental samples, but they were always considered “clutter” in view of the target research. One day he wondered if there was “enough” human DNA in the sample that might reveal something. While researching sea turtles, Duffy and his team decided to see how much information it could reveal about people in an area.

Brown writes: “As a proof of concept in one of their experiments, the researchers scooped up a soda-can-size sample of water from a creek in St. Augustine, Fla. They then fed the genetic material from the sample through a nanopore sequencer, which allows researchers to read longer stretches of DNA. The one they used cost about $1000, is the size of a cigarette lighter and plugs into a laptop like a flash drive.”

The researcher found enough mitochondrial DNA that they were able to estimate the demographics of the population near the creek. Their results were fairly close to recent census information. One DNA strand had enough information to meet the criteria for submission to the national missing persons database. Another sample revealed a DNA marker that someone had a mutation that could lead to a rare disease that causes progressive neurological impairment and is often fatal. The illness is hereditary and may not emerge until a patient’s 40s. Dr. Duffy couldn’t help but wonder — does that person know? Does the person’s family? Does the person’s insurance company? And then in dystopian speculation, one has to wonder what this might potentially say about surveillance and forensics.

Currently law enforcement uses 20 DNA markers to identify someone in their CODIS database (Combined DNA Index System). So even the coke-can sized sample from a Florida creek would be a the jigsaw puzzle from your worst nightmare. Brown writes: “However, forensic researchers suggest that individual identification from eDNA could already be possible in enclosed spaces where fewer people have been. Last October, a team from the Oslo University Hospital’s forensic research center piloted a new technique to recover human DNA from air samples and was able to construct full CODIS profiles from airborne DNA inside an office.”

Is this (or will this) technology form a reliable foundation for the use in legal proceedings? Or will it go the way of pseudo-science such as microscopic hair analysis, blood spatter analysis and bite mark evidence? Didn’t Abby on NCIS use those things? Say it ain’t so!

Brown points out: “The Fourth Amendment’s prohibition of “unreasonable search and seizure” without probable cause is also supposed to prevent the erosion of privacy by a powerful new technology. However, since the early 2000s, many prosecutors and courts have taken the stance that any DNA not still attached to a person has been abandoned, meaning that the police don’t need a warrant to collect it.”

While interesting from the technical point of view, this certainly opens up a “can of worms” as regards surveillance, law enforcement, legal proceedings, medical and insurance policy, and more. Can you imagine a scenario where you interview for a job, leaving behind DNA in the air, and your potential employer screens that for who knows what? Futurist, crime novelists, and conspiracy theorists should have a field day with this.

Meanwhile, try not to breathe in confined spaces, minimize your excess DNA shedding, and have a good day.

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